/*!
 * script.js - script interpreter for bcoin
 * Copyright (c) 2014-2015, Fedor Indutny (MIT License)
 * Copyright (c) 2014-2017, Christopher Jeffrey (MIT License).
 * https://github.com/bcoin-org/bcoin
 */

'use strict';

const assert = require('assert');
const BN = require('../crypto/bn');
const consensus = require('../protocol/consensus');
const policy = require('../protocol/policy');
const util = require('../utils/util');
const digest = require('../crypto/digest');
const merkle = require('../crypto/merkle');
const BufferWriter = require('../utils/writer');
const BufferReader = require('../utils/reader');
const StaticWriter = require('../utils/staticwriter');
const Program = require('./program');
const Opcode = require('./opcode');
const Stack = require('./stack');
const common = require('./common');
const encoding = require('../utils/encoding');
const secp256k1 = require('../crypto/secp256k1');
const Address = require('../primitives/address');
const opcodes = common.opcodes;
const scriptTypes = common.types;
const ScriptError = common.ScriptError;
const STACK_TRUE = common.STACK_TRUE;
const STACK_FALSE = common.STACK_FALSE;
const STACK_NEGATE = common.STACK_NEGATE;

/**
 * Represents a input or output script.
 * @alias module:script.Script
 * @constructor
 * @param {Buffer|Array|Object|NakedScript} code - Array
 * of script code or a serialized script Buffer.
 * @property {Array} code - Parsed script code.
 * @property {Buffer?} raw - Serialized script.
 * @property {Number} length - Number of parsed opcodes.
 */

function Script(options) {
  if (!(this instanceof Script))
    return new Script(options);

  this.raw = STACK_FALSE;
  this.code = [];

  if (options)
    this.fromOptions(options);
}

/**
 * Script opcodes.
 * @enum {Number}
 * @default
 */

Script.opcodes = common.opcodes;

/**
 * Opcodes by value.
 * @const {RevMap}
 */

Script.opcodesByVal = common.opcodesByVal;

/**
 * Script and locktime flags. See {@link VerifyFlags}.
 * @enum {Number}
 */

Script.flags = common.flags;

/**
 * Sighash Types.
 * @enum {SighashType}
 * @default
 */

Script.hashType = common.hashType;

/**
 * Sighash types by value.
 * @const {RevMap}
 */

Script.hashTypeByVal = common.hashTypeByVal;

/**
 * Output script types.
 * @enum {Number}
 */

Script.types = common.types;

/**
 * Output script types by value.
 * @const {RevMap}
 */

Script.typesByVal = common.typesByVal;

/**
 * Getter to retrieve code length.
 * @name module:script.Script#length_getter
 * @method
 * @private
 * @returns {Number}
 */

Script.prototype.__defineGetter__('length', function() {
  return this.code.length;
});

/**
 * Setter to set code length.
 * @name module:script.Script#length_setter
 * @method
 * @private
 * @param {Number} value
 * @returns {Number}
 */

Script.prototype.__defineSetter__('length', function(length) {
  this.code.length = length;
  return length;
});

/**
 * Inject properties from options object.
 * @private
 * @param {Object} options
 */

Script.prototype.fromOptions = function fromOptions(options) {
  assert(options, 'Script data is required.');

  if (Buffer.isBuffer(options))
    return this.fromRaw(options);

  if (Array.isArray(options))
    return this.fromArray(options);

  if (options.raw) {
    if (!options.code)
      return this.fromRaw(options.raw);
    assert(Buffer.isBuffer(options.raw), 'Raw must be a Buffer.');
    this.raw = options.raw;
  }

  if (options.code) {
    if (!options.raw)
      return this.fromCode(options.code);
    assert(Array.isArray(options.code), 'Code must be an array.');
    this.code = options.code;
  }

  return this;
};

/**
 * Insantiate script from options object.
 * @param {Object} options
 * @returns {Script}
 */

Script.fromOptions = function fromOptions(options) {
  return new Script().fromOptions(options);
};

/**
 * Convert the script to an array of
 * Buffers (pushdatas) and Numbers
 * (opcodes).
 * @returns {Array}
 */

Script.prototype.toArray = function toArray() {
  const code = [];

  for (const op of this.code)
    code.push(op.data || op.value);

  return code;
};

/**
 * Inject properties from an array of
 * of buffers and numbers.
 * @private
 * @param {Array} code
 * @returns {Script}
 */

Script.prototype.fromArray = function fromArray(code) {
  assert(Array.isArray(code));

  if (code.length === 0)
    return this;

  if (code[0] instanceof Opcode)
    return this.fromCode(code);

  for (const op of code) {
    if (Buffer.isBuffer(op)) {
      this.code.push(Opcode.fromData(op));
      continue;
    }
    if (typeof op === 'string') {
      this.code.push(Opcode.fromSymbol(op));
      continue;
    }
    assert(typeof op === 'number');
    this.code.push(Opcode.fromOp(op));
  }

  this.compile();

  return this;
};

/**
 * Instantiate script from an array
 * of buffers and numbers.
 * @param {Array} code
 * @returns {Script}
 */

Script.fromArray = function fromArray(code) {
  return new Script().fromArray(code);
};

/**
 * Return an array of opcodes.
 * @returns {Opcode[]}
 */

Script.prototype.toCode = function toCode() {
  return this.code.slice();
};

/**
 * Inject properties from an array of opcodes.
 * @param {Opcode[]} code
 * @private
 */

Script.prototype.fromCode = function fromCode(code) {
  assert(Array.isArray(code));

  if (code.length === 0)
    return this;

  assert(code[0] instanceof Opcode);

  this.code = code;
  this.compile();

  return this;
};

/**
 * Instantiate script from an array of opcodes.
 * @param {Opcode[]} code
 * @returns {Script}
 */

Script.fromCode = function fromCode(code) {
  return new Script().fromCode(code);
};

/**
 * Clone the script.
 * @returns {Script} Cloned script.
 */

Script.prototype.clone = function clone() {
  return new Script().inject(this);
};

/**
 * Inject properties from script.
 * Used for cloning.
 * @private
 * @param {Script} script
 * @returns {Script}
 */

Script.prototype.inject = function inject(script) {
  this.code = script.code.slice();
  this.raw = script.raw;
  return this;
};

/**
 * Inspect the script.
 * @returns {String} Human-readable script code.
 */

Script.prototype.inspect = function inspect() {
  return `<Script: ${this.toString()}>`;
};

/**
 * Convert the script to a bitcoind test string.
 * @returns {String} Human-readable script code.
 */

Script.prototype.toString = function toString() {
  return common.formatCode(this.code);
};

/**
 * Format the script as bitcoind asm.
 * @param {Boolean?} decode - Attempt to decode hash types.
 * @returns {String} Human-readable script.
 */

Script.prototype.toASM = function toASM(decode) {
  return common.formatASM(this.code, decode);
};

/**
 * Calculate size of code to be compiled.
 * @returns {Number}
 */

Script.prototype.getCodeSize = function getCodeSize() {
  let size = 0;

  for (const op of this.code)
    size += op.getSize();

  return size;
};

/**
 * Re-encode the script internally. Useful if you
 * changed something manually in the `code` array.
 */

Script.prototype.compile = function compile() {
  const size = this.getCodeSize();
  const bw = new StaticWriter(size);

  for (const op of this.code)
    op.toWriter(bw);

  this.raw = bw.render();

  return this;
};

/**
 * Write the script to a buffer writer.
 * @param {BufferWriter} bw
 */

Script.prototype.toWriter = function toWriter(bw) {
  bw.writeVarBytes(this.raw);
  return bw;
};

/**
 * Encode the script to a Buffer. See {@link Script#encode}.
 * @param {String} enc - Encoding, either `'hex'` or `null`.
 * @returns {Buffer|String} Serialized script.
 */

Script.prototype.toRaw = function toRaw() {
  return this.raw;
};

/**
 * Convert script to a hex string.
 * @returns {String}
 */

Script.prototype.toJSON = function toJSON() {
  return this.toRaw().toString('hex');
};

/**
 * Inject properties from json object.
 * @private
 * @param {String} json
 */

Script.prototype.fromJSON = function fromJSON(json) {
  assert(typeof json === 'string', 'Code must be a string.');
  return this.fromRaw(Buffer.from(json, 'hex'));
};

/**
 * Instantiate script from a hex string.
 * @params {String} json
 * @returns {Script}
 */

Script.fromJSON = function fromJSON(json) {
  return new Script().fromJSON(json);
};

/**
 * Get the script's "subscript" starting at a separator.
 * @param {Number?} lastSep - The last separator to sign/verify beyond.
 * @returns {Script} Subscript.
 */

Script.prototype.getSubscript = function getSubscript(lastSep) {
  if (lastSep === 0)
    return this.clone();

  const code = [];

  for (let i = lastSep; i < this.code.length; i++) {
    const op = this.code[i];

    if (op.value === -1)
      break;

    code.push(op);
  }

  return Script.fromCode(code);
};

/**
 * Get the script's "subscript" starting at a separator.
 * Remove all OP_CODESEPARATORs if present. This bizarre
 * behavior is necessary for signing and verification when
 * code separators are present.
 * @returns {Script} Subscript.
 */

Script.prototype.removeSeparators = function removeSeparators() {
  let found = false;

  // Optimizing for the common case:
  // Check for any separators first.
  for (const op of this.code) {
    if (op.value === -1)
      break;

    if (op.value === opcodes.OP_CODESEPARATOR) {
      found = true;
      break;
    }
  }

  if (!found)
    return this;

  // Uncommon case: someone actually
  // has a code separator. Go through
  // and remove them all.
  const code = [];

  for (const op of this.code) {
    if (op.value === -1)
      break;

    if (op.value !== opcodes.OP_CODESEPARATOR)
      code.push(op);
  }

  return Script.fromCode(code);
};

/**
 * Execute and interpret the script.
 * @param {Stack} stack - Script execution stack.
 * @param {Number?} flags - Script standard flags.
 * @param {TX?} tx - Transaction being verified.
 * @param {Number?} index - Index of input being verified.
 * @param {Amount?} value - Previous output value.
 * @param {Number?} version - Signature hash version (0=legacy, 1=segwit).
 * @throws {ScriptError} Will be thrown on VERIFY failures, among other things.
 * @returns {Boolean} Whether the execution was successful.
 */

Script.prototype.execute = function execute(stack, flags, tx, index, value, version) {
  if (flags == null)
    flags = Script.flags.STANDARD_VERIFY_FLAGS;

  if (version == null)
    version = 0;

  if (this.getSize() > consensus.MAX_SCRIPT_SIZE)
    throw new ScriptError('SCRIPT_SIZE');

  const state = [];
  const alt = [];

  let lastSep = 0;
  let opCount = 0;
  let negate = 0;
  let minimal = false;

  if (flags & Script.flags.VERIFY_MINIMALDATA)
    minimal = true;

  for (let ip = 0; ip < this.code.length; ip++) {
    const op = this.code[ip];

    if (op.value === -1)
      throw new ScriptError('BAD_OPCODE', op, ip);

    if (op.data) {
      if (op.data.length > consensus.MAX_SCRIPT_PUSH)
        throw new ScriptError('PUSH_SIZE', op, ip);

      if (negate === 0) {
        if (minimal && !op.isMinimal())
          throw new ScriptError('MINIMALDATA', op, ip);
        stack.push(op.data);
      }

      continue;
    }

    if (op.value > opcodes.OP_16 && ++opCount > consensus.MAX_SCRIPT_OPS)
      throw new ScriptError('OP_COUNT', op, ip);

    if (op.isDisabled())
      throw new ScriptError('DISABLED_OPCODE', op, ip);

    if (negate !== 0 && !op.isBranch())
      continue;

    switch (op.value) {
      case opcodes.OP_0: {
        stack.push(STACK_FALSE);
        break;
      }
      case opcodes.OP_1NEGATE: {
        stack.push(STACK_NEGATE);
        break;
      }
      case opcodes.OP_1: {
        stack.push(STACK_TRUE);
        break;
      }
      case opcodes.OP_2:
      case opcodes.OP_3:
      case opcodes.OP_4:
      case opcodes.OP_5:
      case opcodes.OP_6:
      case opcodes.OP_7:
      case opcodes.OP_8:
      case opcodes.OP_9:
      case opcodes.OP_10:
      case opcodes.OP_11:
      case opcodes.OP_12:
      case opcodes.OP_13:
      case opcodes.OP_14:
      case opcodes.OP_15:
      case opcodes.OP_16: {
        stack.push(Buffer.from([op.value - 0x50]));
        break;
      }
      case opcodes.OP_NOP: {
        break;
      }
      case opcodes.OP_CHECKLOCKTIMEVERIFY: {
        // OP_CHECKLOCKTIMEVERIFY = OP_NOP2
        if (!(flags & Script.flags.VERIFY_CHECKLOCKTIMEVERIFY)) {
          if (flags & Script.flags.VERIFY_DISCOURAGE_UPGRADABLE_NOPS)
            throw new ScriptError('DISCOURAGE_UPGRADABLE_NOPS', op, ip);
          break;
        }

        if (!tx)
          throw new ScriptError('UNKNOWN_ERROR', 'No TX passed in.');

        if (stack.length === 0)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        let locktime = Script.num(stack.top(-1), minimal, 5);

        if (locktime.cmpn(0) < 0)
          throw new ScriptError('NEGATIVE_LOCKTIME', op, ip);

        locktime = locktime.toNumber();

        if (!tx.verifyLocktime(index, locktime))
          throw new ScriptError('UNSATISFIED_LOCKTIME', op, ip);

        break;
      }
      case opcodes.OP_CHECKSEQUENCEVERIFY: {
        // OP_CHECKSEQUENCEVERIFY = OP_NOP3
        if (!(flags & Script.flags.VERIFY_CHECKSEQUENCEVERIFY)) {
          if (flags & Script.flags.VERIFY_DISCOURAGE_UPGRADABLE_NOPS)
            throw new ScriptError('DISCOURAGE_UPGRADABLE_NOPS', op, ip);
          break;
        }

        if (!tx)
          throw new ScriptError('UNKNOWN_ERROR', 'No TX passed in.');

        if (stack.length === 0)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        let locktime = Script.num(stack.top(-1), minimal, 5);

        if (locktime.cmpn(0) < 0)
          throw new ScriptError('NEGATIVE_LOCKTIME', op, ip);

        locktime = locktime.toNumber();

        if (!tx.verifySequence(index, locktime))
          throw new ScriptError('UNSATISFIED_LOCKTIME', op, ip);

        break;
      }
      case opcodes.OP_NOP1:
      case opcodes.OP_NOP4:
      case opcodes.OP_NOP5:
      case opcodes.OP_NOP6:
      case opcodes.OP_NOP7:
      case opcodes.OP_NOP8:
      case opcodes.OP_NOP9:
      case opcodes.OP_NOP10: {
        if (flags & Script.flags.VERIFY_DISCOURAGE_UPGRADABLE_NOPS)
          throw new ScriptError('DISCOURAGE_UPGRADABLE_NOPS', op, ip);
        break;
      }
      case opcodes.OP_IF:
      case opcodes.OP_NOTIF: {
        let val = false;

        if (negate === 0) {
          if (stack.length < 1)
            throw new ScriptError('UNBALANCED_CONDITIONAL', op, ip);

          val = stack.top(-1);

          if (version === 1 && (flags & Script.flags.VERIFY_MINIMALIF)) {
            if (val.length > 1)
              throw new ScriptError('MINIMALIF');

            if (val.length === 1 && val[0] !== 1)
              throw new ScriptError('MINIMALIF');
          }

          val = Script.bool(val);

          if (op.value === opcodes.OP_NOTIF)
            val = !val;

          stack.pop();
        }

        state.push(val);

        if (!val)
          negate++;

        break;
      }
      case opcodes.OP_ELSE: {
        if (state.length === 0)
          throw new ScriptError('UNBALANCED_CONDITIONAL', op, ip);

        state[state.length - 1] = !state[state.length - 1];

        if (!state[state.length - 1])
          negate++;
        else
          negate--;

        break;
      }
      case opcodes.OP_ENDIF: {
        if (state.length === 0)
          throw new ScriptError('UNBALANCED_CONDITIONAL', op, ip);

        if (!state.pop())
          negate--;

        break;
      }
      case opcodes.OP_VERIFY: {
        if (stack.length === 0)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        if (!Script.bool(stack.top(-1)))
          throw new ScriptError('VERIFY', op, ip);

        stack.pop();

        break;
      }
      case opcodes.OP_RETURN: {
        throw new ScriptError('OP_RETURN', op, ip);
      }
      case opcodes.OP_TOALTSTACK: {
        if (stack.length === 0)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        alt.push(stack.pop());
        break;
      }
      case opcodes.OP_FROMALTSTACK: {
        if (alt.length === 0)
          throw new ScriptError('INVALID_ALTSTACK_OPERATION', op, ip);

        stack.push(alt.pop());
        break;
      }
      case opcodes.OP_2DROP: {
        if (stack.length < 2)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.pop();
        stack.pop();
        break;
      }
      case opcodes.OP_2DUP: {
        if (stack.length < 2)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        const v1 = stack.top(-2);
        const v2 = stack.top(-1);

        stack.push(v1);
        stack.push(v2);
        break;
      }
      case opcodes.OP_3DUP: {
        if (stack.length < 3)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        const v1 = stack.top(-3);
        const v2 = stack.top(-2);
        const v3 = stack.top(-1);

        stack.push(v1);
        stack.push(v2);
        stack.push(v3);
        break;
      }
      case opcodes.OP_2OVER: {
        if (stack.length < 4)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        const v1 = stack.top(-4);
        const v2 = stack.top(-3);

        stack.push(v1);
        stack.push(v2);
        break;
      }
      case opcodes.OP_2ROT: {
        if (stack.length < 6)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        const v1 = stack.top(-6);
        const v2 = stack.top(-5);

        stack.erase(-6, -4);
        stack.push(v1);
        stack.push(v2);
        break;
      }
      case opcodes.OP_2SWAP: {
        if (stack.length < 4)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.swap(-4, -2);
        stack.swap(-3, -1);
        break;
      }
      case opcodes.OP_IFDUP: {
        if (stack.length === 0)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        const val = stack.top(-1);

        if (Script.bool(val))
          stack.push(val);
        break;
      }
      case opcodes.OP_DEPTH: {
        stack.push(Script.array(stack.length));
        break;
      }
      case opcodes.OP_DROP: {
        if (stack.length === 0)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.pop();
        break;
      }
      case opcodes.OP_DUP: {
        if (stack.length === 0)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.push(stack.top(-1));
        break;
      }
      case opcodes.OP_NIP: {
        if (stack.length < 2)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.remove(-2);
        break;
      }
      case opcodes.OP_OVER: {
        if (stack.length < 2)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.push(stack.top(-2));
        break;
      }
      case opcodes.OP_PICK:
      case opcodes.OP_ROLL: {
        if (stack.length < 2)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        const num = Script.num(stack.top(-1), minimal).toNumber();
        stack.pop();

        if (num < 0 || num >= stack.length)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        const val = stack.top(-num - 1);

        if (op.value === opcodes.OP_ROLL)
          stack.remove(-num - 1);

        stack.push(val);
        break;
      }
      case opcodes.OP_ROT: {
        if (stack.length < 3)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.swap(-3, -2);
        stack.swap(-2, -1);
        break;
      }
      case opcodes.OP_SWAP: {
        if (stack.length < 2)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.swap(-2, -1);
        break;
      }
      case opcodes.OP_TUCK: {
        if (stack.length < 2)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.insert(-2, stack.top(-1));
        break;
      }
      case opcodes.OP_SIZE: {
        if (stack.length < 1)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.push(Script.array(stack.top(-1).length));
        break;
      }
      case opcodes.OP_EQUAL:
      case opcodes.OP_EQUALVERIFY: {
        if (stack.length < 2)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        const v1 = stack.top(-2);
        const v2 = stack.top(-1);

        const res = v1.equals(v2);

        stack.pop();
        stack.pop();

        stack.push(res ? STACK_TRUE : STACK_FALSE);

        if (op.value === opcodes.OP_EQUALVERIFY) {
          if (!res)
            throw new ScriptError('EQUALVERIFY', op, ip);
          stack.pop();
        }

        break;
      }
      case opcodes.OP_1ADD:
      case opcodes.OP_1SUB:
      case opcodes.OP_NEGATE:
      case opcodes.OP_ABS:
      case opcodes.OP_NOT:
      case opcodes.OP_0NOTEQUAL: {
        if (stack.length < 1)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        let num = Script.num(stack.top(-1), minimal);

        switch (op.value) {
          case opcodes.OP_1ADD:
            num.iaddn(1);
            break;
          case opcodes.OP_1SUB:
            num.isubn(1);
            break;
          case opcodes.OP_NEGATE:
            num.ineg();
            break;
          case opcodes.OP_ABS:
            num.iabs();
            break;
          case opcodes.OP_NOT:
            num = num.cmpn(0) === 0;
            num = new BN(num ? 1 : 0);
            break;
          case opcodes.OP_0NOTEQUAL:
            num = num.cmpn(0) !== 0;
            num = new BN(num ? 1 : 0);
            break;
          default:
            assert(false, 'Fatal script error.');
            break;
        }

        stack.pop();
        stack.push(Script.array(num));

        break;
      }
      case opcodes.OP_ADD:
      case opcodes.OP_SUB:
      case opcodes.OP_BOOLAND:
      case opcodes.OP_BOOLOR:
      case opcodes.OP_NUMEQUAL:
      case opcodes.OP_NUMEQUALVERIFY:
      case opcodes.OP_NUMNOTEQUAL:
      case opcodes.OP_LESSTHAN:
      case opcodes.OP_GREATERTHAN:
      case opcodes.OP_LESSTHANOREQUAL:
      case opcodes.OP_GREATERTHANOREQUAL:
      case opcodes.OP_MIN:
      case opcodes.OP_MAX: {
        if (stack.length < 2)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        const n1 = Script.num(stack.top(-2), minimal);
        const n2 = Script.num(stack.top(-1), minimal);
        let num;

        switch (op.value) {
          case opcodes.OP_ADD:
            num = n1.iadd(n2);
            break;
          case opcodes.OP_SUB:
            num = n1.isub(n2);
            break;
          case opcodes.OP_BOOLAND:
            num = n1.cmpn(0) !== 0 && n2.cmpn(0) !== 0;
            num = new BN(num ? 1 : 0);
            break;
          case opcodes.OP_BOOLOR:
            num = n1.cmpn(0) !== 0 || n2.cmpn(0) !== 0;
            num = new BN(num ? 1 : 0);
            break;
          case opcodes.OP_NUMEQUAL:
            num = n1.cmp(n2) === 0;
            num = new BN(num ? 1 : 0);
            break;
          case opcodes.OP_NUMEQUALVERIFY:
            num = n1.cmp(n2) === 0;
            num = new BN(num ? 1 : 0);
            break;
          case opcodes.OP_NUMNOTEQUAL:
            num = n1.cmp(n2) !== 0;
            num = new BN(num ? 1 : 0);
            break;
          case opcodes.OP_LESSTHAN:
            num = n1.cmp(n2) < 0;
            num = new BN(num ? 1 : 0);
            break;
          case opcodes.OP_GREATERTHAN:
            num = n1.cmp(n2) > 0;
            num = new BN(num ? 1 : 0);
            break;
          case opcodes.OP_LESSTHANOREQUAL:
            num = n1.cmp(n2) <= 0;
            num = new BN(num ? 1 : 0);
            break;
          case opcodes.OP_GREATERTHANOREQUAL:
            num = n1.cmp(n2) >= 0;
            num = new BN(num ? 1 : 0);
            break;
          case opcodes.OP_MIN:
            num = n1.cmp(n2) < 0 ? n1 : n2;
            break;
          case opcodes.OP_MAX:
            num = n1.cmp(n2) > 0 ? n1 : n2;
            break;
          default:
            assert(false, 'Fatal script error.');
            break;
        }

        stack.pop();
        stack.pop();
        stack.push(Script.array(num));

        if (op.value === opcodes.OP_NUMEQUALVERIFY) {
          if (!Script.bool(stack.top(-1)))
            throw new ScriptError('NUMEQUALVERIFY', op, ip);
          stack.pop();
        }

        break;
      }
      case opcodes.OP_WITHIN: {
        if (stack.length < 3)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        const n1 = Script.num(stack.top(-3), minimal);
        const n2 = Script.num(stack.top(-2), minimal);
        const n3 = Script.num(stack.top(-1), minimal);

        const val = n2.cmp(n1) <= 0 && n1.cmp(n3) < 0;

        stack.pop();
        stack.pop();
        stack.pop();

        stack.push(val ? STACK_TRUE : STACK_FALSE);
        break;
      }
      case opcodes.OP_RIPEMD160: {
        if (stack.length === 0)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.push(digest.ripemd160(stack.pop()));
        break;
      }
      case opcodes.OP_SHA1: {
        if (stack.length === 0)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.push(digest.sha1(stack.pop()));
        break;
      }
      case opcodes.OP_SHA256: {
        if (stack.length === 0)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.push(digest.sha256(stack.pop()));
        break;
      }
      case opcodes.OP_HASH160: {
        if (stack.length === 0)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.push(digest.hash160(stack.pop()));
        break;
      }
      case opcodes.OP_HASH256: {
        if (stack.length === 0)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        stack.push(digest.hash256(stack.pop()));
        break;
      }
      case opcodes.OP_CODESEPARATOR: {
        lastSep = ip + 1;
        break;
      }
      case opcodes.OP_CHECKSIG:
      case opcodes.OP_CHECKSIGVERIFY: {
        if (!tx)
          throw new ScriptError('UNKNOWN_ERROR', 'No TX passed in.');

        if (stack.length < 2)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        const sig = stack.top(-2);
        const key = stack.top(-1);

        const subscript = this.getSubscript(lastSep);

        if (version === 0)
          subscript.removeData(sig);

        validateSignature(sig, flags);
        validateKey(key, flags, version);

        let res = false;

        if (sig.length > 0) {
          const type = sig[sig.length - 1];
          const hash = tx.signatureHash(index, subscript, value, type, version);
          res = checksig(hash, sig, key);
        }

        if (!res && (flags & Script.flags.VERIFY_NULLFAIL)) {
          if (sig.length !== 0)
            throw new ScriptError('NULLFAIL', op, ip);
        }

        stack.pop();
        stack.pop();

        stack.push(res ? STACK_TRUE : STACK_FALSE);

        if (op.value === opcodes.OP_CHECKSIGVERIFY) {
          if (!res)
            throw new ScriptError('CHECKSIGVERIFY', op, ip);
          stack.pop();
        }

        break;
      }
      case opcodes.OP_CHECKMULTISIG:
      case opcodes.OP_CHECKMULTISIGVERIFY: {
        if (!tx)
          throw new ScriptError('UNKNOWN_ERROR', 'No TX passed in.');

        let i = 1;
        if (stack.length < i)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        let n = Script.num(stack.top(-i), minimal).toNumber();
        let ikey2 = n + 2;

        if (!(n >= 0 && n <= consensus.MAX_MULTISIG_PUBKEYS))
          throw new ScriptError('PUBKEY_COUNT', op, ip);

        opCount += n;

        if (opCount > consensus.MAX_SCRIPT_OPS)
          throw new ScriptError('OP_COUNT', op, ip);

        i++;
        let ikey = i;
        i += n;

        if (stack.length < i)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        let m = Script.num(stack.top(-i), minimal).toNumber();

        if (!(m >= 0 && m <= n))
          throw new ScriptError('SIG_COUNT', op, ip);

        i++;
        let isig = i;
        i += m;

        if (stack.length < i)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        const subscript = this.getSubscript(lastSep);

        for (let j = 0; j < m; j++) {
          const sig = stack.top(-isig - j);
          if (version === 0)
            subscript.removeData(sig);
        }

        let res = true;
        while (res && m > 0) {
          const sig = stack.top(-isig);
          const key = stack.top(-ikey);

          validateSignature(sig, flags);
          validateKey(key, flags, version);

          if (sig.length > 0) {
            const type = sig[sig.length - 1];
            const hash = tx.signatureHash(
              index,
              subscript,
              value,
              type,
              version
            );

            if (checksig(hash, sig, key)) {
              isig++;
              m--;
            }
          }

          ikey++;
          n--;

          if (m > n)
            res = false;
        }

        while (i-- > 1) {
          if (!res && (flags & Script.flags.VERIFY_NULLFAIL)) {
            if (ikey2 === 0 && stack.top(-1).length !== 0)
              throw new ScriptError('NULLFAIL', op, ip);
          }
          if (ikey2 > 0)
            ikey2--;
          stack.pop();
        }

        if (stack.length < 1)
          throw new ScriptError('INVALID_STACK_OPERATION', op, ip);

        if (flags & Script.flags.VERIFY_NULLDUMMY) {
          if (stack.top(-1).length !== 0)
            throw new ScriptError('SIG_NULLDUMMY', op, ip);
        }

        stack.pop();

        stack.push(res ? STACK_TRUE : STACK_FALSE);

        if (op.value === opcodes.OP_CHECKMULTISIGVERIFY) {
          if (!res)
            throw new ScriptError('CHECKMULTISIGVERIFY', op, ip);
          stack.pop();
        }

        break;
      }
      default: {
        throw new ScriptError('BAD_OPCODE', op, ip);
      }
    }
  }

  if (stack.length + alt.length > consensus.MAX_SCRIPT_STACK)
    throw new ScriptError('STACK_SIZE');

  if (state.length !== 0)
    throw new ScriptError('UNBALANCED_CONDITIONAL');

  return true;
};

/**
 * Cast a big number or Buffer to a bool.
 * @see CastToBool
 * @param {BN|Buffer} value
 * @returns {Boolean}
 */

Script.bool = function bool(value) {
  assert(Buffer.isBuffer(value));

  for (let i = 0; i < value.length; i++) {
    if (value[i] !== 0) {
      // Cannot be negative zero
      if (i === value.length - 1 && value[i] === 0x80)
        return false;
      return true;
    }
  }

  return false;
};

/**
 * Create a CScriptNum.
 * @param {Buffer} value
 * @param {Boolean?} minimal
 * @param {Number?} size - Max size in bytes.
 * @returns {BN}
 * @throws {ScriptError}
 */

Script.num = function num(value, minimal, size) {
  return common.num(value, minimal, size);
};

/**
 * Create a script array. Will convert Numbers and big
 * numbers to a little-endian buffer while taking into
 * account negative zero, minimaldata, etc.
 * @example
 * assert.deepEqual(Script.array(0), Buffer.alloc(0));
 * assert.deepEqual(Script.array(0xffee), Buffer.from('eeff00', 'hex'));
 * assert.deepEqual(Script.array(new BN(0xffee)), Buffer.from('eeff00', 'hex'));
 * assert.deepEqual(Script.array(new BN(0x1e).neg()), Buffer.from('9e', 'hex'));
 * @param {Number|BN} value
 * @returns {Buffer}
 */

Script.array = function array(value) {
  return common.array(value);
};

/**
 * Remove all matched data elements from
 * a script's code (used to remove signatures
 * before verification). Note that this
 * compares and removes data on the _byte level_.
 * It also reserializes the data to a single
 * script with minimaldata encoding beforehand.
 * A signature will _not_ be removed if it is
 * not minimaldata.
 * @see https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2014-November/006878.html
 * @see https://test.webbtc.com/tx/19aa42fee0fa57c45d3b16488198b27caaacc4ff5794510d0c17f173f05587ff
 * @param {Buffer} data - Data element to match against.
 * @returns {Number} Total.
 */

Script.prototype.removeData = function removeData(data) {
  const index = [];

  // We need to go forward first. We can't go
  // backwards (this is consensus code and we
  // need to be aware of bad pushes).
  for (let i = 0; i < this.code.length; i++) {
    const op = this.code[i];

    if (op.value === -1) {
      // Can't reserialize
      // a parse error.
      if (index.length > 0)
        index.push(i);
      break;
    }

    if (!op.data)
      continue;

    if (!op.isMinimal())
      continue;

    if (op.data.equals(data))
      index.push(i);
  }

  if (index.length === 0)
    return 0;

  // Go backwards and splice out the data.
  for (let i = index.length - 1; i >= 0; i--)
    this.code.splice(index[i], 1);

  this.compile();

  return index.length;
};

/**
 * Find a data element in a script.
 * @param {Buffer} data - Data element to match against.
 * @returns {Number} Index (`-1` if not present).
 */

Script.prototype.indexOf = function indexOf(data) {
  for (let i = 0; i < this.code.length; i++) {
    const op = this.code[i];

    if (op.value === -1)
      break;

    if (!op.data)
      continue;

    if (op.data.equals(data))
      return i;
  }

  return -1;
};

/**
 * Test a script to see if it is valid
 * script code (no non-existent opcodes).
 * @returns {Boolean}
 */

Script.prototype.isCode = function isCode() {
  for (const op of this.code) {
    if (op.data)
      continue;

    if (op.value === -1)
      return false;

    if (op.value > opcodes.OP_NOP10)
      return false;
  }

  return true;
};

/**
 * Inject properties from a pay-to-pubkey script.
 * @private
 * @param {Buffer} key
 */

Script.prototype.fromPubkey = function fromPubkey(key) {
  assert(Buffer.isBuffer(key) && key.length >= 33 && key.length <= 65);

  this.raw = Buffer.allocUnsafe(1 + key.length + 1);
  this.raw[0] = key.length;
  key.copy(this.raw, 1);
  this.raw[1 + key.length] = opcodes.OP_CHECKSIG;

  key = this.raw.slice(1, 1 + key.length);

  this.code.push(new Opcode(key.length, key));
  this.code.push(new Opcode(opcodes.OP_CHECKSIG));

  return this;
};

/**
 * Create a pay-to-pubkey script.
 * @param {Buffer} key
 * @returns {Script}
 */

Script.fromPubkey = function fromPubkey(key) {
  return new Script().fromPubkey(key);
};

/**
 * Inject properties from a pay-to-pubkeyhash script.
 * @private
 * @param {Buffer} hash
 */

Script.prototype.fromPubkeyhash = function fromPubkeyhash(hash) {
  assert(Buffer.isBuffer(hash) && hash.length === 20);

  this.raw = Buffer.allocUnsafe(25);
  this.raw[0] = opcodes.OP_DUP;
  this.raw[1] = opcodes.OP_HASH160;
  this.raw[2] = 0x14;
  hash.copy(this.raw, 3);
  this.raw[23] = opcodes.OP_EQUALVERIFY;
  this.raw[24] = opcodes.OP_CHECKSIG;

  hash = this.raw.slice(3, 23);

  this.code.push(new Opcode(opcodes.OP_DUP));
  this.code.push(new Opcode(opcodes.OP_HASH160));
  this.code.push(new Opcode(0x14, hash));
  this.code.push(new Opcode(opcodes.OP_EQUALVERIFY));
  this.code.push(new Opcode(opcodes.OP_CHECKSIG));

  return this;
};

/**
 * Create a pay-to-pubkeyhash script.
 * @param {Buffer} hash
 * @returns {Script}
 */

Script.fromPubkeyhash = function fromPubkeyhash(hash) {
  return new Script().fromPubkeyhash(hash);
};

/**
 * Inject properties from pay-to-multisig script.
 * @private
 * @param {Number} m
 * @param {Number} n
 * @param {Buffer[]} keys
 */

Script.prototype.fromMultisig = function fromMultisig(m, n, keys) {
  assert(util.isNumber(m) && util.isNumber(n));
  assert(Array.isArray(keys));
  assert(keys.length === n, '`n` keys are required for multisig.');
  assert(m >= 1 && m <= n);
  assert(n >= 1 && n <= 15);

  keys = sortKeys(keys);

  this.push(Opcode.fromSmall(m));

  for (const key of keys)
    this.push(key);

  this.push(Opcode.fromSmall(n));
  this.push(opcodes.OP_CHECKMULTISIG);

  this.compile();

  return this;
};

/**
 * Create a pay-to-multisig script.
 * @param {Number} m
 * @param {Number} n
 * @param {Buffer[]} keys
 * @returns {Script}
 */

Script.fromMultisig = function fromMultisig(m, n, keys) {
  return new Script().fromMultisig(m, n, keys);
};

/**
 * Inject properties from a pay-to-scripthash script.
 * @private
 * @param {Buffer} hash
 */

Script.prototype.fromScripthash = function fromScripthash(hash) {
  assert(Buffer.isBuffer(hash) && hash.length === 20);

  this.raw = Buffer.allocUnsafe(23);
  this.raw[0] = opcodes.OP_HASH160;
  this.raw[1] = 0x14;
  hash.copy(this.raw, 2);
  this.raw[22] = opcodes.OP_EQUAL;

  hash = this.raw.slice(2, 22);

  this.code.push(new Opcode(opcodes.OP_HASH160));
  this.code.push(new Opcode(0x14, hash));
  this.code.push(new Opcode(opcodes.OP_EQUAL));

  return this;
};

/**
 * Create a pay-to-scripthash script.
 * @param {Buffer} hash
 * @returns {Script}
 */

Script.fromScripthash = function fromScripthash(hash) {
  return new Script().fromScripthash(hash);
};

/**
 * Inject properties from a nulldata/opreturn script.
 * @private
 * @param {Buffer} flags
 */

Script.prototype.fromNulldata = function fromNulldata(flags) {
  assert(Buffer.isBuffer(flags));
  assert(flags.length <= policy.MAX_OP_RETURN, 'Nulldata too large.');
  this.push(opcodes.OP_RETURN);
  this.push(flags);
  this.compile();
  return this;
};

/**
 * Create a nulldata/opreturn script.
 * @param {Buffer} flags
 * @returns {Script}
 */

Script.fromNulldata = function fromNulldata(flags) {
  return new Script().fromNulldata(flags);
};

/**
 * Inject properties from a witness program.
 * @private
 * @param {Number} version
 * @param {Buffer} data
 */

Script.prototype.fromProgram = function fromProgram(version, data) {
  assert(util.isNumber(version) && version >= 0 && version <= 16);
  assert(Buffer.isBuffer(data) && data.length >= 2 && data.length <= 40);

  const op = Opcode.fromSmall(version);

  this.raw = Buffer.allocUnsafe(2 + data.length);
  this.raw[0] = op.value;
  this.raw[1] = data.length;
  data.copy(this.raw, 2);

  data = this.raw.slice(2, 2 + data.length);

  this.code.push(op);
  this.code.push(new Opcode(data.length, data));

  return this;
};

/**
 * Create a witness program.
 * @param {Number} version
 * @param {Buffer} data
 * @returns {Script}
 */

Script.fromProgram = function fromProgram(version, data) {
  return new Script().fromProgram(version, data);
};

/**
 * Inject properties from an address.
 * @private
 * @param {Address|Base58Address} address
 */

Script.prototype.fromAddress = function fromAddress(address) {
  if (typeof address === 'string')
    address = Address.fromString(address);

  assert(address instanceof Address, 'Not an address.');

  if (address.isPubkeyhash())
    return this.fromPubkeyhash(address.hash);

  if (address.isScripthash())
    return this.fromScripthash(address.hash);

  if (address.isProgram())
    return this.fromProgram(address.version, address.hash);

  throw new Error('Unknown address type.');
};

/**
 * Create an output script from an address.
 * @param {Address|Base58Address} address
 * @returns {Script}
 */

Script.fromAddress = function fromAddress(address) {
  return new Script().fromAddress(address);
};

/**
 * Inject properties from a witness block commitment.
 * @private
 * @param {Buffer} hash
 * @param {String|Buffer} flags
 */

Script.prototype.fromCommitment = function fromCommitment(hash, flags) {
  const bw = new StaticWriter(36);

  bw.writeU32BE(0xaa21a9ed);
  bw.writeHash(hash);

  this.push(opcodes.OP_RETURN);
  this.push(bw.render());

  if (flags)
    this.push(flags);

  this.compile();

  return this;
};

/**
 * Create a witness block commitment.
 * @param {Buffer} hash
 * @param {String|Buffer} flags
 * @returns {Script}
 */

Script.fromCommitment = function fromCommitment(hash, flags) {
  return new Script().fromCommitment(hash, flags);
};

/**
 * Grab and deserialize the redeem script.
 * @returns {Script|null} Redeem script.
 */

Script.prototype.getRedeem = function getRedeem() {
  if (this.code.length === 0)
    return null;

  if (!this.isPushOnly())
    return null;

  const redeem = this.code[this.code.length - 1];

  if (!redeem.data)
    return null;

  return Script.fromRaw(redeem.data);
};

/**
 * Get the standard script type.
 * @returns {ScriptType}
 */

Script.prototype.getType = function getType() {
  if (this.isPubkey())
    return scriptTypes.PUBKEY;

  if (this.isPubkeyhash())
    return scriptTypes.PUBKEYHASH;

  if (this.isScripthash())
    return scriptTypes.SCRIPTHASH;

  if (this.isWitnessPubkeyhash())
    return scriptTypes.WITNESSPUBKEYHASH;

  if (this.isWitnessScripthash())
    return scriptTypes.WITNESSSCRIPTHASH;

  if (this.isWitnessMasthash())
    return scriptTypes.WITNESSMASTHASH;

  if (this.isMultisig())
    return scriptTypes.MULTISIG;

  if (this.isNulldata())
    return scriptTypes.NULLDATA;

  return scriptTypes.NONSTANDARD;
};

/**
 * Test whether a script is of an unknown/non-standard type.
 * @returns {Boolean}
 */

Script.prototype.isUnknown = function isUnknown() {
  return this.getType() === scriptTypes.NONSTANDARD;
};

/**
 * Test whether the script is standard by policy standards.
 * @returns {Boolean}
 */

Script.prototype.isStandard = function isStandard() {
  const type = this.getType();

  switch (type) {
    case scriptTypes.MULTISIG: {
      const m = this.getSmall(0);
      const n = this.getSmall(this.code.length - 2);

      if (n < 1 || n > 3)
        return false;

      if (m < 1 || m > n)
        return false;

      return true;
    }
    case scriptTypes.NULLDATA: {
      if (this.raw.length > policy.MAX_OP_RETURN_BYTES)
        return false;
      return true;
    }
    default: {
      return type !== scriptTypes.NONSTANDARD;
    }
  }
};

/**
 * Calculate the size of the script
 * excluding the varint size bytes.
 * @returns {Number}
 */

Script.prototype.getSize = function getSize() {
  return this.raw.length;
};

/**
 * Calculate the size of the script
 * including the varint size bytes.
 * @returns {Number}
 */

Script.prototype.getVarSize = function getVarSize() {
  return encoding.sizeVarBytes(this.raw);
};

/**
 * "Guess" the address of the input script.
 * This method is not 100% reliable.
 * @returns {Address|null}
 */

Script.prototype.getInputAddress = function getInputAddress() {
  return Address.fromInputScript(this);
};

/**
 * Get the address of the script if present. Note that
 * pubkey and multisig scripts will be treated as though
 * they are pubkeyhash and scripthashes respectively.
 * @returns {Address|null}
 */

Script.prototype.getAddress = function getAddress() {
  return Address.fromScript(this);
};

/**
 * Get the hash160 of the raw script.
 * @param {String?} enc
 * @returns {Hash}
 */

Script.prototype.hash160 = function hash160(enc) {
  let hash = digest.hash160(this.toRaw());
  if (enc === 'hex')
    hash = hash.toString('hex');
  return hash;
};

/**
 * Get the sha256 of the raw script.
 * @param {String?} enc
 * @returns {Hash}
 */

Script.prototype.sha256 = function sha256(enc) {
  let hash = digest.sha256(this.toRaw());
  if (enc === 'hex')
    hash = hash.toString('hex');
  return hash;
};

/**
 * Test whether the output script is pay-to-pubkey.
 * @param {Boolean} [minimal=false] - Minimaldata only.
 * @returns {Boolean}
 */

Script.prototype.isPubkey = function isPubkey(minimal) {
  if (minimal) {
    return this.raw.length >= 35
      && this.raw[0] >= 33 && this.raw[0] <= 65
      && this.raw[0] + 2 === this.raw.length
      && this.raw[this.raw.length - 1] === opcodes.OP_CHECKSIG;
  }

  return this.code.length === 2
    && this.code[0].data
    && common.isKey(this.code[0].data)
    && this.code[1].value === opcodes.OP_CHECKSIG;
};

/**
 * Test whether the output script is pay-to-pubkeyhash.
 * @param {Boolean} [minimal=false] - Minimaldata only.
 * @returns {Boolean}
 */

Script.prototype.isPubkeyhash = function isPubkeyhash(minimal) {
  if (minimal) {
    return this.raw.length === 25
      && this.raw[0] === opcodes.OP_DUP
      && this.raw[1] === opcodes.OP_HASH160
      && this.raw[2] === 0x14
      && this.raw[23] === opcodes.OP_EQUALVERIFY
      && this.raw[24] === opcodes.OP_CHECKSIG;
  }

  return this.code.length === 5
    && this.code[0].value === opcodes.OP_DUP
    && this.code[1].value === opcodes.OP_HASH160
    && common.isHash(this.code[2].data)
    && this.code[3].value === opcodes.OP_EQUALVERIFY
    && this.code[4].value === opcodes.OP_CHECKSIG;
};

/**
 * Test whether the output script is pay-to-multisig.
 * @param {Boolean} [minimal=false] - Minimaldata only.
 * @returns {Boolean}
 */

Script.prototype.isMultisig = function isMultisig(minimal) {
  if (this.raw.length < 41)
    return false;

  if (this.raw[this.raw.length - 1] !== opcodes.OP_CHECKMULTISIG)
    return false;

  const n = common.getSmall(this.raw[this.raw.length - 2]);

  if (n < 1)
    return false;

  const m = common.getSmall(this.raw[0]);

  if (!(m >= 1 && m <= n))
    return false;

  if (n + 3 !== this.code.length)
    return false;

  for (let i = 1; i < n + 1; i++) {
    const op = this.code[i];

    if (!common.isKey(op.data))
      return false;

    if (minimal && !op.isMinimal())
      return false;
  }

  return true;
};

/**
 * Test whether the output script is pay-to-scripthash. Note that
 * bitcoin itself requires scripthashes to be in strict minimaldata
 * encoding. Using `OP_HASH160 OP_PUSHDATA1 [hash] OP_EQUAL` will
 * _not_ be recognized as a scripthash.
 * @returns {Boolean}
 */

Script.prototype.isScripthash = function isScripthash() {
  return this.raw.length === 23
    && this.raw[0] === opcodes.OP_HASH160
    && this.raw[1] === 0x14
    && this.raw[22] === opcodes.OP_EQUAL;
};

/**
 * Test whether the output script is nulldata/opreturn.
 * @param {Boolean} [minimal=false] - Minimaldata only.
 * @returns {Boolean}
 */

Script.prototype.isNulldata = function isNulldata(minimal) {
  if (this.raw.length === 0)
    return false;

  if (this.raw[0] !== opcodes.OP_RETURN)
    return false;

  if (this.raw.length === 1)
    return true;

  if (minimal) {
    if (this.raw.length > policy.MAX_OP_RETURN_BYTES)
      return false;

    if (this.raw.length === 2)
      return common.getSmall(this.raw[1]) !== -1;

    if (this.raw[1] >= 0x01 && this.raw[1] <= 0x4b)
      return this.raw[1] + 2 === this.raw.length;

    if (this.raw[1] === opcodes.OP_PUSHDATA1)
      return this.raw[2] > 75 && this.raw[2] + 3 === this.raw.length;

    return false;
  }

  for (let i = 1; i < this.code.length; i++) {
    const op = this.code[i];

    if (op.data)
      continue;

    if (op.value === -1)
      return false;

    if (op.value > opcodes.OP_16)
      return false;
  }

  return true;
};

/**
 * Test whether the output script is a segregated witness
 * commitment.
 * @returns {Boolean}
 */

Script.prototype.isCommitment = function isCommitment() {
  return this.raw.length >= 38
    && this.raw[0] === opcodes.OP_RETURN
    && this.raw[1] === 0x24
    && this.raw.readUInt32BE(2, true) === 0xaa21a9ed;
};

/**
 * Get the commitment hash if present.
 * @returns {Buffer|null}
 */

Script.prototype.getCommitmentHash = function getCommitmentHash() {
  if (!this.isCommitment())
    return null;

  return this.raw.slice(6, 38);
};

/**
 * Test whether the output script is a witness program.
 * Note that this will return true even for malformed
 * witness v0 programs.
 * @return {Boolean}
 */

Script.prototype.isProgram = function isProgram() {
  if (!(this.raw.length >= 4 && this.raw.length <= 42))
    return false;

  if (this.raw[0] !== opcodes.OP_0
      && !(this.raw[0] >= opcodes.OP_1 && this.raw[0] <= opcodes.OP_16)) {
    return false;
  }

  if (this.raw[1] + 2 !== this.raw.length)
    return false;

  return true;
};

/**
 * Get the witness program if present.
 * @returns {Program|null}
 */

Script.prototype.toProgram = function toProgram() {
  if (!this.isProgram())
    return null;

  const version = common.getSmall(this.raw[0]);
  const data = this.raw.slice(2);

  return new Program(version, data);
};

/**
 * Get the script to the equivalent witness
 * program (mimics bitcoind's scriptForWitness).
 * @returns {Program|null}
 */

Script.prototype.forWitness = function forWitness() {
  if (this.isProgram())
    return this;

  if (this.isPubkey()) {
    const hash = digest.hash160(this.get(0));
    return Script.fromProgram(0, hash);
  }

  if (this.isPubkeyhash())
    return Script.fromProgram(0, this.get(2));

  return Script.fromProgram(0, this.sha256());
};

/**
 * Test whether the output script is
 * a pay-to-witness-pubkeyhash program.
 * @returns {Boolean}
 */

Script.prototype.isWitnessPubkeyhash = function isWitnessPubkeyhash() {
  return this.raw.length === 22
    && this.raw[0] === opcodes.OP_0
    && this.raw[1] === 0x14;
};

/**
 * Test whether the output script is
 * a pay-to-witness-scripthash program.
 * @returns {Boolean}
 */

Script.prototype.isWitnessScripthash = function isWitnessScripthash() {
  return this.raw.length === 34
    && this.raw[0] === opcodes.OP_0
    && this.raw[1] === 0x20;
};

/**
 * Test whether the output script
 * is a pay-to-mast program.
 * @returns {Boolean}
 */

Script.prototype.isWitnessMasthash = function isWitnessMasthash() {
  return this.raw.length === 34
    && this.raw[0] === opcodes.OP_1
    && this.raw[1] === 0x20;
};

/**
 * Test whether the output script is unspendable.
 * @returns {Boolean}
 */

Script.prototype.isUnspendable = function isUnspendable() {
  if (this.raw.length > consensus.MAX_SCRIPT_SIZE)
    return true;

  return this.raw.length > 0 && this.raw[0] === opcodes.OP_RETURN;
};

/**
 * "Guess" the type of the input script.
 * This method is not 100% reliable.
 * @returns {ScriptType}
 */

Script.prototype.getInputType = function getInputType() {
  if (this.isPubkeyInput())
    return scriptTypes.PUBKEY;

  if (this.isPubkeyhashInput())
    return scriptTypes.PUBKEYHASH;

  if (this.isScripthashInput())
    return scriptTypes.SCRIPTHASH;

  if (this.isMultisigInput())
    return scriptTypes.MULTISIG;

  return scriptTypes.NONSTANDARD;
};

/**
 * "Guess" whether the input script is an unknown/non-standard type.
 * This method is not 100% reliable.
 * @returns {Boolean}
 */

Script.prototype.isUnknownInput = function isUnknownInput() {
  return this.getInputType() === scriptTypes.NONSTANDARD;
};

/**
 * "Guess" whether the input script is pay-to-pubkey.
 * This method is not 100% reliable.
 * @returns {Boolean}
 */

Script.prototype.isPubkeyInput = function isPubkeyInput() {
  if (this.raw.length < 10)
    return false;

  if (this.raw.length > 78)
    return false;

  if (this.raw[0] > opcodes.OP_PUSHDATA4)
    return false;

  return this.code.length === 1
    && this.code[1].data
    && common.isSignature(this.code[0].data);
};

/**
 * "Guess" whether the input script is pay-to-pubkeyhash.
 * This method is not 100% reliable.
 * @returns {Boolean}
 */

Script.prototype.isPubkeyhashInput = function isPubkeyhashInput() {
  if (this.raw.length < 44)
    return false;

  if (this.raw.length > 148)
    return false;

  if (this.raw[0] > opcodes.OP_PUSHDATA4)
    return false;

  return this.code.length === 2
    && this.code[0].data
    && common.isSignature(this.code[0].data)
    && this.code[1].data
    && common.isKey(this.code[1].data);
};

/**
 * "Guess" whether the input script is pay-to-multisig.
 * This method is not 100% reliable.
 * @returns {Boolean}
 */

Script.prototype.isMultisigInput = function isMultisigInput() {
  if (this.raw.length < 20)
    return false;

  if (this.raw[0] !== opcodes.OP_0)
    return false;

  if (this.raw[1] > opcodes.OP_PUSHDATA4)
    return false;

  // We need to rule out scripthash
  // because it may look like multisig.
  if (this.isScripthashInput())
    return false;

  if (this.code.length < 3)
    return false;

  for (let i = 1; i < this.code.length; i++) {
    const op = this.code[i];

    if (!op.data)
      return false;

    if (!common.isSignature(op.data))
      return false;
  }

  return true;
};

/**
 * "Guess" whether the input script is pay-to-scripthash.
 * This method is not 100% reliable.
 * @returns {Boolean}
 */

Script.prototype.isScripthashInput = function isScripthashInput() {
  if (this.raw.length < 2)
    return false;

  // Grab the raw redeem script.
  const op = this.code[this.code.length - 1];

  // Last data element should be an array
  // for the redeem script.
  if (!op.data)
    return false;

  // Testing for scripthash inputs requires
  // some evil magic to work. We do it by
  // ruling things _out_. This test will not
  // be correct 100% of the time. We rule
  // out that the last data element is: a
  // null dummy, a valid signature, a valid
  // key, and we ensure that it is at least
  // a script that does not use undefined
  // opcodes.
  if (op.data.length === 0)
    return false;

  if (common.isSignatureEncoding(op.data))
    return false;

  if (common.isKeyEncoding(op.data))
    return false;

  const redeem = Script.fromRaw(op.data);

  if (!redeem.isCode())
    return false;

  return true;
};

/**
 * Get coinbase height.
 * @returns {Number} `-1` if not present.
 */

Script.prototype.getCoinbaseHeight = function getCoinbaseHeight() {
  return Script.getCoinbaseHeight(this.raw);
};

/**
 * Get coinbase height.
 * @param {Buffer} raw - Raw script.
 * @returns {Number} `-1` if not present.
 */

Script.getCoinbaseHeight = function getCoinbaseHeight(raw) {
  if (raw.length === 0)
    return -1;

  // Small ints are allowed.
  const smi = common.getSmall(raw[0]);

  if (smi !== -1)
    return smi;

  // No more than 6 bytes (we can't
  // handle 7 byte JS numbers and
  // height 281 trillion is far away).
  if (raw[0] > 0x06)
    return -1;

  // No bad pushes allowed.
  if (raw.length < 1 + raw[0])
    return -1;

  const data = raw.slice(1, 1 + raw[0]);

  // Deserialize the height.
  let height;
  try {
    height = Script.num(data, true, 6);
  } catch (e) {
    return -1;
  }

  // Reserialize the height.
  const op = Opcode.fromNumber(height);

  // Should have been OP_0-OP_16.
  if (!op.data)
    return -1;

  // Ensure the miner serialized the
  // number in the most minimal fashion.
  if (!data.equals(op.data))
    return -1;

  return height.toNumber();
};

/**
 * Test the script against a bloom filter.
 * @param {Bloom} filter
 * @returns {Boolean}
 */

Script.prototype.test = function test(filter) {
  for (const op of this.code) {
    if (op.value === -1)
      break;

    if (!op.data || op.data.length === 0)
      continue;

    if (filter.test(op.data))
      return true;
  }

  return false;
};

/**
 * Unshift an item onto the `code` array.
 * @param {Number|String|BN|Buffer} data
 * @returns {Number} Length.
 */

Script.prototype.unshift = function unshift(data) {
  return this.code.unshift(Opcode.from(data));
};

/**
 * Push an item onto the `code` array.
 * @param {Number|String|BN|Buffer} data
 * @returns {Number} Length.
 */

Script.prototype.push = function push(data) {
  return this.code.push(Opcode.from(data));
};

/**
 * Shift an item off of the `code` array.
 * @returns {Buffer}
 */

Script.prototype.shift = function shift() {
  const op = this.code.shift();

  if (!op)
    return null;

  return op.data || op.value;
};

/**
 * Pop an item off of the `code` array.
 * @returns {Buffer}
 */

Script.prototype.pop = function pop(data) {
  const op = this.code.pop();

  if (!op)
    return null;

  return op.data || op.value;
};

/**
 * Remove an item from the `code` array.
 * @param {Number} index
 * @returns {Buffer|Number}
 */

Script.prototype.remove = function remove(i) {
  const op = this.code.splice(i, 1)[0];

  if (!op)
    return null;

  return op.data || op.value;
};

/**
 * Insert an item into the `code` array.
 * @param {Number} index
 * @param {Number|String|BN|Buffer} data
 */

Script.prototype.insert = function insert(i, data) {
  assert(i <= this.code.length, 'Index out of bounds.');
  this.code.splice(i, 0, Opcode.from(data));
};

/**
 * Get an item from the `code` array.
 * @param {Number} index
 * @returns {Buffer}
 */

Script.prototype.get = function get(i) {
  const op = this.code[i];

  if (!op)
    return null;

  return op.data || op.value;
};

/**
 * Get a small integer from an opcode (OP_0-OP_16).
 * @param {Number} index
 * @returns {Number}
 */

Script.prototype.getSmall = function getSmall(i) {
  const op = this.code[i];

  if (!op)
    return -1;

  return common.getSmall(op.value);
};

/**
 * Get a number from the `code` array (5-byte limit).
 * @params {Number} index
 * @returns {BN}
 */

Script.prototype.getNumber = function getNumber(i) {
  const small = this.getSmall(i);
  const op = this.code[i];

  if (small !== -1)
    return new BN(small);

  if (!op || !op.data || op.data.length > 5)
    return null;

  return Script.num(op.data, false, 5);
};

/**
 * Get a string from the `code` array (utf8).
 * @params {Number} index
 * @returns {String}
 */

Script.prototype.getString = function getString(i) {
  const op = this.code[i];

  if (!op || !op.data)
    return null;

  return op.data.toString('utf8');
};

/**
 * Clear the script code.
 */

Script.prototype.clear = function clear() {
  this.code.length = 0;
};

/**
 * Set an item in the `code` array.
 * @param {Number} index
 * @param {Buffer|Number|String|BN} data
 */

Script.prototype.set = function set(i, data) {
  assert(i <= this.code.length, 'Index out of bounds.');
  this.code[i] = Opcode.from(data);
};

/**
 * Test whether the data element is a public key. Note that
 * this does not verify the format of the key, only the length.
 * @param {Buffer?} key
 * @returns {Boolean}
 */

Script.isKey = function isKey(key) {
  return common.isKey(key);
};

/**
 * Test whether the data element is a signature. Note that
 * this does not verify the format of the signature, only the length.
 * @param {Buffer?} sig
 * @returns {Boolean}
 */

Script.isSignature = function isSignature(sig) {
  return common.isSignature(sig);
};

/**
 * Test the script to see if it contains only push ops.
 * Push ops are: OP_1NEGATE, OP_0-OP_16 and all PUSHDATAs.
 * @returns {Boolean}
 */

Script.prototype.isPushOnly = function isPushOnly() {
  for (const op of this.code) {
    if (op.data)
      continue;

    if (op.value === -1)
      return false;

    if (op.value > opcodes.OP_16)
      return false;
  }

  return true;
};

/**
 * Count the sigops in the script.
 * @param {Boolean} accurate - Whether to enable accurate counting. This will
 * take into account the `n` value for OP_CHECKMULTISIG(VERIFY).
 * @returns {Number} sigop count
 */

Script.prototype.getSigops = function getSigops(accurate) {
  let total = 0;
  let lastOp = -1;

  for (const op of this.code) {
    if (op.data)
      continue;

    if (op.value === -1)
      break;

    switch (op.value) {
      case opcodes.OP_CHECKSIG:
      case opcodes.OP_CHECKSIGVERIFY:
        total++;
        break;
      case opcodes.OP_CHECKMULTISIG:
      case opcodes.OP_CHECKMULTISIGVERIFY:
        if (accurate && lastOp >= opcodes.OP_1 && lastOp <= opcodes.OP_16)
          total += lastOp - 0x50;
        else
          total += consensus.MAX_MULTISIG_PUBKEYS;
        break;
    }

    lastOp = op.value;
  }

  return total;
};

/**
 * Count the sigops in the script, taking into account redeem scripts.
 * @param {Script} input - Input script, needed for access to redeem script.
 * @returns {Number} sigop count
 */

Script.prototype.getScripthashSigops = function getScripthashSigops(input) {
  if (!this.isScripthash())
    return this.getSigops(true);

  if (input.code.length === 0)
    return 0;

  let op;

  for (op of input.code) {
    if (op.data)
      continue;

    if (op.value === -1)
      return 0;

    if (op.value > opcodes.OP_16)
      return 0;
  }

  if (!op.data)
    return 0;

  const redeem = new Script(op.data);

  return redeem.getSigops(true);
};

/**
 * Count the sigops for a program.
 * @param {Program} program
 * @param {Witness} witness
 * @returns {Number} sigop count
 */

Script.witnessSigops = function witnessSigops(program, witness) {
  if (program.version === 0) {
    if (program.data.length === 20)
      return 1;

    if (program.data.length === 32 && witness.items.length > 0) {
      const redeem = witness.getRedeem();
      return redeem.getSigops(true);
    }
  }

  return 0;
};

/**
 * Count the sigops in a script, taking into account witness programs.
 * @param {Script} input
 * @param {Witness} witness
 * @returns {Number} sigop count
 */

Script.prototype.getWitnessSigops = function getWitnessSigops(input, witness) {
  if (this.isProgram())
    return Script.witnessSigops(this.toProgram(), witness);

  // This is a unique situation in terms of consensus
  // rules. We can just grab the redeem script without
  // "parsing" (i.e. checking for pushdata parse errors)
  // the script. This is because isPushOnly is called
  // which checks for parse errors and will return
  // false if one is found. Even the bitcoind code
  // does not check the return value of GetOp.
  if (this.isScripthash() && input.isPushOnly()) {
    const redeem = input.getRedeem();
    if (redeem && redeem.isProgram())
      return Script.witnessSigops(redeem.toProgram(), witness);
  }

  return 0;
};

/**
 * Inject properties from bitcoind test string.
 * @private
 * @param {String} items - Script string.
 * @throws Parse error.
 */

Script.prototype.fromString = function fromString(code) {
  assert(typeof code === 'string');

  code = code.trim();

  if (code.length === 0)
    return this;

  const items = code.split(/\s+/);
  const bw = new BufferWriter();

  for (const item of items) {
    let symbol = item;

    if (!util.isUpperCase(symbol))
      symbol = symbol.toUpperCase();

    if (!util.startsWith(symbol, 'OP_'))
      symbol = `OP_${symbol}`;

    const value = opcodes[symbol];

    if (value == null) {
      if (item[0] === '\'') {
        assert(item[item.length - 1] === '\'', 'Unknown opcode.');
        const str = item.slice(1, -1);
        const op = Opcode.fromString(str);
        bw.writeBytes(op.toRaw());
        continue;
      }

      if (/^-?\d+$/.test(item)) {
        const num = new BN(item, 10);
        const op = Opcode.fromNumber(num);
        bw.writeBytes(op.toRaw());
        continue;
      }

      assert(item.indexOf('0x') === 0, 'Unknown opcode.');

      const str = item.substring(2);
      const data = Buffer.from(str, 'hex');

      assert(data.length === str.length / 2, 'Unknown opcode.');

      bw.writeBytes(data);

      continue;
    }

    bw.writeU8(value);
  }

  return this.fromRaw(bw.render());
};

/**
 * Parse a bitcoind test script
 * string into a script object.
 * @param {String} items - Script string.
 * @returns {Script}
 * @throws Parse error.
 */

Script.fromString = function fromString(code) {
  return new Script().fromString(code);
};

/**
 * Verify an input and output script, and a witness if present.
 * @param {Script} input
 * @param {Witness} witness
 * @param {Script} output
 * @param {TX} tx
 * @param {Number} i
 * @param {Amount} value
 * @param {VerifyFlags} flags
 * @returns {Boolean}
 * @throws {ScriptError}
 */

Script.verify = function verify(input, witness, output, tx, i, value, flags) {
  if (flags == null)
    flags = Script.flags.STANDARD_VERIFY_FLAGS;

  if (flags & Script.flags.VERIFY_SIGPUSHONLY) {
    if (!input.isPushOnly())
      throw new ScriptError('SIG_PUSHONLY');
  }

  // Setup a stack.
  let stack = new Stack();

  // Execute the input script
  input.execute(stack, flags, tx, i, value, 0);

  // Copy the stack for P2SH
  let copy;
  if (flags & Script.flags.VERIFY_P2SH)
    copy = stack.clone();

  // Execute the previous output script.
  output.execute(stack, flags, tx, i, value, 0);

  // Verify the stack values.
  if (stack.length === 0 || !Script.bool(stack.top(-1)))
    throw new ScriptError('EVAL_FALSE');

  let hadWitness = false;

  if ((flags & Script.flags.VERIFY_WITNESS) && output.isProgram()) {
    hadWitness = true;

    // Input script must be empty.
    if (input.raw.length !== 0)
      throw new ScriptError('WITNESS_MALLEATED');

    // Verify the program in the output script.
    Script.verifyProgram(witness, output, flags, tx, i, value);

    // Force a cleanstack
    stack.length = 1;
  }

  // If the script is P2SH, execute the real output script
  if ((flags & Script.flags.VERIFY_P2SH) && output.isScripthash()) {
    // P2SH can only have push ops in the scriptSig
    if (!input.isPushOnly())
      throw new ScriptError('SIG_PUSHONLY');

    // Reset the stack
    stack = copy;

    // Stack should not be empty at this point
    if (stack.length === 0)
      throw new ScriptError('EVAL_FALSE');

    // Grab the real redeem script
    const raw = stack.pop();
    const redeem = new Script(raw);

    // Execute the redeem script.
    redeem.execute(stack, flags, tx, i, value, 0);

    // Verify the the stack values.
    if (stack.length === 0 || !Script.bool(stack.top(-1)))
      throw new ScriptError('EVAL_FALSE');

    if ((flags & Script.flags.VERIFY_WITNESS) && redeem.isProgram()) {
      hadWitness = true;

      // Input script must be exactly one push of the redeem script.
      if (!input.raw.equals(Opcode.fromPush(raw).toRaw()))
        throw new ScriptError('WITNESS_MALLEATED_P2SH');

      // Verify the program in the redeem script.
      Script.verifyProgram(witness, redeem, flags, tx, i, value);

      // Force a cleanstack.
      stack.length = 1;
    }
  }

  // Ensure there is nothing left on the stack.
  if (flags & Script.flags.VERIFY_CLEANSTACK) {
    assert((flags & Script.flags.VERIFY_P2SH) !== 0);
    if (stack.length !== 1)
      throw new ScriptError('CLEANSTACK');
  }

  // If we had a witness but no witness program, fail.
  if (flags & Script.flags.VERIFY_WITNESS) {
    assert((flags & Script.flags.VERIFY_P2SH) !== 0);
    if (!hadWitness && witness.items.length > 0)
      throw new ScriptError('WITNESS_UNEXPECTED');
  }

  return true;
};

/**
 * Verify a witness program. This runs after regular script
 * execution if a witness program is present. It will convert
 * the witness to a stack and execute the program.
 * @param {Witness} witness
 * @param {Script} output
 * @param {VerifyFlags} flags
 * @param {TX} tx
 * @param {Number} i
 * @param {Amount} value
 * @returns {Boolean}
 * @throws {ScriptError}
 */

Script.verifyProgram = function verifyProgram(witness, output, flags, tx, i, value) {
  const program = output.toProgram();

  assert(program, 'verifyProgram called on non-witness-program.');
  assert((flags & Script.flags.VERIFY_WITNESS) !== 0);

  const stack = witness.toStack();
  let redeem;

  if (program.version === 0) {
    if (program.data.length === 32) {
      if (stack.length === 0)
        throw new ScriptError('WITNESS_PROGRAM_WITNESS_EMPTY');

      const witnessScript = stack.pop();

      if (!digest.sha256(witnessScript).equals(program.data))
        throw new ScriptError('WITNESS_PROGRAM_MISMATCH');

      redeem = new Script(witnessScript);
    } else if (program.data.length === 20) {
      if (stack.length !== 2)
        throw new ScriptError('WITNESS_PROGRAM_MISMATCH');

      redeem = Script.fromPubkeyhash(program.data);
    } else {
      // Failure on version=0 (bad program data length).
      throw new ScriptError('WITNESS_PROGRAM_WRONG_LENGTH');
    }
  } else if ((flags & Script.flags.VERIFY_MAST) && program.version === 1) {
    return Script.verifyMast(program, stack, output, flags, tx, i);
  } else {
    // Anyone can spend (we can return true here
    // if we want to always relay these transactions).
    // Otherwise, if we want to act like an "old"
    // implementation and only accept them in blocks,
    // we can use the regular output script which will
    // succeed in a block, but fail in the mempool
    // due to VERIFY_CLEANSTACK.
    if (flags & Script.flags.VERIFY_DISCOURAGE_UPGRADABLE_WITNESS_PROGRAM)
      throw new ScriptError('DISCOURAGE_UPGRADABLE_WITNESS_PROGRAM');
    return true;
  }

  // Witnesses still have push limits.
  for (let j = 0; j < stack.length; j++) {
    if (stack.get(j).length > consensus.MAX_SCRIPT_PUSH)
      throw new ScriptError('PUSH_SIZE');
  }

  // Verify the redeem script.
  redeem.execute(stack, flags, tx, i, value, 1);

  // Verify the stack values.
  if (stack.length !== 1 || !Script.bool(stack.top(-1)))
    throw new ScriptError('EVAL_FALSE');

  return true;
};

/**
 * Verify a MAST witness program.
 * @param {Program} program
 * @param {Stack} stack
 * @param {Script} output
 * @param {VerifyFlags} flags
 * @param {TX} tx
 * @param {Number} i
 * @param {Amount} value
 * @returns {Boolean}
 * @throws {ScriptError}
 */

Script.verifyMast = function verifyMast(program, stack, output, flags, tx, i, value) {
  assert(program.version === 1);
  assert((flags & Script.flags.VERIFY_MAST) !== 0);

  if (stack.length < 4)
    throw new ScriptError('INVALID_MAST_STACK');

  const metadata = stack.top(-1);
  if (metadata.length < 1 || metadata.length > 5)
    throw new ScriptError('INVALID_MAST_STACK');

  const subscripts = metadata[0];
  if (subscripts === 0 || stack.length < subscripts + 3)
    throw new ScriptError('INVALID_MAST_STACK');

  let ops = subscripts;
  let scriptRoot = new BufferWriter();
  scriptRoot.writeU8(subscripts);

  if (metadata[metadata.length - 1] === 0x00)
    throw new ScriptError('INVALID_MAST_STACK');

  let version = 0;

  for (let j = 1; j < metadata.length; j++)
    version |= metadata[i] << 8 * (j - 1);

  if (version < 0)
    version += 0x100000000;

  if (version > 0) {
    if (flags & Script.flags.DISCOURAGE_UPGRADABLE_WITNESS_PROGRAM)
      throw new ScriptError('DISCOURAGE_UPGRADABLE_WITNESS_PROGRAM');
  }

  let mastRoot = new BufferWriter();
  mastRoot.writeU32(version);

  const pathdata = stack.top(-2);

  if (pathdata.length & 0x1f)
    throw new ScriptError('INVALID_MAST_STACK');

  const depth = pathdata.length >>> 5;

  if (depth > 32)
    throw new ScriptError('INVALID_MAST_STACK');

  ops += depth;
  if (version === 0) {
    if (ops > consensus.MAX_SCRIPT_OPS)
      throw new ScriptError('OP_COUNT');
  }

  const path = [];

  for (let j = 0; j < depth; j++)
    path.push(pathdata.slice(j * 32, j * 32 + 32));

  const posdata = stack.top(-3);

  if (posdata.length > 4)
    throw new ScriptError('INVALID_MAST_STACK');

  let pos = 0;
  if (posdata.length > 0) {
    if (posdata[posdata.length - 1] === 0x00)
      throw new ScriptError('INVALID_MAST_STACK');

    for (let j = 0; j < posdata.length; j++)
      pos |= posdata[i] << 8 * j;

    if (pos < 0)
      pos += 0x100000000;
  }

  if (depth < 32) {
    if (pos >= ((1 << depth) >>> 0))
      throw new ScriptError('INVALID_MAST_STACK');
  }

  let scripts = new BufferWriter();
  scripts.writeBytes(output.raw);

  for (let j = 0; j < subscripts; j++) {
    const script = stack.top(-(4 + j));
    if (version === 0) {
      if ((scripts.written + script.length) > consensus.MAX_SCRIPT_SIZE)
        throw new ScriptError('SCRIPT_SIZE');
    }
    scriptRoot.writeBytes(digest.hash256(script));
    scripts.writeBytes(script);
  }

  scriptRoot = digest.hash256(scriptRoot.render());
  scriptRoot = merkle.verifyBranch(scriptRoot, path, pos);

  mastRoot.writeBytes(scriptRoot);
  mastRoot = digest.hash256(mastRoot.render());

  if (!mastRoot.equals(program.data))
    throw new ScriptError('WITNESS_PROGRAM_MISMATCH');

  if (version === 0) {
    stack.length -= 3 + subscripts;

    for (let j = 0; j < stack.length; j++) {
      if (stack.get(j).length > consensus.MAX_SCRIPT_PUSH)
        throw new ScriptError('PUSH_SIZE');
    }

    scripts = scripts.render();
    output = new Script(scripts);
    output.execute(stack, flags, tx, i, value, 1);

    if (stack.length !== 0)
      throw new ScriptError('EVAL_FALSE');
  }

  return true;
};

/**
 * Inject properties from buffer reader.
 * @private
 * @param {BufferReader} br
 */

Script.prototype.fromReader = function fromReader(br) {
  return this.fromRaw(br.readVarBytes());
};

/**
 * Inject properties from serialized data.
 * @private
 * @param {Buffer}
 */

Script.prototype.fromRaw = function fromRaw(data) {
  const br = new BufferReader(data, true);

  this.raw = data;

  while (br.left())
    this.code.push(Opcode.fromReader(br));

  return this;
};

/**
 * Create a script from buffer reader.
 * @param {BufferReader} br
 * @param {String?} enc - Either `"hex"` or `null`.
 * @returns {Script}
 */

Script.fromReader = function fromReader(br) {
  return new Script().fromReader(br);
};

/**
 * Create a script from a serialized buffer.
 * @param {Buffer|String} data - Serialized script.
 * @param {String?} enc - Either `"hex"` or `null`.
 * @returns {Script}
 */

Script.fromRaw = function fromRaw(data, enc) {
  if (typeof data === 'string')
    data = Buffer.from(data, enc);
  return new Script().fromRaw(data);
};

/**
 * Test whether an object a Script.
 * @param {Object} obj
 * @returns {Boolean}
 */

Script.isScript = function isScript(obj) {
  return obj
    && Buffer.isBuffer(obj.raw)
    && typeof obj.getSubscript === 'function';
};

/*
 * Helpers
 */

function sortKeys(keys) {
  return keys.slice().sort((a, b) => {
    return a.compare(b);
  });
}

/**
 * Test whether the data element is a valid key if VERIFY_STRICTENC is enabled.
 * @param {Buffer} key
 * @param {VerifyFlags?} flags
 * @returns {Boolean}
 * @throws {ScriptError}
 */

function validateKey(key, flags, version) {
  assert(Buffer.isBuffer(key));
  assert(typeof flags === 'number');
  assert(typeof version === 'number');

  if (flags & Script.flags.VERIFY_STRICTENC) {
    if (!common.isKeyEncoding(key))
      throw new ScriptError('PUBKEYTYPE');
  }

  if (version === 1) {
    if (flags & Script.flags.VERIFY_WITNESS_PUBKEYTYPE) {
      if (!common.isCompressedEncoding(key))
        throw new ScriptError('WITNESS_PUBKEYTYPE');
    }
  }

  return true;
}

/**
 * Test whether the data element is a valid signature based
 * on the encoding, S value, and sighash type. Requires
 * VERIFY_DERSIG|VERIFY_LOW_S|VERIFY_STRICTENC, VERIFY_LOW_S
 * and VERIFY_STRING_ENC to be enabled respectively. Note that
 * this will allow zero-length signatures.
 * @param {Buffer} sig
 * @param {VerifyFlags?} flags
 * @returns {Boolean}
 * @throws {ScriptError}
 */

function validateSignature(sig, flags) {
  assert(Buffer.isBuffer(sig));
  assert(typeof flags === 'number');

  // Allow empty sigs
  if (sig.length === 0)
    return true;

  if ((flags & Script.flags.VERIFY_DERSIG)
      || (flags & Script.flags.VERIFY_LOW_S)
      || (flags & Script.flags.VERIFY_STRICTENC)) {
    if (!common.isSignatureEncoding(sig))
      throw new ScriptError('SIG_DER');
  }

  if (flags & Script.flags.VERIFY_LOW_S) {
    if (!common.isLowDER(sig))
      throw new ScriptError('SIG_HIGH_S');
  }

  if (flags & Script.flags.VERIFY_STRICTENC) {
    if (!common.isHashType(sig))
      throw new ScriptError('SIG_HASHTYPE');
  }

  return true;
}

/**
 * Verify a signature, taking into account sighash type.
 * @param {Buffer} msg - Signature hash.
 * @param {Buffer} sig
 * @param {Buffer} key
 * @returns {Boolean}
 */

function checksig(msg, sig, key) {
  return secp256k1.verify(msg, sig.slice(0, -1), key);
}

/*
 * Expose
 */

module.exports = Script;