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

var bcoin = require('../bcoin');
var bn = require('bn.js');
var constants = bcoin.protocol.constants;
var utils = require('./utils');
var assert = utils.assert;
var BufferWriter = require('./writer');

function Witness(items) {
  if (!(this instanceof Witness))
    return new Witness(items);

  if (Buffer.isBuffer(items))
    this.items = Witness.decode(items);
  else if (items)
    this.items = items || [];

  this.redeem = null;
}

Witness.prototype.inspect = function inspect() {
  return Script.format(this.items);
};

Witness.prototype.encode = function encode() {
  return bcoin.protocol.framer.witness(this);
};

Witness.encode = function encode(witness) {
  return bcoin.protocol.framer.witness(witness);
};

Witness.decode = function decode(buf) {
  return bcoin.protocol.parser.parseWitness(buf).witness.items;
};

Witness.prototype.clone = function clone() {
  return new Witness(this.items.slice());
};

Witness.prototype.toStack = function toStack() {
  return new Stack(this.items.slice());
};

Witness.prototype.getInputType = function getInputType(prev) {
  return Script.getInputType(this.items, prev, true);
};

Witness.prototype.getInputAddress = function getInputAddress(prev) {
  return Script.getInputAddress(this.items, prev, true);
};

Witness.prototype.getInputHash = function getInputHash(prev) {
  return Script.getInputHash(this.items, prev, true);
};

Witness.prototype.isPubkeyInput = function isPubkeyInput(key) {
  return Script.isPubkeyInput(this.items, key);
};

Witness.prototype.isPubkeyhashInput = function isPubkeyhashInput(hash) {
  return Script.isPubkeyhashInput(this.items, hash);
};

Witness.prototype.isMultisigInput = function isMultisigInput(keys) {
  return Script.isMultisigInput(this.items, keys, true);
};

Witness.prototype.isScripthashInput = function isScripthashInput(redeem) {
  return Script.isScripthashInput(this.items, redeem, true);
};

Witness.prototype.getRedeem = function getRedeem() {
  if (!this.redeem)
    this.redeem = Script.getRedeem(this.items);

  return this.redeem;
};

Witness.fromString = function fromString(items) {
  var i, op;

  items = items.trim().split(/\s+/);

  // Remove OP_ prefixes and lowercase
  for (i = 0; i < items.length; i++) {
    op = items[i];
    if (typeof op === 'string') {
      op = op.toLowerCase();
      if (op.indexOf('op_') === 0)
        op = op.slice(3);
    }
    items[i] = op;
  }

  // Convert OP_FALSE to 0, convert OP_1-OP_16
  // to number literals, convert -1 to OP_1NEGATE.
  // Convert hex strings to arrays.
  for (i = 0; i < items.length; i++) {
    op = items[i];

    if (op === '-1' || op === '1negate') {
      op = new Buffer([0xff]);
    } else if (op === '0' || op === 'false') {
      op = new Buffer([]);
    } else if (op === 'true') {
      op = new Buffer([1]);
    } else if (+op >= 1 && +op <= 16) {
      op = new Buffer([+op]);
    } else if (constants.opcodes[op] == null) {
      if (op[0] === '[')
        op = op.slice(1, -1);
      if (op.indexOf('0x') === 0)
        op = op.substring(2);
      assert(utils.isHex(op), 'Non hex-string.');
      op = new Buffer(op, 'hex');
    } else {
      assert(false, 'Non-stack item in witness string.');
    }

    items[i] = op;
  }

  return new Witness(items);
};

Witness.isWitness = function isWitness(obj) {
  return obj
    && Array.isArray(obj.items)
    && typeof obj.toStack === 'function';
};

function Stack(items) {
  this.items = items || [];
  this.alt = [];
}

Stack.prototype.inspect = function inspect() {
  return Script.format(this.items);
};

Stack.prototype.__defineGetter__('length', function() {
  return this.items.length;
});

Stack.prototype.__defineSetter__('length', function(value) {
  return this.items.length = value;
});

Stack.prototype.getRedeem = function getRedeem() {
  var redeem = Script.getRedeem(this.items);
  if (!redeem)
    return;
  this.pop();
  return redeem;
};

Stack.prototype.clone = function clone() {
  var stack = new Stack(this.items.slice());
  stack.alt = this.alt.slice();
  return stack;
};

Stack.prototype.getSize = function getSize() {
  return this.items.length + this.alt.length;
};

Stack.prototype.push = function push(item) {
  return this.items.push(item);
};

Stack.prototype.unshift = function unshift(item) {
  return this.items.unshift(item);
};

Stack.prototype.slice = function slice(start, end) {
  return this.items.slice(start, end);
};

Stack.prototype.splice = function splice(i, remove, insert) {
  return this.items.splice(i, remove, insert);
};

Stack.prototype.pop = function pop() {
  return this.items.pop();
};

Stack.prototype.shift = function shift() {
  return this.items.shift();
};

Stack.prototype.get = function get(i) {
  return this.items[i];
};

Stack.prototype.top = function top(i) {
  return this.items[this.items.length + i];
};

Stack.prototype.set = function set(i, value) {
  return this.items[i] = value;
};

Stack.prototype._swap = function _swap(i1, i2) {
  var v1, v2;

  i1 = this.items.length + i1;
  i2 = this.items.length + i2;

  v1 = this.items[i1];
  v2 = this.items[i2];

  this.items[i1] = v2;
  this.items[i2] = v1;
};

Stack.prototype.toalt = function toalt() {
  if (this.length === 0)
    throw new Error('Bad stack length.');

  this.alt.push(this.pop());
};

Stack.prototype.fromalt = function fromalt() {
  if (this.alt.length === 0)
    throw new Error('Bad stack length.');

  this.push(this.alt.pop());
};

Stack.prototype.ifdup = function ifdup() {
  if (this.length === 0)
    throw new Error('Bad stack length.');

  if (Script.bool(this.top(-1)))
    this.push(Script.array(this.top(-1)));
};

Stack.prototype.depth = function depth() {
  this.push(Script.array(this.length));
};

Stack.prototype.drop = function drop() {
  if (this.length === 0)
    throw new Error('Bad stack length.');

  this.pop();
};

Stack.prototype.dup = function dup() {
  if (this.length === 0)
    throw new Error('Bad stack length.');

  this.push(this.top(-1));
};

Stack.prototype.nip = function nip() {
  if (this.length < 2)
    throw new Error('Bad stack length.');

  this.splice(this.length - 2, 1);
};

Stack.prototype.over = function over() {
  if (this.length < 2)
    throw new Error('Bad stack length.');

  this.push(this.top(-2));
};

Stack.prototype.pick = function pick(flags) {
  return this._pickroll('pick', flags);
};

Stack.prototype.roll = function roll(flags) {
  return this._pickroll('roll', flags);
};

Stack.prototype._pickroll = function pickroll(op, flags) {
  var val, n;

  if (this.length < 2)
    throw new Error('Bad stack length.');

  val = this.pop();
  n = Script.num(val, flags).toNumber();

  if (n <= 0 || n > this.length)
    throw new Error('Bad value.');

  val = this.get(-n - 1);

  if (op === 'roll')
    this.splice(this.length - n - 1, 1);

  this.push(val);
};

Stack.prototype.rot = function rot() {
  if (this.length < 3)
    throw new Error('Bad stack length.');

  this._swap(-3, -2);
  this._swap(-2, -1);
};

Stack.prototype.swap = function swap() {
  if (this.length < 2)
    throw new Error('Bad stack length.');

  this._swap(-2, -1);
};

Stack.prototype.tuck = function tuck() {
  if (this.length < 2)
    throw new Error('Bad stack length.');

  this.splice(this.length - 2, 0, this.top(-1));
};

Stack.prototype.drop2 = function drop2() {
  if (this.length < 2)
    throw new Error('Bad stack length.');

  this.pop();
  this.pop();
};

Stack.prototype.dup2 = function dup2() {
  var v1, v2;

  if (this.length < 2)
    throw new Error('Bad stack length.');

  v1 = this.top(-2);
  v2 = this.top(-1);

  this.push(v1);
  this.push(v2);
};

Stack.prototype.dup3 = function dup3() {
  var v1, v2, v3;

  if (this.length < 3)
    throw new Error('Bad stack length.');

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

  this.push(v1);
  this.push(v2);
  this.push(v3);
};

Stack.prototype.over2 = function over2() {
  var v1, v2;

  if (this.length < 4)
    throw new Error('Bad stack length.');

  v1 = this.top(-4);
  v2 = this.top(-3);

  this.push(v1);
  this.push(v2);
};

Stack.prototype.rot2 = function rot2() {
  var v1, v2;

  if (this.length < 6)
    throw new Error('Bad stack length.');

  v1 = this.top(-6);
  v2 = this.top(-5);

  this.splice(this.length - 6, 2);
  this.push(v1);
  this.push(v2);
};

Stack.prototype.swap2 = function swap2() {
  this._swap(-4, -2);
  this._swap(-3, -1);
};

Stack.prototype.size = function size() {
  if (this.length < 1)
    throw new Error('Bad stack length.');

  this.push(Script.array(this.top(-1).length));
};

Stack.isStack = function isStack(obj) {
  return obj && Array.isArray(obj.alt) && typeof obj.swap2 === 'function';
};

/**
 * Script
 */

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

  if (Buffer.isBuffer(code)) {
    this.raw = code;
    this.code = Script.decode(code);
  } else {
    if (!code)
      code = [];
    assert(Array.isArray(code));
    this.raw = null;
    this.code = code;
  }

  this.redeem = null;
}

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

Script.prototype.inspect = function inspect() {
  return Script.format(this.code);
};

Script.prototype.encode = function encode() {
  if (!this.raw)
    this.raw = Script.encode(this.code);
  return this.raw;
};

Script.prototype.getSubscript = function getSubscript(lastSep) {
  var res = [];
  var i;

  if (lastSep == null)
    lastSep = -1;

  assert(lastSep <= 0 || this.code[lastSep] === 'codeseparator');

  for (i = lastSep + 1; i < this.code.length; i++) {
    if (this.code[i] !== 'codeseparator')
      res.push(this.code[i]);
  }

  // Optimization: avoid re-rendering
  // of the script in 99.9% of cases.
  if (res.length === this.code.length) {
    res = this.clone();
    res.raw = this.raw;
    return res;
  }

  return new Script(res);
};

Script.prototype._next = function _next(to, code, ip) {
  var depth = 0;
  var op;

  while (code[ip]) {
    op = code[ip];

    if (op === 'if' || op === 'notif')
      depth++;
    else if (op === 'else')
      depth--;
    else if (op === 'endif')
      depth--;

    if (depth < 0)
      break;

    if (depth === 0 && op === to)
      return ip;

    if (op === 'else')
      depth++;

    ip++;
  }

  return -1;
};

Script.prototype.execute = function execute(stack, tx, index, flags, version) {
  try {
    return this._execute(stack, tx, index, flags, version);
  } catch (e) {
    utils.debug('Script error: %s.', e.message);
    return false;
  }
};

Script.prototype._execute = function _execute(stack, tx, index, flags, version) {
  var code = this.code.slice();
  var ip = 0;
  var lastSep = -1;
  var op, val;
  var if_, else_, endif;
  var n, n1, n2, n3;
  var res;
  var key, sig, type, subscript, hash;
  var keys, i, j, m;
  var succ;
  var locktime;

  if (flags == null)
    flags = constants.flags.STANDARD_VERIFY_FLAGS;

  if (code.length > constants.script.maxOps)
    return false;

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

    if (Buffer.isBuffer(op)) {
      if (op.length > constants.script.maxPush)
        return false;
      if (!Script.checkPush(op, flags))
        return false;
      stack.push(op);
      continue;
    }

    if (op === 0) {
      stack.push(new Buffer([]));
      continue;
    }

    if (op >= 1 && op <= 16) {
      stack.push(new Buffer([op]));
      continue;
    }

    switch (op) {
      case 'nop':
      case 'nop1':
      case 'nop4':
      case 'nop5':
      case 'nop6':
      case 'nop7':
      case 'nop8':
      case 'nop9':
      case 'nop10': {
        if (flags & constants.flags.VERIFY_DISCOURAGE_UPGRADABLE_NOPS)
          return false;
        break;
      }
      case '1negate': {
        stack.push(new Buffer([0xff]));
        break;
      }
      case 'if':
      case 'notif': {
        if (stack.length < 1)
          return false;
        val = Script.bool(stack.pop());
        if (op === 'notif')
          val = !val;
        if_ = ip;
        else_ = this._next('else', code, ip);
        endif = this._next('endif', code, ip);
        // Splice out the statement blocks we don't need
        if (val) {
          if (endif === -1)
            return false;
          if (else_ === -1) {
            code.splice(endif, 1);
            code.splice(if_, 1);
          } else {
            code.splice(else_, (endif - else_) + 1);
            code.splice(if_, 1);
          }
        } else {
          if (endif === -1)
            return false;
          if (else_ === -1) {
            code.splice(if_, (endif - if_) + 1);
          } else {
            code.splice(endif, 1);
            code.splice(if_, (else_ - if_) + 1);
          }
        }
        // Subtract one since we removed the if/notif opcode
        ip--;
        break;
      }
      case 'else': {
        return false;
      }
      case 'endif': {
        return false;
      }
      case 'verify': {
        if (stack.length === 0)
          return false;
        if (!Script.bool(stack.pop()))
          return false;
        break;
      }
      case 'return': {
        return false;
      }
      case 'toaltstack': {
        stack.toalt();
        break;
      }
      case 'fromaltstack': {
        stack.fromalt();
        break;
      }
      case 'ifdup': {
        stack.ifdup();
        break;
      }
      case 'depth': {
        stack.depth();
        break;
      }
      case 'drop': {
        stack.drop();
        break;
      }
      case 'dup': {
        stack.dup();
        break;
      }
      case 'nip': {
        stack.nip();
        break;
      }
      case 'over': {
        stack.over();
        break;
      }
      case 'pick': {
        stack.pick(flags);
        break;
      }
      case 'roll': {
        stack.roll(flags);
        break;
      }
      case 'rot': {
        stack.rot();
        break;
      }
      case 'swap': {
        stack.swap();
        break;
      }
      case 'tuck': {
        stack.tuck();
        break;
      }
      case '2drop': {
        stack.drop2();
        break;
      }
      case '2dup': {
        stack.dup2();
        break;
      }
      case '3dup': {
        stack.dup3();
        break;
      }
      case '2over': {
        stack.over2();
        break;
      }
      case '2rot': {
        stack.rot2();
        break;
      }
      case '2swap': {
        stack.swap2();
        break;
      }
      case 'size': {
        stack.size();
        break;
      }
      case '1add':
      case '1sub':
      case 'negate':
      case 'abs':
      case 'not':
      case '0notequal': {
        if (stack.length < 1)
          return false;
        n = Script.num(stack.pop(), flags);
        switch (op) {
          case '1add':
            n.iadd(1);
            break;
          case '1sub':
            n.isub(1);
            break;
          case 'negate':
            n = n.neg();
            break;
          case 'abs':
            if (n.cmpn(0) < 0)
              n = n.neg();
            break;
          case 'not':
            n = n.cmpn(0) === 0;
            break;
          case '0notequal':
            n = n.cmpn(0) !== 0;
            break;
          default:
            return false;
        }
        if (typeof n === 'boolean')
          n = new bn(n ? 1 : 0, 'le');
        stack.push(Script.array(n));
        break;
      }
      case 'add':
      case 'sub':
      case 'booland':
      case 'boolor':
      case 'numequal':
      case 'numequalverify':
      case 'numnotequal':
      case 'lessthan':
      case 'greaterthan':
      case 'lessthanorequal':
      case 'greaterthanorequal':
      case 'min':
      case 'max': {
        switch (op) {
          case 'add':
          case 'sub':
          case 'booland':
          case 'boolor':
          case 'numequal':
          case 'numequalverify':
          case 'numnotequal':
          case 'lessthan':
          case 'greaterthan':
          case 'lessthanorequal':
          case 'greaterthanorequal':
          case 'min':
          case 'max':
            if (stack.length < 2)
              return false;
            n2 = Script.num(stack.pop(), flags);
            n1 = Script.num(stack.pop(), flags);
            n = new bn(0, 'le');
            switch (op) {
              case 'add':
                n = n1.add(n2);
                break;
              case 'sub':
                n = n1.sub(n2);
                break;
              case 'booland':
                n = n1.cmpn(0) !== 0 && n2.cmpn(0) !== 0;
                break;
              case 'boolor':
                n = n1.cmpn(0) !== 0 || n2.cmpn(0) !== 0;
                break;
              case 'numequal':
                n = n1.cmp(n2) === 0;
                break;
              case 'numequalverify':
                n = n1.cmp(n2) === 0;
                break;
              case 'numnotequal':
                n = n1.cmp(n2) !== 0;
                break;
              case 'lessthan':
                n = n1.cmp(n2) < 0;
                break;
              case 'greaterthan':
                n = n1.cmp(n2) > 0;
                break;
              case 'lessthanorequal':
                n = n1.cmp(n2) <= 0;
                break;
              case 'greaterthanorequal':
                n = n1.cmp(n2) >= 0;
                break;
              case 'min':
                n = n1.cmp(n2) < 0 ? n1 : n2;
                break;
              case 'max':
                n = n1.cmp(n2) > 0 ? n1 : n2;
                break;
              default:
                return false;
            }
            if (typeof n === 'boolean')
              n = new bn(n ? 1 : 0, 'le');
            res = Script.bool(n);
            if (op === 'numequalverify') {
              if (!res)
                return false;
            } else {
              stack.push(Script.array(n));
            }
            break;
          case 'within':
            if (stack.length < 3)
              return false;
            n3 = Script.num(stack.pop(), flags);
            n2 = Script.num(stack.pop(), flags);
            n1 = Script.num(stack.pop(), flags);
            val = n2.cmp(n1) <= 0 && n1.cmp(n3) < 0;
            stack.push(val.cmpn(0) !== 0 ? new Buffer([1]) : new Buffer([]));
            break;
        }

        break;
      }
      case 'codeseparator': {
        lastSep = ip;
        break;
      }
      case 'ripemd160': {
        if (stack.length === 0)
          return false;
        stack.push(utils.ripemd160(stack.pop()));
        break;
      }
      case 'sha1': {
        if (stack.length === 0)
          return false;
        stack.push(utils.sha1(stack.pop()));
        break;
      }
      case 'sha256': {
        if (stack.length === 0)
          return false;
        stack.push(utils.sha256(stack.pop()));
        break;
      }
      case 'hash256': {
        if (stack.length === 0)
          return false;
        stack.push(utils.dsha256(stack.pop()));
        break;
      }
      case 'hash160': {
        if (stack.length === 0)
          return false;
        stack.push(utils.ripesha(stack.pop()));
        break;
      }
      case 'equalverify':
      case 'equal': {
        if (stack.length < 2)
          return false;
        res = utils.isEqual(stack.pop(), stack.pop());
        if (op === 'equalverify') {
          if (!res)
            return false;
        } else {
          stack.push(res ? new Buffer([1]) : new Buffer([]));
        }
        break;
      }
      case 'checksigverify':
      case 'checksig': {
        if (!tx || stack.length < 2)
          return false;

        key = stack.pop();
        sig = stack.pop();

        if (!Script.isValidKey(key, flags))
          return false;

        if (!Script.isValidSignature(sig, flags))
          return false;

        type = sig[sig.length - 1];

        subscript = this.getSubscript(lastSep);
        subscript.removeData(sig);

        hash = tx.signatureHash(index, subscript, type, version);

        res = Script.checksig(hash, sig, key, flags);
        if (op === 'checksigverify') {
          if (!res)
            return false;
        } else {
          stack.push(res ? new Buffer([1]) : new Buffer([]));
        }

        break;
      }
      case 'checkmultisigverify':
      case 'checkmultisig': {
        if (!tx || stack.length < 4)
          return false;

        n = Script.num(stack.pop(), flags).toNumber();

        if (!(n >= 1 && n <= 15))
          return false;

        if (stack.length < n + 1)
          return false;

        keys = [];
        for (i = 0; i < n; i++) {
          key = stack.pop();

          if (!Script.isValidKey(key, flags))
            return false;

          keys.push(key);
        }

        m = Script.num(stack.pop(), flags).toNumber();

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

        if (stack.length < m)
          return false;

        subscript = this.getSubscript(lastSep);

        for (i = 0; i < m; i++) {
          sig = stack.get(stack.length - 1 - i);
          subscript.removeData(sig);
        }

        succ = 0;
        for (i = 0, j = 0; i < m; i++) {
          sig = stack.pop();

          if (!Script.isValidSignature(sig, flags))
            return false;

          type = sig[sig.length - 1];

          hash = tx.signatureHash(index, subscript, type, version);

          res = false;
          for (; !res && j < n; j++)
            res = Script.checksig(hash, sig, keys[j], flags);

          if (res)
            succ++;
        }

        if (stack.length < 1)
          return false;

        val = stack.pop();

        if (flags & constants.flags.VERIFY_NULLDUMMY) {
          if (!Script.isDummy(val))
            return false;
        }

        res = succ >= m;

        if (!res)
          utils.debug('checkmultisig failed: succ: %d, m: %d', succ, m);

        if (op === 'checkmultisigverify') {
          if (!res)
            return false;
        } else {
          stack.push(res ? new Buffer([1]) : new Buffer([]));
        }

        break;
      }
      case 'checklocktimeverify': {
        // OP_CHECKLOCKTIMEVERIFY = OP_NOP2
        if (!(flags & constants.flags.VERIFY_CHECKLOCKTIMEVERIFY)) {
          if (flags & constants.flags.VERIFY_DISCOURAGE_UPGRADABLE_NOPS)
            return false;
          break;
        }

        if (!tx || stack.length === 0)
          return false;

        locktime = stack.top(-1);

        if (!Buffer.isBuffer(locktime))
          return false;

        // NOTE: Bitcoind accepts 5 byte locktimes.
        // 4 byte locktimes become useless in 2106
        // (will people still be using bcoin then?).
        locktime = Script.num(locktime, flags, 4).toNumber();

        if (locktime < 0)
          return false;

        if (!Script.checkLocktime(locktime, tx, index))
          return false;

        break;
      }
      case 'checksequenceverify': {
        // OP_CHECKSEQUENCEVERIFY = OP_NOP3
        if (!(flags & constants.flags.VERIFY_CHECKSEQUENCEVERIFY)) {
          if (flags & constants.flags.VERIFY_DISCOURAGE_UPGRADABLE_NOPS)
            return false;
          break;
        }

        if (!tx || stack.length === 0)
          return false;

        locktime = stack.top(-1);

        if (!Buffer.isBuffer(locktime))
          return false;

        // NOTE: Bitcoind accepts 5 byte locktimes.
        // 4 byte locktimes become useless in 2106
        // (will people still be using bcoin then?).
        locktime = Script.num(locktime, flags, 4).toNumber();

        if (locktime < 0)
          return false;

        if ((locktime & constants.sequenceLocktimeDisableFlag) !== 0)
          break;

        if (!Script.checkSequence(locktime, tx, index))
          return false;

        break;
      }
      default: {
        // Unknown operation
        utils.debug('Unknown opcode "%s" at offset %d', op, ip);
        return false;
      }
    }
  }

  if (stack.getSize() > constants.script.maxStack)
    return false;

  return true;
};

Script.checkLocktime = function checkLocktime(locktime, tx, i) {
  var threshold = constants.locktimeThreshold;

  if (!(
    (tx.locktime < threshold && locktime < threshold)
    || (tx.locktime >= threshold && locktime >= threshold)
  )) {
    return false;
  }

  if (locktime > tx.locktime)
    return false;

  if (tx.inputs[i].sequence === 0xffffffff)
    return false;

  return true;
};

Script.checkSequence = function checkSequence(sequence, tx, i) {
  var txSequence = tx.inputs[i].sequence;
  var locktimeMask, txSequenceMasked, sequenceMasked;

  if (tx.version < 2)
    return false;

  if (txSequence & constants.sequenceLocktimeDisableFlag)
    return false;

  locktimeMask = constants.sequenceLocktimeTypeFlag
    | constants.sequenceLocktimeMask;
  txSequenceMasked = txSequence & locktimeMask;
  sequenceMasked = sequence & locktimeMask;

  if (!(
    (txSequenceMasked < constants.sequenceLocktimeTypeFlag
    && sequenceMasked < constants.sequenceLocktimeTypeFlag)
    || (txSequenceMasked >= constants.sequenceLocktimeTypeFlag
    && sequenceMasked >= constants.sequenceLocktimeTypeFlag)
  )) {
    return false;
  }

  if (sequenceMasked > txSequenceMasked)
    return false;

  return true;
};

Script.bool = function bool(value) {
  var i;

  // Should never happen:
  // if (typeof value === 'boolean')
  //   return value;

  // Should never happen:
  // if (utils.isFinite(value))
  //   return value !== 0;

  if (bn.isBN(value))
    return value.cmpn(0) !== 0;

  assert(Buffer.isBuffer(value));

  for (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;
};

Script.num = function num(value, flags, size) {
  assert(Buffer.isBuffer(value));

  if (flags == null)
    flags = constants.flags.STANDARD_VERIFY_FLAGS;

  if (size == null)
    size = 4;

  if (value.length > size)
    throw new Error('Script number overflow.');

  if ((flags & constants.flags.VERIFY_MINIMALDATA) && value.length > 0) {
    // If the low bits on the last byte are unset,
    // fail if the value's second to last byte does
    // not have the high bit set. A number can't
    // justify having the last byte's low bits unset
    // unless they ran out of space for the sign bit
    // in the second to last bit. We also fail on [0]
    // to avoid negative zero (also avoids positive
    // zero).
    if (!(value[value.length - 1] & 0x7f)) {
      if (value.length === 1 || !(value[value.length - 2] & 0x80))
        throw new Error('Non-minimally encoded Script number.');
    }
  }

  // If we are signed, do (~num + 1) to get
  // the positive counterpart and set bn's
  // negative flag.
  if (value[value.length - 1] & 0x80) {
    if (utils.isNegZero(value, 'le')) {
      value = new bn(0, 'le');
    } else {
      value = new bn(value, 'le');
      value = value.notn(value.bitLength()).addn(1).neg();
    }
  } else {
    value = new bn(value, 'le');
  }

  return value;
};

Script.array = function(value) {
  if (Buffer.isBuffer(value))
    return value;

  if (utils.isFinite(value))
    value = new bn(value, 'le');

  assert(bn.isBN(value));

  // Convert the number to the
  // negative byte representation.
  if (value.isNeg()) {
    if (value.cmpn(0) === 0)
      value = new bn(0);
    else
      value = value.neg().notn(value.bitLength()).subn(1);
  }

  if (value.cmpn(0) === 0)
    return new Buffer([]);

  return value.toBuffer('le');
};

Script.prototype.removeData = function removeData(data) {
  for (var i = this.code.length - 1; i >= 0; i--) {
    if (utils.isEqual(this.code[i], data))
      this.code.splice(i, 1);
  }
};

Script.checkPush = function checkPush(value, flags) {
  var pushdata = value.pushdata;

  if (flags == null)
    flags = constants.flags.STANDARD_VERIFY_FLAGS;

  if (!(flags & constants.flags.VERIFY_MINIMALDATA))
    return true;

  if (!pushdata)
    return true;

  if (value.length === 1 && value[0] === 0)
    return false;

  if (value.length === 1 && value[0] >= 1 && value[0] <= 16)
    return false;

  if (value.length === 1 && value[0] === 0xff)
    return false;

  if (value.length <= 75)
    return pushdata.opcode == null && pushdata.len === value.length;

  if (value.length <= 255)
    return pushdata.opcode === constants.opcodes.pushdata1;

  if (value.length <= 65535)
    return pushdata.opcode === constants.opcodes.pushdata2;

  return true;
};

Script.isCode = function isCode(buf) {
  var i, b;

  if (!buf)
    return false;

  if (!Buffer.isBuffer(buf))
    return false;

  buf = Script.decode(buf);

  for (i = 0; i < buf.length; i++) {
    b = buf[i];
    if (Buffer.isBuffer(b))
      continue;
    if (constants.opcodes[b] == null)
      return false;
  }

  return true;
};

Script.prototype.concat = function concat(scripts) {
  scripts.unshift(this);
  return Script.concat(scripts);
};

Script.createPubkey = function createPubkey(key) {
  return new Script([key, 'checksig']);
};

Script.createPubkeyhash = function createPubkeyhash(hash) {
  return new Script([
    'dup',
    'hash160',
    hash,
    'equalverify',
    'checksig'
  ]);
};

Script.createMultisig = function createMultisig(keys, m, n) {
  if (keys.length !== n)
    throw new Error(n + ' keys are required to generate multisig script');

  assert(m >= 1 && m <= n);
  assert(n >= 1 && n <= 15);

  return new Script([m].concat(
    utils.sortKeys(keys),
    [n, 'checkmultisig']
  ));
};

Script.createScripthash = function createScripthash(hash) {
  return new Script([
    'hash160',
    hash,
    'equal'
  ]);
};

Script.createNulldata = function createNulldata(flags) {
  return new Script([
    'return',
    flags
  ]);
};

Script.prototype.getRedeem = function getRedeem() {
  if (!this.redeem)
    this.redeem = Script.getRedeem(this.code);

  return this.redeem;
};

Script.getRedeem = function getRedeem(code) {
  var redeem = code[code.length - 1];

  if (!Buffer.isBuffer(redeem))
    return;

  return new Script(redeem);
};

Script.prototype.getType = function getType() {
  if (this.isCommitment())
    return 'commitment';

  if (this.isWitnessProgram()) {
    if (this.isWitnessPubkeyhash())
      return 'witnesspubkeyhash';
    if (this.isWitnessScripthash())
      return 'witnessscripthash';
    return 'unknown';
  }

  return (this.isPubkey() && 'pubkey')
    || (this.isPubkeyhash() && 'pubkeyhash')
    || (this.isMultisig() && 'multisig')
    || (this.isScripthash() && 'scripthash')
    || (this.isNulldata() && 'nulldata')
    || 'unknown';
};

Script.prototype.isStandard = function isStandard() {
  var type = this.getType();
  var m, n;

  if (type === 'multisig') {
    m = this.code[0];
    n = this.code[this.code.length - 2];

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

    if (m < 1 || m > n)
      return false;
  } else if (type === 'nulldata') {
    if (this.getSize() > constants.script.maxOpReturnBytes)
      return false;
  }

  return type !== 'unknown';
};

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

Script.prototype._locktime = function _locktime() {
  if (this.code.length < 2)
    return;

  if (!Buffer.isBuffer(this.code[0]))
    return;

  if (this.code[1] !== 'checklocktimeverify')
    return;

  return this.code[0];
};

Script.prototype.isLocktime = function isLocktime() {
  return this._locktime() != null;
};

Script.prototype.getLocktime = function getLocktime() {
  var locktime = this._locktime();

  if (!locktime)
    return;

  try {
    locktime = Script.num(locktime, null, 4).toNumber();
  } catch (e) {
    locktime = 0;
  }

  if (locktime < constants.locktimeThreshold)
    return { type: 'height', value: locktime };

  return { type: 'time', value: locktime };
};

Script.prototype.getInputAddress = function getInputAddress(prev) {
  return Script.getInputAddress(this.code, prev, false);
};

Script.getInputAddress = function getInputAddress(code, prev, isWitness) {
  if (prev)
    return prev.getAddress();

  if (Script.isPubkeyInput(code))
    return;

  if (Script.isPubkeyhashInput(code)) {
    return bcoin.address.compileData(code[1],
      isWitness ? 'witnesspubkeyhash' : 'pubkeyhash');
  }

  if (Script.isMultisigInput(code, null, isWitness))
    return;

  if (Script.isScripthashInput(code, null, isWitness)) {
    return bcoin.address.compileData(code[code.length - 1],
      isWitness ? 'witnessscripthash' : 'scripthash');
  }
};

Script.prototype.getAddress = function getAddress() {
  var program;

  if (this.isWitnessProgram()) {
    program = this.getWitnessProgram();
    if (!program.type || program.type === 'unknown')
      return;
    return bcoin.address.compileHash(program.data, program.type);
  }

  // Convert p2pk to p2pkh addresses
  if (this.isPubkey())
    return bcoin.address.compileData(this.code[0], 'pubkeyhash');

  if (this.isPubkeyhash())
    return bcoin.address.compileHash(this.code[2], 'pubkeyhash');

  // Convert bare multisig to scripthash address
  if (this.isMultisig())
    return bcoin.address.compileData(this.encode(), 'scripthash');

  if (this.isScripthash())
    return bcoin.address.compileHash(this.code[1], 'scripthash');
};

Script.prototype.getInputHash = function getInputHash(prev) {
  return Script.getInputHash(this.code, prev, false);
};

Script.getInputHash = function getInputHash(prev, isWitness) {
  if (prev)
    return prev.getHash();

  if (Script.isPubkeyInput(code))
    return;

  if (Script.isPubkeyhashInput(code))
    return utils.ripesha(code[1]);

  if (Script.isMultisigInput(code, null, isWitness))
    return;

  if (Script.isScripthashInput(code, null, isWitness)) {
    return isWitness
      ? utils.sha256(code[code.length - 1])
      : utils.ripesha(code[code.length - 1]);
  }
};

Script.prototype.getHash = function getHash() {
  var program;

  if (this.isWitnessProgram()) {
    program = this.getWitnessProgram();
    if (!program.type || program.type === 'unknown')
      return;
    return program.data;
  }

  if (this.isPubkey())
    return utils.ripesha(this.code[0]);

  if (this.isPubkeyhash())
    return this.code[2];

  if (this.isMultisig())
    return utils.ripesha(this.encode());

  if (this.isScripthash())
    return this.code[1];
};

Script.prototype.isPubkey = function isPubkey(key) {
  var res;

  if (this.code.length !== 2)
    return false;

  res = Script.isKey(this.code[0]) && this.code[1] === 'checksig';

  if (!res)
    return false;

  if (key) {
    if (!utils.isEqual(this.code[0], key))
      return false;
  }

  return true;
};

Script.prototype.isPubkeyhash = function isPubkeyhash(hash) {
  var res;

  if (this.code.length !== 5)
    return false;

  res = this.code[0] === 'dup'
    && this.code[1] === 'hash160'
    && Script.isHash(this.code[2])
    && this.code[3] === 'equalverify'
    && this.code[4] === 'checksig';

  if (!res)
    return false;

  if (hash) {
    if (!utils.isEqual(this.code[2], hash))
      return false;
  }

  return true;
};

Script.prototype.isMultisig = function isMultisig(keys) {
  var m, n, i, j;
  var total = 0;

  if (this.code.length < 4)
    return false;

  if (this.code[this.code.length - 1] !== 'checkmultisig')
    return false;

  n = this.code[this.code.length - 2];

  if (Buffer.isBuffer(n)) {
    if (n.length !== 0)
      return false;
    n = 0;
  }

  if (typeof n !== 'number')
    return false;

  // Bitcoind technically doesn't check for the
  // 15 limit here. It just counts the sigops
  // later.
  if (!(n >= 1 && n <= 15))
    return false;

  m = this.code[0];

  if (Buffer.isBuffer(m)) {
    if (m.length !== 0)
      return false;
    m = 0;
  }

  if (typeof m !== 'number')
    return false;

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

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

  for (i = 1; i < n + 1; i++) {
    if (!Script.isKey(this.code[i]))
      return false;
  }

  if (keys) {
    for (i = 1; i < n + 1; i++) {
      for (j = 0; j < keys.length; j++) {
        if (utils.isEqual(this.code[i], keys[j])) {
          total++;
          break;
        }
      }
    }

    if (total !== n)
      return false;
  }

  return true;
};

Script.prototype.isScripthash = function isScripthash(hash) {
  var res;

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

  res = this.code[0] === 'hash160'
    && Script.isHash(this.code[1])
    && this.code[2] === 'equal';

  if (!res)
    return false;

  if (hash) {
    if (!utils.isEqual(this.code[1], hash))
      return false;
  }

  return true;
};

Script.prototype.isNulldata = function isNulldata() {
  var res;

  if (this.code.length !== 2)
    return false;

  res = this.code[0] === 'return' && Script.isData(this.code[1]);

  if (!res)
    return false;

  return true;
};

Script.prototype.isCommitment = function isCommitment() {
  return this.code.length >= 2
    && this.code[0] === 'return'
    && Buffer.isBuffer(this.code[1])
    && this.code[1].length === 36
    && utils.readU32BE(this.code[1], 0) === 0xaa21a9ed;
};

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

  return this.code[1].slice(4, 36);
};

Script.prototype.isWitnessProgram = function isWitnessProgram() {
  if (this.code.length !== 2)
    return false;

  if (typeof this.code[0] !== 'number')
    return false;

  if (!Buffer.isBuffer(this.code[1]))
    return false;

  return this.code[0] >= 0 && this.code[0] <= 16
    && this.code[1].length >= 2 && this.code[1].length <= 32;
};

Script.prototype.getWitnessProgram = function getWitnessProgram() {
  var version, data, type;

  if (!this.isWitnessProgram())
    return;

  version = this.code[0];
  data = this.code[1];

  if (version > 0) {
    // No interpretation of script (anyone can spend)
    type = 'unknown';
  } else if (version === 0 && data.length === 20) {
    type = 'witnesspubkeyhash';
  } else if (version === 0 && data.length === 32) {
    type = 'witnessscripthash';
  } else {
    // Fail on bad version=0
    type = null;
  }

  return {
    version: version,
    type: type,
    data: data
  };
};

Script.prototype.isWitnessPubkeyhash = function isWitnessPubkeyhash() {
  if (!this.isWitnessProgram())
    return false;

  return this.code[0] === 0 && this.code[1].length === 20;
};

Script.prototype.isWitnessScripthash = function isWitnessScripthash() {
  if (!this.isWitnessProgram())
    return false;

  return this.code[0] === 0 && this.code[1].length === 32;
};

Script.createWitnessProgram = function createWitnessProgram(version, data) {
  assert(typeof version === 'number' && version >= 0 && version <= 16);
  assert(Buffer.isBuffer(data));
  assert(data.length === 20 || data.length === 32);
  return new Script([version, data]);
};

Script.prototype.getInputType = function getInputType(prev) {
  return Script.getInputType(this.code, prev);
};

Script.getInputType = function getInputType(code, prev, isWitness) {
  var type;

  if (prev)
    return prev.getType();

  type = (Script.isPubkeyInput(code) && 'pubkey')
    || (Script.isPubkeyhashInput(code) && 'pubkeyhash')
    || (Script.isMultisigInput(code, null, isWitness) && 'multisig')
    || (Script.isScripthashInput(code, null, isWitness) && 'scripthash')
    || 'unknown';

  if (isWitness) {
    if (type === 'pubkeyhash')
      return 'witnesspubkeyhash';
    if (type === 'scripthash')
      return 'witnessscripthash';
    return 'unknown';
  }

  return type;
};

Script.createOutputScript = function(options) {
  var script, keys, m, n, hash, flags, address, redeem;

  if (!options)
    options = {};

  if (options.keys) {
    keys = options.keys.map(utils.ensureBuffer);

    m = options.m;
    n = options.n || keys.length;

    assert(m >= 1 && m <= n, 'm must be between 1 and n');

    assert(
      n >= 1 && n <= (options.scriptHash ? 15 : 3),
      'n must be between 1 and 15');

    script = Script.createMultisig(keys, m, n);
  } else if (options.address) {
    address = bcoin.address.parse(options.address);

    if (!address)
      throw new Error(options.address + ' is not a valid address.');

    if (address.type === 'pubkeyhash')
      script = Script.createPubkeyhash(address.hash);
    else if (address.type === 'scripthash')
      script = Script.createScripthash(address.hash);
    else if (address.version !== -1)
      script = Script.createWitnessProgram(address.version, address.hash);
    else
      throw new Error('Cannot parse address: ' + options.address);
  } else if (options.key) {
    script = Script.createPubkey(utils.ensureBuffer(options.key));
  } else if (options.flags) {
    flags = options.flags;
    if (typeof flags === 'string')
      flags = new Buffer(flags, 'ascii');
    assert(Buffer.isBuffer(flags));
    assert(flags.length <= constants.script.maxOpReturn);
    script = Script.createNulldata(flags);
  }

  if (options.scriptHash) {
    if (options.locktime != null) {
      script = new Script([
        Script.array(options.locktime),
        'checklocktimeverify',
        'drop'
      ].concat(script.code));
    }
    redeem = script;
    hash = utils.ripesha(script.encode());
    script = Script.createScripthash(hash);
    script.redeem = redeem;
  }

  return script;
};

Script.prototype.isPubkeyInput = function isPubkeyInput(key) {
  return Script.isPubkeyInput(this.code, key);
};

Script.isPubkeyInput = function isPubkeyInput(code, key) {
  if (code.length !== 1)
    return false;

  if (!Script.isSignature(code[0]))
    return false;

  assert(!key);

  return true;
};

Script.prototype.isPubkeyhashInput = function isPubkeyhashInput(key) {
  return Script.isPubkeyhashInput(this.code, key);
};

Script.isPubkeyhashInput = function isPubkeyhashInput(code, key) {
  if (code.length !== 2)
    return false;

  if (!Script.isSignature(code[0]))
    return false;

  if (!Script.isKey(code[1]))
    return false;

  if (key) {
    if (!utils.isEqual(code[1], key))
      return false;
  }

  return true;
};

Script.prototype.isMultisigInput = function isMultisigInput(keys) {
  return Script.isMultisigInput(this.code, keys);
};

Script.isMultisigInput = function isMultisigInput(code, keys, isWitness) {
  var i;

  // We need to rule out scripthash because
  // it may look like multisig. This is
  // strange because it's technically a
  // recursive call.
  if (Script.isScripthashInput(code, null, isWitness))
    return false;

  if (code.length < 3)
    return false;

  if (isWitness) {
    if (!Script.isDummy(code[0]))
      return false;
  } else {
    if (code[0] !== 0)
      return false;
  }

  for (i = 1; i < code.length; i++) {
    if (!Script.isSignature(code[i]))
      return false;
  }

  assert(!keys);

  return true;
};

Script.prototype.isScripthashInput = function isScripthashInput(redeem) {
  return Script.isScripthashInput(this.code, redeem);
};

Script.isScripthashInput = function isScripthashInput(code, redeem, isWitness) {
  var raw;

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

  // Need at least one data element with
  // the redeem script. NOTE: NOT THE CASE FOR SEGWIT!
  if (isWitness) {
    if (code.length < 1)
      return false;
  } else {
    if (code.length < 2)
      return false;
  }

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

  // Check data against last array in case
  // a raw redeem script was passed in.
  if (redeem)
    return utils.isEqual(redeem.encode(), raw);

  // 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 (Script.isDummy(raw))
    return false;

  if (Script.isSignatureEncoding(raw))
    return false;

  if (Script.isKeyEncoding(raw))
    return false;

  if (!Script.isCode(raw))
    return false;

  return true;
};

Script.prototype.getCoinbaseData = function getCoinbaseData() {
  var coinbase, flags;

  coinbase = {
    script: this
  };

  if (Buffer.isBuffer(this.code[0]) && this.code[0].length <= 6)
    coinbase.height = new bn(this.code[0], 'le').toNumber();
  else
    coinbase.height = -1;

  if (Buffer.isBuffer(this.code[1]))
    coinbase.extraNonce = new bn(this.code[1], 'le');
  else
    coinbase.extraNonce = new bn(0, 'le');

  flags = this.code.slice(2).filter(function(chunk) {
    return Buffer.isBuffer(chunk) && chunk.length !== 0;
  });

  coinbase.flags = flags;

  flags = flags.map(function(flag) {
    return flag.toString('utf8');
  });

  coinbase.text = flags.join('').replace(/[\u0000-\u0019\u007f-\u00ff]/g, '');

  return coinbase;
};

// Detect script array types. Note: these functions
// are not mutually exclusive. Only use for
// verification, not detection.

Script.isHash = function isHash(hash) {
  if (!Buffer.isBuffer(hash))
    return false;

  return hash.length === 20;
};

Script.isKey = function isKey(key) {
  if (!Buffer.isBuffer(key))
    return false;

  return key.length >= 33 && key.length <= 65;
};

Script.isSignature = function isSignature(sig) {
  if (!Buffer.isBuffer(sig))
    return false;

  return sig.length >= 9 && sig.length <= 73;
};

Script.isDummy = function isDummy(data) {
  if (!Buffer.isBuffer(data))
    return false;

  return data.length === 0;
};

Script.isZero = function isZero(data) {
  if (data === 0)
    return true;

  return Script.isDummy(data);
};

Script.isData = function isData(data) {
  if (!Buffer.isBuffer(data))
    return false;

  return data.length <= constants.script.maxOpReturn;
};

Script.isValidKey = function isValidKey(key, flags) {
  if (flags == null)
    flags = constants.flags.STANDARD_VERIFY_FLAGS;

  if (!Buffer.isBuffer(key))
    return false;

  if (flags & constants.flags.VERIFY_STRICTENC) {
    if (!Script.isKeyEncoding(key)) {
      utils.debug('Script failed key encoding test.');
      return false;
    }
  }

  return true;
};

Script.isKeyEncoding = function isKeyEncoding(key) {
  if (!Buffer.isBuffer(key))
    return false;

  if (key.length < 33)
    return false;

  if (key[0] === 0x04) {
    if (key.length !== 65)
      return false;
  } else if (key[0] === 0x02 || key[0] === 0x03) {
    if (key.length !== 33)
      return false;
  } else {
    return false;
  }

  return true;
};

Script.isValidSignature = function isValidSignature(sig, flags) {
  if (flags == null)
    flags = constants.flags.STANDARD_VERIFY_FLAGS;

  if (!Buffer.isBuffer(sig))
    return false;

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

  if ((flags & constants.flags.VERIFY_DERSIG)
      || (flags & constants.flags.VERIFY_LOW_S)
      || (flags & constants.flags.VERIFY_STRICTENC)) {
    if (!Script.isSignatureEncoding(sig)) {
      utils.debug('Script does not have a proper signature encoding.');
      return false;
    }
  }

  if (flags & constants.flags.VERIFY_LOW_S) {
    if (!Script.isLowDER(sig)) {
      utils.debug('Script does not have a low DER.');
      return false;
    }
  }

  if (flags & constants.flags.VERIFY_STRICTENC) {
    if (!Script.isHashType(sig)) {
      utils.debug('Script does not have a valid hash type.');
      return false;
    }
  }

  return true;
};

// https://github.com/bitcoin/bips/blob/master/bip-0066.mediawiki
/**
 * A canonical signature exists of: <30> <total len> <02> <len R> <R> <02> <len S> <S> <hashtype>
 * Where R and S are not negative (their first byte has its highest bit not set), and not
 * excessively padded (do not start with a 0 byte, unless an otherwise negative number follows,
 * in which case a single 0 byte is necessary and even required).
 *
 * See https://bitcointalk.org/index.php?topic=8392.msg127623#msg127623
 *
 * This function is consensus-critical since BIP66.
 */
Script.isSignatureEncoding = function isSignatureEncoding(sig) {
  var lenR, lenS;

  if (!Buffer.isBuffer(sig))
    return false;

  // Format: 0x30 [total-length] 0x02 [R-length] [R] 0x02 [S-length] [S] [sighash]
  // * total-length: 1-byte length descriptor of everything that follows,
  //   excluding the sighash byte.
  // * R-length: 1-byte length descriptor of the R value that follows.
  // * R: arbitrary-length big-endian encoded R value. It must use the shortest
  //   possible encoding for a positive integers (which means no null bytes at
  //   the start, except a single one when the next byte has its highest bit set).
  // * S-length: 1-byte length descriptor of the S value that follows.
  // * S: arbitrary-length big-endian encoded S value. The same rules apply.
  // * sighash: 1-byte value indicating what data is hashed (not part of the DER
  //   signature)

  // Minimum and maximum size constraints.
  if (sig.length < 9)
    return false;

  if (sig.length > 73)
    return false;

  // A signature is of type 0x30 (compound).
  if (sig[0] !== 0x30)
    return false;

  // Make sure the length covers the entire signature.
  if (sig[1] !== sig.length - 3)
    return false;

  // Extract the length of the R element.
  lenR = sig[3];

  // Make sure the length of the S element is still inside the signature.
  if (5 + lenR >= sig.length)
    return false;

  // Extract the length of the S element.
  lenS = sig[5 + lenR];

  // Verify that the length of the signature matches the sum of the length
  // of the elements.
  if (lenR + lenS + 7 !== sig.length)
    return false;

  // Check whether the R element is an integer.
  if (sig[2] !== 0x02)
    return false;

  // Zero-length integers are not allowed for R.
  if (lenR === 0)
    return false;

  // Negative numbers are not allowed for R.
  if (sig[4] & 0x80)
    return false;

  // Null bytes at the start of R are not allowed, unless R would
  // otherwise be interpreted as a negative number.
  if (lenR > 1 && (sig[4] === 0x00) && !(sig[5] & 0x80))
    return false;

  // Check whether the S element is an integer.
  if (sig[lenR + 4] !== 0x02)
    return false;

  // Zero-length integers are not allowed for S.
  if (lenS === 0)
    return false;

  // Negative numbers are not allowed for S.
  if (sig[lenR + 6] & 0x80)
    return false;

  // Null bytes at the start of S are not allowed, unless S would otherwise be
  // interpreted as a negative number.
  if (lenS > 1 && (sig[lenR + 6] === 0x00) && !(sig[lenR + 7] & 0x80))
    return false;

  return true;
};

Script.isHashType = function isHashType(sig) {
  var type;

  if (!Buffer.isBuffer(sig))
    return false;

  if (sig.length === 0)
    return false;

  type = sig[sig.length - 1] & ~constants.hashType.anyonecanpay;

  if (!constants.hashTypeByVal[type])
    return false;

  return true;
};

Script.isLowDER = function isLowDER(sig) {
  if (!sig.s) {
    if (!Buffer.isBuffer(sig))
      return false;

    if (!Script.isSignatureEncoding(sig))
      return false;

    sig = sig.slice(0, -1);
  }

  return bcoin.ec.isLowS(sig);
};

Script.format = function format(code) {
  var scripts = [];

  if (Array.isArray(code)) {
    scripts.push({ code: code });
  } else if (code instanceof Stack) {
    scripts.push({ code: code.items });
  } else if (code instanceof Witness) {
    scripts.push({ code: code.items });
  } else if (code instanceof Script) {
    scripts.push(code);
  } else if (code instanceof bcoin.input) {
    scripts.push(code.script);
    if (code.witness.length > 0)
      scripts.push({ code: code.witness.items });
    if (code.output) {
      scripts.push(code.output.script);
      if (code.output.script.isScripthash())
        scripts.push(code.output.script.getRedeem());
    }
  } else if (code instanceof bcoin.output) {
    scripts.push(code.script);
  }

  return Script.concat(scripts).map(function(chunk) {
    if (Buffer.isBuffer(chunk))
      return '[' + utils.toHex(chunk) + ']';

    if (typeof chunk === 'number')
      return chunk + '';

    return chunk;
  }).join(' ');
};

Script.prototype.isPushOnly = function isPushOnly() {
  var i, op;
  for (i = 0; i < this.code.length; i++) {
    op = this.code[i];
    if (Buffer.isBuffer(op) || op === '1negate' || (op >= 0 && op <= 16))
      continue;
    return false;
  }
  return true;
};

Script.prototype.getSigops = function getSigops(accurate) {
  var total = 0;
  var lastOp = -1;
  var i, op;

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

    if (Buffer.isBuffer(op))
      continue;

    if (constants.opcodes[op] == null)
      return 0;

    if (op === 'checksig' || op === 'checksigverify') {
      total++;
    } else if (op === 'checkmultisig' || op === 'checkmultisigverify') {
      if (accurate && lastOp >= 1 && lastOp <= 16)
        total += lastOp;
      else
        total += constants.script.maxPubkeysPerMultisig;
    }

    lastOp = op;
  }

  return total;
};

Script.prototype.getArgs = function getArgs() {
  var keys, m;

  if (this.isPubkey())
    return 1;

  if (this.isPubkeyhash())
    return 2;

  if (this.isMultisig()) {
    keys = this.code.slice(1, -2);
    m = this.code[0];
    if (keys.length < 1 || m < 1)
      return -1;
    return m + 1;
  }

  if (this.isScripthash())
    return 1;

  if (this.isNulldata())
    return -1;

  if (this.isWitnessScripthash())
    return 1;

  if (this.isWitnessPubkeyhash())
    return 2;

  return -1;
};

Script.fromString = function fromString(code) {
  var i, op;

  code = code.trim().split(/\s+/);

  // Remove OP_ prefixes and lowercase
  for (i = 0; i < code.length; i++) {
    op = code[i];
    if (typeof op === 'string') {
      op = op.toLowerCase();
      if (op.indexOf('op_') === 0)
        op = op.slice(3);
    }
    code[i] = op;
  }

  // Convert OP_FALSE to 0, convert OP_1-OP_16
  // to number literals, convert -1 to OP_1NEGATE.
  // Convert hex strings to arrays.
  for (i = 0; i < code.length; i++) {
    op = code[i];

    if (op === '-1') {
      op = '1negate';
    } else if (op === '0' || op === 'false') {
      op = 0;
    } else if (op === 'true') {
      op = 1;
    } else if (+op >= 1 && +op <= 16) {
      op = +op;
    } else if (constants.opcodes[op] == null) {
      if (op[0] === '[')
        op = op.slice(1, -1);
      if (op.indexOf('0x') === 0)
        op = op.substring(2);
      assert(utils.isHex(op), 'Non hex-string.');
      op = new Buffer(op, 'hex');
    }

    code[i] = op;
  }

  return new Script(code);
};

Script.verify = function verify(input, witness, output, tx, i, flags) {
  var copy, res, raw, redeem, hadWitness;
  var stack = new Stack();

  if (flags == null)
    flags = constants.flags.STANDARD_VERIFY_FLAGS;

  if (flags & constants.flags.VERIFY_SIGPUSHONLY) {
    if (!input.isPushOnly())
      return false;
  }

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

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

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

  // Verify the script did not fail as well as the stack values
  if (!res || stack.length === 0 || !Script.bool(stack.pop()))
    return false;

  if ((flags & constants.flags.VERIFY_WITNESS) && output.isWitnessProgram()) {
    hadWitness = true;

    // Input script must be empty.
    if (input.code.length !== 0)
      return false;

    // Verify the program in the output script
    if (!Script.verifyProgram(witness, output, tx, i, flags))
      return false;

    // Force a cleanstack
    stack.length = 0;
  }

  // If the script is P2SH, execute the real output script
  if ((flags & constants.flags.VERIFY_P2SH) && output.isScripthash()) {
    // P2SH can only have push ops in the scriptSig
    if (!input.isPushOnly())
      return false;

    // Reset the stack
    stack = copy;

    // Stack should not be empty at this point
    if (stack.length === 0)
      return false;

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

    if (!Buffer.isBuffer(raw))
      return false;

    redeem = new Script(raw);

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

    // Verify the script did not fail as well as the stack values
    if (!res || stack.length === 0 || !Script.bool(stack.pop()))
      return false;

    if ((flags & constants.flags.VERIFY_WITNESS) && redeem.isWitnessProgram()) {
      hadWitness = true;

      // Input script must be exactly one push of the redeem script.
      if (!(input.code.length === 1 && utils.isEqual(input.code[0], raw)))
        return false;

      // Verify the program in the redeem script
      if (!Script.verifyProgram(witness, redeem, tx, i, flags))
        return false;

      // Force a cleanstack
      stack.length = 0;
    }
  }

  // Ensure there is nothing left on the stack
  if (flags & constants.flags.VERIFY_CLEANSTACK) {
    assert((flags & constants.flags.VERIFY_P2SH) !== 0);
    // assert((flags & constants.flags.VERIFY_WITNESS) !== 0);
    if (stack.length !== 0)
      return false;
  }

  // If we had a witness but no witness program, fail.
  if (flags & constants.flags.VERIFY_WITNESS) {
    assert((flags & constants.flags.VERIFY_P2SH) !== 0);
    if (!hadWitness && witness.length > 0)
      return false;
  }

  return true;
};

Script.verifyProgram = function verifyProgram(witness, output, tx, i, flags) {
  var program, witnessScript, redeem, stack, j, res;

  assert((flags & constants.flags.VERIFY_WITNESS) !== 0);
  assert(output.isWitnessProgram());

  program = output.getWitnessProgram();

  // Failure on version=0 (bad program data length)
  if (!program.type) {
    utils.debug('Malformed witness program.');
    return false;
  }

  if (program.version > 0) {
    utils.debug('Unknown witness program version: %s', program.version);
    // 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 regalar output script which will
    // succeed in a block, but fail in the mempool
    // due to VERIFY_CLEANSTACK.
    if (flags & constants.flags.VERIFY_DISCOURAGE_UPGRADABLE_WITNESS_PROGRAM)
      return false;
    return true;
  }

  stack = witness.toStack();

  if (program.type === 'witnesspubkeyhash') {
    if (stack.length !== 2)
      return false;

    redeem = Script.createPubkeyhash(program.data);
  } else if (program.type === 'witnessscripthash') {
    if (stack.length === 0)
      return false;

    witnessScript = stack.pop();

    if (!utils.isEqual(utils.sha256(witnessScript), program.data))
      return false;

    redeem = new Script(witnessScript);
  } else {
    assert(false);
  }

  for (j = 0; j < stack.length; j++) {
    if (stack.get(j).length > constants.script.maxSize)
      return false;
  }

  res = redeem.execute(stack, tx, i, flags, 1);

  // Verify the script did not fail as well as the stack values
  if (!res || stack.length === 0 || !Script.bool(stack.pop()))
    return false;

  // Witnesses always require cleanstack
  if (stack.length !== 0)
    return false;

  return true;
};

Script.concat = function concat(scripts) {
  var s = [];
  var i;

  s = s.concat(scripts[0].code);

  for (i = 1; i < scripts.length; i++) {
    s.push('codeseparator');
    s = s.concat(scripts[i].code);
  }

  return s;
};

Script.checksig = function checksig(msg, sig, key, flags) {
  var historical = false;

  if (flags == null)
    flags = constants.flags.STANDARD_VERIFY_FLAGS;

  if (!Buffer.isBuffer(sig))
    return false;

  if (sig.length === 0)
    return false;

  // Attempt to normalize the signature
  // length before passing to elliptic.
  // Note: We only do this for historical data!
  // https://github.com/indutny/elliptic/issues/78
  if (!((flags & constants.flags.VERIFY_DERSIG)
      || (flags & constants.flags.VERIFY_LOW_S)
      || (flags & constants.flags.VERIFY_STRICTENC))) {
    historical = true;
  }

  return bcoin.ec.verify(msg, sig.slice(0, -1), key, historical);
};

Script.sign = function sign(msg, key, type) {
  var sig = bcoin.ec.sign(msg, key);

  // Add the sighash type as a single byte
  // to the signature.
  sig = Buffer.concat([sig, new Buffer([type])]);

  return sig;
};

Script.decode = function decode(buf) {
  var code = [];
  var off = 0;
  var b, len;

  assert(Buffer.isBuffer(buf));

  // NOTE: We can't use a BufferReader here since
  // script parsing was originally non-strict/ridiculous.
  // Something could do a direct push of 30 bytes with
  // only 20 bytes after it.
  // NOTE 2: We use reference Buffer slices here. Larger
  // buffer slices should _never_ be passed in here.
  while (off < buf.length) {
    b = buf[off++];

    // OP_0, OP_FALSE
    if (b === 0x00) {
      code.push(0);
      continue;
    }

    // Direct Push
    // Next `b` bytes should be pushed to stack
    if (b >= 0x01 && b <= 0x4b) {
      code.push(buf.slice(off, off + b));
      off += b;
      if (off > buf.length) {
        utils.hidden(code[code.length - 1], 'pushdata', {
          opcode: null,
          len: b
        });
      }
      continue;
    }

    // OP_1, OP_TRUE, OP_2-OP_16
    // Special case: these get to be number
    // literals. Note: 1negate is not included.
    if (b >= 0x51 && b <= 0x60) {
      code.push(b - 0x50);
      continue;
    }

    if (off >= buf.length) {
      code.push(constants.opcodesByVal[b] || b);
      continue;
    }

    if (b === constants.opcodes.pushdata1) {
      len = buf[off];
      off += 1;
      code.push(buf.slice(off, off + len));
      off += len;
      if (len <= 0x4b || off > buf.length) {
        utils.hidden(code[code.length - 1], 'pushdata', {
          opcode: b,
          len: len
        });
      }
    } else if (b === constants.opcodes.pushdata2) {
      len = utils.readU16(buf, off);
      off += 2;
      code.push(buf.slice(off, off + len));
      off += len;
      if (len <= 0xff || off > buf.length) {
        utils.hidden(code[code.length - 1], 'pushdata', {
          opcode: b,
          len: len
        });
      }
    } else if (b === constants.opcodes.pushdata4) {
      len = utils.readU32(buf, off);
      off += 4;
      code.push(buf.slice(off, off + len));
      off += len;
      if (len <= 0xffff || off > buf.length) {
        utils.hidden(code[code.length - 1], 'pushdata', {
          opcode: b,
          len: len
        });
      }
    } else {
      code.push(constants.opcodesByVal[b] || b);
    }
  }

  return code;
};

Script.encode = function encode(code) {
  var p = new BufferWriter();
  var opcodes = constants.opcodes;
  var i = 0;
  var op;

  assert(Array.isArray(code));

  for (i = 0; i < code.length; i++) {
    op = code[i];

    // Push value to stack
    if (Buffer.isBuffer(op)) {
      // Check for nonstandard pushdatas that
      // may have been decoded from before.
      if (op.pushdata) {
        if (op.pushdata.opcode === null) {
          p.writeU8(op.pushdata.len);
          p.writeBytes(op);
        } else if (op.pushdata.opcode === opcodes.pushdata1) {
          p.writeU8(opcodes.pushdata1);
          p.writeU8(op.pushdata.len);
          p.writeBytes(op);
        } else if (op.pushdata.opcode === opcodes.pushdata2) {
          p.writeU8(opcodes.pushdata2);
          p.writeU16(op.pushdata.len);
          p.writeBytes(op);
        } else if (op.pushdata.opcode === opcodes.pushdata4) {
          p.writeU8(opcodes.pushdata4);
          p.writeU32(op.pushdata.len);
          p.writeBytes(op);
        }
        continue;
      }
      // Standard minimaldata encoding
      if (op.length === 0) {
        p.writeU8(opcodes['0']);
      } else if (op.length <= 0x4b) {
        p.writeU8(op.length);
        p.writeBytes(op);
      } else if (op.length <= 0xff) {
        p.writeU8(opcodes.pushdata1);
        p.writeU8(op.length);
        p.writeBytes(op);
      } else if (op.length <= 0xffff) {
        p.writeU8(opcodes.pushdata2);
        p.writeU16(op.length);
        p.writeBytes(op);
      } else {
        p.writeU8(opcodes.pushdata4);
        p.writeU32(op.length);
        p.writeBytes(op);
      }
      continue;
    }

    assert(opcodes[op] != null || typeof op === 'number');

    p.writeU8(opcodes[op] || op);
  }

  return p.render();
};

Script.isScript = function isScript(obj) {
  return obj
    && Array.isArray(obj.code)
    && typeof obj.getSubscript === 'function';
};

Script.witness = Witness;
Script.stack = Stack;
module.exports = Script;