'use strict';

var bitcore = require('bitcore');
var $ = bitcore.util.preconditions;
var _ = bitcore.deps._;
var BufferUtil = bitcore.util.buffer;

var NULL = '0000000000000000000000000000000000000000000000000000000000000000';

function BlockChain() {
  this.tip = NULL;
  this.work = {};
  this.work[NULL] = 0;
  this.height = {};
  this.height[NULL] = -1;
  this.hashByHeight = {
    '-1': NULL
  };
  this.next = {};
  this.prev = {};
}

BlockChain.NULL = NULL;

BlockChain.fromObject = function(obj) {
  var blockchain = new BlockChain();
  blockchain.tip = obj.tip;
  blockchain.work = obj.work;
  blockchain.hashByHeight = obj.hashByHeight;
  blockchain.height = obj.height;
  blockchain.next = obj.next;
  blockchain.prev = obj.prev;
  return blockchain;
};

var getWork = function(bits) {
  var bytes = ((bits >>> 24) & 0xff) >>> 0;
  return ((bits & 0xffffff) << (8 * (bytes - 3))) >>> 0;
};

BlockChain.prototype.addData = function(header) {
  $.checkArgument(header instanceof bitcore.Block.BlockHeader, 'Argument is not a BlockHeader instance');

  var prevHash = BufferUtil.reverse(header.prevHash).toString('hex');
  var hash = header.hash;

  this.work[hash] = this.work[prevHash] + getWork(header.bits);
  this.prev[hash] = prevHash;
};

BlockChain.prototype._appendNewBlock = function(hash) {
  var toUnconfirm = [];
  var toConfirm = [];
  var self = this;

  var pointer = hash;
  while (_.isUndefined(this.height[pointer])) {
    toConfirm.push(pointer);
    pointer = this.prev[pointer];
  }
  var commonAncestor = pointer;

  pointer = this.tip;
  while (pointer !== commonAncestor) {
    toUnconfirm.push(pointer);
    pointer = this.prev[pointer];
  }

  toConfirm.reverse();
  toUnconfirm.map(function(hash) {
    self.unconfirm(hash);
  });
  toConfirm.map(function(hash) {
    self.confirm(hash);
  });
  return {
    unconfirmed: toUnconfirm,
    confirmed: toConfirm
  };
};

BlockChain.prototype.proposeNewHeader = function(header) {
  $.checkArgument(header instanceof bitcore.Block.BlockHeader, 'Argument is not a BlockHeader instance');
  var prevHash = BufferUtil.reverse(header.prevHash).toString('hex');
  var hash = header.hash;

  $.checkState(this.hasData(prevHash), 'No previous data to estimate work');
  this.addData(header);
  var work = this.work[hash];
  var tipWork = this.work[this.tip];
  $.checkState(!_.isUndefined(work), 'No work found for ' + hash);
  $.checkState(!_.isUndefined(tipWork), 'No work found for tip ' + this.tip);
  if (work > tipWork) {
    return this._appendNewBlock(hash);
  }
  return {
    unconfirmed: [],
    confirmed: []
  };
};
BlockChain.prototype.proposeNewBlock = function(block) {
  $.checkArgument(block instanceof bitcore.Block, 'Argument is not a Block instance');
  return this.proposeNewHeader(block.header);
};

BlockChain.prototype.confirm = function(hash) {
  var prevHash = this.prev[hash];
  $.checkState(prevHash === this.tip, 'Attempting to confirm a non-contiguous block.');

  this.tip = hash;
  var height = this.height[prevHash] + 1;
  this.next[prevHash] = hash;
  this.hashByHeight[height] = hash;
  this.height[hash] = height;
};

BlockChain.prototype.unconfirm = function(hash) {
  var prevHash = this.prev[hash];
  $.checkState(hash === this.tip, 'Attempting to unconfirm a non-tip block');

  this.tip = prevHash;
  var height = this.height[hash];
  delete this.next[prevHash];
  delete this.hashByHeight[height];
  delete this.height[hash];
};

BlockChain.prototype.hasData = function(hash) {
  return !_.isUndefined(this.work[hash]);
};

BlockChain.prototype.prune = function() {
  var self = this;
  _.each(this.prev, function(key) {
    if (!self.height[key]) {
      delete self.prev[key];
      delete self.work[key];
    }
  });
};

BlockChain.prototype.toObject = function() {
  return {
    tip: this.tip,
    work: this.work,
    next: this.next,
    hashByHeight: this.hashByHeight,
    height: this.height,
    prev: this.prev
  };
};

BlockChain.prototype.toJSON = function() {
  return JSON.stringify(this.toObject());
};

BlockChain.prototype.getBlockLocator = function() {
  $.checkState(this.tip);
  $.checkState(!_.isUndefined(this.height[this.tip]));

  var result = [];
  var currentHeight = this.getCurrentHeight();
  var exponentialBackOff = 1;
  for (var i = 0; i < 10; i++) {
    if (currentHeight >= 0) {
      result.push(this.hashByHeight[currentHeight--]);
    }
  }
  while (currentHeight > 0) {
    result.push(this.hashByHeight[currentHeight]);
    currentHeight -= exponentialBackOff;
    exponentialBackOff *= 2;
  }
  return result;
};

BlockChain.prototype.getCurrentHeight = function() {
  return this.height[this.tip];
};

module.exports = BlockChain;