'use strict';

var buffer = require('buffer');

var Signature = require('../crypto/signature');
var Script = require('../script');
var Input = require('./input');
var Output = require('./output');
var BufferReader = require('../encoding/bufferreader');
var BufferWriter = require('../encoding/bufferwriter');
var BN = require('../crypto/bn');
var Hash = require('../crypto/hash');
var ECDSA = require('../crypto/ecdsa');

var SIGHASH_SINGLE_BUG = '0000000000000000000000000000000000000000000000000000000000000001';
var BITS_64_ON = 'ffffffffffffffff';

/**
 * Returns a buffer of length 32 bytes with the hash that needs to be signed
 * for OP_CHECKSIG.
 *
 * @param {Transaction} transaction the transaction to sign
 * @param {number} sighashType the type of the hash
 * @param {number} inputNumber the input index for the signature
 * @param {Script} subscript the script that will be signed
 */
function sighash(transaction, sighashType, inputNumber, subscript) {
  var i;
  // Copy transaction
  var Transaction = require('./transaction');
  var txcopy = Transaction.shallowCopy(transaction);

  // Copy script
  subscript = new Script(subscript);
  subscript.removeCodeseparators();

  for (i = 0; i < txcopy.inputs.length; i++) {
    // Blank signatures for other inputs
    txcopy.inputs[i] = new Input(txcopy.inputs[i]).setScript(Script.empty());
  }
  
  txcopy.inputs[inputNumber] = new Input(txcopy.inputs[inputNumber]).setScript(subscript);

  if ((sighashType & 31) === Signature.SIGHASH_NONE ||
      (sighashType & 31) === Signature.SIGHASH_SINGLE) {

    // clear all sequenceNumbers
    for (i = 0; i < txcopy.inputs.length; i++) {
      if (i !== inputNumber) {
        txcopy.inputs[i].sequenceNumber = 0;
      }
    }
  }

  if ((sighashType & 31) === Signature.SIGHASH_NONE) {
    txcopy.outputs = [];

  } else if ((sighashType & 31) === Signature.SIGHASH_SINGLE) {
    // The SIGHASH_SINGLE bug.
    // https://bitcointalk.org/index.php?topic=260595.0
    if (inputNumber > txcopy.outputs.length - 1) {
      return new Buffer(SIGHASH_SINGLE_BUG, 'hex');
    }
    if (txcopy.outputs.length <= inputNumber) {
      throw new Error('Missing output to sign');
    }

    txcopy.outputs.length = inputNumber + 1;

    for (i = 0; i < inputNumber; i++) {
      txcopy.outputs[i] = new Output({
        satoshis: BN().fromBuffer(new buffer.Buffer(BITS_64_ON, 'hex')),
        script: Script.empty()
      });
    }
  }

  if (sighashType & Signature.SIGHASH_ANYONECANPAY) {
    txcopy.inputs = [txcopy.inputs[inputNumber]];
  }

  var buf = BufferWriter()
    .write(txcopy.toBuffer())
    .writeInt32LE(sighashType)
    .toBuffer();
  return BufferReader(Hash.sha256sha256(buf)).readReverse();
}

function sign(transaction, keypair, nhashtype, nin, subscript) {
  var hashbuf = sighash(transaction, nhashtype, nin, subscript);
  var sig = ECDSA.sign(hashbuf, keypair, 'little').set({nhashtype: nhashtype});
  return sig;
}

function verify(transaction, sig, pubkey, nin, subscript) {
  var hashbuf = sighash(transaction, sig.nhashtype, nin, subscript);
  return ECDSA.verify(hashbuf, sig, pubkey, 'little');
}

module.exports = {
  sighash: sighash,
  sign: sign,
  verify: verify
};