var bufferutils = require('./bufferutils')
var bcrypto = require('./crypto')
var bufferReverse = require('buffer-reverse')
var fastMerkleRoot = require('merkle-lib/fastRoot')

var Transaction = require('./transaction')

function Block () {
  this.version = 1
  this.prevHash = null
  this.merkleRoot = null
  this.timestamp = 0
  this.bits = 0
  this.nonce = 0
}

Block.fromBuffer = function (buffer) {
  if (buffer.length < 80) throw new Error('Buffer too small (< 80 bytes)')

  var offset = 0
  function readSlice (n) {
    offset += n
    return buffer.slice(offset - n, offset)
  }

  function readUInt32 () {
    var i = buffer.readUInt32LE(offset)
    offset += 4
    return i
  }

  var block = new Block()
  block.version = readUInt32()
  block.prevHash = readSlice(32)
  block.merkleRoot = readSlice(32)
  block.timestamp = readUInt32()
  block.bits = readUInt32()
  block.nonce = readUInt32()

  if (buffer.length === 80) return block

  function readVarInt () {
    var vi = bufferutils.readVarInt(buffer, offset)
    offset += vi.size
    return vi.number
  }

  function readTransaction () {
    var tx = Transaction.fromBuffer(buffer.slice(offset), true)

    offset += tx.byteLength()
    return tx
  }

  var nTransactions = readVarInt()
  block.transactions = []

  for (var i = 0; i < nTransactions; ++i) {
    var tx = readTransaction()
    block.transactions.push(tx)
  }

  return block
}

Block.fromHex = function (hex) {
  return Block.fromBuffer(new Buffer(hex, 'hex'))
}

Block.prototype.getHash = function () {
  return bcrypto.hash256(this.toBuffer(true))
}

Block.prototype.getId = function () {
  return bufferReverse(this.getHash()).toString('hex')
}

Block.prototype.getUTCDate = function () {
  var date = new Date(0) // epoch
  date.setUTCSeconds(this.timestamp)

  return date
}

Block.prototype.toBuffer = function (headersOnly) {
  var buffer = new Buffer(80)

  var offset = 0
  function writeSlice (slice) {
    slice.copy(buffer, offset)
    offset += slice.length
  }

  function writeUInt32 (i) {
    buffer.writeUInt32LE(i, offset)
    offset += 4
  }

  writeUInt32(this.version)
  writeSlice(this.prevHash)
  writeSlice(this.merkleRoot)
  writeUInt32(this.timestamp)
  writeUInt32(this.bits)
  writeUInt32(this.nonce)

  if (headersOnly || !this.transactions) return buffer

  var txLenBuffer = bufferutils.varIntBuffer(this.transactions.length)
  var txBuffers = this.transactions.map(function (tx) {
    return tx.toBuffer()
  })

  return Buffer.concat([buffer, txLenBuffer].concat(txBuffers))
}

Block.prototype.toHex = function (headersOnly) {
  return this.toBuffer(headersOnly).toString('hex')
}

Block.calculateTarget = function (bits) {
  var exponent = ((bits & 0xff000000) >> 24) - 3
  var mantissa = bits & 0x007fffff
  var i = 31 - exponent

  var target = new Buffer(32)
  target.fill(0)

  target[i] = mantissa & 0xff
  target[i - 1] = mantissa >> 8
  target[i - 2] = mantissa >> 16
  target[i - 3] = mantissa >> 24

  return target
}

Block.calculateMerkleRoot = function (transactions) {
  if (transactions.length === 0) throw TypeError('Cannot compute merkle root for zero transactions')

  var hashes = transactions.map(function (transaction) {
    return transaction.getHash()
  })

  return fastMerkleRoot(hashes, bcrypto.hash256)
}

Block.prototype.checkMerkleRoot = function () {
  if (!this.transactions) return false

  var actualMerkleRoot = Block.calculateMerkleRoot(this.transactions)
  return this.merkleRoot.compare(actualMerkleRoot) === 0
}

Block.prototype.checkProofOfWork = function () {
  var hash = bufferReverse(this.getHash())
  var target = Block.calculateTarget(this.bits)

  return hash.compare(target) <= 0
}

module.exports = Block