var bip66 = require('bip66')
var typeforce = require('typeforce')
var types = require('./types')

var BigInteger = require('bigi')

function ECSignature (r, s) {
  typeforce(types.tuple(types.BigInt, types.BigInt), arguments)

  this.r = r
  this.s = s
}

ECSignature.parseCompact = function (buffer) {
  typeforce(types.BufferN(65), buffer)

  var flagByte = buffer.readUInt8(0) - 27
  if (flagByte !== (flagByte & 7)) throw new Error('Invalid signature parameter')

  var compressed = !!(flagByte & 4)
  var recoveryParam = flagByte & 3
  var signature = ECSignature.fromRSBuffer(buffer.slice(1))

  return {
    compressed: compressed,
    i: recoveryParam,
    signature: signature
  }
}

ECSignature.fromRSBuffer = function (buffer) {
  typeforce(types.BufferN(64), buffer)

  var r = BigInteger.fromBuffer(buffer.slice(0, 32))
  var s = BigInteger.fromBuffer(buffer.slice(32, 64))
  return new ECSignature(r, s)
}

ECSignature.fromDER = function (buffer) {
  var decode = bip66.decode(buffer)
  var r = BigInteger.fromDERInteger(decode.r)
  var s = BigInteger.fromDERInteger(decode.s)

  return new ECSignature(r, s)
}

// BIP62: 1 byte hashType flag (only 0x01, 0x02, 0x03, 0x81, 0x82 and 0x83 are allowed)
ECSignature.parseScriptSignature = function (buffer) {
  var hashType = buffer.readUInt8(buffer.length - 1)
  var hashTypeMod = hashType & ~0x80

  if (hashTypeMod <= 0x00 || hashTypeMod >= 0x04) throw new Error('Invalid hashType ' + hashType)

  return {
    signature: ECSignature.fromDER(buffer.slice(0, -1)),
    hashType: hashType
  }
}

ECSignature.prototype.toCompact = function (i, compressed) {
  if (compressed) {
    i += 4
  }

  i += 27

  var buffer = Buffer.alloc(65)
  buffer.writeUInt8(i, 0)
  this.toRSBuffer(buffer, 1)
  return buffer
}

ECSignature.prototype.toDER = function () {
  var r = Buffer.from(this.r.toDERInteger())
  var s = Buffer.from(this.s.toDERInteger())

  return bip66.encode(r, s)
}

ECSignature.prototype.toRSBuffer = function (buffer, offset) {
  buffer = buffer || Buffer.alloc(64)
  this.r.toBuffer(32).copy(buffer, offset)
  this.s.toBuffer(32).copy(buffer, offset + 32)
  return buffer
}

ECSignature.prototype.toScriptSignature = function (hashType) {
  var hashTypeMod = hashType & ~0x80
  if (hashTypeMod <= 0 || hashTypeMod >= 4) throw new Error('Invalid hashType ' + hashType)

  var hashTypeBuffer = Buffer.alloc(1)
  hashTypeBuffer.writeUInt8(hashType, 0)

  return Buffer.concat([this.toDER(), hashTypeBuffer])
}

module.exports = ECSignature