var assert = require('assert')
var BigInteger = require('bigi')

function ECSignature(r, s) {
  assert(r instanceof BigInteger, 'Expected BigInteger, got ' + r)
  assert(s instanceof BigInteger, 'Expected BigInteger, got ' + s)
  this.r = r
  this.s = s
}

// Import operations
ECSignature.parseCompact = function(buffer) {
  assert.equal(buffer.length, 65, 'Invalid signature length')
  var i = buffer.readUInt8(0) - 27

  // At most 3 bits
  assert.equal(i, i & 7, 'Invalid signature parameter')
  var compressed = !!(i & 4)

  // Recovery param only
  i = i & 3

  var r = BigInteger.fromBuffer(buffer.slice(1, 33))
  var s = BigInteger.fromBuffer(buffer.slice(33))

  return {
    compressed: compressed,
    i: i,
    signature: new ECSignature(r, s)
  }
}

ECSignature.fromDER = function(buffer) {
  assert.equal(buffer.readUInt8(0), 0x30, 'Not a DER sequence')
  assert.equal(buffer.readUInt8(1), buffer.length - 2, 'Invalid sequence length')
  assert.equal(buffer.readUInt8(2), 0x02, 'Expected a DER integer')

  var rLen = buffer.readUInt8(3)
  assert(rLen > 0, 'R length is zero')

  var offset = 4 + rLen
  assert.equal(buffer.readUInt8(offset), 0x02, 'Expected a DER integer (2)')

  var sLen = buffer.readUInt8(offset + 1)
  assert(sLen > 0, 'S length is zero')

  var rB = buffer.slice(4, offset)
  var sB = buffer.slice(offset + 2)
  offset += 2 + sLen

  if (rLen > 1 && rB.readUInt8(0) === 0x00) {
    assert(rB.readUInt8(1) & 0x80, 'R value excessively padded')
  }

  if (sLen > 1 && sB.readUInt8(0) === 0x00) {
    assert(sB.readUInt8(1) & 0x80, 'S value excessively padded')
  }

  assert.equal(offset, buffer.length, 'Invalid DER encoding')
  var r = BigInteger.fromDERInteger(rB)
  var s = BigInteger.fromDERInteger(sB)

  assert(r.signum() >= 0, 'R value is negative')
  assert(s.signum() >= 0, 'S value is negative')

  return new ECSignature(r, s)
}

// FIXME: 0x00, 0x04, 0x80 are SIGHASH_* boundary constants, importing Transaction causes a circular dependency
ECSignature.parseScriptSignature = function(buffer) {
  var hashType = buffer.readUInt8(buffer.length - 1)
  var hashTypeMod = hashType & ~0x80

  assert(hashTypeMod > 0x00 && hashTypeMod < 0x04, 'Invalid hashType')

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

// Export operations
ECSignature.prototype.toCompact = function(i, compressed) {
  if (compressed) i += 4
  i += 27

  var buffer = new Buffer(65)
  buffer.writeUInt8(i, 0)

  this.r.toBuffer(32).copy(buffer, 1)
  this.s.toBuffer(32).copy(buffer, 33)

  return buffer
}

ECSignature.prototype.toDER = function() {
  var rBa = this.r.toDERInteger()
  var sBa = this.s.toDERInteger()

  var sequence = []
  sequence.push(0x02) // INTEGER
  sequence.push(rBa.length)
  sequence = sequence.concat(rBa)

  sequence.push(0x02) // INTEGER
  sequence.push(sBa.length)
  sequence = sequence.concat(sBa)

  sequence.unshift(sequence.length)
  sequence.unshift(0x30) // SEQUENCE

  return new Buffer(sequence)
}

ECSignature.prototype.toScriptSignature = function(hashType) {
  var hashTypeBuffer = new Buffer(1)
  hashTypeBuffer.writeUInt8(hashType, 0)

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

module.exports = ECSignature