var opcodes = require('./opcodes.json')
var varuint = require('varuint-bitcoin')

function pushDataSize (i) {
  return i < opcodes.OP_PUSHDATA1 ? 1
  : i <= 0xff ? 2
  : i <= 0xffff ? 3
  : 5
}

function readPushDataInt (buffer, offset) {
  var opcode = buffer.readUInt8(offset)
  var number, size

  // ~6 bit
  if (opcode < opcodes.OP_PUSHDATA1) {
    number = opcode
    size = 1

  // 8 bit
  } else if (opcode === opcodes.OP_PUSHDATA1) {
    if (offset + 2 > buffer.length) return null
    number = buffer.readUInt8(offset + 1)
    size = 2

  // 16 bit
  } else if (opcode === opcodes.OP_PUSHDATA2) {
    if (offset + 3 > buffer.length) return null
    number = buffer.readUInt16LE(offset + 1)
    size = 3

  // 32 bit
  } else {
    if (offset + 5 > buffer.length) return null
    if (opcode !== opcodes.OP_PUSHDATA4) throw new Error('Unexpected opcode')

    number = buffer.readUInt32LE(offset + 1)
    size = 5
  }

  return {
    opcode: opcode,
    number: number,
    size: size
  }
}

// https://github.com/feross/buffer/blob/master/index.js#L1127
function verifuint (value, max) {
  if (typeof value !== 'number') throw new Error('cannot write a non-number as a number')
  if (value < 0) throw new Error('specified a negative value for writing an unsigned value')
  if (value > max) throw new Error('RangeError: value out of range')
  if (Math.floor(value) !== value) throw new Error('value has a fractional component')
}

function readUInt64LE (buffer, offset) {
  var a = buffer.readUInt32LE(offset)
  var b = buffer.readUInt32LE(offset + 4)
  b *= 0x100000000

  verifuint(b + a, 0x001fffffffffffff)

  return b + a
}

function writePushDataInt (buffer, number, offset) {
  var size = pushDataSize(number)

  // ~6 bit
  if (size === 1) {
    buffer.writeUInt8(number, offset)

  // 8 bit
  } else if (size === 2) {
    buffer.writeUInt8(opcodes.OP_PUSHDATA1, offset)
    buffer.writeUInt8(number, offset + 1)

  // 16 bit
  } else if (size === 3) {
    buffer.writeUInt8(opcodes.OP_PUSHDATA2, offset)
    buffer.writeUInt16LE(number, offset + 1)

  // 32 bit
  } else {
    buffer.writeUInt8(opcodes.OP_PUSHDATA4, offset)
    buffer.writeUInt32LE(number, offset + 1)
  }

  return size
}

function writeUInt64LE (buffer, value, offset) {
  verifuint(value, 0x001fffffffffffff)

  buffer.writeInt32LE(value & -1, offset)
  buffer.writeUInt32LE(Math.floor(value / 0x100000000), offset + 4)
}

// TODO: remove in 4.0.0?
function readVarInt (buffer, offset) {
  var result = varuint.decode(buffer, offset)

  return {
    number: result,
    size: varuint.decode.bytes
  }
}

// TODO: remove in 4.0.0?
function writeVarInt (buffer, number, offset) {
  varuint.encode(number, buffer, offset)
  return varuint.encode.bytes
}

module.exports = {
  pushDataSize: pushDataSize,
  readPushDataInt: readPushDataInt,
  readUInt64LE: readUInt64LE,
  readVarInt: readVarInt,
  varIntBuffer: varuint.encode,
  varIntSize: varuint.encodingLength,
  writePushDataInt: writePushDataInt,
  writeUInt64LE: writeUInt64LE,
  writeVarInt: writeVarInt
}