import { toUTF8String, readUInt32BE } from './utils'

/**
 * ICNS Header
 *
 * | Offset | Size | Purpose                                                |
 * | 0	    | 4    | Magic literal, must be "icns" (0x69, 0x63, 0x6e, 0x73) |
 * | 4      | 4    | Length of file, in bytes, msb first.                   |
 *
 */
const SIZE_HEADER = 4 + 4 // 8
const FILE_LENGTH_OFFSET = 4 // MSB => BIG ENDIAN

/**
 * Image Entry
 *
 * | Offset | Size | Purpose                                                          |
 * | 0	    | 4    | Icon type, see OSType below.                                     |
 * | 4      | 4    | Length of data, in bytes (including type and length), msb first. |
 * | 8      | n    | Icon data                                                        |
 */
const ENTRY_LENGTH_OFFSET = 4 // MSB => BIG ENDIAN

const ICON_TYPE_SIZE = {
  ICON: 32,
  'ICN#': 32,
  // m => 16 x 16
  'icm#': 16,
  icm4: 16,
  icm8: 16,
  // s => 16 x 16
  'ics#': 16,
  ics4: 16,
  ics8: 16,
  is32: 16,
  s8mk: 16,
  icp4: 16,
  // l => 32 x 32
  icl4: 32,
  icl8: 32,
  il32: 32,
  l8mk: 32,
  icp5: 32,
  ic11: 32,
  // h => 48 x 48
  ich4: 48,
  ich8: 48,
  ih32: 48,
  h8mk: 48,
  // . => 64 x 64
  icp6: 64,
  ic12: 32,
  // t => 128 x 128
  it32: 128,
  t8mk: 128,
  ic07: 128,
  // . => 256 x 256
  ic08: 256,
  ic13: 256,
  // . => 512 x 512
  ic09: 512,
  ic14: 512,
  // . => 1024 x 1024
  ic10: 1024
}

function readImageHeader (
  input,
  imageOffset
) {
  const imageLengthOffset = imageOffset + ENTRY_LENGTH_OFFSET
  return [
    toUTF8String(input, imageOffset, imageLengthOffset),
    readUInt32BE(input, imageLengthOffset)
  ]
}

function getImageSize (type) {
  const size = ICON_TYPE_SIZE[type]
  return { width: size, height: size, type }
}

export const ICNS = {
  validate: (input) => toUTF8String(input, 0, 4) === 'icns',

  calculate (input) {
    const inputLength = input.length
    const fileLength = readUInt32BE(input, FILE_LENGTH_OFFSET)
    let imageOffset = SIZE_HEADER

    let imageHeader = readImageHeader(input, imageOffset)
    let imageSize = getImageSize(imageHeader[0])
    imageOffset += imageHeader[1]

    if (imageOffset === fileLength) return imageSize

    const result = {
      height: imageSize.height,
      images: [imageSize],
      width: imageSize.width
    }

    while (imageOffset < fileLength && imageOffset < inputLength) {
      imageHeader = readImageHeader(input, imageOffset)
      imageSize = getImageSize(imageHeader[0])
      imageOffset += imageHeader[1]
      result.images.push(imageSize)
    }

    return result
  }
}
