import fs from 'fs';
import zlib from 'zlib';

class PNG {
  static decode(path, fn) {
    {
      return fs.readFile(path, function(err, file) {
        const png = new PNG(file);
        return png.decode(pixels => fn(pixels));
      });
    }
  }

  static load(path) {
    {
      const file = fs.readFileSync(path);
      return new PNG(file);
    }
  }

  constructor(data) {
    let i;
    this.data = data;
    this.pos = 8; // Skip the default header

    this.palette = [];
    this.imgData = [];
    this.transparency = {};
    this.text = {};

    while (true) {
      const chunkSize = this.readUInt32();
      let section = '';
      for (i = 0; i < 4; i++) {
        section += String.fromCharCode(this.data[this.pos++]);
      }

      switch (section) {
        case 'IHDR':
          // we can grab  interesting values from here (like width, height, etc)
          this.width = this.readUInt32();
          this.height = this.readUInt32();
          this.bits = this.data[this.pos++];
          this.colorType = this.data[this.pos++];
          this.compressionMethod = this.data[this.pos++];
          this.filterMethod = this.data[this.pos++];
          this.interlaceMethod = this.data[this.pos++];
          break;

        case 'PLTE':
          this.palette = this.read(chunkSize);
          break;

        case 'IDAT':
          for (i = 0; i < chunkSize; i++) {
            this.imgData.push(this.data[this.pos++]);
          }
          break;

        case 'tRNS':
          // This chunk can only occur once and it must occur after the
          // PLTE chunk and before the IDAT chunk.
          this.transparency = {};
          switch (this.colorType) {
            case 3:
              // Indexed color, RGB. Each byte in this chunk is an alpha for
              // the palette index in the PLTE ("palette") chunk up until the
              // last non-opaque entry. Set up an array, stretching over all
              // palette entries which will be 0 (opaque) or 1 (transparent).
              this.transparency.indexed = this.read(chunkSize);
              var short = 255 - this.transparency.indexed.length;
              if (short > 0) {
                for (i = 0; i < short; i++) {
                  this.transparency.indexed.push(255);
                }
              }
              break;
            case 0:
              // Greyscale. Corresponding to entries in the PLTE chunk.
              // Grey is two bytes, range 0 .. (2 ^ bit-depth) - 1
              this.transparency.grayscale = this.read(chunkSize)[0];
              break;
            case 2:
              // True color with proper alpha channel.
              this.transparency.rgb = this.read(chunkSize);
              break;
          }
          break;

        case 'tEXt':
          var text = this.read(chunkSize);
          var index = text.indexOf(0);
          var key = String.fromCharCode.apply(String, text.slice(0, index));
          this.text[key] = String.fromCharCode.apply(
            String,
            text.slice(index + 1)
          );
          break;

        case 'IEND':
          // we've got everything we need!
          switch (this.colorType) {
            case 0:
            case 3:
            case 4:
              this.colors = 1;
              break;
            case 2:
            case 6:
              this.colors = 3;
              break;
          }

          this.hasAlphaChannel = [4, 6].includes(this.colorType);
          var colors = this.colors + (this.hasAlphaChannel ? 1 : 0);
          this.pixelBitlength = this.bits * colors;

          switch (this.colors) {
            case 1:
              this.colorSpace = 'DeviceGray';
              break;
            case 3:
              this.colorSpace = 'DeviceRGB';
              break;
          }

          this.imgData = Buffer.from(this.imgData);
          return;

        default:
          // unknown (or unimportant) section, skip it
          this.pos += chunkSize;
      }

      this.pos += 4; // Skip the CRC

      if (this.pos > this.data.length) {
        throw new Error('Incomplete or corrupt PNG file');
      }
    }
  }

  read(bytes) {
    const result = new Array(bytes);
    for (let i = 0; i < bytes; i++) {
      result[i] = this.data[this.pos++];
    }
    return result;
  }

  readUInt32() {
    const b1 = this.data[this.pos++] << 24;
    const b2 = this.data[this.pos++] << 16;
    const b3 = this.data[this.pos++] << 8;
    const b4 = this.data[this.pos++];
    return b1 | b2 | b3 | b4;
  }

  readUInt16() {
    const b1 = this.data[this.pos++] << 8;
    const b2 = this.data[this.pos++];
    return b1 | b2;
  }

  decodePixels(fn) {
    return zlib.inflate(this.imgData, (err, data) => {
      if (err) {
        throw err;
      }

      const { width, height } = this;
      const pixelBytes = this.pixelBitlength / 8;

      const pixels = Buffer.alloc(width * height * pixelBytes);
      const { length } = data;
      let pos = 0;

      function pass(x0, y0, dx, dy, singlePass = false) {
        const w = Math.ceil((width - x0) / dx);
        const h = Math.ceil((height - y0) / dy);
        const scanlineLength = pixelBytes * w;
        const buffer = singlePass ? pixels : Buffer.alloc(scanlineLength * h);
        let row = 0;
        let c = 0;
        while (row < h && pos < length) {
          var byte, col, i, left, upper;
          switch (data[pos++]) {
            case 0: // None
              for (i = 0; i < scanlineLength; i++) {
                buffer[c++] = data[pos++];
              }
              break;

            case 1: // Sub
              for (i = 0; i < scanlineLength; i++) {
                byte = data[pos++];
                left = i < pixelBytes ? 0 : buffer[c - pixelBytes];
                buffer[c++] = (byte + left) % 256;
              }
              break;

            case 2: // Up
              for (i = 0; i < scanlineLength; i++) {
                byte = data[pos++];
                col = (i - (i % pixelBytes)) / pixelBytes;
                upper =
                  row &&
                  buffer[
                    (row - 1) * scanlineLength +
                      col * pixelBytes +
                      (i % pixelBytes)
                  ];
                buffer[c++] = (upper + byte) % 256;
              }
              break;

            case 3: // Average
              for (i = 0; i < scanlineLength; i++) {
                byte = data[pos++];
                col = (i - (i % pixelBytes)) / pixelBytes;
                left = i < pixelBytes ? 0 : buffer[c - pixelBytes];
                upper =
                  row &&
                  buffer[
                    (row - 1) * scanlineLength +
                      col * pixelBytes +
                      (i % pixelBytes)
                  ];
                buffer[c++] = (byte + Math.floor((left + upper) / 2)) % 256;
              }
              break;

            case 4: // Paeth
              for (i = 0; i < scanlineLength; i++) {
                var paeth, upperLeft;
                byte = data[pos++];
                col = (i - (i % pixelBytes)) / pixelBytes;
                left = i < pixelBytes ? 0 : buffer[c - pixelBytes];

                if (row === 0) {
                  upper = upperLeft = 0;
                } else {
                  upper =
                    buffer[
                      (row - 1) * scanlineLength +
                        col * pixelBytes +
                        (i % pixelBytes)
                    ];
                  upperLeft =
                    col &&
                    buffer[
                      (row - 1) * scanlineLength +
                        (col - 1) * pixelBytes +
                        (i % pixelBytes)
                    ];
                }

                const p = left + upper - upperLeft;
                const pa = Math.abs(p - left);
                const pb = Math.abs(p - upper);
                const pc = Math.abs(p - upperLeft);

                if (pa <= pb && pa <= pc) {
                  paeth = left;
                } else if (pb <= pc) {
                  paeth = upper;
                } else {
                  paeth = upperLeft;
                }

                buffer[c++] = (byte + paeth) % 256;
              }
              break;

            default:
              throw new Error(`Invalid filter algorithm: ${data[pos - 1]}`);
          }

          if (!singlePass) {
            let pixelsPos = ((y0 + row * dy) * width + x0) * pixelBytes;
            let bufferPos = row * scanlineLength;
            for (i = 0; i < w; i++) {
              for (let j = 0; j < pixelBytes; j++)
                pixels[pixelsPos++] = buffer[bufferPos++];
              pixelsPos += (dx - 1) * pixelBytes;
            }
          }

          row++;
        }
      }

      if (this.interlaceMethod === 1) {
        /*
          1 6 4 6 2 6 4 6
          7 7 7 7 7 7 7 7
          5 6 5 6 5 6 5 6
          7 7 7 7 7 7 7 7
          3 6 4 6 3 6 4 6
          7 7 7 7 7 7 7 7
          5 6 5 6 5 6 5 6
          7 7 7 7 7 7 7 7
        */
        pass(0, 0, 8, 8); // 1
        pass(4, 0, 8, 8); // 2
        pass(0, 4, 4, 8); // 3
        pass(2, 0, 4, 4); // 4
        pass(0, 2, 2, 4); // 5
        pass(1, 0, 2, 2); // 6
        pass(0, 1, 1, 2); // 7
      } else {
        pass(0, 0, 1, 1, true);
      }

      return fn(pixels);
    });
  }

  decodePalette() {
    const { palette } = this;
    const { length } = palette;
    const transparency = this.transparency.indexed || [];
    const ret = Buffer.alloc(transparency.length + length);
    let pos = 0;
    let c = 0;

    for (let i = 0; i < length; i += 3) {
      var left;
      ret[pos++] = palette[i];
      ret[pos++] = palette[i + 1];
      ret[pos++] = palette[i + 2];
      ret[pos++] = (left = transparency[c++]) != null ? left : 255;
    }

    return ret;
  }

  copyToImageData(imageData, pixels) {
    let j, k;
    let { colors } = this;
    let palette = null;
    let alpha = this.hasAlphaChannel;

    if (this.palette.length) {
      palette =
        this._decodedPalette || (this._decodedPalette = this.decodePalette());
      colors = 4;
      alpha = true;
    }

    const data = imageData.data || imageData;
    const { length } = data;
    const input = palette || pixels;
    let i = (j = 0);

    if (colors === 1) {
      while (i < length) {
        k = palette ? pixels[i / 4] * 4 : j;
        const v = input[k++];
        data[i++] = v;
        data[i++] = v;
        data[i++] = v;
        data[i++] = alpha ? input[k++] : 255;
        j = k;
      }
    } else {
      while (i < length) {
        k = palette ? pixels[i / 4] * 4 : j;
        data[i++] = input[k++];
        data[i++] = input[k++];
        data[i++] = input[k++];
        data[i++] = alpha ? input[k++] : 255;
        j = k;
      }
    }
  }

  decode(fn) {
    const ret = Buffer.alloc(this.width * this.height * 4);
    return this.decodePixels(pixels => {
      this.copyToImageData(ret, pixels);
      return fn(ret);
    });
  }
}

export { PNG as default };
