import { decode } from 'fast-bmp';

import { Image } from '../Image.ts';
import { Mask } from '../Mask.ts';
import type { ImageColorModel } from '../utils/constants/colorModels.ts';

import type { Resolution } from './load.types.ts';

type DecodedBmp = ReturnType<typeof decode>;

/**
 * Decode a BMP. See the fast-bmp npm module.
 * @param data - The data to decode.
 * @returns The decoded image or mask.
 */
export function decodeBmp(data: Uint8Array): Image {
  const decodedData = decode(data);
  if (decodedData.bitsPerPixel === 1) {
    const mask = new Mask(decodedData.width, decodedData.height, {
      data: decodedData.data as Uint8Array,
    });
    return mask.convertColor('GREY');
  } else {
    let colorModel: ImageColorModel;
    switch (decodedData.channels) {
      case 1:
        colorModel = 'GREY';
        break;
      case 3:
        colorModel = 'RGB';
        break;
      default:
        colorModel = 'RGBA';
        break;
    }
    return new Image(decodedData.width, decodedData.height, {
      colorModel,
      data: decodedData.data as Uint8Array,
      resolution: getBmpResolution(decodedData),
    });
  }
}

/**
 * Gets image's resolution from its parsed data. BMP stores resolution in
 * pixels per meter.
 * @param bmp - Parsed BMP image.
 * @returns Object with resolution data if it is defined.
 */
function getBmpResolution(bmp: DecodedBmp): Resolution | undefined {
  if (!bmp.xPixelsPerMeter || !bmp.yPixelsPerMeter) {
    return undefined;
  }
  return {
    x: bmp.xPixelsPerMeter,
    y: bmp.yPixelsPerMeter,
    unit: 'meter',
  };
}