import { InitialValuesType, MergeVideoInput, MergeVideoOutput } from './types';
import { FFmpeg } from '@ffmpeg/ffmpeg';
import { fetchFile } from '@ffmpeg/util';

const ffmpeg = new FFmpeg();

// This function will use ffmpeg.wasm to merge multiple video files in the browser.
// Returns a Promise that resolves to a Blob of the merged video.
export async function main(
  input: MergeVideoInput,
  options: InitialValuesType
): Promise<MergeVideoOutput> {
  if (!Array.isArray(input) || input.length < 2) {
    throw new Error('Please provide at least two video files to merge.');
  }

  if (!ffmpeg.loaded) {
    await ffmpeg.load({
      wasmURL:
        'https://cdn.jsdelivr.net/npm/@ffmpeg/core@0.12.9/dist/esm/ffmpeg-core.wasm'
    });
  }

  // Write all input files to ffmpeg FS
  const fileNames = input.map((file, idx) => `input${idx}.mp4`);
  for (let i = 0; i < input.length; i++) {
    await ffmpeg.writeFile(fileNames[i], await fetchFile(input[i]));
  }

  // Create concat list file
  const concatList = fileNames.map((name) => `file '${name}'`).join('\n');
  await ffmpeg.writeFile(
    'concat_list.txt',
    new TextEncoder().encode(concatList)
  );

  // Run ffmpeg concat demuxer
  const outputName = 'output.mp4';
  await ffmpeg.exec([
    '-f',
    'concat',
    '-safe',
    '0',
    '-i',
    'concat_list.txt',
    '-c',
    'copy',
    outputName
  ]);

  const mergedData = await ffmpeg.readFile(outputName);
  return new Blob([mergedData], { type: 'video/mp4' });
}