import { existsSync, writeFileSync, readFileSync, unlinkSync } from 'node:fs'
import { dirname, join } from 'node:path'
import { spawn } from 'node:child_process'

function collectError(stderr: string, fallback: string) {
  const text = stderr.replace(/\r/g, '').trim()
  const lines = text.split('\n').map(line => line.trim()).filter(Boolean)
  return lines.slice(-6).join(' ') || fallback
}

export function runFfmpeg(args: string[], timeoutMs = 120000) {
  return new Promise<void>((resolve, reject) => {
    const proc = spawn('ffmpeg', args, { stdio: ['ignore', 'ignore', 'pipe'] })
    let stderr = ''
    proc.stderr?.on('data', (chunk: Buffer | string) => { stderr += String(chunk) })
    const timer = setTimeout(() => {
      try { proc.kill('SIGKILL') } catch { /* ignore */ }
      reject(new Error(`FFmpeg timed out after ${Math.round(timeoutMs / 1000)}s`))
    }, timeoutMs)
    proc.on('error', (error) => {
      clearTimeout(timer)
      const message = (error as NodeJS.ErrnoException).code === 'ENOENT'
        ? 'FFmpeg is not installed on this server'
        : error.message
      reject(new Error(message))
    })
    proc.on('close', (code) => {
      clearTimeout(timer)
      if (code === 0) resolve()
      else reject(new Error(collectError(stderr, `FFmpeg exited with code ${code}`)))
    })
  })
}

function runFfprobe(args: string[], timeoutMs = 15000) {
  return new Promise<string>((resolve, reject) => {
    const proc = spawn('ffprobe', args, { stdio: ['ignore', 'pipe', 'pipe'] })
    let out = ''
    let err = ''
    proc.stdout?.on('data', (chunk: Buffer | string) => { out += String(chunk) })
    proc.stderr?.on('data', (chunk: Buffer | string) => { err += String(chunk) })
    const timer = setTimeout(() => {
      try { proc.kill('SIGKILL') } catch { /* ignore */ }
      reject(new Error('ffprobe timed out'))
    }, timeoutMs)
    proc.on('error', (error) => {
      clearTimeout(timer)
      reject(error)
    })
    proc.on('close', (code) => {
      clearTimeout(timer)
      if (code === 0) resolve(out.trim())
      else reject(new Error(collectError(err, `ffprobe exited with code ${code}`)))
    })
  })
}

function concatPath(filePath: string) {
  return filePath.replace(/\\/g, '/').replace(/'/g, "'\\''")
}

export async function extractLastFrame(inputPath: string, outputPath: string) {
  if (!existsSync(inputPath)) {
    throw new Error('Source video is missing')
  }
  await runFfmpeg([
    '-y',
    '-sseof', '-1',
    '-i', inputPath,
    '-update', '1',
    '-frames:v', '1',
    '-q:v', '1',
    outputPath
  ], 30000)
  if (!existsSync(outputPath)) {
    throw new Error('FFmpeg did not write the last frame')
  }
}

export async function probeHasAudio(filePath: string) {
  try {
    const out = await runFfprobe([
      '-v', 'error',
      '-select_streams', 'a:0',
      '-show_entries', 'stream=codec_type',
      '-of', 'csv=p=0',
      filePath
    ])
    return out.includes('audio')
  } catch {
    return false
  }
}

const XFADE_DURATION = 0.12

async function probeDuration(filePath: string) {
  const out = await runFfprobe([
    '-v', 'error',
    '-show_entries', 'format=duration',
    '-of', 'default=nokey=1:noprint_wrappers=1',
    filePath
  ])
  const duration = Number(out)
  if (!Number.isFinite(duration) || duration <= 0) {
    throw new Error('Could not read video duration')
  }
  return duration
}

async function probeFps(filePath: string) {
  const out = await runFfprobe([
    '-v', 'error',
    '-select_streams', 'v:0',
    '-show_entries', 'stream=avg_frame_rate,r_frame_rate',
    '-of', 'default=nokey=1:noprint_wrappers=1',
    filePath
  ])
  const line = out.split(/\r?\n/).map(item => item.trim()).find(Boolean) || ''
  const [num, den] = line.split('/').map(Number)
  if (Number.isFinite(num) && Number.isFinite(den) && den > 0) return num / den
  const fps = Number(line)
  return Number.isFinite(fps) && fps > 0 ? fps : 24
}

async function probeSize(filePath: string) {
  const out = await runFfprobe([
    '-v', 'error',
    '-select_streams', 'v:0',
    '-show_entries', 'stream=width,height',
    '-of', 'csv=p=0',
    filePath
  ])
  const [width, height] = out.split(',').map(Number)
  return {
    width: Number.isFinite(width) && width > 0 ? width : 1344,
    height: Number.isFinite(height) && height > 0 ? height : 768
  }
}

async function trimLeadingFrame(inputPath: string, outputPath: string) {
  const fps = await probeFps(inputPath)
  const hasAudio = await probeHasAudio(inputPath)
  const args = [
    '-y',
    '-i', inputPath,
    '-vf', 'trim=start_frame=1,setpts=PTS-STARTPTS'
  ]
  if (hasAudio) {
    args.push('-af', `atrim=start=${(1 / fps).toFixed(6)},asetpts=PTS-STARTPTS`, '-c:a', 'aac')
  } else {
    args.push('-an')
  }
  args.push(
    '-c:v', 'libx264',
    '-preset', 'fast',
    '-crf', '17',
    '-pix_fmt', 'yuv420p',
    '-movflags', '+faststart',
    outputPath
  )
  await runFfmpeg(args, 180000)
  if (!existsSync(outputPath)) {
    throw new Error('FFmpeg did not write the trimmed extension segment')
  }
}

async function xfadeStitch(part1Path: string, part2Path: string, outputPath: string) {
  const [duration1, duration2, fps, size, audio1, audio2] = await Promise.all([
    probeDuration(part1Path),
    probeDuration(part2Path),
    probeFps(part1Path),
    probeSize(part1Path),
    probeHasAudio(part1Path),
    probeHasAudio(part2Path)
  ])
  const fade = Math.min(
    XFADE_DURATION,
    Math.max(0.04, duration1 - 0.05),
    Math.max(0.04, duration2 - 0.05)
  )
  const offset = Math.max(0, Number((duration1 - fade).toFixed(3)))
  const fpsLabel = Number.isInteger(fps) ? String(fps) : fps.toFixed(3)
  const prepare = `fps=${fpsLabel},scale=${size.width}:${size.height}:flags=bicubic,format=yuv420p,setpts=PTS-STARTPTS`
  const videoFilter = `[0:v]${prepare}[v0];[1:v]${prepare}[v1];[v0][v1]xfade=transition=fade:duration=${fade.toFixed(3)}:offset=${offset},setpts=PTS-STARTPTS[v]`
  const encode = [
    '-c:v', 'libx264',
    '-preset', 'fast',
    '-crf', '17',
    '-pix_fmt', 'yuv420p',
    '-movflags', '+faststart'
  ]
  if (audio1 && audio2) {
    await runFfmpeg([
      '-y',
      '-i', part1Path,
      '-i', part2Path,
      '-filter_complex', `${videoFilter};[0:a]asetpts=PTS-STARTPTS[a0];[1:a]asetpts=PTS-STARTPTS[a1];[a0][a1]acrossfade=d=${fade.toFixed(3)}:c1=tri:c2=tri[a]`,
      '-map', '[v]',
      '-map', '[a]',
      ...encode,
      '-c:a', 'aac',
      outputPath
    ], 300000)
  } else {
    await runFfmpeg([
      '-y',
      '-i', part1Path,
      '-i', part2Path,
      '-filter_complex', videoFilter,
      '-map', '[v]',
      ...encode,
      outputPath
    ], 300000)
  }
  if (!existsSync(outputPath)) {
    throw new Error('FFmpeg did not write the blended video')
  }
}

export async function concatMp4(part1Path: string, part2Path: string, outputPath: string) {
  const listPath = join(dirname(outputPath), 'concat_list.txt')
  writeFileSync(listPath, `file '${concatPath(part1Path)}'\nfile '${concatPath(part2Path)}'\n`)
  try {
    await runFfmpeg(['-y', '-f', 'concat', '-safe', '0', '-i', listPath, '-c', 'copy', outputPath], 180000)
  } catch (copyError) {
    const audio1 = await probeHasAudio(part1Path)
    const audio2 = await probeHasAudio(part2Path)
    try {
      if (audio1 && audio2) {
        await runFfmpeg([
          '-y',
          '-i', part1Path,
          '-i', part2Path,
          '-filter_complex', '[0:v][0:a][1:v][1:a]concat=n=2:v=1:a=1[v][a]',
          '-map', '[v]',
          '-map', '[a]',
          '-c:v', 'libx264',
          '-preset', 'fast',
          '-crf', '17',
          '-pix_fmt', 'yuv420p',
          '-c:a', 'aac',
          '-movflags', '+faststart',
          outputPath
        ], 300000)
      } else {
        await runFfmpeg([
          '-y',
          '-i', part1Path,
          '-i', part2Path,
          '-filter_complex', '[0:v][1:v]concat=n=2:v=1:a=0[v]',
          '-map', '[v]',
          '-c:v', 'libx264',
          '-preset', 'fast',
          '-crf', '17',
          '-pix_fmt', 'yuv420p',
          '-movflags', '+faststart',
          outputPath
        ], 300000)
      }
    } catch (encodeError) {
      const copyMessage = copyError instanceof Error ? copyError.message : String(copyError)
      const encodeMessage = encodeError instanceof Error ? encodeError.message : String(encodeError)
      throw new Error(`FFmpeg concat failed (${copyMessage}). Re-encode also failed (${encodeMessage}).`)
    }
  }
  if (!existsSync(outputPath)) {
    throw new Error('FFmpeg did not write the stitched video')
  }
}

export async function stitchExtension(params: { part1Path: string; part2: Buffer; tmpDir: string }) {
  const part2Path = join(params.tmpDir, 'part2.mp4')
  const trimmedPath = join(params.tmpDir, 'part2_trim.mp4')
  const finalPath = join(params.tmpDir, 'final_stitched_video.mp4')
  writeFileSync(part2Path, params.part2)
  try {
    await trimLeadingFrame(part2Path, trimmedPath)
    await xfadeStitch(params.part1Path, trimmedPath, finalPath)
  } catch (blendError) {
    try {
      const trimmedReady = existsSync(trimmedPath)
      await concatMp4(params.part1Path, trimmedReady ? trimmedPath : part2Path, finalPath)
    } catch (concatError) {
      const blendMessage = blendError instanceof Error ? blendError.message : String(blendError)
      const concatMessage = concatError instanceof Error ? concatError.message : String(concatError)
      throw new Error(`Seam blend failed (${blendMessage}). Concat fallback also failed (${concatMessage}).`)
    }
  }
  const stitched = readFileSync(finalPath)
  for (const extra of [part2Path, trimmedPath, join(params.tmpDir, 'concat_list.txt'), join(params.tmpDir, 'last_frame.png')]) {
    try { unlinkSync(extra) } catch { /* ignore */ }
  }
  return stitched
}