import type { Scene } from '@/types/scene'
import { drawSceneFrame, loadSceneImages } from './render'

function effectiveEnd(scene: Scene): number {
  let max = 0
  for (const layer of scene.layers) {
    for (const kf of layer.keyframes) {
      if (kf.time > max) max = kf.time
    }
  }
  if (max <= 0) return scene.duration
  return Math.min(max, scene.duration)
}

export interface VideoExportResult {
  blob: Blob
  mimeType: string
  extension: string
}

export interface VideoExportOptions {
  onProgress?: (progress: number) => void
  signal?: AbortSignal
  bitsPerSecond?: number
}

const MIME_CANDIDATES = [
  'video/webm;codecs=vp9',
  'video/webm;codecs=vp8',
  'video/webm',
  'video/mp4;codecs=h264',
  'video/mp4',
]

export function pickMimeType(): string | null {
  if (typeof MediaRecorder === 'undefined') return null
  for (const mime of MIME_CANDIDATES) {
    if (MediaRecorder.isTypeSupported?.(mime)) return mime
  }
  return null
}

export async function renderSceneToVideo(
  scene: Scene,
  opts: VideoExportOptions = {},
): Promise<VideoExportResult> {
  const mimeType = pickMimeType()
  if (!mimeType) {
    throw new Error('MediaRecorder wird von diesem Browser nicht unterstützt.')
  }

  const canvas = document.createElement('canvas')
  canvas.width = scene.canvas.width
  canvas.height = scene.canvas.height
  const ctx = canvas.getContext('2d')
  if (!ctx) throw new Error('2D context unavailable')

  const images = await loadSceneImages(scene)

  drawSceneFrame(ctx, scene, 0, images)

  const stream = canvas.captureStream(scene.fps)
  const recorder = new MediaRecorder(stream, {
    mimeType,
    videoBitsPerSecond: opts.bitsPerSecond ?? 8_000_000,
  })

  const chunks: Blob[] = []
  recorder.ondataavailable = (e) => {
    if (e.data && e.data.size > 0) chunks.push(e.data)
  }

  const stopped = new Promise<void>((resolve) => {
    recorder.onstop = () => resolve()
  })

  recorder.start()
  const startedAt = performance.now()
  const renderDuration = effectiveEnd(scene)

  const finished = new Promise<void>((resolve, reject) => {
    let raf = 0
    const step = () => {
      if (opts.signal?.aborted) {
        cancelAnimationFrame(raf)
        try {
          recorder.stop()
        } catch {
          /* ignore */
        }
        stream.getTracks().forEach((t) => t.stop())
        reject(new DOMException('aborted', 'AbortError'))
        return
      }
      const elapsed = (performance.now() - startedAt) / 1000
      const t = Math.min(elapsed, renderDuration)
      drawSceneFrame(ctx, scene, t, images)
      opts.onProgress?.(renderDuration > 0 ? Math.min(1, t / renderDuration) : 1)
      if (elapsed >= renderDuration) {
        try {
          recorder.stop()
        } catch {
          /* ignore */
        }
        stream.getTracks().forEach((t) => t.stop())
        resolve()
        return
      }
      raf = requestAnimationFrame(step)
    }
    raf = requestAnimationFrame(step)
  })

  await finished
  await stopped

  const blob = new Blob(chunks, { type: mimeType })
  const extension = mimeType.includes('mp4') ? 'mp4' : 'webm'
  return { blob, mimeType, extension }
}

export async function downloadSceneAsVideo(
  scene: Scene,
  opts: VideoExportOptions = {},
): Promise<void> {
  const { blob, extension } = await renderSceneToVideo(scene, opts)
  const url = URL.createObjectURL(blob)
  const a = document.createElement('a')
  a.href = url
  a.download = `animation.${extension}`
  document.body.appendChild(a)
  a.click()
  document.body.removeChild(a)
  setTimeout(() => URL.revokeObjectURL(url), 1000)
}