import { spawn } from "node:child_process";
import { constants } from "node:fs";
import { access, rm, stat } from "node:fs/promises";
import { setPriority } from "node:os";
import { delimiter, join } from "node:path";

/**
 * ffmpeg and ffprobe from PATH. Every call passes an argument array (never a shell), opens
 * inputs through the `file` protocol only, and forces the demuxer from the artifact's MIME type
 * so a crafted upload cannot make ffmpeg probe it as a playlist that reads other files or URLs.
 */

export interface FfmpegInfo {
  ffmpegPath: string;
  ffprobePath: string;
}

export interface MediaProbe {
  durationMs: number;
  /** Width and height as displayed: swapped when the stream is rotated by 90 or 270 degrees. */
  video?: {
    codec: string;
    width: number;
    height: number;
    rotation: 0 | 90 | 180 | 270;
    /** Frames per second; 0 when unknown or implausible (variable frame rate files). */
    fps: number;
    /** Pixel aspect ratio of the displayed frame; 1 for square pixels. */
    sampleAspectRatio: number;
  };
  audio?: { codec: string; sampleRate: number; channels: number };
  hasAudio: boolean;
}

export interface FfmpegProgress {
  outTimeUs?: number;
  totalSize?: number;
  done: boolean;
}

export interface RunFfmpegOptions {
  signal?: AbortSignal;
  /** Expected output duration; progress is reported as out_time / durationMs. */
  durationMs?: number;
  onProgress?: (fraction: number) => void;
  cwd?: string;
  /** Kills ffmpeg once the output grows past this size. */
  maxOutputBytes?: number;
  /** Files removed when the run fails or is aborted. */
  outputs?: readonly string[];
}

export class FfmpegError extends Error {
  constructor(
    message: string,
    readonly exitCode: number | null,
    readonly stderrTail: string,
  ) {
    super(message);
    this.name = "FfmpegError";
  }
}

/** ffmpeg reports progress twice a second while it works; silence this long means a hang. */
const STALL_TIMEOUT_MS = 2 * 60_000;
const PROBE_TIMEOUT_MS = 60_000;
const STDERR_TAIL_BYTES = 8 * 1024;
const KILL_GRACE_MS = 5_000;
const MAX_PLAUSIBLE_FPS = 240;

const DEMUXERS: Record<string, string> = {
  "video/mp4": "mov",
  "video/quicktime": "mov",
  "audio/mp4": "mov",
  "video/webm": "matroska",
  "audio/webm": "matroska",
  "audio/mpeg": "mp3",
  "audio/wav": "wav",
  "audio/ogg": "ogg",
};

let detection: Promise<FfmpegInfo | null> | undefined;

/** Finds ffmpeg and ffprobe on PATH once per process; null when either is missing or broken. */
export function detectFfmpeg(): Promise<FfmpegInfo | null> {
  detection ??= locateFfmpeg();
  return detection;
}

async function locateFfmpeg(): Promise<FfmpegInfo | null> {
  const [ffmpegPath, ffprobePath] = await Promise.all([
    findExecutable("ffmpeg"),
    findExecutable("ffprobe"),
  ]);
  if (!ffmpegPath || !ffprobePath) return null;
  try {
    const [ffmpeg, ffprobe] = await Promise.all([
      capture(ffmpegPath, ["-hide_banner", "-version"], { timeoutMs: 10_000 }),
      capture(ffprobePath, ["-hide_banner", "-version"], { timeoutMs: 10_000 }),
    ]);
    return ffmpeg.code === 0 && ffprobe.code === 0 ? { ffmpegPath, ffprobePath } : null;
  } catch {
    return null;
  }
}

async function findExecutable(name: string): Promise<string | null> {
  const extensions =
    process.platform === "win32"
      ? (process.env.PATHEXT ?? ".EXE").split(";").filter(Boolean)
      : [""];
  for (const directory of (process.env.PATH ?? "").split(delimiter)) {
    if (!directory) continue;
    for (const extension of extensions) {
      const candidate = join(directory, `${name}${extension}`);
      try {
        await access(candidate, constants.X_OK);
        if ((await stat(candidate)).isFile()) return candidate;
      } catch {
        // Not in this directory.
      }
    }
  }
  return null;
}

async function requireFfmpeg(): Promise<FfmpegInfo> {
  const info = await detectFfmpeg();
  if (!info) throw new Error("ffmpeg and ffprobe are not installed on this server.");
  return info;
}

/** ffmpeg time argument with millisecond precision and no exponent notation. */
export function ffmpegSeconds(seconds: number): string {
  return String(Number(Math.max(0, seconds).toFixed(3)));
}

/** Input arguments for a local file: optional seek, file protocol only, forced demuxer. */
export function ffmpegInputArgs(
  path: string,
  options: { mimeType?: string; startSeconds?: number; durationSeconds?: number } = {},
): string[] {
  const demuxer = options.mimeType ? DEMUXERS[options.mimeType] : undefined;
  return [
    ...(options.startSeconds ? ["-ss", ffmpegSeconds(options.startSeconds)] : []),
    ...(options.durationSeconds !== undefined
      ? ["-t", ffmpegSeconds(options.durationSeconds)]
      : []),
    "-protocol_whitelist",
    "file",
    ...(demuxer ? ["-f", demuxer] : []),
    "-i",
    `file:${path}`,
  ];
}

export async function probeMedia(
  path: string,
  options: { signal?: AbortSignal; mimeType?: string } = {},
): Promise<MediaProbe> {
  const { ffprobePath } = await requireFfmpeg();
  const input = ffmpegInputArgs(path, { mimeType: options.mimeType });
  const result = await capture(
    ffprobePath,
    ["-v", "error", ...input, "-print_format", "json", "-show_format", "-show_streams"],
    { signal: options.signal, timeoutMs: PROBE_TIMEOUT_MS },
  );
  if (result.code !== 0) throw ffmpegFailure("ffprobe", result.code, result.stderr);
  const probe = parseProbeOutput(result.stdout);
  if (probe.durationMs > 0 || (!probe.video && !probe.audio)) return probe;
  // Recordings streamed by browsers often carry no duration header; read it from the packets.
  const packets = await capture(
    ffprobePath,
    [
      "-v",
      "error",
      ...input,
      "-select_streams",
      probe.video ? "v:0" : "a:0",
      "-show_entries",
      "packet=pts_time,duration_time",
      "-of",
      "csv=p=0",
    ],
    { signal: options.signal, timeoutMs: PROBE_TIMEOUT_MS * 5 },
  );
  if (packets.code !== 0) throw ffmpegFailure("ffprobe", packets.code, packets.stderr);
  return { ...probe, durationMs: packetDurationMs(packets.stdout) };
}

/** End of the last packet, from ffprobe `packet=pts_time,duration_time` CSV lines. */
export function packetDurationMs(csv: string): number {
  let end = 0;
  for (const line of csv.split("\n")) {
    const [pts, duration] = line.split(",").map(Number);
    if (pts === undefined || !Number.isFinite(pts)) continue;
    end = Math.max(end, pts + (duration !== undefined && Number.isFinite(duration) ? duration : 0));
  }
  return Math.round(end * 1000);
}

interface ProbeStream {
  codec_type?: string;
  codec_name?: string;
  width?: number;
  height?: number;
  avg_frame_rate?: string;
  r_frame_rate?: string;
  sample_aspect_ratio?: string;
  sample_rate?: string;
  channels?: number;
  duration?: string;
  disposition?: { attached_pic?: number };
  tags?: { rotate?: string };
  side_data_list?: { rotation?: number }[];
}

/** Parses `ffprobe -print_format json -show_format -show_streams` output. */
export function parseProbeOutput(json: string): MediaProbe {
  const data = JSON.parse(json) as {
    format?: { duration?: string };
    streams?: ProbeStream[];
  };
  const streams = data.streams ?? [];
  // Cover art in audio files is a single attached picture, not a video track.
  const video = streams.find(
    (stream) => stream.codec_type === "video" && stream.disposition?.attached_pic !== 1,
  );
  const audio = streams.find((stream) => stream.codec_type === "audio");
  const seconds =
    positive(Number(data.format?.duration)) ??
    Math.max(0, ...streams.map((stream) => positive(Number(stream.duration)) ?? 0));
  return {
    durationMs: Math.round(seconds * 1000),
    ...(video?.width && video.height
      ? { video: probeVideo(video, video.width, video.height) }
      : {}),
    ...(audio
      ? {
          audio: {
            codec: audio.codec_name ?? "",
            sampleRate: Number(audio.sample_rate) || 0,
            channels: audio.channels ?? 0,
          },
        }
      : {}),
    hasAudio: Boolean(audio),
  };
}

function probeVideo(stream: ProbeStream, width: number, height: number) {
  const rotation = normalizeRotation(
    stream.side_data_list?.find((entry) => typeof entry.rotation === "number")?.rotation ??
      Number(stream.tags?.rotate ?? 0),
  );
  const sideways = rotation === 90 || rotation === 270;
  const sar = ratio(stream.sample_aspect_ratio, ":") || 1;
  const fps = ratio(stream.avg_frame_rate, "/") || ratio(stream.r_frame_rate, "/");
  return {
    codec: stream.codec_name ?? "",
    width: sideways ? height : width,
    height: sideways ? width : height,
    rotation,
    fps: fps > 0 && fps <= MAX_PLAUSIBLE_FPS ? fps : 0,
    sampleAspectRatio: sideways ? 1 / sar : sar,
  };
}

function normalizeRotation(degrees: number): 0 | 90 | 180 | 270 {
  if (!Number.isFinite(degrees)) return 0;
  const quarter = (((Math.round(degrees / 90) % 4) + 4) % 4) as 0 | 1 | 2 | 3;
  return ([0, 90, 180, 270] as const)[quarter];
}

function ratio(value: string | undefined, separator: string): number {
  if (!value) return 0;
  const [numerator, denominator] = value.split(separator).map(Number);
  if (!numerator || !denominator || !Number.isFinite(numerator / denominator)) return 0;
  return numerator / denominator;
}

function positive(value: number): number | undefined {
  return Number.isFinite(value) && value > 0 ? value : undefined;
}

/** Feeds ffmpeg `-progress` output (key=value lines) and reports each completed block. */
export function createFfmpegProgressParser(
  onUpdate: (progress: FfmpegProgress) => void,
): (chunk: string) => void {
  let buffer = "";
  let current: Omit<FfmpegProgress, "done"> = {};
  return (chunk) => {
    buffer += chunk;
    for (let newline = buffer.indexOf("\n"); newline >= 0; newline = buffer.indexOf("\n")) {
      const line = buffer.slice(0, newline).trim();
      buffer = buffer.slice(newline + 1);
      const separator = line.indexOf("=");
      if (separator < 0) continue;
      const key = line.slice(0, separator);
      const value = line.slice(separator + 1).trim();
      const number = Number(value);
      // out_time_ms is microseconds too (a long-standing ffmpeg naming bug).
      if ((key === "out_time_us" || key === "out_time_ms") && value && number >= 0) {
        current.outTimeUs = number;
      } else if (key === "total_size" && value && number >= 0) {
        current.totalSize = number;
      } else if (key === "progress") {
        onUpdate({ ...current, done: value === "end" });
        current = {};
      }
    }
  };
}

/** Runs ffmpeg with progress on stdout; rejects with the stderr tail when it fails. */
export async function runFfmpeg(
  args: readonly string[],
  options: RunFfmpegOptions = {},
): Promise<void> {
  options.signal?.throwIfAborted();
  const { ffmpegPath } = await requireFfmpeg();
  try {
    await spawnFfmpeg(ffmpegPath, args, options);
  } catch (error) {
    await Promise.all((options.outputs ?? []).map((path) => rm(path, { force: true })));
    throw error;
  }
}

function spawnFfmpeg(
  ffmpegPath: string,
  args: readonly string[],
  options: RunFfmpegOptions,
): Promise<void> {
  const { signal, durationMs, onProgress, maxOutputBytes } = options;
  return new Promise((resolve, reject) => {
    const child = spawn(
      ffmpegPath,
      [
        "-hide_banner",
        "-nostdin",
        "-nostats",
        "-loglevel",
        "error",
        "-progress",
        "pipe:1",
        "-y",
        ...args,
      ],
      { cwd: options.cwd, stdio: ["ignore", "pipe", "pipe"], windowsHide: true },
    );
    if (child.pid) {
      try {
        // Long encodes must not starve the API process that shares this machine.
        setPriority(child.pid, 10);
      } catch {
        // Lowering priority is best effort.
      }
    }
    let stderr = "";
    let settled = false;
    let reported = 0;
    let failure: unknown;
    let stallTimer: NodeJS.Timeout | undefined;
    const finish = (error?: unknown) => {
      if (settled) return;
      settled = true;
      clearTimeout(stallTimer);
      signal?.removeEventListener("abort", abort);
      if (error === undefined) resolve();
      else reject(error);
    };
    // Settles once the process is gone, so callers can delete its files right away.
    const kill = (error: unknown) => {
      if (failure !== undefined || settled) return;
      failure = error;
      clearTimeout(stallTimer);
      child.kill("SIGKILL");
      setTimeout(() => finish(error), KILL_GRACE_MS).unref?.();
    };
    const abort = () => kill(signal?.reason ?? new Error("aborted"));
    const armStallTimer = () => {
      clearTimeout(stallTimer);
      stallTimer = setTimeout(
        () => kill(new FfmpegError("ffmpeg stopped making progress.", null, tail(stderr))),
        STALL_TIMEOUT_MS,
      );
      stallTimer.unref?.();
    };
    const parse = createFfmpegProgressParser((progress) => {
      if (failure !== undefined) return;
      if (maxOutputBytes !== undefined && (progress.totalSize ?? 0) > maxOutputBytes) {
        kill(new Error(outputTooLargeMessage(maxOutputBytes)));
        return;
      }
      if (!onProgress) return;
      const fraction = progress.done
        ? 1
        : durationMs && progress.outTimeUs !== undefined
          ? Math.min(1, progress.outTimeUs / (durationMs * 1000))
          : 0;
      if (fraction > reported) {
        reported = fraction;
        onProgress(fraction);
      }
    });
    signal?.addEventListener("abort", abort, { once: true });
    armStallTimer();
    child.stdout.setEncoding("utf8");
    child.stdout.on("data", (chunk: string) => {
      if (failure === undefined) armStallTimer();
      parse(chunk);
    });
    child.stderr.setEncoding("utf8");
    child.stderr.on("data", (chunk: string) => {
      stderr = tail(stderr + chunk);
    });
    child.on("error", (error) => finish(failure ?? error));
    child.on("close", (code) => {
      if (failure !== undefined) finish(failure);
      else if (code === 0) finish();
      else finish(ffmpegFailure("ffmpeg", code, stderr));
    });
    if (signal?.aborted) abort();
  });
}

export function outputTooLargeMessage(maxBytes: number): string {
  return `The result would exceed ${Math.round(maxBytes / (1024 * 1024))} MB.`;
}

function tail(text: string): string {
  return text.length > STDERR_TAIL_BYTES ? text.slice(-STDERR_TAIL_BYTES) : text;
}

function ffmpegFailure(tool: string, code: number | null, stderr: string): FfmpegError {
  // The cause is usually the line before ffmpeg's generic summary ("Conversion failed!").
  const lines = stderr
    .split("\n")
    .map((line) => line.trim())
    .filter(Boolean)
    .slice(-2);
  // Name files by their base name only; the job's temp paths mean nothing to the reader.
  const detail = lines.join(" ").replaceAll(/(?:file:)?(?:[A-Za-z]:)?[\\/][^\s'"]*[\\/]/g, "");
  return new FfmpegError(
    detail ? `${tool} failed: ${detail}` : `${tool} failed with exit code ${code}.`,
    code,
    tail(stderr),
  );
}

/** Extracts the first audio track as 16 kHz mono 16-bit WAV, the format speech models expect. */
export async function extractAudio(
  input: string,
  output: string,
  options: {
    signal?: AbortSignal;
    mimeType?: string;
    startMs?: number;
    endMs?: number;
    onProgress?: (fraction: number) => void;
  } = {},
): Promise<void> {
  const probe = await probeMedia(input, { signal: options.signal, mimeType: options.mimeType });
  if (!probe.hasAudio) throw new Error("The file has no audio track.");
  const startMs = Math.max(0, options.startMs ?? 0);
  const endMs = Math.min(probe.durationMs, options.endMs ?? probe.durationMs);
  if (endMs <= startMs) throw new Error("The audio range is empty.");
  await runFfmpeg(
    [
      ...ffmpegInputArgs(input, {
        mimeType: options.mimeType,
        startSeconds: startMs / 1000,
        durationSeconds: (endMs - startMs) / 1000,
      }),
      "-map",
      "0:a:0",
      "-ac",
      "1",
      "-ar",
      "16000",
      "-c:a",
      "pcm_s16le",
      "-map_metadata",
      "-1",
      "-f",
      "wav",
      `file:${output}`,
    ],
    {
      signal: options.signal,
      durationMs: endMs - startMs,
      onProgress: options.onProgress,
      outputs: [output],
    },
  );
}

/** Writes one JPEG frame at atMs (default 0), falling back to the first frame past the end. */
export async function renderPoster(
  input: string,
  output: string,
  options: { signal?: AbortSignal; mimeType?: string; atMs?: number } = {},
): Promise<void> {
  const render = (atMs: number) =>
    runFfmpeg(
      [
        ...ffmpegInputArgs(input, { mimeType: options.mimeType, startSeconds: atMs / 1000 }),
        "-map",
        "0:v:0",
        "-frames:v",
        "1",
        "-c:v",
        "mjpeg",
        "-q:v",
        "3",
        "-map_metadata",
        "-1",
        "-f",
        "image2",
        "-update",
        "1",
        `file:${output}`,
      ],
      { signal: options.signal, outputs: [output] },
    );
  const atMs = Math.max(0, options.atMs ?? 0);
  await render(atMs);
  // Seeking into the last frame's gap writes nothing; the first frame is better than no poster.
  if (atMs > 0 && !(await nonEmptyFile(output))) await render(0);
  if (!(await nonEmptyFile(output))) throw new Error("Could not render a poster frame.");
}

async function nonEmptyFile(path: string): Promise<boolean> {
  try {
    return (await stat(path)).size > 0;
  } catch {
    return false;
  }
}

interface CaptureResult {
  code: number | null;
  stdout: string;
  stderr: string;
}

function capture(
  command: string,
  args: readonly string[],
  options: { signal?: AbortSignal; timeoutMs: number },
): Promise<CaptureResult> {
  options.signal?.throwIfAborted();
  return new Promise((resolve, reject) => {
    const child = spawn(command, args, { stdio: ["ignore", "pipe", "pipe"], windowsHide: true });
    const stdout: Buffer[] = [];
    let stderr = "";
    let settled = false;
    const finish = (error: unknown, result?: CaptureResult) => {
      if (settled) return;
      settled = true;
      clearTimeout(timer);
      options.signal?.removeEventListener("abort", abort);
      if (result) resolve(result);
      else reject(error);
    };
    const kill = (error: unknown) => {
      child.kill("SIGKILL");
      finish(error);
    };
    const abort = () => kill(options.signal?.reason ?? new Error("aborted"));
    const timer = setTimeout(
      () => kill(new Error(`${command} timed out after ${options.timeoutMs} ms`)),
      options.timeoutMs,
    );
    timer.unref?.();
    options.signal?.addEventListener("abort", abort, { once: true });
    child.stdout.on("data", (chunk: Buffer) => stdout.push(chunk));
    child.stderr.setEncoding("utf8");
    child.stderr.on("data", (chunk: string) => {
      stderr = tail(stderr + chunk);
    });
    child.on("error", (error) => finish(error));
    child.on("close", (code) =>
      finish(undefined, { code, stdout: Buffer.concat(stdout).toString("utf8"), stderr }),
    );
  });
}