import { execFile, execFileSync } from "node:child_process";
import fs from "node:fs";
import path from "node:path";
import { promisify } from "node:util";
import { buildSrt, type Clip } from "./subtitles";

const execFileAsync = promisify(execFile);

function hasFfmpeg() {
  try {
    execFileSync("ffmpeg", ["-version"], { stdio: "ignore" });
    return true;
  } catch {
    return false;
  }
}

const SUBTITLE_STYLE =
  "FontSize=22,PrimaryColour=&H00FFFFFF,BackColour=&H80000000,BorderStyle=3,Outline=1,Shadow=0,MarginV=40";

function escapeForFilter(p: string) {
  // ffmpeg filter arguments treat ':' and '\' specially — escape both.
  return p.replace(/\\/g, "\\\\").replace(/:/g, "\\:");
}

export async function renderFinalVideo({
  rawWebmPath,
  clips,
  outDir,
}: {
  rawWebmPath: string;
  clips: Clip[];
  outDir: string;
}): Promise<{ videoFile: string; degraded: string[] }> {
  const degraded: string[] = [];
  const srtPath = path.join(outDir, "captions.srt");
  fs.writeFileSync(srtPath, buildSrt(clips));

  if (!hasFfmpeg()) {
    const dest = path.join(outDir, "video.webm");
    fs.renameSync(rawWebmPath, dest);
    degraded.push("ffmpeg not found — kept raw video.webm, no subtitles burned in, no narration.");
    return { videoFile: dest, degraded };
  }

  const narrated = clips.filter((c) => c.narration);
  const mp4Path = path.join(outDir, "video.mp4");
  const srtArg = `subtitles=${escapeForFilter(srtPath)}:force_style='${SUBTITLE_STYLE}'`;

  if (narrated.length === 0) {
    degraded.push("No narration available — burned-in subtitles only.");
    await execFileAsync("ffmpeg", [
      "-y", "-i", rawWebmPath,
      "-vf", srtArg,
      "-c:v", "libx264", "-crf", "20", "-pix_fmt", "yuv420p",
      "-movflags", "+faststart",
      "-an",
      mp4Path,
    ]);
  } else {
    const audioInputs = narrated.flatMap((c) => ["-i", c.narration!.path]);
    const adelayParts = narrated.map(
      (c, i) => `[${i + 1}:a]adelay=${Math.max(0, Math.round(c.startMs))}|${Math.max(0, Math.round(c.startMs))}[a${i}]`,
    );
    const mixInputs = narrated.map((_, i) => `[a${i}]`).join("");
    const filterComplex = [
      `[0:v]${srtArg}[vout]`,
      ...adelayParts,
      `${mixInputs}amix=inputs=${narrated.length}:normalize=0[aout]`,
    ].join(";");

    await execFileAsync("ffmpeg", [
      "-y", "-i", rawWebmPath, ...audioInputs,
      "-filter_complex", filterComplex,
      "-map", "[vout]", "-map", "[aout]",
      "-c:v", "libx264", "-crf", "20", "-pix_fmt", "yuv420p",
      "-c:a", "aac",
      "-shortest",
      "-movflags", "+faststart",
      mp4Path,
    ]);
  }

  fs.rmSync(rawWebmPath, { force: true });
  for (const c of narrated) fs.rmSync(c.narration!.path, { force: true });

  return { videoFile: mp4Path, degraded };
}