import { writeFileSync } from 'node:fs';

export interface NarrationCue {
  text: string;
  videoTimeMs: number;
  durationMs: number;
}

/**
 * Narration manifest writer.
 *
 * The runner knows the exact video-time of each narration block from the
 * storyboard itself, so cues come in with an explicit `videoTimeMs` instead
 * of being stamped against a wall-clock origin. That keeps the manifest in
 * lockstep with the trimmed video even if step durations drift slightly.
 */
class NarrationLog {
  private cues: NarrationCue[] = [];

  reset(): void {
    this.cues = [];
  }

  add(cue: NarrationCue): void {
    if (cue.videoTimeMs < 0) return;
    this.cues.push(cue);
  }

  flush(path: string, totalDurationMs: number): NarrationCue[] {
    const sorted = [...this.cues].sort((a, b) => a.videoTimeMs - b.videoTimeMs);
    const manifest = { totalDurationMs, cues: sorted };
    writeFileSync(path, JSON.stringify(manifest, null, 2));
    return sorted;
  }
}

export const narrationLog = new NarrationLog();

function formatVttTimestamp(ms: number): string {
  const clamped = Math.max(0, Math.round(ms));
  const totalSeconds = Math.floor(clamped / 1000);
  const millis = clamped % 1000;
  const hours = Math.floor(totalSeconds / 3600);
  const minutes = Math.floor((totalSeconds % 3600) / 60);
  const seconds = totalSeconds % 60;
  const pad = (n: number, width: number): string =>
    n.toString().padStart(width, '0');
  return `${pad(hours, 2)}:${pad(minutes, 2)}:${pad(seconds, 2)}.${pad(millis, 3)}`;
}

/**
 * Render narration cues as a WebVTT document.
 *
 * Pure helper: takes cues (already ordered by the caller) and produces a
 * caption sidecar string. Cue text is trimmed and any internal blank lines
 * are collapsed so a single cue stays a single VTT block.
 */
export function cuesToVtt(cues: NarrationCue[]): string {
  let out = 'WEBVTT\n\n';
  for (const cue of cues) {
    const start = formatVttTimestamp(cue.videoTimeMs);
    const end = formatVttTimestamp(cue.videoTimeMs + cue.durationMs);
    const text = cue.text
      .split('\n')
      .map((line) => line.trim())
      .filter((line) => line.length > 0)
      .join('\n')
      .trim();
    out += `${start} --> ${end}\n${text}\n\n`;
  }
  return out;
}