export interface Clip {
  title: string;
  caption: string;
  file: string;
  startMs: number;
  endMs: number;
  narration: { path: string; durationMs: number } | null;
}

export function msToSrtTimestamp(ms: number): string {
  const clamped = Math.max(0, Math.round(ms));
  const hours = Math.floor(clamped / 3_600_000);
  const minutes = Math.floor((clamped % 3_600_000) / 60_000);
  const seconds = Math.floor((clamped % 60_000) / 1000);
  const millis = clamped % 1000;
  const pad = (n: number, len = 2) => String(n).padStart(len, "0");
  return `${pad(hours)}:${pad(minutes)}:${pad(seconds)},${pad(millis, 3)}`;
}

/** One subtitle cue per step, spanning its full on-screen duration. */
export function buildSrt(clips: Clip[]): string {
  return clips
    .map((clip, i) => {
      const index = i + 1;
      return [
        String(index),
        `${msToSrtTimestamp(clip.startMs)} --> ${msToSrtTimestamp(clip.endMs)}`,
        clip.caption,
        "",
      ].join("\n");
    })
    .join("\n");
}