/** One line of time-synced lyrics; empty text is an instrumental gap. */
export interface LyricLine {
  timeMs: number;
  text: string;
}

export interface LyricsDTO {
  /** Lines with timestamps, when the song has synced lyrics. */
  synced: LyricLine[] | null;
  /** Plain text, when there are no synced lyrics (or as a fallback). */
  plain: string | null;
  instrumental: boolean;
  /** Where they came from, for attribution. */
  source: { name: string; url: string };
}

const TIME_TAG = /\[(\d{1,3}):(\d{1,2}(?:\.\d{1,3})?)\]/g;

/**
 * Parse LRC ("[01:23.45] words"). A line may carry several time tags; tags
 * that aren't times (like [ar:Artist]) are skipped. Sorted by time.
 */
export function parseLrc(lrc: string): LyricLine[] {
  const lines: LyricLine[] = [];
  for (const raw of lrc.split(/\r?\n/)) {
    const times = [...raw.matchAll(TIME_TAG)];
    if (times.length === 0) continue;
    const text = raw.replace(TIME_TAG, '').trim();
    for (const [, min, sec] of times) lines.push({ timeMs: Math.round((Number(min) * 60 + Number(sec)) * 1000), text });
  }
  return lines.sort((a, b) => a.timeMs - b.timeMs);
}

/** Index of the line being sung at `positionMs`, or -1 before the first one. */
export function currentLyricIndex(lines: LyricLine[], positionMs: number): number {
  let lo = 0;
  let hi = lines.length - 1;
  let found = -1;
  while (lo <= hi) {
    const mid = (lo + hi) >> 1;
    if (lines[mid]!.timeMs <= positionMs) {
      found = mid;
      lo = mid + 1;
    } else hi = mid - 1;
  }
  return found;
}