export type SongSort = 'title' | 'difficulty-asc' | 'difficulty-desc';

export type SongChartSummary = {
  songId: string;
  title: string;
  difficulty: string;
  difficultyLevel?: number | null;
  scoreCalibrationSource?: 'measured' | 'local-estimated-v1' | string;
  releaseTime?: number | null;
};

export type SongOption = {
  id: string;
  title: string;
  difficultyLevel: number | null;
};

const englishTitleCollator = new Intl.Collator('en', {
  sensitivity: 'base',
  numeric: true
});

function normalizedSearch(value: string): string {
  return value.normalize('NFKD').toLocaleLowerCase('en').replace(/[^a-z0-9]+/g, ' ').trim();
}

export function songOptions(
  charts: readonly SongChartSummary[],
  difficulty: string,
  query = '',
  sort: SongSort = 'title'
): SongOption[] {
  const levelBySongId = new Map(charts
    .filter((chart) => chart.difficulty === difficulty)
    .map((chart) => [chart.songId, chart.difficultyLevel ?? null]));
  const options = Array.from(new Map(charts.map((chart) => [chart.songId, {
    id: chart.songId,
    title: chart.title,
    difficultyLevel: levelBySongId.get(chart.songId) ?? null
  }])).values());
  const search = normalizedSearch(query);
  const filtered = search
    ? options.filter((song) => normalizedSearch(`${song.title} ${song.id}`).includes(search))
    : options;
  const titleOrder = (left: SongOption, right: SongOption) =>
    englishTitleCollator.compare(left.title, right.title) || left.id.localeCompare(right.id);

  return filtered.sort((left, right) => {
    if (sort === 'title') return titleOrder(left, right);
    if (left.difficultyLevel === null) return right.difficultyLevel === null ? titleOrder(left, right) : 1;
    if (right.difficultyLevel === null) return -1;
    const leftLevel = left.difficultyLevel;
    const rightLevel = right.difficultyLevel;
    const levelOrder = sort === 'difficulty-desc' ? rightLevel - leftLevel : leftLevel - rightLevel;
    return levelOrder || titleOrder(left, right);
  });
}