/**
 * Encode test tracks as the backend's `TrackTable` (#281), so a stub of
 * `library.Library.GetTrackTable` can be written as a list of tracks.
 *
 * Test fixtures are partial tracks; a missing field encodes as the
 * zero value Go would have sent. The encoding mirrors
 * `backend/library/tracktable.go` closely enough to exercise the real
 * decoder: shared string table with "" at 0, genre lists interned.
 */
import type * as library from '@go/library/models.js';

/** A fixture: any subset of a track's fields, loosely typed as fixtures are. */
type PartialTrack = { FilePath: string } & Record<string, unknown>;

const STRING_COLS = [
  ['trackName', 'TrackName'],
  ['artistName', 'ArtistName'],
  ['album', 'Album'],
  ['composer', 'Composer'],
  ['fileType', 'FileType'],
  ['artistMbid', 'ArtistMBID'],
  ['releaseGroupMbid', 'ReleaseGroupMBID'],
  ['recordingMbid', 'RecordingMBID'],
  ['coverArtSmall', 'CoverArtSmall'],
] as const;

const INT_COLS = [
  ['trackNumber', 'TrackNumber'],
  ['discNumber', 'DiscNumber'],
  ['year', 'Year'],
  ['sampleRate', 'SampleRate'],
  ['bitDepth', 'BitDepth'],
  ['channels', 'Channels'],
  ['bitrate', 'Bitrate'],
  ['fileSize', 'FileSize'],
  ['playCount', 'PlayCount'],
] as const;

export function trackTable(tracks: readonly PartialTrack[]): library.TrackTable {
  const strings = [''];
  const index = new Map<string, number>([['', 0]]);
  const intern = (s: string | undefined): number => {
    const v = s ?? '';
    let i = index.get(v);

    if (i === undefined) {
      i = strings.length;
      strings.push(v);
      index.set(v, i);
    }

    return i;
  };

  const genreSets: number[][] = [];
  const genreIndex = new Map<string, number>();
  const table: Record<string, unknown> = {
    strings,
    genreSets,
    filePath: tracks.map((t) => t.FilePath),
    lengthMs: tracks.map((t) => Number(t['TrackLength'] ?? 0) || 0),
    genre: tracks.map((t) => {
      const genres = (t['Genre'] as string[] | null | undefined) ?? [];
      const key = genres.join('\u0000');
      let i = genreIndex.get(key);

      if (i === undefined) {
        i = genreSets.length;
        genreSets.push(genres.map(intern));
        genreIndex.set(key, i);
      }

      return i;
    }),
  };

  for (const [col, field] of STRING_COLS) {
    table[col] = tracks.map((t) => intern(t[field] as string | undefined));
  }

  for (const [col, field] of INT_COLS) {
    table[col] = tracks.map((t) => (t[field] as number | undefined) ?? 0);
  }

  return table as unknown as library.TrackTable;
}