Function computeDailyDeltasByManga

Source

export function computeDailyDeltasByManga(
  history: ReadingHistory,
): Map<string, Map<string | number, number>> {
  const dailyDeltaMap = new Map<string, Map<string | number, number>>();
  const prevChaptersPerManga = new Map<string | number, number>();

  // Sort entries by timestamp to ensure chronological order
  const sortedEntries = [...history.entries].sort(
    (a, b) => a.timestamp - b.timestamp,
  );

  for (const entry of sortedEntries) {
    const date = getDateKey(entry.timestamp);
    const mangaId = entry.mangaId;
    const prevChapters = prevChaptersPerManga.get(mangaId) ?? 0;
    const delta = Math.max(0, entry.chaptersRead - prevChapters);

    // Only record if there's progress that day
    if (delta > 0) {
      if (!dailyDeltaMap.has(date)) {
        dailyDeltaMap.set(date, new Map());
      }
      dailyDeltaMap.get(date)!.set(mangaId, delta);
    }

    // Update previous chapters for next iteration
    prevChaptersPerManga.set(mangaId, entry.chaptersRead);
  }

  return dailyDeltaMap;
}
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