Function computeReadingVelocity

Source

export function computeReadingVelocity(
  history: ReadingHistory,
  timeRange: TimeRange,
): {
  perDay: number;
  perWeek: number;
  perMonth: number;
  totalChapters: number;
  activeDays: number;
} {
  const filtered = filterHistoryByTimeRange(history, timeRange);
  if (!filtered.length) {
    return {
      perDay: 0,
      perWeek: 0,
      perMonth: 0,
      totalChapters: 0,
      activeDays: 0,
    };
  }

  // Establish baseline from pre-range history
  const now = Date.now();
  const ranges = {
    "7d": 7 * 24 * 60 * 60 * 1000,
    "30d": 30 * 24 * 60 * 60 * 1000,
    "90d": 90 * 24 * 60 * 60 * 1000,
  };
  const cutoff = timeRange === "all" ? 0 : now - ranges[timeRange];
  const preRangeBaseline =
    timeRange === "all" ? new Map() : getPreRangeBaseline(history, cutoff);

  // Calculate total chapters read (sum of deltas)
  const sorted = [...filtered].sort((a, b) => a.timestamp - b.timestamp);
  const previousChapters = new Map<string | number, number>(preRangeBaseline);
  let totalChapters = 0;
  const activeDates = new Set<string>();

  for (const entry of sorted) {
    const prev = previousChapters.get(entry.mangaId) ?? 0;
    const delta = Math.max(0, entry.chaptersRead - prev);
    if (delta > 0) {
      totalChapters += delta;
      const date = getDateKey(entry.timestamp);
      activeDates.add(date);
    }
    previousChapters.set(entry.mangaId, entry.chaptersRead);
  }

  const activeDays = activeDates.size;

  const perDay = activeDays > 0 ? totalChapters / activeDays : 0;
  const perWeek = perDay * 7;
  const perMonth = perDay * 30;

  return {
    perDay: Math.round(perDay * 10) / 10,
    perWeek: Math.round(perWeek * 10) / 10,
    perMonth: Math.round(perMonth * 10) / 10,
    totalChapters,
    activeDays,
  };
}
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