'use strict';

/**
 * Time-bucketing helpers for financial analytics (daily / weekly / monthly /
 * forward-looking forecast windows). Weeks follow the Iranian convention of
 * starting on Saturday, ending on Friday.
 */

const startOfDay = (date) => {
  const d = new Date(date);
  d.setHours(0, 0, 0, 0);
  return d;
};

const endOfDay = (date) => {
  const d = new Date(date);
  d.setHours(23, 59, 59, 999);
  return d;
};

const addDays = (date, days) => {
  const d = new Date(date);
  d.setDate(d.getDate() + days);
  return d;
};

const addMonths = (date, months) => {
  const d = new Date(date);
  d.setMonth(d.getMonth() + months);
  return d;
};

/** JS getDay(): Sun=0..Sat=6. Iranian week starts Saturday, so Sat -> offset 0, Sun -> 1, ... Fri -> 6. */
const getWeekStart = (date) => {
  const d = startOfDay(date);
  const offset = (d.getDay() + 1) % 7;
  return addDays(d, -offset);
};

/** Builds `days` daily buckets ending on (and including) `endDate`, oldest first. */
const buildDailyBuckets = (days, endDate = new Date()) => {
  const end = startOfDay(endDate);
  const buckets = [];
  for (let i = days - 1; i >= 0; i--) {
    const dayStart = addDays(end, -i);
    buckets.push({ start: dayStart, end: endOfDay(dayStart), key: dayStart.toISOString().slice(0, 10) });
  }
  return buckets;
};

/** Builds `weeks` weekly buckets (Sat-Fri) ending on the week containing `endDate`, oldest first. */
const buildWeeklyBuckets = (weeks, endDate = new Date()) => {
  const currentWeekStart = getWeekStart(endDate);
  const buckets = [];
  for (let i = weeks - 1; i >= 0; i--) {
    const weekStart = addDays(currentWeekStart, -7 * i);
    buckets.push({ start: weekStart, end: endOfDay(addDays(weekStart, 6)), key: weekStart.toISOString().slice(0, 10) });
  }
  return buckets;
};

/** Builds `weeks` forward-looking weekly buckets (Sat-Fri) starting from the week containing `startDate`. */
const buildForecastWeeklyBuckets = (weeks, startDate = new Date()) => {
  const currentWeekStart = getWeekStart(startDate);
  const buckets = [];
  for (let i = 0; i < weeks; i++) {
    const weekStart = addDays(currentWeekStart, 7 * i);
    buckets.push({ start: weekStart, end: endOfDay(addDays(weekStart, 6)), key: weekStart.toISOString().slice(0, 10) });
  }
  return buckets;
};

/** Builds `months` monthly (Gregorian calendar month) buckets ending on the month containing `endDate`, oldest first. */
const buildMonthlyBuckets = (months, endDate = new Date()) => {
  const base = new Date(endDate.getFullYear(), endDate.getMonth(), 1, 0, 0, 0, 0);
  const buckets = [];
  for (let i = months - 1; i >= 0; i--) {
    const monthStart = addMonths(base, -i);
    const monthEnd = endOfDay(addDays(addMonths(monthStart, 1), -1));
    buckets.push({
      start: monthStart,
      end: monthEnd,
      year: monthStart.getFullYear(),
      month: monthStart.getMonth() + 1,
      key: `${monthStart.getFullYear()}-${String(monthStart.getMonth() + 1).padStart(2, '0')}`
    });
  }
  return buckets;
};

/** Linear search is fine — bucket arrays used here are always small (<=~90 entries). */
const findBucketIndex = (buckets, date) => {
  if (!date) return -1;
  const d = date instanceof Date ? date : new Date(date);
  if (Number.isNaN(d.getTime())) return -1;
  const t = d.getTime();
  return buckets.findIndex((b) => t >= b.start.getTime() && t <= b.end.getTime());
};

module.exports = {
  startOfDay,
  endOfDay,
  addDays,
  addMonths,
  getWeekStart,
  buildDailyBuckets,
  buildWeeklyBuckets,
  buildForecastWeeklyBuckets,
  buildMonthlyBuckets,
  findBucketIndex
};