export type CheckRassInput = {
  amount: number;
  dueDate: Date | string;
};

export type CheckRassResult = {
  checkCount: number;
  totalAmount: number;
  nearestDueDate: string | null;
  farthestDueDate: string | null;
  rassDays: number;
  rassDate: string | null;
};

import {
  addDays,
  calendarDayOf,
  diffInDays,
  tehranCalendarDay,
} from './tehran-time';

/** وضعیتی که فاکتور قیمت‌گذاری‌شده برای مشتری ارسال می‌شود. */
const INVOICE_ISSUED_STATUS = 'awaiting_settlement';

/**
 * مبدأ راس چک، تاریخ صدور فاکتور است نه امروز و نه تاریخ ثبت پیش‌سفارش.
 * اگر فاکتور دوباره ارسال شده باشد، آخرین صدور ملاک است.
 */
export function invoiceAnchorDate(
  createdAt: Date,
  history: { toStatus: string; changedAt: Date }[] = [],
): Date {
  for (let i = history.length - 1; i >= 0; i -= 1) {
    const row = history[i];
    if (row?.toStatus === INVOICE_ISSUED_STATUS) return row.changedAt;
  }
  return createdAt;
}

export function calculateCheckRass(
  checks: CheckRassInput[],
  baseDate: Date,
): CheckRassResult {
  if (checks.length === 0) {
    return {
      checkCount: 0,
      totalAmount: 0,
      nearestDueDate: null,
      farthestDueDate: null,
      rassDays: 0,
      rassDate: null,
    };
  }

  const base = tehranCalendarDay(baseDate);
  let totalAmount = 0;
  let weightedDays = 0;
  const dueDates: Date[] = [];

  for (const check of checks) {
    const due = calendarDayOf(check.dueDate);
    dueDates.push(due);
    const days = Math.max(0, diffInDays(base, due));
    totalAmount += check.amount;
    weightedDays += check.amount * days;
  }

  const rassDays = totalAmount > 0 ? Math.round(weightedDays / totalAmount) : 0;
  const rassDate = addDays(base, rassDays);
  dueDates.sort((a, b) => a.getTime() - b.getTime());

  return {
    checkCount: checks.length,
    totalAmount,
    nearestDueDate: dueDates[0]?.toISOString() ?? null,
    farthestDueDate: dueDates[dueDates.length - 1]?.toISOString() ?? null,
    rassDays,
    rassDate: rassDate.toISOString(),
  };
}