'use strict';

// Monthly traffic reset — Node port of panel-go/reset.go (the two panel
// implementations must stay behavior-identical). A customer with
// trafficResetDay (1-31) gets the cycle counters zeroed once per monthly
// period. Due-ness derives only from the persisted trafficResetPeriod
// marker, so a reset missed while the panel was down fires at the first
// housekeeping pass after it is back. All dates are panel-local.

function daysInMonth(year, monthIndex) {
  return new Date(Date.UTC(year, monthIndex + 1, 0)).getUTCDate();
}

function resetInstant(year, monthIndex, day) {
  const dim = daysInMonth(year, monthIndex);
  return new Date(year, monthIndex, Math.min(day, dim), 0, 0, 0, 0);
}

function periodKeyOf(date) {
  const pad = (n) => String(n).padStart(2, '0');
  return `${date.getFullYear()}-${pad(date.getMonth() + 1)}`;
}

// The "YYYY-MM" of the most recent scheduled reset instant at or before now.
function trafficResetPeriodKey(now, day) {
  let year = now.getFullYear();
  let month = now.getMonth();
  let cand = resetInstant(year, month, day);
  if (now.getTime() < cand.getTime()) {
    month -= 1;
    if (month < 0) { month = 11; year -= 1; }
    cand = resetInstant(year, month, day);
  }
  return periodKeyOf(cand);
}

// (Re)arm a customer's period marker for its current reset day WITHOUT
// zeroing usage: the schedule takes effect from the next reset instant.
function armTrafficReset(customer, now = new Date()) {
  const day = Number(customer.trafficResetDay || 0);
  if (!Number.isInteger(day) || day < 1 || day > 31) {
    delete customer.trafficResetPeriod;
    return;
  }
  customer.trafficResetPeriod = trafficResetPeriodKey(now, day);
}

// Validate a trafficResetDay request value: 0 disables, 1-31 is the day of
// month. null/absent means 0. Mirrors panel-go ParseResetDay.
function parseResetDay(value) {
  if (value == null) return 0;
  const number = Number(value);
  if (!Number.isFinite(number) || number < 0 || !Number.isInteger(number)) {
    const error = new Error('每月重置日必须是非负整数');
    error.statusCode = 400;
    throw error;
  }
  if (number > 31) {
    const error = new Error('每月重置日须在 0–31 之间（0 表示不重置）');
    error.statusCode = 400;
    throw error;
  }
  return number;
}

// Perform due monthly resets for all customers in data as of now. Returns
// the list of customers whose counters were zeroed (the caller mirrors the
// manual reset-usage semantics: a traffic_limit suspension may lift).
// auditFn(data, customer, previousUsed, day, period) records the event.
function applyMonthlyTrafficResets(data, now, auditFn) {
  const reset = [];
  for (const customer of data.customers) {
    const day = Number(customer.trafficResetDay || 0);
    if (!Number.isInteger(day) || day < 1 || day > 31) continue;
    const key = trafficResetPeriodKey(now, day);
    if (!customer.trafficResetPeriod) {
      // First sight: arm only — usage already accrued in the current
      // period must survive until the next reset day.
      customer.trafficResetPeriod = key;
      continue;
    }
    if (customer.trafficResetPeriod === key) continue;
    const previousUsed = customer.usedBytes || 0;
    customer.usedBytes = 0;
    customer.usedUplinkBytes = 0;
    customer.usedDownlinkBytes = 0;
    customer.trafficResetPeriod = key;
    customer.trafficResetAt = now.toISOString();
    customer.updatedAt = now.toISOString();
    if (auditFn) auditFn(data, customer, previousUsed, day, key);
    reset.push(customer);
  }
  return reset;
}

module.exports = { trafficResetPeriodKey, armTrafficReset, parseResetDay, applyMonthlyTrafficResets, daysInMonth, resetInstant };