<?php

function normalize_card_kind(array $account): ?string
{
    $kind = strtolower(trim((string)($account['card_kind'] ?? '')));

    if ($kind === 'credit') {
        return 'credit';
    }

    if ($kind === 'check') {
        return 'check';
    }

    return null;
}

function safe_date_ts(string $date): ?int
{
    $ts = strtotime($date);
    return $ts === false ? null : $ts;
}

function card_month_day_date(string $billingYearMonth, int $monthOffset, int $day): ?DateTime
{
    if (!preg_match('/^\d{4}-\d{2}$/', $billingYearMonth)) {
        return null;
    }

    if ($day < 1 || $day > 31) {
        return null;
    }

    $base = new DateTime($billingYearMonth . '-01');

    if ($monthOffset !== 0) {
        $base->modify(($monthOffset > 0 ? '+' : '') . $monthOffset . ' month');
    }

    $lastDay = (int)$base->format('t');
    $realDay = min($day, $lastDay);

    $base->setDate(
        (int)$base->format('Y'),
        (int)$base->format('m'),
        $realDay
    );

    return $base;
}

function account_has_statement_period(array $account): bool
{
    return isset(
        $account['statement_start_month_offset'],
        $account['statement_start_day'],
        $account['statement_end_month_offset'],
        $account['statement_end_day']
    )
    && $account['statement_start_month_offset'] !== null
    && $account['statement_start_day'] !== null
    && $account['statement_end_month_offset'] !== null
    && $account['statement_end_day'] !== null
    && (int)$account['statement_start_day'] >= 1
    && (int)$account['statement_start_day'] <= 31
    && (int)$account['statement_end_day'] >= 1
    && (int)$account['statement_end_day'] <= 31;
}

function transaction_date_in_card_statement_month(array $account, string $transactionDate, string $billingYearMonth): bool
{
    $txTs = safe_date_ts($transactionDate);
    if ($txTs === null) {
        return false;
    }

    if (!account_has_statement_period($account)) {
        return false;
    }

    $start = card_month_day_date(
        $billingYearMonth,
        (int)$account['statement_start_month_offset'],
        (int)$account['statement_start_day']
    );

    $end = card_month_day_date(
        $billingYearMonth,
        (int)$account['statement_end_month_offset'],
        (int)$account['statement_end_day']
    );

    if (!$start || !$end) {
        return false;
    }

    $tx = new DateTime(date('Y-m-d', $txTs));

    return $tx >= $start && $tx <= $end;
}

function get_card_billing_year_month_by_statement_period(array $account, string $transactionDate): ?string
{
    $txTs = safe_date_ts($transactionDate);
    if ($txTs === null) {
        return null;
    }

    if (!account_has_statement_period($account)) {
        return null;
    }

    $tx = new DateTime(date('Y-m-d', $txTs));

    /*
     * 청구월 기준 사용기간 예:
     * 2026-05 청구월 = 2026-04-11 ~ 2026-05-10
     *
     * 거래일 주변의 청구월만 검사하면 됨.
     * 전월/당월/익월/익익월까지 여유 있게 검사.
     */
    $base = new DateTime($tx->format('Y-m-01'));

    for ($i = -1; $i <= 2; $i++) {
        $candidate = clone $base;
        if ($i !== 0) {
            $candidate->modify(($i > 0 ? '+' : '') . $i . ' month');
        }

        $candidateYm = $candidate->format('Y-m');

        if (transaction_date_in_card_statement_month($account, $transactionDate, $candidateYm)) {
            return $candidateYm;
        }
    }

    return null;
}

function get_card_billing_year_month(array $account, string $transactionDate): ?string
{
    if (($account['account_type'] ?? '') !== 'card') {
        return null;
    }

    $ts = safe_date_ts($transactionDate);
    if ($ts === null) {
        return null;
    }

    $cardKind = normalize_card_kind($account);

    // 체크카드는 즉시형으로 보고 거래월 그대로
    if ($cardKind === 'check') {
        return date('Y-m', $ts);
    }

    // 신용카드인데 신용공여기간 계산을 안 쓰면 거래월 그대로
    if (empty($account['use_credit_grace_period'])) {
        return date('Y-m', $ts);
    }

    // 신규 방식: 카드사별 실제 사용기간 설정 우선
    $statementYm = get_card_billing_year_month_by_statement_period($account, $transactionDate);
    if ($statementYm !== null) {
        return $statementYm;
    }

    // fallback: 기존 billing_day 단순 방식
    $billingDay = (int)($account['billing_day'] ?? 0);
    if ($billingDay <= 0 || $billingDay > 31) {
        return date('Y-m', $ts);
    }

    $dt = new DateTime(date('Y-m-d', $ts));
    $day = (int)$dt->format('d');

    if ($day <= $billingDay) {
        return $dt->format('Y-m');
    }

    $dt->modify('first day of next month');
    return $dt->format('Y-m');
}

function get_card_payment_date(array $account, string $billingYearMonth): ?string
{
    if (($account['account_type'] ?? '') !== 'card') {
        return null;
    }

    if (!preg_match('/^\d{4}-\d{2}$/', $billingYearMonth)) {
        return null;
    }

    $paymentDay = (int)($account['payment_day'] ?? 0);
    if ($paymentDay <= 0 || $paymentDay > 31) {
        return null;
    }

    [$year, $month] = explode('-', $billingYearMonth);
    $year = (int)$year;
    $month = (int)$month;

    $firstDay = new DateTime(sprintf('%04d-%02d-01', $year, $month));
    $lastDay = (int)$firstDay->format('t');
    $day = min($paymentDay, $lastDay);

    $firstDay->setDate($year, $month, $day);
    return $firstDay->format('Y-m-d');
}

function get_card_statement_period_label(array $account): ?string
{
    if (!account_has_statement_period($account)) {
        return null;
    }

    $startOffset = (int)$account['statement_start_month_offset'];
    $startDay = (int)$account['statement_start_day'];
    $endOffset = (int)$account['statement_end_month_offset'];
    $endDay = (int)$account['statement_end_day'];

    $monthText = function (int $offset): string {
        if ($offset === -2) return '전전월';
        if ($offset === -1) return '전월';
        if ($offset === 0) return '당월';
        if ($offset === 1) return '익월';
        if ($offset === 2) return '익익월';
        return $offset . '개월';
    };

    return $monthText($startOffset) . ' ' . $startDay . '일 ~ ' .
           $monthText($endOffset) . ' ' . $endDay . '일 사용분';
}

function get_card_billing_label(array $account): string
{
    if (($account['account_type'] ?? '') !== 'card') {
        return '-';
    }

    $cardKind = normalize_card_kind($account);

    if ($cardKind === 'check') {
        return '체크카드 · 즉시출금';
    }

    if ($cardKind === 'credit') {
        $paymentDay = (int)($account['payment_day'] ?? 0);

        if (!empty($account['billing_cycle_memo'])) {
            return (string)$account['billing_cycle_memo'];
        }

        $periodLabel = get_card_statement_period_label($account);
        if ($periodLabel !== null && $paymentDay > 0) {
            return '신용카드 · ' . $periodLabel . ' / 납부일 ' . $paymentDay . '일';
        }

        if ($periodLabel !== null) {
            return '신용카드 · ' . $periodLabel;
        }

        $billingDay = (int)($account['billing_day'] ?? 0);
        if ($billingDay > 0 && $paymentDay > 0) {
            return '신용카드 · 결제기준일 ' . $billingDay . '일 / 납부일 ' . $paymentDay . '일';
        }

        return '신용카드';
    }

    return '카드';
}