<?php

require_once __DIR__ . '/db.php';
require_once __DIR__ . '/account_service.php';
require_once __DIR__ . '/card_billing_service.php';

function split_amount_evenly(float $amount, int $months): array
{
    if ($months <= 0) {
        throw new RuntimeException('개월 수가 올바르지 않습니다.');
    }

    // 원화 기준: 소수점 제거
    $amount = (int)floor($amount);

    $base = intdiv($amount, $months);
    $remainder = $amount % $months;

    $amounts = array_fill(0, $months, $base);

    // 남는 원 단위는 마지막 회차에 몰아줌
    if ($remainder > 0) {
        $amounts[$months - 1] += $remainder;
    }

    return $amounts;
}

function calculate_installment_interest_total(
    float $principalAmount,
    int $installmentMonths,
    float $annualInterestRate
): float {
    if ($installmentMonths <= 1 || $annualInterestRate <= 0) {
        return 0.0;
    }

    $principalAmount = floor($principalAmount);
    $monthlyRate = ($annualInterestRate / 100.0) / 12.0;

    $averageOutstanding = $principalAmount / 2.0;
    $interestTotal = $averageOutstanding * $monthlyRate * $installmentMonths;

    // 원화 기준 버림
    return (float)floor($interestTotal);
}

function create_installment_schedule(
    int $userId,
    int $transactionId,
    int $accountId,
    float $principalAmount,
    int $installmentMonths,
    string $transactionDate,
    float $annualInterestRate = 0.0,
    ?float $interestTotal = null,
    ?float $totalBilledAmount = null,
    string $interestType = 'none'
): void {
    $pdo = db();

    if ($installmentMonths <= 1) {
        return;
    }

    // 원화 기준
    $principalAmount = (float)floor($principalAmount);
    $annualInterestRate = round($annualInterestRate, 4);

    if ($interestTotal === null) {
        $interestTotal = calculate_installment_interest_total(
            $principalAmount,
            $installmentMonths,
            $annualInterestRate
        );
    }

    $interestTotal = (float)floor($interestTotal);

    if ($totalBilledAmount === null) {
        $totalBilledAmount = $principalAmount + $interestTotal;
    }

    $totalBilledAmount = (float)floor($totalBilledAmount);

    if ($totalBilledAmount < $principalAmount) {
        throw new RuntimeException('총 청구금액은 원금보다 작을 수 없습니다.');
    }

    if (($principalAmount + $interestTotal) !== $totalBilledAmount) {
        throw new RuntimeException('원금 + 총이자와 총 청구금액이 일치해야 합니다.');
    }

    $pdo->beginTransaction();

    try {
        $stmtAcc = $pdo->prepare("
            SELECT *
            FROM accounts
            WHERE id = ?
              AND user_id = ?
            LIMIT 1
        ");
        $stmtAcc->execute([$accountId, $userId]);
        $account = $stmtAcc->fetch();

        /*
         * 핵심:
         * 1회차 시작월은 거래월이 아니라
         * 카드사 신용공여기간 계산 결과인 billing_year_month 기준.
         *
         * 예:
         * 2026-04-24 사용 + 우리카드 25일 결제
         * => startYm = 2026-05
         * => 1회차 2026-05
         */
        $startYm = null;

        if ($account) {
            $startYm = get_card_billing_year_month($account, $transactionDate);
        }

        if (!$startYm) {
            $startYm = date('Y-m', strtotime($transactionDate));
        }

        $principalParts = split_amount_evenly($principalAmount, $installmentMonths);
        $interestParts = split_amount_evenly($interestTotal, $installmentMonths);

        $stmt = $pdo->prepare("
            INSERT INTO installments
            (
                user_id,
                transaction_id,
                account_id,
                principal_amount,
                interest_total,
                total_billed_amount,
                installment_months,
                annual_interest_rate,
                start_year_month,
                interest_type,
                current_cycle,
                is_completed,
                prepaid_principal_amount,
                prepaid_interest_amount
            )
            VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, 1, 0, 0, 0)
        ");

        $stmt->execute([
            $userId,
            $transactionId,
            $accountId,
            $principalAmount,
            $interestTotal,
            $totalBilledAmount,
            $installmentMonths,
            $annualInterestRate,
            $startYm,
            $annualInterestRate > 0 ? $interestType : 'none'
        ]);

        $installmentId = (int)$pdo->lastInsertId();

        $stmt = $pdo->prepare("
            INSERT INTO installment_schedules
            (
                installment_id,
                cycle_no,
                bill_year_month,
                principal_amount,
                interest_amount,
                total_amount,
                is_billed,
                billed_at
            )
            VALUES (?, ?, ?, ?, ?, ?, ?, ?)
        ");

        $currentYm = date('Y-m');

        for ($i = 1; $i <= $installmentMonths; $i++) {
            $ym = date('Y-m', strtotime($startYm . '-01 +' . ($i - 1) . ' month'));

            $principalPart = (float)$principalParts[$i - 1];
            $interestPart = (float)$interestParts[$i - 1];
            $totalPart = $principalPart + $interestPart;

            // 과거 청구월은 자동 청구완료
            $isBilled = ($ym < $currentYm) ? 1 : 0;
            $billedAt = $isBilled ? date('Y-m-d H:i:s') : null;

            $stmt->execute([
                $installmentId,
                $i,
                $ym,
                $principalPart,
                $interestPart,
                $totalPart,
                $isBilled,
                $billedAt
            ]);
        }

        recalculate_installment_status($installmentId);

        $pdo->commit();
    } catch (Throwable $e) {
        $pdo->rollBack();
        throw $e;
    }
}

function delete_installment_by_transaction_id(int $transactionId): void
{
    $pdo = db();
    $stmt = $pdo->prepare("DELETE FROM installments WHERE transaction_id = ?");
    $stmt->execute([$transactionId]);
}

function get_installment_due_this_month(int $userId, string $yearMonth): float
{
    $pdo = db();

    $stmt = $pdo->prepare("
        SELECT COALESCE(SUM(s.total_amount), 0) AS total_due
        FROM installment_schedules s
        JOIN installments i ON i.id = s.installment_id
        WHERE i.user_id = ?
          AND s.bill_year_month = ?
          AND s.is_billed = 0
    ");
    $stmt->execute([$userId, $yearMonth]);
    $row = $stmt->fetch();

    return (float)($row['total_due'] ?? 0);
}

function get_installment_remaining_principal(int $userId): float
{
    $pdo = db();

    $stmt = $pdo->prepare("
        SELECT COALESCE(SUM(s.principal_amount), 0) AS total_principal
        FROM installment_schedules s
        JOIN installments i ON i.id = s.installment_id
        WHERE i.user_id = ?
          AND s.is_billed = 0
    ");
    $stmt->execute([$userId]);
    $row = $stmt->fetch();

    return (float)($row['total_principal'] ?? 0);
}

function get_installment_remaining_interest(int $userId): float
{
    $pdo = db();

    $stmt = $pdo->prepare("
        SELECT COALESCE(SUM(s.interest_amount), 0) AS total_interest
        FROM installment_schedules s
        JOIN installments i ON i.id = s.installment_id
        WHERE i.user_id = ?
          AND s.is_billed = 0
    ");
    $stmt->execute([$userId]);
    $row = $stmt->fetch();

    return (float)($row['total_interest'] ?? 0);
}

function get_installment_remaining_total(int $userId): float
{
    $pdo = db();

    $stmt = $pdo->prepare("
        SELECT COALESCE(SUM(s.total_amount), 0) AS remaining_total
        FROM installment_schedules s
        JOIN installments i ON i.id = s.installment_id
        WHERE i.user_id = ?
          AND s.is_billed = 0
    ");
    $stmt->execute([$userId]);
    $row = $stmt->fetch();

    return (float)($row['remaining_total'] ?? 0);
}

function recalculate_installment_status(int $installmentId): void
{
    $pdo = db();

    $stmt = $pdo->prepare("
        SELECT
            COALESCE(SUM(CASE WHEN is_billed = 0 THEN 1 ELSE 0 END), 0) AS remaining_count,
            COALESCE(MIN(CASE WHEN is_billed = 0 THEN cycle_no ELSE NULL END), 0) AS next_cycle
        FROM installment_schedules
        WHERE installment_id = ?
    ");
    $stmt->execute([$installmentId]);
    $row = $stmt->fetch();

    $remainingCount = (int)($row['remaining_count'] ?? 0);
    $nextCycle = (int)($row['next_cycle'] ?? 0);

    $stmt = $pdo->prepare("
        UPDATE installments
        SET
            current_cycle = ?,
            is_completed = ?
        WHERE id = ?
    ");
    $stmt->execute([
        $nextCycle > 0 ? $nextCycle : 0,
        $remainingCount === 0 ? 1 : 0,
        $installmentId
    ]);
}

function mark_installment_month_billed_for_card_payment(
    int $userId,
    int $cardAccountId,
    string $yearMonth
): int {
    $pdo = db();
    $pdo->beginTransaction();

    try {
        $stmt = $pdo->prepare("
            SELECT s.id, s.installment_id
            FROM installment_schedules s
            JOIN installments i ON i.id = s.installment_id
            WHERE i.user_id = ?
              AND i.account_id = ?
              AND s.bill_year_month = ?
              AND s.is_billed = 0
            ORDER BY s.id ASC
        ");
        $stmt->execute([$userId, $cardAccountId, $yearMonth]);
        $rows = $stmt->fetchAll();

        if (!$rows) {
            $pdo->commit();
            return 0;
        }

        $scheduleIds = array_column($rows, 'id');
        $installmentIds = array_values(array_unique(array_map(
            fn($r) => (int)$r['installment_id'],
            $rows
        )));

        $placeholders = implode(',', array_fill(0, count($scheduleIds), '?'));

        $stmt = $pdo->prepare("
            UPDATE installment_schedules
            SET is_billed = 1,
                billed_at = NOW()
            WHERE id IN ($placeholders)
        ");
        $stmt->execute($scheduleIds);

        foreach ($installmentIds as $installmentId) {
            recalculate_installment_status($installmentId);
        }

        $pdo->commit();
        return count($scheduleIds);
    } catch (Throwable $e) {
        $pdo->rollBack();
        throw $e;
    }
}

function prepay_installment(
    int $userId,
    int $installmentId,
    int $paymentAccountId,
    string $prepayDate,
    float $prepayPrincipalAmount,
    float $prepayInterestAmount = 0.0,
    ?string $description = null,
    ?int $targetScheduleId = null
): void {
    $pdo = db();
    $pdo->beginTransaction();

    try {
        $stmt = $pdo->prepare("
            SELECT i.*, t.merchant_name
            FROM installments i
            JOIN transactions t ON t.id = i.transaction_id
            WHERE i.id = ?
              AND i.user_id = ?
        ");
        $stmt->execute([$installmentId, $userId]);
        $installment = $stmt->fetch();

        if (!$installment) {
            throw new RuntimeException('할부 정보를 찾을 수 없습니다.');
        }

        $prepayPrincipalAmount = (float)floor($prepayPrincipalAmount);
        $prepayInterestAmount = (float)floor($prepayInterestAmount);

        if ($prepayPrincipalAmount <= 0 && $prepayInterestAmount <= 0) {
            throw new RuntimeException('선결제 금액이 0보다 커야 합니다.');
        }

        $sql = "
            SELECT id, principal_amount, interest_amount, total_amount
            FROM installment_schedules
            WHERE installment_id = ?
            AND is_billed = 0
        ";

        $params = [$installmentId];

        if ($targetScheduleId !== null && $targetScheduleId > 0) {
            $sql .= " AND id = ? ";
            $params[] = $targetScheduleId;
        }

        $sql .= " ORDER BY cycle_no ASC ";

        $stmt = $pdo->prepare($sql);
        $stmt->execute($params);
        $remainingSchedules = $stmt->fetchAll();

        if (!$remainingSchedules) {
            throw new RuntimeException('남아있는 회차가 없습니다.');
        }

        $remainingPrincipal = (float)floor(array_sum(array_map(
            fn($r) => (float)$r['principal_amount'],
            $remainingSchedules
        )));

        $remainingInterest = (float)floor(array_sum(array_map(
            fn($r) => (float)$r['interest_amount'],
            $remainingSchedules
        )));

        // 초과 입력 시 남은 금액까지만 자동 보정
        if ($prepayPrincipalAmount > $remainingPrincipal) {
            $prepayPrincipalAmount = $remainingPrincipal;
        }

        if ($prepayInterestAmount > $remainingInterest) {
            $prepayInterestAmount = $remainingInterest;
        }

        if ($prepayPrincipalAmount <= 0 && $prepayInterestAmount <= 0) {
            throw new RuntimeException('남아있는 선결제 가능 금액이 없습니다.');
        }

        $remainingPrincipalToApply = $prepayPrincipalAmount;
        $remainingInterestToApply = $prepayInterestAmount;

        foreach ($remainingSchedules as $schedule) {
            $scheduleId = (int)$schedule['id'];
            $principal = (float)$schedule['principal_amount'];
            $interest = (float)$schedule['interest_amount'];

            $newPrincipal = $principal;
            $newInterest = $interest;

            if ($remainingPrincipalToApply > 0) {
                $deduct = min($newPrincipal, $remainingPrincipalToApply);
                $newPrincipal = $newPrincipal - $deduct;
                $remainingPrincipalToApply = $remainingPrincipalToApply - $deduct;
            }

            if ($remainingInterestToApply > 0) {
                $deduct = min($newInterest, $remainingInterestToApply);
                $newInterest = $newInterest - $deduct;
                $remainingInterestToApply = $remainingInterestToApply - $deduct;
            }

            $newPrincipal = (float)max(0, floor($newPrincipal));
            $newInterest = (float)max(0, floor($newInterest));
            $newTotal = $newPrincipal + $newInterest;

            $isNowZero = ($newTotal <= 0) ? 1 : 0;

            $stmt2 = $pdo->prepare("
                UPDATE installment_schedules
                SET principal_amount = ?,
                    interest_amount = ?,
                    total_amount = ?,
                    is_billed = CASE WHEN ? = 1 THEN 1 ELSE is_billed END,
                    billed_at = CASE WHEN ? = 1 THEN NOW() ELSE billed_at END
                WHERE id = ?
            ");

            $stmt2->execute([
                $newPrincipal,
                $newInterest,
                $newTotal,
                $isNowZero,
                $isNowZero,
                $scheduleId
            ]);
        }

        $totalAmount = $prepayPrincipalAmount + $prepayInterestAmount;

        $stmt = $pdo->prepare("
            INSERT INTO installment_prepayments
            (
                user_id,
                installment_id,
                account_id,
                prepay_date,
                principal_amount,
                interest_amount,
                total_amount,
                description
            )
            VALUES (?, ?, ?, ?, ?, ?, ?, ?)
        ");
        $stmt->execute([
            $userId,
            $installmentId,
            $paymentAccountId,
            $prepayDate,
            $prepayPrincipalAmount,
            $prepayInterestAmount,
            $totalAmount,
            $description
        ]);

        $stmt = $pdo->prepare("
            UPDATE installments
            SET
                prepaid_principal_amount = prepaid_principal_amount + ?,
                prepaid_interest_amount = prepaid_interest_amount + ?
            WHERE id = ?
        ");
        $stmt->execute([
            $prepayPrincipalAmount,
            $prepayInterestAmount,
            $installmentId
        ]);

        recalculate_installment_status($installmentId);

        $stmt = $pdo->prepare("
            INSERT INTO transactions
            (
                user_id,
                account_id,
                category_id,
                transaction_type,
                amount,
                is_installment,
                installment_months,
                installment_interest_rate,
                installment_interest_total,
                installment_total_billed,
                installment_prepay_amount,
                transaction_date,
                merchant_name,
                description,
                related_account_id,
                fingerprint
            )
            VALUES (?, ?, ?, 'expense', ?, 0, NULL, 0, 0, NULL, ?, ?, ?, ?, NULL, ?)
        ");

        $desc = $description ?: '할부 선결제/중도상환';

        $fingerprint = hash('sha256', implode('|', [
            $userId,
            $paymentAccountId,
            'installment_prepay',
            $installmentId,
            $prepayDate,
            number_format($totalAmount, 2, '.', ''),
            $desc
        ]));

        $stmtCat = $pdo->prepare("
            SELECT id
            FROM categories
            WHERE user_id = ?
              AND category_type = 'expense'
              AND name = '기타지출'
            LIMIT 1
        ");
        $stmtCat->execute([$userId]);
        $category = $stmtCat->fetch();

        if (!$category) {
            throw new RuntimeException('선결제 기록용 expense 카테고리(기타지출)를 찾을 수 없습니다.');
        }

        $stmt->execute([
            $userId,
            $paymentAccountId,
            (int)$category['id'],
            $totalAmount,
            $totalAmount,
            $prepayDate,
            $installment['merchant_name'],
            '[할부 선결제] ' . $desc,
            $fingerprint
        ]);

        $pdo->commit();

        recalculate_account_balance($paymentAccountId);
    } catch (Throwable $e) {
        $pdo->rollBack();
        throw $e;
    }
}

function rebuild_all_installments_for_user(int $userId): int
{
    $pdo = db();
    $pdo->beginTransaction();

    try {
        $stmt = $pdo->prepare("
            SELECT
                id,
                account_id,
                amount,
                transaction_date,
                installment_months,
                installment_interest_rate,
                installment_interest_total,
                installment_total_billed
            FROM transactions
            WHERE user_id = ?
              AND transaction_type = 'expense'
              AND is_installment = 1
              AND installment_months > 1
            ORDER BY transaction_date ASC, id ASC
        ");
        $stmt->execute([$userId]);
        $rows = $stmt->fetchAll();

        $stmt = $pdo->prepare("
            DELETE ip
            FROM installment_prepayments ip
            JOIN installments i ON i.id = ip.installment_id
            WHERE i.user_id = ?
        ");
        $stmt->execute([$userId]);

        $stmt = $pdo->prepare("
            DELETE s
            FROM installment_schedules s
            JOIN installments i ON i.id = s.installment_id
            WHERE i.user_id = ?
        ");
        $stmt->execute([$userId]);

        $stmt = $pdo->prepare("
            DELETE FROM installments
            WHERE user_id = ?
        ");
        $stmt->execute([$userId]);

        $pdo->commit();

        $count = 0;

        foreach ($rows as $row) {
            create_installment_schedule(
                $userId,
                (int)$row['id'],
                (int)$row['account_id'],
                (float)$row['amount'],
                (int)$row['installment_months'],
                (string)$row['transaction_date'],
                (float)($row['installment_interest_rate'] ?? 0),
                $row['installment_interest_total'] !== null
                    ? (float)$row['installment_interest_total']
                    : null,
                $row['installment_total_billed'] !== null
                    ? (float)$row['installment_total_billed']
                    : null,
                ((float)($row['installment_interest_rate'] ?? 0) > 0)
                    ? 'fixed_total'
                    : 'none'
            );

            $count++;
        }

        return $count;
    } catch (Throwable $e) {
        if ($pdo->inTransaction()) {
            $pdo->rollBack();
        }

        throw $e;
    }
}