<?php

namespace App\Http\Controllers\Api;

use App\Models\Configuration;
use App\Models\DiscountUsage;
use App\Models\DiscountVoucher;
use App\Models\Invoice;
use App\Models\Payment;
use App\Models\User;
use Illuminate\Support\Facades\DB;
use Illuminate\Support\Facades\URL;
use Symfony\Component\HttpFoundation\Response;

class DiscountController extends BaseApiController
{
    protected DiscountVoucher $discount;
    protected DiscountUsage $discountUsage;
    protected Invoice $invoice;
    protected User $user;
    protected Payment $payment;
    protected Configuration $config;

    protected string $schoolYear;
    protected ?string $semester;

    public function __construct()
    {
        parent::__construct();
        $this->discount      = model(DiscountVoucher::class);
        $this->discountUsage = model(DiscountUsage::class);
        $this->invoice       = model(Invoice::class);
        $this->user          = model(User::class);
        $this->payment       = model(Payment::class);
        $this->config        = model(Configuration::class);

        $this->schoolYear = $this->config->getConfig('school_year') ?? '';
        $sem             = $this->config->getConfig('semester');
        $this->semester   = is_string($sem) && $sem !== '' ? $sem : null;
    }

    public function index()
    {
        $activeOnly = $this->request->getGet('active') === 'true';
        $query = $this->discount->newQuery();

        if ($activeOnly) {
            $today = now()->toDateString();
            $query->where('is_active', 1)
                ->where(function ($q) use ($today) {
                    $q->whereNull('valid_from')->orWhere('valid_from', '<=', $today);
                })
                ->where(function ($q) use ($today) {
                    $q->whereNull('valid_until')->orWhere('valid_until', '>=', $today);
                });
        }

        $discounts = $query->orderBy('created_at', 'DESC')->get()->toArray();
        return $this->success($discounts, 'Discount vouchers retrieved successfully');
    }

    public function getByCode($code = null)
    {
        $discount = $this->findActiveDiscount($code);

        if (!$discount) {
            return $this->respondError('Discount voucher not found or expired', Response::HTTP_NOT_FOUND);
        }

        if ($this->isUsageLimitReached($discount)) {
            return $this->respondError('Discount voucher has reached maximum usage limit', Response::HTTP_BAD_REQUEST);
        }

        return $this->success($discount->toArray(), 'Discount voucher retrieved successfully');
    }

    public function apply()
    {
        $user = $this->getCurrentUser();
        if (!$user) {
            return $this->respondError('Unauthorized', Response::HTTP_UNAUTHORIZED);
        }

        $data = $this->payloadData();
        if (empty($data)) {
            return $this->respondError('Invalid request data', Response::HTTP_BAD_REQUEST);
        }

        $rules = [
            'code'       => 'required',
            'invoice_id' => 'required|integer',
        ];

        $errors = $this->validateRequest($data, $rules);
        if (!empty($errors)) {
            return $this->respondValidationError($errors);
        }

        $code = strtoupper(trim((string) ($data['code'] ?? '')));
        $discount = $this->findActiveDiscount($code);
        if (!$discount) {
            return $this->respondError('Invalid or expired discount voucher', Response::HTTP_BAD_REQUEST);
        }

        if ($this->isUsageLimitReached($discount)) {
            return $this->respondError('Discount voucher has reached maximum usage limit', Response::HTTP_BAD_REQUEST);
        }

        $exists = $this->discountUsage->newQuery()
            ->where('voucher_id', $discount->id)
            ->where('invoice_id', $data['invoice_id'])
            ->exists();

        if ($exists) {
            return $this->respondError('Discount voucher already applied to this invoice', Response::HTTP_BAD_REQUEST);
        }

        try {
            $usage = $this->discountUsage->create([
                'voucher_id' => $discount->id,
                'invoice_id' => $data['invoice_id'],
                'used_by'    => $user->id,
                'used_at'    => now()->toDateTimeString(),
            ]);

            $discount->increment('times_used');

            return $this->success([
                'discount' => $discount->fresh()->toArray(),
                'applied'  => true,
            ], 'Discount voucher applied successfully');
        } catch (\Throwable $e) {
            log_message('error', 'Discount apply error: ' . $e->getMessage());
            return $this->respondError('Failed to apply discount voucher', Response::HTTP_INTERNAL_SERVER_ERROR);
        }
    }

    public function parents()
    {
        $parents = $this->user->getParents();
        $result = [];
        foreach ($parents as $parent) {
            $discount = DB::table('discount_usages as du')
                ->selectRaw('COALESCE(SUM(du.discount_amount),0) AS total_discount')
                ->join('invoices as i', 'i.id', '=', 'du.invoice_id')
                ->where('i.parent_id', $parent['id'])
                ->where('i.school_year', $this->schoolYear)
                ->first();

            $totalDiscount = (float) ($discount->total_discount ?? 0);
            $result[] = [
                'id'               => $parent['id'],
                'firstname'        => $parent['firstname'],
                'lastname'         => $parent['lastname'],
                'email'            => $parent['email'],
                'school_id'        => $parent['school_id'] ?? null,
                'total_discount'   => $totalDiscount,
                'has_discount'     => $totalDiscount > 0 ? 1 : 0,
            ];
        }

        return $this->success($result, 'Parent discounts retrieved');
    }

    public function applyVoucher()
    {
        $data = $this->payloadData();
        $rules = [
            'voucher_id' => 'required|integer',
            'parent_ids' => 'required',
        ];

        $errors = $this->validateRequest($data, $rules);
        if (!empty($errors)) {
            return $this->respondValidationError($errors);
        }

        $voucherId = (int) $data['voucher_id'];
        $parentIds = $this->normalizeParentIds($data['parent_ids']);
        if (empty($parentIds)) {
            return $this->respondError('At least one parent is required', Response::HTTP_BAD_REQUEST);
        }

        $voucher = $this->discount->find($voucherId);
        if (!$voucher) {
            return $this->respondError('Voucher not found', Response::HTTP_NOT_FOUND);
        }

        $remainingUses = max(0, (int) ($voucher['max_uses'] ?? 1) - (int) ($voucher['times_used'] ?? 0));
        if ($remainingUses <= 0) {
            return $this->respondError('Voucher has reached its maximum allowed uses', Response::HTTP_BAD_REQUEST);
        }

        $description = $this->normalizeDescription($voucher['description'] ?? '');
        $now = utc_now();
        $fullyCoveredInvoiceIds = [];
        $appliedInvoices = [];
        $errors = [];
        $usedCount = 0;

        DB::beginTransaction();
        try {
            foreach ($parentIds as $parentId) {
                $invoices = $this->invoice->getInvoicesByUserId($parentId, $this->schoolYear);
                if (empty($invoices)) {
                    $errors[] = "Parent {$parentId} has no invoices for {$this->schoolYear}.";
                    continue;
                }

                foreach ($invoices as $invoice) {
                    if ($invoice['balance'] <= 0) {
                        continue;
                    }
                    if ($remainingUses <= 0) {
                        break 2;
                    }

                    $initialPreBalance = $this->getCurrentInvoiceBalance($invoice['id'], $this->schoolYear);

                    $already = $this->discountUsage->newQuery()
                        ->where('voucher_id', $voucherId)
                        ->where('invoice_id', $invoice['id'])
                        ->exists();
                    if ($already) {
                        continue;
                    }

                    $rawDiscount = ($voucher['discount_type'] === 'percent')
                        ? round(((float) $invoice['total_amount'] * (float) $voucher['discount_value']) / 100, 2)
                        : (float) $voucher['discount_value'];

                    $discountAmount = min($rawDiscount, $initialPreBalance);
                    if ($discountAmount <= 0) {
                        continue;
                    }

                    $this->db->table('discount_usages')->insert([
                        'voucher_id'      => $voucherId,
                        'invoice_id'      => $invoice['id'],
                        'parent_id'       => $parentId,
                        'discount_amount' => $discountAmount,
                        'description'     => $description,
                        'school_year'     => $this->schoolYear,
                        'semester'        => $this->semester,
                        'updated_by'      => $this->getCurrentUserId() ?? 0,
                        'used_at'         => $now,
                        'created_at'      => $now,
                        'updated_at'      => $now,
                    ]);

                    $newBalance = max(0.0, round(((float) $invoice['balance']) - $discountAmount, 2));
                    $this->invoice->update($invoice['id'], [
                        'balance'      => $newBalance,
                        'has_discount' => 1,
                        'updated_at'   => $now,
                    ]);

                    $postBalance = max(0.0, round($initialPreBalance - $discountAmount, 2));
                    $currentBalance = $this->getCurrentInvoiceBalance($invoice['id'], $this->schoolYear);

                    $this->discount->newQuery()
                        ->where('id', $voucherId)
                        ->set('times_used', 'times_used + 1', false)
                        ->update();

                    [$eventData, $studentData] = $this->buildPaymentEventData(
                        $invoice['id'],
                        (string) $voucherId,
                        $discountAmount,
                        'discount',
                        $now,
                        '',
                        0,
                        $initialPreBalance,
                        $postBalance
                    );
                    event('paymentReceived', [$eventData, $studentData]);

                    $epsilon = 0.01;
                    $fullyCovered = (abs($discountAmount - $initialPreBalance) <= $epsilon)
                        || ($postBalance <= $epsilon)
                        || ($currentBalance <= $epsilon);

                    if ($fullyCovered) {
                        $fullyCoveredInvoiceIds[] = (int) $invoice['id'];
                    }

                    $appliedInvoices[] = (int) $invoice['id'];
                    $remainingUses--;
                    $usedCount++;

                    if ($remainingUses <= 0) {
                        $this->discount->update($voucherId, [
                            'is_active'  => 0,
                            'updated_at' => $now,
                        ]);
                        break 2;
                    }
                }
            }

            DB::commit();
        } catch (\Throwable $e) {
            DB::rollBack();
            log_message('error', 'Voucher application failed: ' . $e->getMessage());
            return $this->respondError('Voucher application failed. Transaction rolled back.', Response::HTTP_INTERNAL_SERVER_ERROR);
        }

        $enrollmentUpdates = 0;
        foreach (array_unique($fullyCoveredInvoiceIds) as $invoiceId) {
            try {
                $enrollmentUpdates += $this->updateEnrollmentStatusIfPaid($invoiceId);
            } catch (\Throwable $e) {
                log_message('error', 'updateEnrollmentStatusIfPaid failed for invoice {iid}: {err}', [
                    'iid' => $invoiceId,
                    'err' => $e->getMessage(),
                ]);
            }
        }

        return $this->success([
            'applied_invoices' => array_values(array_unique($appliedInvoices)),
            'errors'           => $errors,
            'enrollments'      => $enrollmentUpdates,
            'used_count'       => $usedCount,
        ], 'Voucher applied successfully');
    }

    public function createVoucher()
    {
        $data = $this->payloadData();
        $rules = [
            'code'           => 'required|string',
            'discount_type'  => 'required|in:percent,fixed',
            'discount_value' => 'required|numeric',
        ];

        $errors = $this->validateRequest($data, $rules);
        if (!empty($errors)) {
            return $this->respondValidationError($errors);
        }

        $code = strtoupper(preg_replace('/[^A-Z0-9\-]/i', '', trim((string) $data['code'])));
        if ($code === '') {
            return $this->respondError('Voucher code is required', Response::HTTP_BAD_REQUEST);
        }

        $payload = [
            'code'           => $code,
            'discount_type'  => strtolower((string) $data['discount_type']),
            'discount_value' => (float) $data['discount_value'],
            'max_uses'       => isset($data['max_uses']) && $data['max_uses'] !== '' ? (int) $data['max_uses'] : null,
            'valid_from'     => $this->normalizeDate($data['valid_from'] ?? null),
            'valid_until'    => $this->normalizeDate($data['valid_until'] ?? null),
            'is_active'      => isset($data['is_active']) ? (bool) $data['is_active'] : true,
            'description'    => trim((string) ($data['description'] ?? '')),
        ];

        if ($payload['valid_from'] && $payload['valid_until'] && $payload['valid_from'] > $payload['valid_until']) {
            return $this->respondError('Valid until must be the same as or after valid from', Response::HTTP_BAD_REQUEST);
        }

        try {
            $voucher = $this->discount->create($payload);
        } catch (\Throwable $e) {
            log_message('error', 'Voucher creation failed: ' . $e->getMessage());
            return $this->respondError('Failed to save voucher: ' . $e->getMessage());
        }

        return $this->respondCreated($voucher->toArray(), 'Voucher created successfully');
    }

    public function editVoucher($id)
    {
        $voucher = $this->discount->find($id);
        if (!$voucher) {
            return $this->respondError('Voucher not found', Response::HTTP_NOT_FOUND);
        }

        $data = $this->payloadData();
        if (empty($data)) {
            return $this->respondError('Invalid request data', Response::HTTP_BAD_REQUEST);
        }

        $update = [];
        foreach (['code', 'discount_type', 'discount_value', 'max_uses', 'valid_from', 'valid_until', 'is_active', 'description'] as $field) {
            if (array_key_exists($field, $data)) {
                $value = $data[$field];
                if (in_array($field, ['valid_from', 'valid_until'], true)) {
                    $value = $this->normalizeDate($value);
                }
                $update[$field] = $value;
            }
        }

        if (!empty($update)) {
            $this->discount->update($id, $update);
        }

        return $this->success($this->discount->find($id), 'Voucher updated successfully');
    }

    protected function findActiveDiscount(?string $code)
    {
        if (empty($code)) {
            return null;
        }

        $today = now()->toDateString();
        return $this->discount->newQuery()
            ->where('code', $code)
            ->where('is_active', 1)
            ->where(function ($q) use ($today) {
                $q->whereNull('valid_from')->orWhere('valid_from', '<=', $today);
            })
            ->where(function ($q) use ($today) {
                $q->whereNull('valid_until')->orWhere('valid_until', '>=', $today);
            })
            ->first();
    }

    protected function isUsageLimitReached($discount): bool
    {
        if (!$discount->max_uses) {
            return false;
        }
        return isset($discount->times_used) && $discount->times_used >= $discount->max_uses;
    }

    private function normalizeParentIds($input): array
    {
        $values = [];
        if (is_string($input)) {
            $decoded = json_decode($input, true);
            if (json_last_error() === JSON_ERROR_NONE && is_array($decoded)) {
                $values = $decoded;
            } else {
                $values = [$input];
            }
        } elseif (is_array($input)) {
            $values = $input;
        }

        return array_values(array_filter(array_map('intval', $values), fn($id) => $id > 0));
    }

    private function normalizeDescription(?string $description): string
    {
        if ($description === null) {
            return '';
        }
        $description = trim($description);
        return preg_replace(
            '/^Auto-generated on \d{4}-\d{2}-\d{2}\s*[—-]\s*reason:\s*/i',
            '',
            $description
        );
    }

    private function normalizeDate($value): ?string
    {
        if ($value === null || $value === '') {
            return null;
        }

        $date = preg_replace('/[^0-9\-]/', '', (string) $value);
        return preg_match('/^\d{4}-\d{2}-\d{2}$/', $date) ? $date : null;
    }

    private function getCurrentInvoiceBalance($invoiceId, $schoolYear): float
    {
        $invoice = $this->invoice->find($invoiceId);
        if (!$invoice) {
            return 0.0;
        }

        $qb = $this->payment
            ->select('COALESCE(SUM(paid_amount),0) AS total_paid')
            ->where('invoice_id', $invoiceId)
            ->where('school_year', $schoolYear);

        $table = $this->payment->table;
        if ($this->db->getSchemaBuilder()->hasColumn($table, 'status')) {
            $qb->where(function ($q) {
                $q->whereNotIn('status', ['void', 'voided', 'refunded', 'failed', 'chargeback', 'declined', 'reversed', 'canceled', 'cancelled'])
                    ->orWhereNull('status');
            });
        }
        if ($this->db->getSchemaBuilder()->hasColumn($table, 'is_void')) {
            $qb->where(function ($q) {
                $q->where('is_void', 0)
                    ->orWhereNull('is_void');
            });
        }

        $rowPaid = $qb->first();
        $totalPaid = (float) ($rowPaid['total_paid'] ?? 0);

        $rowDisc = DB::table('discount_usages as du')
            ->selectRaw('COALESCE(SUM(du.discount_amount),0) AS total_disc')
            ->join('invoices as i', 'i.id', '=', 'du.invoice_id')
            ->where('du.invoice_id', $invoiceId)
            ->where('i.school_year', $schoolYear)
            ->first();
        $totalDisc = (float) ($rowDisc->total_disc ?? 0);

        $rowRefund = DB::table('refunds')
            ->selectRaw('COALESCE(SUM(refund_paid_amount),0) AS total_refund_paid')
            ->where('invoice_id', $invoiceId)
            ->where('school_year', $schoolYear)
            ->whereIn('status', ['Partial', 'Paid'])
            ->first();
        $totalRefundPaid = (float) ($rowRefund->total_refund_paid ?? 0);

        $total = (float) ($invoice['total_amount'] ?? 0);
        return max(0.0, round($total - $totalPaid - $totalDisc - $totalRefundPaid, 2));
    }

    private function updateEnrollmentStatusIfPaid(int $invoiceId): int
    {
        $invoice = $this->invoice->find($invoiceId);
        if (!$invoice) {
            log_message('warning', 'Invoice not found: {id}', ['id' => $invoiceId]);
            return 0;
        }

        $total = (float) ($invoice['total_amount'] ?? 0);
        $balance = (float) ($invoice['balance'] ?? 0);
        if (!($total > 0 && $balance < $total)) {
            log_message('info', 'No payment yet. Skipping enrollment update. Invoice #{id}', ['id' => $invoiceId]);
            return 0;
        }

        $parentId = (int) ($invoice['parent_id'] ?? 0);
        if ($parentId <= 0 || $this->schoolYear === '') {
            log_message('warning', 'Missing parent_id/school_year for invoice #{id}', ['id' => $invoiceId]);
            return 0;
        }

        $paidEnrollmentIds = [];
        try {
            $rows = DB::table('invoice_items')
                ->select('enrollment_id')
                ->where('invoice_id', $invoiceId)
                ->whereNotNull('enrollment_id')
                ->get()
                ->pluck('enrollment_id')
                ->map('intval')
                ->filter(fn($eid) => $eid > 0)
                ->unique()
                ->values()
                ->toArray();
            $paidEnrollmentIds = $rows;
        } catch (\Throwable $e) {
            // ignore
        }

        $builder = DB::table('enrollments')
            ->where('parent_id', $parentId)
            ->where('school_year', $this->schoolYear)
            ->where(function ($query) {
                $query->where('enrollment_status', 'payment pending')
                    ->orWhere('enrollment_status', 'Payment pending')
                    ->orWhere('enrollment_status', 'Payment Pending')
                    ->orWhere('enrollment_status', 'PAYMENT PENDING')
                    ->orWhereRaw("LOWER(TRIM(REPLACE(enrollment_status, CHAR(160), ' '))) = 'payment pending'");
            });

        if ($this->semester !== null) {
            $builder->where('semester', $this->semester);
        }
        if (!empty($paidEnrollmentIds)) {
            $builder->whereIn('id', $paidEnrollmentIds);
        }

        $toUpdateIds = $builder->pluck('id')->map('intval')->toArray();
        if (empty($toUpdateIds)) {
            return 0;
        }

        $updated = DB::table('enrollments')
            ->whereIn('id', $toUpdateIds)
            ->update([
                'enrollment_status' => 'enrolled',
                'enrollment_date'   => local_date(utc_now(), 'Y-m-d'),
            ]);

        return $updated;
    }

    private function buildPaymentEventData(
        int $invoiceId,
        string $transactionId,
        float $amount,
        string $paymentMethod,
        string $paymentDate,
        ?string $checkNumber,
        int $installmentSeq,
        float $preBalance,
        float $postBalance
    ): array {
        $invoice = $this->invoice->find($invoiceId);
        if (!$invoice) {
            throw new \RuntimeException("Invoice {$invoiceId} not found");
        }

        $parentRow = DB::table('users')
            ->select('id', 'firstname', 'lastname', 'email')
            ->where('id', $invoice['parent_id'])
            ->first();

        if (!$parentRow) {
            throw new \RuntimeException("Parent not found for invoice {$invoiceId}");
        }

        $studentRows = DB::table('students as s')
            ->select('s.id', 's.firstname', 's.lastname', 'sc.class_section_id')
            ->join('student_class as sc', 'sc.student_id', '=', 's.id')
            ->where('s.parent_id', $invoice['parent_id'])
            ->where('sc.school_year', $this->schoolYear)
            ->when($this->semester !== null, fn($q) => $q->where('sc.semester', $this->semester))
            ->get()
            ->toArray();

        $data = [
            'user_id'         => (int) $parentRow->id,
            'email'           => $parentRow->email,
            'firstname'       => $parentRow->firstname,
            'lastname'        => $parentRow->lastname,
            'school_year'     => $this->schoolYear,
            'semester'        => $this->semester,
            'invoice_id'      => $invoiceId,
            'transaction_id'  => $transactionId,
            'payment_date'    => $paymentDate,
            'amount'          => $amount,
            'method'          => $paymentMethod,
            'check_number'    => $checkNumber,
            'installment_seq' => $installmentSeq,
            'invoice_total'   => (float) $invoice['total_amount'],
            'pre_balance'     => $preBalance,
            'post_balance'    => $postBalance,
            'portalLink'      => URL::to('/parent/invoices/' . $invoiceId),
        ];

        return [$data, $studentRows];
    }
}