<?php

namespace App\Services;

use App\Models\SchoolYearClosingBatchModel;
use App\Models\SchoolYearClosingItemModel;
use App\Models\SchoolYearModel;
use App\Support\SchoolYear\SchoolYearStatus;
use CodeIgniter\Database\BaseConnection;
use InvalidArgumentException;
use RuntimeException;

final class SchoolYearClosingService
{
    public function __construct(
        private readonly SchoolYearModel $schoolYearModel,
        private readonly SchoolYearClosingBatchModel $batchModel,
        private readonly SchoolYearClosingItemModel $itemModel,
        private readonly SchoolYearManagementService $managementService,
        private readonly BaseConnection $db,
    ) {
    }

    public function preview(int $sourceYearId, ?int $targetYearId = null): array
    {
        $source = $this->requireYear($sourceYearId);
        $target = $targetYearId !== null ? $this->schoolYearModel->find($targetYearId) : $this->nextDraftYear((string) $source['name']);
        $sourceName = (string) $source['name'];

        $finance = $this->financialSummary($sourceName);
        $overview = [
            'students' => $this->countBySchoolYear('student_class', $sourceName, 'student_id'),
            'families' => $this->countFamilies($sourceName),
            'classes' => $this->countBySchoolYear('classSection', $sourceName, 'class_id'),
            'teachers' => $this->countBySchoolYear('teacher_class', $sourceName, 'teacher_id'),
            'invoices' => $finance['invoice_count'],
            'total_invoiced' => $finance['total_invoiced'],
            'total_paid' => $finance['total_paid'],
            'total_outstanding' => $finance['total_outstanding'],
        ];

        $findings = [];
        if ($target === null) {
            $findings[] = $this->finding('blocking', 'Missing target year', 'Create a draft target school year before starting closing.');
        } elseif (! in_array((string) $target['status'], [SchoolYearStatus::DRAFT, SchoolYearStatus::ACTIVE], true)) {
            $findings[] = $this->finding('blocking', 'Invalid target year', 'The target school year must be draft or active.');
        }

        foreach ($this->unpaidInvoiceFindings($sourceName) as $finding) {
            $findings[] = $finding;
        }

        if ($this->countMissingSchoolYearRows('invoices') > 0) {
            $findings[] = $this->finding('blocking', 'Invoices missing school year', 'Some invoice records are not assigned to a school year.');
        }

        $carryForward = $this->carryForwardFamilies($sourceName);
        $warnings = array_values(array_filter($findings, static fn (array $f): bool => $f['severity'] === 'warning'));
        $blockers = array_values(array_filter($findings, static fn (array $f): bool => $f['severity'] === 'blocking'));

        $result = [
            'source' => $source,
            'target' => $target,
            'overview' => $overview,
            'finance' => $finance,
            'findings' => $findings,
            'blockers' => $blockers,
            'warnings' => $warnings,
            'carry_forward' => $carryForward,
            'generated_at' => date('Y-m-d H:i:s'),
        ];
        $result['hash'] = $this->hashPreview($result);

        return $result;
    }

    public function start(int $sourceYearId, int $targetYearId, ?int $userId = null): void
    {
        $this->assertClosingTablesExist();

        $source = $this->requireYear($sourceYearId);

        if (($source['status'] ?? '') !== SchoolYearStatus::ACTIVE) {
            throw new InvalidArgumentException('Only an active school year can begin closing.');
        }

        $preview = $this->preview($sourceYearId, $targetYearId);
        if ($preview['blockers'] !== []) {
            throw new InvalidArgumentException('Resolve blocking closing issues before starting closing.');
        }

        $this->db->transStart();
        $now = date('Y-m-d H:i:s');
        $batchId = $this->batchModel->insert([
            'source_school_year_id' => $sourceYearId,
            'target_school_year_id' => $targetYearId,
            'status' => 'started',
            'preview_hash' => $preview['hash'],
            'total_families' => count($preview['carry_forward']),
            'total_positive_balance' => $preview['finance']['positive_balance'],
            'total_credit_balance' => $preview['finance']['credit_balance'],
            'started_by' => $userId,
            'started_at' => $now,
        ], true);

        foreach ($preview['carry_forward'] as $row) {
            $this->itemModel->insert([
                'closing_batch_id' => $batchId,
                'family_id' => (int) $row['family_id'],
                'source_balance' => $row['source_balance'],
                'credit_amount' => $row['credit_amount'],
                'carry_forward_amount' => $row['carry_forward_amount'],
                'status' => 'pending',
            ]);
        }

        $this->schoolYearModel->update($sourceYearId, [
            'status' => SchoolYearStatus::CLOSING,
            'closing_started_at' => $now,
            'updated_by' => $userId,
        ]);
        $this->managementService->log($sourceYearId, SchoolYearStatus::ACTIVE, SchoolYearStatus::CLOSING, 'closing_start', $userId, [
            'target_school_year_id' => $targetYearId,
            'closing_batch_id' => $batchId,
            'preview_hash' => $preview['hash'],
        ]);
        $this->db->transComplete();

        if ($this->db->transStatus() === false) {
            throw new RuntimeException('Unable to start school year closing.');
        }
    }

    public function execute(int $sourceYearId, ?int $userId = null): void
    {
        $this->assertClosingTablesExist();

        $batch = $this->latestOpenBatch($sourceYearId);
        if ($batch === null) {
            throw new InvalidArgumentException('No open closing batch exists.');
        }

        $preview = $this->preview($sourceYearId, (int) $batch['target_school_year_id']);
        if ($preview['hash'] !== (string) $batch['preview_hash']) {
            throw new InvalidArgumentException('Closing preview has changed. Refresh and restart closing before executing carry-forward.');
        }

        $this->db->transStart();
        $items = $this->itemModel->where('closing_batch_id', (int) $batch['id'])->findAll();
        foreach ($items as $item) {
            if (($item['status'] ?? '') === 'completed') {
                continue;
            }

            $this->itemModel->update((int) $item['id'], ['status' => 'completed']);
        }
        $this->batchModel->update((int) $batch['id'], ['status' => 'executed']);
        $this->managementService->log($sourceYearId, SchoolYearStatus::CLOSING, SchoolYearStatus::CLOSING, 'carry_forward_execute', $userId, [
            'closing_batch_id' => (int) $batch['id'],
            'note' => 'Marked previewed carry-forward items complete. Target accounting records require the dedicated opening-balance schema.',
        ]);
        $this->db->transComplete();

        if ($this->db->transStatus() === false) {
            throw new RuntimeException('Unable to execute carry-forward.');
        }
    }

    public function complete(int $sourceYearId, ?int $userId = null): void
    {
        $this->assertClosingTablesExist();

        $batch = $this->latestOpenBatch($sourceYearId);
        if ($batch === null || ($batch['status'] ?? '') !== 'executed') {
            throw new InvalidArgumentException('Carry-forward must be executed before completing closing.');
        }

        $pending = $this->itemModel
            ->where('closing_batch_id', (int) $batch['id'])
            ->where('status !=', 'completed')
            ->countAllResults();
        if ($pending > 0) {
            throw new InvalidArgumentException('All closing batch items must complete before the year can be closed.');
        }

        $this->db->transStart();
        $now = date('Y-m-d H:i:s');
        $this->batchModel->update((int) $batch['id'], [
            'status' => 'completed',
            'completed_by' => $userId,
            'completed_at' => $now,
        ]);
        $this->schoolYearModel->update($sourceYearId, [
            'status' => SchoolYearStatus::CLOSED,
            'closed_at' => $now,
            'updated_by' => $userId,
        ]);
        $this->managementService->log($sourceYearId, SchoolYearStatus::CLOSING, SchoolYearStatus::CLOSED, 'closing_complete', $userId, [
            'closing_batch_id' => (int) $batch['id'],
        ]);
        $this->db->transComplete();

        if ($this->db->transStatus() === false) {
            throw new RuntimeException('Unable to complete closing.');
        }
    }

    public function cancel(int $sourceYearId, ?int $userId = null): void
    {
        $this->assertClosingTablesExist();

        $batch = $this->latestOpenBatch($sourceYearId);
        if ($batch !== null && in_array((string) $batch['status'], ['executed', 'completed'], true)) {
            throw new InvalidArgumentException('Closing cannot be cancelled after carry-forward has executed.');
        }

        $this->db->transStart();
        if ($batch !== null) {
            $this->batchModel->update((int) $batch['id'], ['status' => 'cancelled']);
        }
        $this->schoolYearModel->update($sourceYearId, [
            'status' => SchoolYearStatus::ACTIVE,
            'updated_by' => $userId,
        ]);
        $this->managementService->log($sourceYearId, SchoolYearStatus::CLOSING, SchoolYearStatus::ACTIVE, 'closing_cancel', $userId, [
            'closing_batch_id' => $batch['id'] ?? null,
        ]);
        $this->db->transComplete();

        if ($this->db->transStatus() === false) {
            throw new RuntimeException('Unable to cancel closing.');
        }
    }

    public function latestBatch(int $sourceYearId): ?array
    {
        if (! $this->db->tableExists('school_year_closing_batches')) {
            return null;
        }

        return $this->batchModel
            ->where('source_school_year_id', $sourceYearId)
            ->orderBy('id', 'DESC')
            ->first();
    }

    private function requireYear(int $id): array
    {
        $year = $this->schoolYearModel->find($id);
        if ($year === null) {
            throw new InvalidArgumentException('School year not found.');
        }

        return $year;
    }

    private function nextDraftYear(string $sourceName): ?array
    {
        if (! preg_match('/^(\d{4})-(\d{4})$/', $sourceName, $matches)) {
            return null;
        }

        $nextName = $matches[2] . '-' . ((int) $matches[2] + 1);

        return $this->schoolYearModel
            ->where('name', $nextName)
            ->first();
    }

    private function financialSummary(string $schoolYear): array
    {
        $summary = [
            'invoice_count' => 0,
            'total_invoiced' => 0.0,
            'total_paid' => 0.0,
            'total_outstanding' => 0.0,
            'positive_balance' => 0.0,
            'credit_balance' => 0.0,
        ];

        if (! $this->db->tableExists('invoices')) {
            return $summary;
        }

        $row = $this->db->table('invoices')
            ->select('COUNT(*) AS invoice_count')
            ->select('COALESCE(SUM(total_amount), 0) AS total_invoiced')
            ->select('COALESCE(SUM(paid_amount), 0) AS total_paid')
            ->select('COALESCE(SUM(balance), 0) AS total_outstanding')
            ->select('COALESCE(SUM(CASE WHEN balance > 0 THEN balance ELSE 0 END), 0) AS positive_balance', false)
            ->select('COALESCE(SUM(CASE WHEN balance < 0 THEN ABS(balance) ELSE 0 END), 0) AS credit_balance', false)
            ->where('school_year', $schoolYear)
            ->get()
            ->getRowArray() ?? [];

        foreach ($summary as $key => $value) {
            $summary[$key] = $key === 'invoice_count' ? (int) ($row[$key] ?? 0) : round((float) ($row[$key] ?? 0), 2);
        }

        return $summary;
    }

    private function unpaidInvoiceFindings(string $schoolYear): array
    {
        if (! $this->db->tableExists('invoices')) {
            return [];
        }

        $count = $this->db->table('invoices')
            ->where('school_year', $schoolYear)
            ->where('balance >', 0)
            ->countAllResults();

        return $count > 0
            ? [$this->finding('warning', 'Outstanding balances exist', "{$count} invoice(s) still have a positive balance and will require carry-forward review.")]
            : [];
    }

    private function carryForwardFamilies(string $schoolYear): array
    {
        if (! $this->db->tableExists('invoices')) {
            return [];
        }

        $rows = $this->db->table('invoices i')
            ->select('i.parent_id AS family_id')
            ->select('COALESCE(SUM(i.balance), 0) AS source_balance')
            ->where('i.school_year', $schoolYear)
            ->groupBy('i.parent_id')
            ->having('source_balance !=', 0)
            ->orderBy('i.parent_id', 'ASC')
            ->get()
            ->getResultArray();

        return array_map(static function (array $row): array {
            $balance = round((float) $row['source_balance'], 2);

            return [
                'family_id' => (int) $row['family_id'],
                'family' => 'Family #' . (int) $row['family_id'],
                'source_balance' => $balance,
                'credit_amount' => $balance < 0 ? abs($balance) : 0.0,
                'adjustment_amount' => 0.0,
                'carry_forward_amount' => $balance,
            ];
        }, $rows);
    }

    private function countBySchoolYear(string $table, string $schoolYear, string $distinctField): int
    {
        if (! $this->db->tableExists($table) || ! $this->db->fieldExists('school_year', $table)) {
            return 0;
        }

        $row = $this->db->table($table)
            ->select("COUNT(DISTINCT {$distinctField}) AS total", false)
            ->where('school_year', $schoolYear)
            ->get()
            ->getRowArray();

        return (int) ($row['total'] ?? 0);
    }

    private function countFamilies(string $schoolYear): int
    {
        if ($this->db->tableExists('invoices')) {
            $row = $this->db->table('invoices')
                ->select('COUNT(DISTINCT parent_id) AS total', false)
                ->where('school_year', $schoolYear)
                ->get()
                ->getRowArray();

            return (int) ($row['total'] ?? 0);
        }

        return 0;
    }

    private function countMissingSchoolYearRows(string $table): int
    {
        if (! $this->db->tableExists($table) || ! $this->db->fieldExists('school_year', $table)) {
            return 0;
        }

        return $this->db->table($table)
            ->groupStart()
            ->where('school_year', null)
            ->orWhere('school_year', '')
            ->groupEnd()
            ->countAllResults();
    }

    private function latestOpenBatch(int $sourceYearId): ?array
    {
        return $this->batchModel
            ->where('source_school_year_id', $sourceYearId)
            ->whereIn('status', ['started', 'executed'])
            ->orderBy('id', 'DESC')
            ->first();
    }

    private function assertClosingTablesExist(): void
    {
        foreach (['school_year_closing_batches', 'school_year_closing_items', 'school_year_transition_logs'] as $table) {
            if (! $this->db->tableExists($table)) {
                throw new RuntimeException('School year lifecycle tables are missing. Run database migrations before closing a school year.');
            }
        }
    }

    private function finding(string $severity, string $title, string $detail): array
    {
        return [
            'severity' => $severity,
            'title' => $title,
            'detail' => $detail,
        ];
    }

    private function hashPreview(array $preview): string
    {
        return hash('sha256', json_encode([
            'source_id' => $preview['source']['id'] ?? null,
            'target_id' => $preview['target']['id'] ?? null,
            'finance' => $preview['finance'],
            'carry_forward' => $preview['carry_forward'],
            'blockers' => $preview['blockers'],
        ], JSON_UNESCAPED_SLASHES));
    }
}