<?php

namespace App\Services;

use CodeIgniter\Database\BaseConnection;
use InvalidArgumentException;
use RuntimeException;

final class EnrollmentStatusService
{
    public const ACTIVE_STATUSES = [
        'admission under review',
        'review & decision',
        'payment pending',
        'enrolled',
        'withdraw under review',
    ];

    public const INACTIVE_STATUSES = [
        'denied',
        'refund pending',
        'withdrawn',
        'waitlist',
    ];

    public const VALID_STATUSES = [
        'admission under review',
        'review & decision',
        'payment pending',
        'enrolled',
        'withdraw under review',
        'refund pending',
        'withdrawn',
        'waitlist',
        'denied',
    ];

    public function __construct(private readonly BaseConnection $db)
    {
    }

    public function isActiveStatus(string $status): bool
    {
        return in_array($this->normalizeStatus($status), self::ACTIVE_STATUSES, true);
    }

    public function activeFlagForStatus(string $status): int
    {
        return $this->isActiveStatus($status) ? 1 : 0;
    }

    public function normalizeStatus(string $status): string
    {
        $status = strtolower(trim(str_replace("\xc2\xa0", ' ', $status)));
        $status = preg_replace('/\s+/', ' ', $status) ?? $status;

        if (! in_array($status, self::VALID_STATUSES, true)) {
            throw new InvalidArgumentException("Invalid enrollment status: {$status}");
        }

        return $status;
    }

    public function upsertStatus(array $payload, ?int $performedBy = null, string $reason = 'enrollment_status_changed'): array
    {
        $studentId = (int) ($payload['student_id'] ?? 0);
        $schoolYear = trim((string) ($payload['school_year'] ?? ''));
        $status = $this->normalizeStatus((string) ($payload['enrollment_status'] ?? ''));

        if ($studentId <= 0 || $schoolYear === '') {
            throw new InvalidArgumentException('student_id and school_year are required.');
        }

        $now = function_exists('utc_now') ? utc_now() : date('Y-m-d H:i:s');
        $payload['student_id'] = $studentId;
        $payload['school_year'] = $schoolYear;
        $payload['enrollment_status'] = $status;
        $payload['updated_at'] = $payload['updated_at'] ?? $now;

        if (! isset($payload['admission_status'])) {
            $payload['admission_status'] = $this->admissionStatusFor($status);
        }

        if (! isset($payload['is_withdrawn']) && in_array($status, ['withdraw under review', 'refund pending', 'withdrawn'], true)) {
            $payload['is_withdrawn'] = 1;
        } elseif (! isset($payload['is_withdrawn']) && in_array($status, ['admission under review', 'review & decision', 'payment pending', 'enrolled', 'waitlist', 'denied'], true)) {
            $payload['is_withdrawn'] = 0;
        }

        $this->db->transStart();

        $existing = $this->controllingEnrollment($studentId, $schoolYear);
        $oldStatus = $existing['enrollment_status'] ?? null;

        if ($existing !== null) {
            $this->db->table('enrollments')
                ->where('id', (int) $existing['id'])
                ->update($this->filterPayload('enrollments', $payload));
            $enrollmentId = (int) $existing['id'];
        } else {
            $payload['created_at'] = $payload['created_at'] ?? $now;
            $insertPayload = $this->filterPayload('enrollments', $payload);
            $this->db->table('enrollments')->insert($insertPayload);
            $enrollmentId = (int) $this->db->insertID();
        }

        $currentSchoolYear = $this->currentSchoolYear();
        $updatedStudent = false;
        if ($currentSchoolYear === '' || $schoolYear === $currentSchoolYear) {
            $updatedStudent = $this->syncStudentActivityForEnrollment($studentId, $status);
        }

        $newSnapshot = $payload;
        $newSnapshot['id'] = $enrollmentId;
        $newSnapshot['old_enrollment_status'] = $oldStatus;
        $newSnapshot['new_enrollment_status'] = $status;
        $newSnapshot['student_is_active'] = $this->activeFlagForStatus($status);
        $newSnapshot['student_activity_synced'] = $updatedStudent;

        $this->audit($studentId, $schoolYear, $performedBy, $existing, $newSnapshot, $reason);
        $this->db->transComplete();

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

        return [
            'id' => $enrollmentId,
            'old_status' => $oldStatus,
            'new_status' => $status,
            'student_is_active' => $this->activeFlagForStatus($status),
            'student_activity_synced' => $updatedStudent,
        ];
    }

    public function syncStudentActivityForEnrollment(int $studentId, string $status): bool
    {
        if ($studentId <= 0 || ! $this->db->fieldExists('is_active', 'students')) {
            return false;
        }

        return (bool) $this->db->table('students')
            ->where('id', $studentId)
            ->update(['is_active' => $this->activeFlagForStatus($status)]);
    }

    public function controllingEnrollment(int $studentId, string $schoolYear, ?string $semester = null): ?array
    {
        $builder = $this->db->table('enrollments')
            ->where('student_id', $studentId)
            ->where('school_year', $schoolYear);

        if ($semester !== null && $semester !== '') {
            $builder->where('semester', $semester);
        }

        return $builder
            ->orderBy('updated_at', 'DESC')
            ->orderBy('enrollment_date', 'DESC')
            ->orderBy('id', 'DESC')
            ->limit(1)
            ->get()
            ->getRowArray() ?: null;
    }

    public function currentSchoolYear(): string
    {
        if (! $this->db->tableExists('configuration')) {
            return '';
        }

        $row = $this->db->table('configuration')
            ->select('config_value')
            ->where('config_key', 'school_year')
            ->limit(1)
            ->get()
            ->getRowArray();

        return trim((string) ($row['config_value'] ?? ''));
    }

    private function admissionStatusFor(string $status): string
    {
        if ($status === 'denied') {
            return 'denied';
        }

        return in_array($status, ['payment pending', 'enrolled'], true) ? 'accepted' : 'pending';
    }

    private function filterPayload(string $table, array $payload): array
    {
        $fields = $this->db->getFieldNames($table);
        return array_intersect_key($payload, array_flip($fields));
    }

    private function audit(int $studentId, string $schoolYear, ?int $performedBy, ?array $original, array $new, string $reason): void
    {
        if (! $this->db->tableExists('enrollment_transition_audits')) {
            return;
        }

        $this->db->table('enrollment_transition_audits')->insert([
            'student_id' => $studentId,
            'school_year' => $schoolYear,
            'source_school_year' => $original['source_school_year'] ?? $new['source_school_year'] ?? null,
            'action' => 'enrollment_status_sync',
            'performed_by' => $performedBy,
            'original_values_json' => $original !== null ? json_encode($original, JSON_UNESCAPED_SLASHES) : null,
            'new_values_json' => json_encode($new, JSON_UNESCAPED_SLASHES),
            'reason' => $reason,
            'created_at' => function_exists('utc_now') ? utc_now() : date('Y-m-d H:i:s'),
        ]);
    }
}