<?php

namespace App\Services;

use App\Models\StudentYearStatusModel;
use CodeIgniter\Database\BaseConnection;

class StudentYearStatusService
{
    public function __construct(
        private BaseConnection $db,
        private StudentYearStatusModel $yearStatusModel,
    ) {
    }

    public function isNew(int $studentId, string $schoolYear): bool
    {
        if ($studentId <= 0) {
            return true;
        }

        $schoolYear = trim($schoolYear);
        if (! preg_match('/^\d{4}-\d{4}$/', $schoolYear)) {
            return true;
        }

        if (! $this->db->tableExists('student_year_status')) {
            return true;
        }

        $row = $this->yearStatusModel
            ->where('student_id', $studentId)
            ->where('school_year', $schoolYear)
            ->first();

        if (! is_array($row)) {
            return true;
        }

        return (int) ($row['is_new'] ?? 1) === 1;
    }

    public function upsert(int $studentId, string $schoolYear, bool $isNew): bool
    {
        if ($studentId <= 0) {
            return false;
        }

        $schoolYear = trim($schoolYear);
        if (! preg_match('/^\d{4}-\d{4}$/', $schoolYear) || ! $this->db->tableExists('student_year_status')) {
            return false;
        }

        $flag = $isNew ? 1 : 0;

        $existing = $this->yearStatusModel
            ->where('student_id', $studentId)
            ->where('school_year', $schoolYear)
            ->first();

        if (is_array($existing) && isset($existing['id'])) {
            return (bool) $this->yearStatusModel->update((int) $existing['id'], [
                'is_new' => $flag,
            ]);
        }

        return (bool) $this->yearStatusModel->insert([
            'student_id' => $studentId,
            'school_year' => $schoolYear,
            'is_new' => $flag,
        ]);
    }

    public function hasStatus(int $studentId, string $schoolYear): bool
    {
        if ($studentId <= 0) {
            return false;
        }

        $schoolYear = trim($schoolYear);
        if (! preg_match('/^\d{4}-\d{4}$/', $schoolYear) || ! $this->db->tableExists('student_year_status')) {
            return false;
        }

        return $this->yearStatusModel
            ->where('student_id', $studentId)
            ->where('school_year', $schoolYear)
            ->countAllResults() > 0;
    }

    /**
     * Mark students who existed in a source school year as returning in the target year.
     *
     * This is intentionally idempotent so school-year activation/closing and repair
     * migrations can call it safely.
     */
    public function markReturningStudentsForTargetYear(string $sourceSchoolYear, string $targetSchoolYear): int
    {
        $sourceSchoolYear = trim($sourceSchoolYear);
        $targetSchoolYear = trim($targetSchoolYear);

        if (
            ! preg_match('/^\d{4}-\d{4}$/', $sourceSchoolYear)
            || ! preg_match('/^\d{4}-\d{4}$/', $targetSchoolYear)
            || $sourceSchoolYear === $targetSchoolYear
            || ! $this->db->tableExists('student_year_status')
        ) {
            return 0;
        }

        $studentIds = $this->returningStudentIds($sourceSchoolYear);
        foreach ($studentIds as $studentId) {
            $this->upsert($studentId, $targetSchoolYear, false);
        }

        return count($studentIds);
    }

    /**
     * @param list<array<string, mixed>> $students
     */
    public function attachToStudents(array &$students, string $schoolYear): void
    {
        $schoolYear = trim($schoolYear);
        if ($students === [] || ! preg_match('/^\d{4}-\d{4}$/', $schoolYear)) {
            return;
        }

        $ids = [];
        foreach ($students as $student) {
            $id = (int) ($student['id'] ?? $student['student_id'] ?? 0);
            if ($id > 0) {
                $ids[$id] = true;
            }
        }

        $flags = $this->flagsForStudents(array_keys($ids), $schoolYear);

        foreach ($students as &$student) {
            $id = (int) ($student['id'] ?? $student['student_id'] ?? 0);
            if ($id <= 0) {
                continue;
            }

            $student['is_new'] = $flags[$id] ?? 1;
        }
        unset($student);
    }

    /**
     * @param list<int> $studentIds
     * @return array<int, int>
     */
    public function flagsForStudents(array $studentIds, string $schoolYear): array
    {
        $studentIds = array_values(array_unique(array_filter(
            array_map('intval', $studentIds),
            static fn(int $id): bool => $id > 0
        )));

        $schoolYear = trim($schoolYear);
        if ($studentIds === [] || ! preg_match('/^\d{4}-\d{4}$/', $schoolYear)) {
            return [];
        }

        $flags = [];
        foreach ($studentIds as $studentId) {
            $flags[$studentId] = 1;
        }

        if (! $this->db->tableExists('student_year_status')) {
            return $flags;
        }

        $rows = $this->yearStatusModel
            ->select('student_id, is_new')
            ->whereIn('student_id', $studentIds)
            ->where('school_year', $schoolYear)
            ->findAll();

        foreach ($rows as $row) {
            $id = (int) ($row['student_id'] ?? 0);
            if ($id > 0) {
                $flags[$id] = (int) ($row['is_new'] ?? 1) === 1 ? 1 : 0;
            }
        }

        return $flags;
    }

    /**
     * @return list<int>
     */
    private function returningStudentIds(string $sourceSchoolYear): array
    {
        $ids = [];

        foreach (['student_year_status', 'student_class', 'enrollments'] as $table) {
            if (! $this->db->tableExists($table) || ! $this->db->fieldExists('school_year', $table)) {
                continue;
            }

            $rows = $this->db->table($table)
                ->select('student_id')
                ->where('school_year', $sourceSchoolYear)
                ->where('student_id IS NOT NULL', null, false)
                ->groupBy('student_id')
                ->get()
                ->getResultArray();

            foreach ($rows as $row) {
                $studentId = (int) ($row['student_id'] ?? 0);
                if ($studentId > 0) {
                    $ids[$studentId] = true;
                }
            }
        }

        return array_keys($ids);
    }

    public function activeSchoolYear(): ?string
    {
        if ($this->db->tableExists('school_years')) {
            $row = $this->db->table('school_years')
                ->select('name')
                ->where('status', 'active')
                ->orderBy('id', 'DESC')
                ->get(1)
                ->getRowArray();

            $name = trim((string) ($row['name'] ?? ''));
            if (preg_match('/^\d{4}-\d{4}$/', $name)) {
                return $name;
            }
        }

        if (! $this->db->tableExists('configuration')) {
            return null;
        }

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

        $name = trim((string) ($row['config_value'] ?? ''));

        return preg_match('/^\d{4}-\d{4}$/', $name) ? $name : null;
    }
}