<?php
namespace App\Services;

use App\Models\ConfigurationModel;
use App\Models\ClassSectionModel;

class FeeCalculationService
{
    public function calculateEnrollmentTuition(array $students): float
    {
        return round($this->calculateTotalTuitionFee($students), 2);
    }

    public function calculateRefund(array $students, int $parentId): float
    {
        $totalCents = 0;
        $seenEnrollmentIds = [];

        foreach ($students as $student) {
            if ((int) ($student['parent_id'] ?? $parentId) !== $parentId) {
                continue;
            }

            $status = strtolower(trim((string) ($student['enrollment_status'] ?? '')));
            if (! in_array($status, ['withdrawn', 'refund pending', 'withdraw under review'], true)) {
                continue;
            }

            $enrollmentId = (int) ($student['enrollment_id'] ?? $student['id'] ?? 0);
            if ($enrollmentId <= 0 || isset($seenEnrollmentIds[$enrollmentId])) {
                continue;
            }
            $seenEnrollmentIds[$enrollmentId] = true;

            $calculation = $this->latestWithdrawalCalculation($enrollmentId);
            if ($calculation === null || ($calculation['status'] ?? '') === 'superseded') {
                $calculation = $this->previewWithdrawalCalculation($enrollmentId);
            }

            $totalCents += max(0, (int) ($calculation['new_refund_request_cents'] ?? 0));
        }

        return round($totalCents / 100, 2);
    }

    protected function latestWithdrawalCalculation(int $enrollmentId): ?array
    {
        return service('withdrawalFinancial')->latestForEnrollment($enrollmentId);
    }

    protected function previewWithdrawalCalculation(int $enrollmentId): array
    {
        return service('withdrawalFinancial')->preview($enrollmentId, (int) (session()->get('user_id') ?? 0) ?: null);
    }

    /**
     * Refunds reverse the family tuition stack.
     *
     * Example: three students are charged [first, additional, additional].
     * If one student withdraws, refund the last/additional fee first, not the
     * withdrawn student's sorted family position.
     *
     * @return array<int,float>
     */
    private function reverseTuitionRefundFeeStack(
        int $originalStudentCount,
        int $remainingStudentCount,
        float $firstStudentFee,
        float $additionalStudentFee
    ): array {
        $withdrawnCount = max(0, $originalStudentCount - $remainingStudentCount);
        if ($withdrawnCount === 0) {
            return [];
        }

        $fees = [];
        for ($position = $originalStudentCount; $position > $remainingStudentCount; $position--) {
            $fees[] = $position === 1 ? $firstStudentFee : $additionalStudentFee;
        }

        return $fees;
    }


    private function compareGrades($gradeA, $gradeB)
    {
        $valA = $this->getGradeLevel($gradeA);
        $valB = $this->getGradeLevel($gradeB);

        if ($valA !== $valB) return $valA <=> $valB;

        // Same level, compare suffix
        preg_match('/\d+([A-Z]*)$/i', strtoupper($gradeA), $suffixA);
        preg_match('/\d+([A-Z]*)$/i', strtoupper($gradeB), $suffixB);

        return strcmp($suffixA[1] ?? '', $suffixB[1] ?? '');
    }

    private function getGradeLevel($grade)
    {
        if (strtoupper($grade) === 'K') return 0;
        if (strtoupper($grade) === 'Y') return 99;

        if (preg_match('/^(\d+)([A-Z]*)$/i', $grade, $matches)) {
            return (int) $matches[1];
        }

        return 999; // fallback for unknown/malformed grades
    }


    private function calculateTotalTuitionFee(array $students): float
    {
        $configModel = new ConfigurationModel();
        $classSectionModel = new \App\Models\ClassSectionModel();

        $firstStudentFee = (float) ($configModel->getConfig('first_student_fee') ?? 380);
        $secondStudentFee = (float) ($configModel->getConfig('second_student_fee') ?? 280);

        // ✅ Pre-fetch and assign grade/class section names before sorting
        foreach ($students as &$student) {
            $gradeName = $classSectionModel->getClassSectionNameBySectionId((int) ($student['class_section_id'] ?? 0));
            $student['grade'] = strtoupper(trim($gradeName));
        }
        unset($student); // break reference

        // ✅ Sort students by grade
        usort($students, function ($a, $b) {
            return $this->compareGrades($a['grade'], $b['grade']);
        });

        $studentCount = 0;
        $totalFee = 0;

        // ✅ Calculate fee
        foreach ($students as $student) {
            $totalFee += ($studentCount === 0) ? $firstStudentFee : $secondStudentFee;
            $studentCount++;
        }

        return $totalFee;
    }

}