<?php

namespace App\Libraries\Tuition;

use App\Interfaces\TuitionCalculatorInterface;

final class NewTuitionCalculatorService implements TuitionCalculatorInterface
{
    public function calculateFamilyTuition(array $students, array $config): array
    {
        $gradeFee = (int) ($config['grade_fee'] ?? 9);
        $fullAmountCents = $this->toCents($config['new_tuition_full_amount'] ?? $config['first_student_fee'] ?? 380);
        $additionalDiscountCents = $this->additionalDiscountCents($config, $fullAmountCents);

        usort($students, function (array $left, array $right) use ($gradeFee): int {
            $leftLevel = GradeLevelParser::parse($left['grade_level'] ?? null, $gradeFee);
            $rightLevel = GradeLevelParser::parse($right['grade_level'] ?? null, $gradeFee);

            return [$leftLevel, (int) ($left['student_id'] ?? 0)] <=> [$rightLevel, (int) ($right['student_id'] ?? 0)];
        });

        $details = [];
        $familyPosition = 0;

        foreach (array_values($students) as $student) {
            $familyPosition++;
            $discountCents = $familyPosition === 1 ? 0 : $additionalDiscountCents;
            $rule = $familyPosition === 1 ? 'new_first_student_full_amount' : 'new_additional_student_discount';
            $amountCents = max(0, $fullAmountCents - $discountCents);

            $details[] = [
                'student_id' => (int) ($student['student_id'] ?? 0),
                'student_name' => (string) ($student['student_name'] ?? ''),
                'grade_level' => $student['grade_level'] ?? null,
                'family_position' => $familyPosition,
                'full_amount' => $this->fromCents($fullAmountCents),
                'discount' => $this->fromCents($discountCents),
                'rule' => $rule,
                'amount' => $this->fromCents($amountCents),
            ];
        }

        $total = array_sum(array_map(fn (array $detail): int => $this->toCents($detail['amount']), $details));

        return [
            'calculator' => 'new',
            'total' => $this->fromCents($total),
            'details' => $details,
        ];
    }

    private function additionalDiscountCents(array $config, int $fullAmountCents): int
    {
        if (array_key_exists('new_tuition_second_student_discount', $config) && $config['new_tuition_second_student_discount'] !== null && $config['new_tuition_second_student_discount'] !== '') {
            return $this->toCents($config['new_tuition_second_student_discount']);
        }

        if (array_key_exists('second_student_fee', $config) && $config['second_student_fee'] !== null && $config['second_student_fee'] !== '') {
            return max(0, $fullAmountCents - $this->toCents($config['second_student_fee']));
        }

        return $this->toCents(100);
    }

    private function toCents($amount): int
    {
        return (int) round(((float) $amount) * 100);
    }

    private function fromCents(int $cents): string
    {
        return number_format($cents / 100, 2, '.', '');
    }
}