<?php

namespace App\Services;

use DateTimeImmutable;
use InvalidArgumentException;

/**
 * Pure withdrawal calculation. All monetary values are integer cents.
 *
 * This class deliberately has no database, session, calendar, attendance, or
 * active-school-year dependencies. Callers must pass snapshotted inputs.
 */
final class WithdrawalRefundCalculator
{
    /**
     * @param array{
     *   annual_fee_allocation_cents:int,
     *   issued_book_charge_cents:int,
     *   total_instructional_weeks:int,
     *   school_year_start_date:string,
     *   enrollment_date:string,
     *   withdrawal_request_date:string,
     *   valid_payment_cents?:int,
     *   completed_payout_cents?:int,
     *   open_reservation_cents?:int,
     *   other_charge_cents?:int,
     *   annual_fee_includes_books?:bool
     * } $input
     * @return array<string,int|bool|string>
     */
    public function calculate(array $input): array
    {
        $annualFee = $this->nonNegativeInt($input, 'annual_fee_allocation_cents');
        $bookCharge = $this->nonNegativeInt($input, 'issued_book_charge_cents');
        $totalWeeks = $this->positiveInt($input, 'total_instructional_weeks');
        $validPayments = $this->optionalNonNegativeInt($input, 'valid_payment_cents');
        $completedPayouts = $this->optionalNonNegativeInt($input, 'completed_payout_cents');
        $openReservations = $this->optionalNonNegativeInt($input, 'open_reservation_cents');
        $otherCharges = $this->optionalNonNegativeInt($input, 'other_charge_cents');
        $includesBooks = (bool) ($input['annual_fee_includes_books'] ?? true);

        if (! $includesBooks) {
            throw new InvalidArgumentException('The active withdrawal policy requires annual tuition to include books.');
        }
        if ($bookCharge > $annualFee) {
            throw new InvalidArgumentException('Issued-book charges exceed the student annual tuition allocation.');
        }

        $schoolStart = $this->date($input, 'school_year_start_date');
        $enrollmentDate = $this->date($input, 'enrollment_date');
        $withdrawalDate = $this->date($input, 'withdrawal_request_date');
        $chargeStart = $enrollmentDate > $schoolStart ? $enrollmentDate : $schoolStart;

        $totalChargeableDays = $totalWeeks * 7;
        $studiedDays = 0;
        if ($withdrawalDate >= $chargeStart) {
            $studiedDays = ((int) $chargeStart->diff($withdrawalDate)->format('%a')) + 1;
        }
        $studiedDays = min($totalChargeableDays, max(0, $studiedDays));
        $studiedWeeks = $studiedDays === 0
            ? 0
            : min($totalWeeks, intdiv($studiedDays + 6, 7));

        $annualInstruction = $annualFee - $bookCharge;
        $earnedTuition = $this->roundRatio($annualInstruction * $studiedWeeks, $totalWeeks);
        $retainedCharge = $bookCharge + $earnedTuition + $otherCharges;

        $netPayments = max(0, $validPayments - $completedPayouts);
        $refundableCredit = max(0, $netPayments - $retainedCharge);
        $balanceDue = max(0, $retainedCharge - $netPayments);
        $newRefundRequest = max(0, $refundableCredit - $openReservations);

        return [
            'annual_fee_includes_books' => true,
            'school_year_start_date' => $schoolStart->format('Y-m-d'),
            'enrollment_date' => $enrollmentDate->format('Y-m-d'),
            'withdrawal_request_date' => $withdrawalDate->format('Y-m-d'),
            'charge_start_date' => $chargeStart->format('Y-m-d'),
            'total_instructional_weeks' => $totalWeeks,
            'total_chargeable_days' => $totalChargeableDays,
            'studied_calendar_days' => $studiedDays,
            'studied_weeks' => $studiedWeeks,
            'annual_fee_allocation_cents' => $annualFee,
            'issued_book_charge_cents' => $bookCharge,
            'annual_instruction_cents' => $annualInstruction,
            'earned_tuition_cents' => $earnedTuition,
            'other_charge_cents' => $otherCharges,
            'retained_charge_cents' => $retainedCharge,
            'valid_payment_cents' => $validPayments,
            'completed_payout_cents' => $completedPayouts,
            'net_payment_cents' => $netPayments,
            'open_reservation_cents' => $openReservations,
            'refundable_credit_cents' => $refundableCredit,
            'new_refund_request_cents' => $newRefundRequest,
            'balance_due_cents' => $balanceDue,
        ];
    }

    private function date(array $input, string $key): DateTimeImmutable
    {
        $raw = trim((string) ($input[$key] ?? ''));
        $date = DateTimeImmutable::createFromFormat('!Y-m-d', $raw);
        $errors = DateTimeImmutable::getLastErrors();
        if ($date === false || ($errors !== false && ($errors['warning_count'] > 0 || $errors['error_count'] > 0))) {
            throw new InvalidArgumentException($key . ' must be a valid Y-m-d date.');
        }

        return $date;
    }

    private function positiveInt(array $input, string $key): int
    {
        $value = filter_var($input[$key] ?? null, FILTER_VALIDATE_INT);
        if ($value === false || $value <= 0) {
            throw new InvalidArgumentException($key . ' must be a positive integer.');
        }

        return $value;
    }

    private function nonNegativeInt(array $input, string $key): int
    {
        $value = filter_var($input[$key] ?? null, FILTER_VALIDATE_INT);
        if ($value === false || $value < 0) {
            throw new InvalidArgumentException($key . ' must be a non-negative integer.');
        }

        return $value;
    }

    private function optionalNonNegativeInt(array $input, string $key): int
    {
        if (! array_key_exists($key, $input) || $input[$key] === null || $input[$key] === '') {
            return 0;
        }

        return $this->nonNegativeInt($input, $key);
    }

    private function roundRatio(int $numerator, int $denominator): int
    {
        if ($denominator <= 0) {
            throw new InvalidArgumentException('The calculation denominator must be positive.');
        }

        return intdiv($numerator + intdiv($denominator, 2), $denominator);
    }
}