<?php
// api/invoices_post.php

header('Content-Type: application/json');

require_once __DIR__ . '/../db/config.php';
require_once __DIR__ . '/../includes/uuid.php';
require_once __DIR__ . '/../includes/journal_helpers.php';

$response = [
    'status' => 'error',
    'message' => 'Invalid request.'
];

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $input = json_decode(file_get_contents('php://input'), true);

    if (json_last_error() !== JSON_ERROR_NONE || empty($input['student_id']) || empty($input['fee_structure_id'])) {
        $response['message'] = 'Invalid JSON payload or missing student_id/fee_structure_id.';
        http_response_code(400);
        echo json_encode($response);
        exit;
    }

    $pdo = db();
    
    try {
        $pdo->beginTransaction();

        // 1. Fetch Fee Structure details
        $stmt_fsl = $pdo->prepare("SELECT fsl.amount, a.account_code FROM fee_structure_lines fsl JOIN accounts a ON fsl.revenue_account_id = a.id WHERE fsl.fee_structure_id = ?");
        $stmt_fsl->execute([$input['fee_structure_id']]);
        $fee_structure_lines = $stmt_fsl->fetchAll(PDO::FETCH_ASSOC);
        if (empty($fee_structure_lines)) throw new Exception('Fee structure has no lines or revenue accounts not found.');

        // 2. Create Invoice
        $total_amount = array_sum(array_column($fee_structure_lines, 'amount'));
        $invoice_id = uuid_v4();
        $invoice_number = 'INV-' . time();
        $invoice_date = $input['invoice_date'] ?? date('Y-m-d');
        $due_date = $input['due_date'] ?? date('Y-m-d', strtotime('+30 days'));

        $stmt_inv = $pdo->prepare(
            "INSERT INTO invoices (id, student_id, invoice_number, invoice_date, due_date, total_amount, status) VALUES (?, ?, ?, ?, ?, ?, 'Posted')"
        );
        $stmt_inv->execute([$invoice_id, $input['student_id'], $invoice_number, $invoice_date, $due_date, $total_amount]);
        
        // Don't need to insert invoice lines manually if they are based on fee structure, can be joined.
        // For simplicity, let's assume the previous logic of creating them was desired.
        // Re-creating invoice lines for atomicity.
        foreach ($fee_structure_lines as $line) {
             $stmt_inv_line = $pdo->prepare(
                "INSERT INTO invoice_lines (id, invoice_id, description, amount, revenue_account_id) VALUES (?, ?, ?, ?, (SELECT id from accounts where account_code = ?))"
            );
            $stmt_inv_line->execute([uuid_v4(), $invoice_id, 'Fee', $line['amount'], $line['account_code']]);
        }


        // 3. Prepare and Create Journal Entry
        $journal_lines = [];
        // Debit AR
        $journal_lines[] = [
            'account_code' => '1200-AR-STUDENTS',
            'type' => 'DEBIT',
            'amount' => $total_amount
        ];
        // Credit Revenue accounts
        foreach ($fee_structure_lines as $line) {
            $journal_lines[] = [
                'account_code' => $line['account_code'],
                'type' => 'CREDIT',
                'amount' => $line['amount']
            ];
        }

        $journal_payload = [
            'entry_date' => $invoice_date,
            'description' => "Invoice {$invoice_number} for student {$input['student_id']}",
            'lines' => $journal_lines
        ];
        
        $journal_result = post_journal_entry($pdo, $journal_payload);
        if (empty($journal_result['journal_entry_id'])) {
            throw new Exception("Failed to post journal entry: " . ($journal_result['error'] ?? 'Unknown error'));
        }
        $journal_entry_id = $journal_result['journal_entry_id'];

        // Link Invoice to Journal Entry
        $stmt_inv_update = $pdo->prepare("UPDATE invoices SET journal_entry_id = ? WHERE id = ?");
        $stmt_inv_update->execute([$journal_entry_id, $invoice_id]);

        // Log audit trail
        log_audit_trail($pdo, 'create_invoice', ['invoice_id' => $invoice_id, 'student_id' => $input['student_id'], 'total_amount' => $total_amount]);

        $pdo->commit();

        $response = [
            'status' => 'success',
            'message' => 'Invoice created and journal entry posted successfully.',
            'data' => [
                'invoice_id' => $invoice_id,
                'invoice_number' => $invoice_number,
                'journal_entry_id' => $journal_entry_id
            ]
        ];
        http_response_code(201);

    } catch (Exception $e) {
        if ($pdo->inTransaction()) $pdo->rollBack();
        $response['message'] = 'Error creating invoice: ' . $e->getMessage();
        http_response_code(500);
    }
}

echo json_encode($response);