<?php
// backend/api.php

require_once __DIR__ . '/config.php'; // Load environment variables and set CORS headers

/**
 * Handles error responses for the API.
 * @param string $message The error message.
 * @param int $statusCode The HTTP status code (default 500).
 */
function sendErrorResponse($message, $statusCode = 500) {
    http_response_code($statusCode);
    echo json_encode(['status' => 'error', 'message' => $message]);
    exit();
}

// Ensure the request method is POST
if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
    sendErrorResponse('Method Not Allowed', 405);
}

// Check for Authorization header
$headers = getallheaders();
$authHeader = $headers['Authorization'] ?? '';

if (!preg_match('/Bearer\s+(.+)/', $authHeader, $matches)) {
    sendErrorResponse('Authentication required', 401);
}

$accessToken = $matches[1];

// Validate the token (basic validation - check if it looks like a JWT)
if (empty($accessToken) || substr_count($accessToken, '.') !== 2) {
    sendErrorResponse('Invalid authentication token', 401);
}

// Get the raw POST data
$input = file_get_contents('php://input');
$data = json_decode($input, true);

// --- Input Validation ---
if (json_last_error() !== JSON_ERROR_NONE) {
    sendErrorResponse('Invalid JSON payload.', 400);
}

$imageBase64 = $data['image_base64'] ?? null;
$prompt = $data['prompt'] ?? null;
$apiOptions = $data['api_options'] ?? [];

if (empty($imageBase64) || !is_string($imageBase64) || !str_starts_with($imageBase64, 'data:image/')) {
    sendErrorResponse('Invalid or missing image_base64. Must be a base64 encoded image data URL.', 400);
}
if (empty($prompt) || !is_string($prompt) || trim($prompt) === '') {
    sendErrorResponse('Prompt cannot be empty.', 400);
}
if (!is_array($apiOptions)) {
    sendErrorResponse('Invalid api_options. Must be an object/array.', 400);
}

error_log("Received generation request: " . json_encode([
    'prompt' => $prompt,
    'image_size' => round(strlen($imageBase64) / 1024) . ' KB',
    'api_options' => $apiOptions
]));

// --- ACTUAL RUNWAY API INTEGRATION ---
try {
    // --- CONFIGURE THIS SECTION WITH YOUR ACTUAL RUNWAY GEN4 API DETAILS ---
    // Refer to RunwayML's official Gen4 API documentation for the correct model ID and parameters.

    // Endpoint for Image to Video as per documentation:
    $runwayApiEndpoint = 'https://api.dev.runwayml.com/v1/image_to_video';
    
    // Validate image size (base64 data URI should be under 5MB)
    $imageSizeBytes = strlen($imageBase64);
    if ($imageSizeBytes > 5 * 1024 * 1024) {
        throw new Exception('Image too large. Base64 data URI must be under 5MB.');
    }

    // Validate the data URI format
    if (!preg_match('/^data:image\/(jpeg|jpg|png|webp);base64,/', $imageBase64)) {
        throw new Exception('Invalid image format. Must be JPEG, PNG, or WebP.');
    }

    $runwayPayload = [
        'promptImage' => $imageBase64, // Send full data URL format
        'promptText' => $prompt,
        'model' => 'gen4_turbo',
        'ratio' => $apiOptions['ratio'] ?? '1280:720' // Required parameter
    ];

    // Add optional parameters if provided
    if (isset($apiOptions['duration']) && $apiOptions['duration'] !== null) {
        $runwayPayload['duration'] = (int)$apiOptions['duration'];
    }
    if (isset($apiOptions['seed']) && $apiOptions['seed'] !== null) {
        $runwayPayload['seed'] = (int)$apiOptions['seed'];
    }

    // Log payload without the full image data to avoid huge logs
    $logPayload = $runwayPayload;
    $logPayload['promptImage'] = substr($imageBase64, 0, 50) . '... (' . strlen($imageBase64) . ' chars)';
    error_log("Sending to Runway API: " . json_encode($logPayload));

    $ch = curl_init($runwayApiEndpoint);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); // Return response as string
    curl_setopt($ch, CURLOPT_POST, true);           // Set as POST request
    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($runwayPayload)); // Encode payload to JSON
    curl_setopt($ch, CURLOPT_HTTPHEADER, [
        'Content-Type: application/json',
        'Authorization: Bearer ' . RUNWAY_API_KEY, // Use your RUNWAY_API_KEY from .env
        'X-Runway-Version: 2024-11-06' // Required API version header
    ]);
    // Optional: for debugging cURL
    // curl_setopt($ch, CURLOPT_VERBOSE, true);
    // $verbose = fopen('php://temp', 'rw+');
    // curl_setopt($ch, CURLOPT_STDERR, $verbose);

    $response = curl_exec($ch);
    $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
    $curlError = curl_error($ch);
    curl_close($ch);

    if ($response === false) {
        throw new Exception("cURL error connecting to Runway API: " . $curlError);
    }

    $runwayResult = json_decode($response, true);

    if ($httpCode >= 400) {
        // Attempt to extract more specific error message from Runway API response
        $errorMessage = 'Unknown Runway API error';
        if (isset($runwayResult['error']['message'])) {
            $errorMessage = $runwayResult['error']['message'];
        } elseif (isset($runwayResult['message'])) {
            $errorMessage = $runwayResult['message'];
        }
        throw new Exception("Runway API returned error ($httpCode): " . $errorMessage . ". Full response: " . json_encode($runwayResult));
    }

    // --- Handle Runway's async response ---
    $jobId = $runwayResult['id'] ?? null;
    
    if (empty($jobId)) {
        throw new Exception('Runway API did not return a job ID. Full response: ' . json_encode($runwayResult));
    }

    // For async generation, return job ID for polling
    echo json_encode([
        'status' => 'processing',
        'job_id' => $jobId,
        'message' => 'Video generation started. Please wait...'
    ]);

} catch (Exception $e) {
    error_log("Backend processing error: " . $e->getMessage());
    sendErrorResponse("Failed to generate video: " . $e->getMessage(), 500);
}