<?php

namespace App\Core;

use App\Services\InvoiceExtractionService;

/**
 * Gemini AI Integration for Invoice Extraction
 * Optimized for Jordan UBL 2.1 Compliance
 */
class AI
{
    private static string $baseUrl = "https://generativelanguage.googleapis.com/v1beta/models/gemini-flash-lite-latest:generateContent";

    private static int $maxRetries = 3;

    /**
     * Extract Data from Invoice Image or PDF (Base64)
     */
    public static function extractInvoiceData(string $base64Data, string $mimeType): ?array
    {
        $apiKey = env('GEMINI_API_KEY');
        if (!$apiKey) {
            error_log('AI Error: GEMINI_API_KEY is missing');
            return null;
        }

        $service = new InvoiceExtractionService();
        $prompt = $service->buildExtractionPrompt();

        $payload = [
            "contents" => [
                [
                    "parts" => [
                        ["text" => $prompt . " If the image is not an invoice, is blank, or is completely unreadable, return ONLY: {\"error\": \"invalid_invoice\"}. DO NOT guess or invent data."],
                        [
                            "inline_data" => [
                                "mime_type" => $mimeType,
                                "data" => $base64Data
                            ]
                        ]
                    ]
                ]
            ],
            "generationConfig" => [
                "response_mime_type" => "application/json"
            ]
        ];

        // Retry with exponential backoff for 503/429 errors
        for ($attempt = 1; $attempt <= self::$maxRetries; $attempt++) {
            $ch = curl_init(self::$baseUrl . "?key=" . $apiKey);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
            curl_setopt($ch, CURLOPT_POST, true);
            curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($payload));
            curl_setopt($ch, CURLOPT_HTTPHEADER, ['Content-Type: application/json']);
            curl_setopt($ch, CURLOPT_TIMEOUT, 60);
            
            $response = curl_exec($ch);
            $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
            $curlError = curl_error($ch);
            curl_close($ch);

            if ($curlError) {
                error_log("AI Error: cURL failed (attempt $attempt): $curlError");
                if ($attempt < self::$maxRetries) {
                    $wait = pow(2, $attempt) + rand(1, 3);
                    echo "  Retrying in {$wait}s (cURL error)...\n";
                    sleep($wait);
                    continue;
                }
                return null;
            }

            if ($httpCode === 200) {
                break; // Success
            }

            // Retry on 503 (overloaded) or 429 (rate limit)
            if (in_array($httpCode, [503, 429]) && $attempt < self::$maxRetries) {
                $wait = pow(2, $attempt) + rand(1, 3);
                echo "  Gemini $httpCode — retrying in {$wait}s (attempt $attempt/" . self::$maxRetries . ")...\n";
                sleep($wait);
                continue;
            }

            error_log("AI Error: Gemini API returned code $httpCode. Response: " . $response);
            return null;
        }

        if ($httpCode !== 200) {
            error_log("AI Error: All retries exhausted. Last code: $httpCode");
            return null;
        }

        $result = json_decode($response, true);
        $textResponse = $result['candidates'][0]['content']['parts'][0]['text'] ?? null;

        if (!$textResponse) return null;

        $data = json_decode($textResponse, true);
        if (isset($data['error']) && $data['error'] === 'invalid_invoice') {
            return null;
        }

        return $data;
    }
}
