145 lines
5.0 KiB
Dart
145 lines
5.0 KiB
Dart
import 'dart:convert';
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import 'package:flutter_dotenv/flutter_dotenv.dart';
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import 'package:google_generative_ai/google_generative_ai.dart';
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import 'package:http/http.dart' as http;
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class GeminiService {
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static final GeminiService _instance = GeminiService._internal();
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late final String _apiKey;
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/// Cache of valid model IDs (flash/lite, supporting generateContent).
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List<String> _validModels = [];
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factory GeminiService() => _instance;
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GeminiService._internal() {
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final apiKey = dotenv.env['GEMINI_API_KEY'];
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if (apiKey == null || apiKey.isEmpty) {
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throw Exception('GEMINI_API_KEY not found in .env file');
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}
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_apiKey = apiKey;
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}
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// ---------------------------------------------------------------------------
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// Model discovery
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// ---------------------------------------------------------------------------
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/// Queries the Gemini REST API for available models and caches those that
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/// - support `generateContent`, AND
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/// - contain "flash" or "lite" in their name (free-tier / fast models).
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///
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/// Returns a stable cached list on subsequent calls.
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Future<List<String>> _getValidModels() async {
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if (_validModels.isNotEmpty) return _validModels;
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try {
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final uri = Uri.parse(
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'https://generativelanguage.googleapis.com/v1beta/models?key=$_apiKey',
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);
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final response = await http.get(uri);
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if (response.statusCode == 200) {
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final data = jsonDecode(response.body) as Map<String, dynamic>;
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final rawModels = (data['models'] as List<dynamic>?) ?? [];
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final discovered = <String>[];
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for (final m in rawModels) {
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final fullName = (m['name'] as String? ?? '');
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final lower = fullName.toLowerCase();
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final methods =
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(m['supportedGenerationMethods'] as List<dynamic>?) ?? [];
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if (methods.contains('generateContent') &&
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(lower.contains('flash') || lower.contains('lite'))) {
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// Strip the "models/" prefix so it can be passed directly to
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// GenerativeModel(model: ...).
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final id = fullName.startsWith('models/')
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? fullName.substring('models/'.length)
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: fullName;
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discovered.add(id);
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}
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}
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// Sort descending so newer/more-capable models are tried first.
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discovered.sort((a, b) => b.compareTo(a));
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_validModels = discovered;
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}
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} catch (_) {
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// Fall back to hard-coded list of known free-tier models below.
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}
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// If discovery failed or returned nothing, use safe known fallbacks.
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if (_validModels.isEmpty) {
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_validModels = [
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'gemini-2.5-flash-lite',
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'gemini-2.5-flash',
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'gemini-2.0-flash',
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'gemini-1.5-flash',
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];
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}
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return _validModels;
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}
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// ---------------------------------------------------------------------------
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// Public API
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// ---------------------------------------------------------------------------
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/// Fixes spelling/grammar, improves clarity, and translates [text] to
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/// professional English.
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///
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/// Provide a custom [promptInstruction] to give Gemini field-specific
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/// context (subject, description, action-taken). If omitted a sensible
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/// default is used.
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///
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/// Automatically retries with the next available model on 429 / quota
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/// errors to minimise wasted quota calls.
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Future<String> enhanceText(String text, {String? promptInstruction}) async {
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if (text.trim().isEmpty) return text;
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final instruction =
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promptInstruction ??
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'Fix spelling and grammar, improve clarity, and translate to '
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'professional English. Return ONLY the improved text, no explanations:';
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final prompt = '$instruction\n\n"$text"';
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return _generateWithRetry(prompt, fallback: text);
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}
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// ---------------------------------------------------------------------------
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// Internal helpers
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// ---------------------------------------------------------------------------
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/// Sends [prompt] to Gemini, retrying across all valid models on 429 errors.
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/// Returns the model response on success, or throws if all models fail.
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Future<String> _generateWithRetry(
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String prompt, {
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required String fallback,
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}) async {
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final models = await _getValidModels();
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for (int i = 0; i < models.length; i++) {
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try {
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final model = GenerativeModel(model: models[i], apiKey: _apiKey);
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final response = await model.generateContent([Content.text(prompt)]);
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return response.text ?? fallback;
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} catch (e) {
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final msg = e.toString().toLowerCase();
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final is429 =
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msg.contains('429') ||
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msg.contains('quota') ||
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msg.contains('resource_exhausted');
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if (!is429 || i == models.length - 1) {
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// Non-quota error or last model — give up.
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throw Exception('Gemini request failed: $e');
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}
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// Quota hit — try the next model.
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}
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}
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// Should not reach here, but safety fallback.
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throw Exception('All Gemini models exhausted');
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}
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}
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