feat: dynamic model selection for Gemini Flash, Pro, and Gemma

lib/main.dart

@@ -314,14 +314,21 @@ class _TranscriptionScreenState extends State<TranscriptionScreen> with SingleTi
             child: Column(
               crossAxisAlignment: CrossAxisAlignment.start,
               children: [
-                // App header
-                const Text(
-                  'DocPilot',
-                  style: TextStyle(
-                    fontSize: 28,
-                    fontWeight: FontWeight.bold,
-                    color: Colors.white,
-                  ),
+                // App header row with model picker
+                Row(
+                  mainAxisAlignment: MainAxisAlignment.spaceBetween,
+                  crossAxisAlignment: CrossAxisAlignment.center,
+                  children: [
+                    const Text(
+                      'DocPilot',
+                      style: TextStyle(
+                        fontSize: 28,
+                        fontWeight: FontWeight.bold,
+                        color: Colors.white,
+                      ),
+                    ),
+                    _buildModelPicker(),
+                  ],
                 ),
                 const SizedBox(height: 8),
                 Text(
@@ -330,7 +337,7 @@ class _TranscriptionScreenState extends State<TranscriptionScreen> with SingleTi
                       : _isTranscribing
                       ? 'Transcribing your voice...'
                       : _isProcessing
-                      ? 'Processing with Gemini...'
+                      ? 'Processing with ${_chatbotService.selectedModel.displayName}...'
                       : 'Tap the mic to begin',
                   style: const TextStyle(
                     fontSize: 16,
@@ -502,6 +509,44 @@ class _TranscriptionScreenState extends State<TranscriptionScreen> with SingleTi
     );
   }
 
+  Widget _buildModelPicker() {
+    return PopupMenuButton<GeminiModel>(
+      initialValue: _chatbotService.selectedModel,
+      tooltip: 'Select AI model',
+      icon: const Icon(Icons.tune, color: Colors.white70, size: 22),
+      color: Colors.deepPurple.shade700,
+      onSelected: (model) {
+        setState(() {
+          _chatbotService.selectedModel = model;
+        });
+      },
+      itemBuilder: (_) => GeminiModel.values.map((model) {
+        return PopupMenuItem<GeminiModel>(
+          value: model,
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            mainAxisSize: MainAxisSize.min,
+            children: [
+              Text(
+                model.displayName,
+                style: TextStyle(
+                  color: Colors.white,
+                  fontWeight: _chatbotService.selectedModel == model
+                      ? FontWeight.bold
+                      : FontWeight.normal,
+                ),
+              ),
+              Text(
+                model.description,
+                style: const TextStyle(fontSize: 11, color: Colors.white60),
+              ),
+            ],
+          ),
+        );
+      }).toList(),
+    );
+  }
+
   // Helper method to build navigation buttons
   Widget _buildNavigationButton(
       BuildContext context,

lib/services/chatbot_service.dart

@@ -3,45 +3,94 @@ import 'dart:developer' as developer;
 import 'package:http/http.dart' as http;
 import 'package:flutter_dotenv/flutter_dotenv.dart';
 
+/// Supported Gemini/Gemma models via the Gemini API.
+enum GeminiModel {
+  flash('gemini-2.0-flash', 'Gemini 2.0 Flash', 'Fast responses, good for most tasks'),
+  pro('gemini-1.5-pro', 'Gemini 1.5 Pro', 'Higher accuracy for complex reasoning'),
+  gemma('gemma-3-27b-it', 'Gemma 3 27B', 'Open-weight model, efficient summarisation');
+
+  final String modelId;
+  final String displayName;
+  final String description;
+
+  const GeminiModel(this.modelId, this.displayName, this.description);
+}
+
 class ChatbotService {
-  // Get API key from .env file
-  final String apiKey = dotenv.env['GEMINI_API_KEY'] ?? '';
+  final String _apiKey = dotenv.env['GEMINI_API_KEY'] ?? '';
+
+  GeminiModel selectedModel;
+
+  ChatbotService({this.selectedModel = GeminiModel.flash});
+
+  bool get hasValidApiKey {
+    final trimmed = _apiKey.trim();
+    if (trimmed.isEmpty) return false;
+    final lower = trimmed.toLowerCase();
+    return !lower.contains('your_gemini_api_key_here') &&
+        !lower.contains('replace_with') &&
+        !lower.contains('example') &&
+        !lower.contains('dummy');
+  }
 
-  // Get a response from Gemini based on a prompt
   Future<String> getGeminiResponse(String prompt) async {
-    print('\n=== GEMINI PROMPT ===');
-    print(prompt);
+    if (!hasValidApiKey) {
+      return 'Error: GEMINI_API_KEY is missing. Add it to your .env file.';
+    }
+
+    developer.log(
+      'Sending prompt to ${selectedModel.displayName}',
+      name: 'ChatbotService',
+    );
 
-    final url = Uri.parse('https://generativelanguage.googleapis.com/v1beta/models/gemini-2.0-flash:generateContent?key=$apiKey');
+    final url = Uri.parse(
+      'https://generativelanguage.googleapis.com/v1beta/models/${selectedModel.modelId}:generateContent?key=$_apiKey',
+    );
 
     try {
       final response = await http.post(
         url,
         headers: {'Content-Type': 'application/json'},
         body: jsonEncode({
-          "contents": [{"parts": [{"text": prompt}]}],
-          "generationConfig": {
-            "temperature": 0.7,
-            "maxOutputTokens": 1024
-          }
+          'contents': [
+            {
+              'parts': [
+                {'text': prompt}
+              ]
+            }
+          ],
+          'generationConfig': {
+            'temperature': 0.7,
+            'maxOutputTokens': 1024,
+          },
         }),
-      );
+      ).timeout(const Duration(seconds: 30));
 
       if (response.statusCode == 200) {
         final data = jsonDecode(response.body);
-        final result = data['candidates'][0]['content']['parts'][0]['text'];
-
-        print('\n=== GEMINI RESPONSE ===');
-        print(result);
-
-        return result;
+        final candidates = data['candidates'];
+        if (candidates is List && candidates.isNotEmpty) {
+          final text = candidates[0]['content']?['parts']?[0]?['text'];
+          if (text is String && text.trim().isNotEmpty) {
+            developer.log('Response received from ${selectedModel.displayName}', name: 'ChatbotService');
+            return text;
+          }
+        }
+        return 'Error: Unexpected response format from ${selectedModel.displayName}.';
       } else {
-        print('API Error: ${response.statusCode}');
-        return "Error: Could not generate response. Status code: ${response.statusCode}";
+        String message = 'Error: ${selectedModel.displayName} request failed (status ${response.statusCode}).';
+        try {
+          final apiError = jsonDecode(response.body)['error']?['message'];
+          if (apiError is String && apiError.trim().isNotEmpty) {
+            message = 'Error: $apiError';
+          }
+        } catch (_) {}
+        developer.log('API error ${response.statusCode}: ${response.body}', name: 'ChatbotService');
+        return message;
       }
     } catch (e) {
-      print('Exception: $e');
-      return "Error: Could not connect to API: $e";
+      developer.log('Request failed: $e', name: 'ChatbotService', error: e);
+      return 'Error: Could not reach ${selectedModel.displayName}. Check your connection and try again.';
     }
   }
 }