Switch AI diagnostics from OpenAI to Mistral and use .env for API key

- Changed API endpoint to api.mistral.ai, model to mistral-small-latest
- Replaced openAiConfig.json with .env file for secure API key storage
- Added .env loader in Program.cs, added .env to .gitignore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -3,4 +3,4 @@
 **/obj
 *.DotSettings.user
 **/.idea/
-
+**/.env

csharp/App/Backend/Backend.csproj

@@ -43,6 +43,9 @@
       <None Update="Resources/s3cmd.py">
         <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
       </None>
+      <None Update=".env">
+        <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+      </None>
       <None Remove="DbBackups\db-1698326303.sqlite" />
       <None Remove="DbBackups\db-1698327045.sqlite" />
       <None Remove="DbBackups\db-1699453468.sqlite" />

csharp/App/Backend/Controller.cs

@@ -741,7 +741,7 @@ public class Controller : ControllerBase
     /// <summary>
     /// Returns an AI-generated diagnosis for a single error/alarm description.
     /// Responses are cached in memory — repeated calls for the same error code
-    /// do not hit OpenAI again.
+    /// do not hit Mistral again.
     /// </summary>
     [HttpGet(nameof(DiagnoseError))]
     public async Task<ActionResult<DiagnosticResponse>> DiagnoseError(Int64 installationId, string errorDescription, Token authToken)
@@ -791,7 +791,7 @@ public class Controller : ControllerBase
             "Warning 500",
             "Error 408",
             "AFCI Fault",
-            // Unknown alarm (should return null - would call OpenAI)
+            // Unknown alarm (should return null - would call Mistral)
             "Some unknown alarm XYZ123"
         };
 
@@ -803,7 +803,7 @@ public class Controller : ControllerBase
             {
                 Alarm = alarm,
                 FoundInKnowledgeBase = diagnosis != null,
-                Explanation = diagnosis?.Explanation ?? "NOT FOUND - Would call OpenAI API",
+                Explanation = diagnosis?.Explanation ?? "NOT FOUND - Would call Mistral API",
                 CausesCount = diagnosis?.Causes.Count ?? 0,
                 NextStepsCount = diagnosis?.NextSteps.Count ?? 0
             });
@@ -814,7 +814,7 @@ public class Controller : ControllerBase
             TestTime = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"),
             TotalTests = testCases.Length,
             FoundInKnowledgeBase = results.Count(r => ((dynamic)r).FoundInKnowledgeBase),
-            WouldCallOpenAI = results.Count(r => !((dynamic)r).FoundInKnowledgeBase),
+            WouldCallMistral = results.Count(r => !((dynamic)r).FoundInKnowledgeBase),
             Results = results
         });
     }

csharp/App/Backend/Program.cs

@@ -25,6 +25,7 @@ public static class Program
         
         Watchdog.NotifyReady();
         Db.Init();
+        LoadEnvFile();
         DiagnosticService.Initialize();
         var builder = WebApplication.CreateBuilder(args);
         
@@ -89,6 +90,33 @@ public static class Program
         app.Run();
     }
 
+    private static void LoadEnvFile()
+    {
+        var envPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, ".env");
+
+        if (!File.Exists(envPath))
+            envPath = ".env"; // fallback for dev
+
+        if (!File.Exists(envPath))
+            return;
+
+        foreach (var line in File.ReadAllLines(envPath))
+        {
+            var trimmed = line.Trim();
+            if (trimmed.Length == 0 || trimmed.StartsWith('#'))
+                continue;
+
+            var idx = trimmed.IndexOf('=');
+            if (idx <= 0)
+                continue;
+
+            var key   = trimmed[..idx].Trim();
+            var value = trimmed[(idx + 1)..].Trim();
+
+            Environment.SetEnvironmentVariable(key, value);
+        }
+    }
+
     private static OpenApiInfo OpenApiInfo { get; } = new OpenApiInfo
     {
         Title = "Inesco Backend API",

csharp/App/Backend/Resources/openAiConfig.json

@@ -1,3 +0,0 @@
-{
-  "ApiKey": "sk-your-openai-api-key-here"
-}

csharp/App/Backend/Services/AlarmKnowledgeBase.cs

@@ -4,7 +4,7 @@ namespace InnovEnergy.App.Backend.Services;
 
 /// <summary>
 /// Static knowledge base for Sinexcel and Growatt alarms.
-/// Provides pre-defined diagnostics without requiring OpenAI API calls.
+/// Provides pre-defined diagnostics without requiring Mistral API calls.
 /// Data sourced from vendor alarm documentation.
 /// </summary>
 public static class AlarmKnowledgeBase

csharp/App/Backend/Services/DiagnosticService.cs

@@ -7,7 +7,7 @@ using Newtonsoft.Json;
 namespace InnovEnergy.App.Backend.Services;
 
 /// <summary>
-/// Calls OpenAI to generate plain-English diagnostics for errors/warnings.
+/// Calls Mistral AI to generate plain-English diagnostics for errors/warnings.
 /// Caches responses in-memory keyed by error description so the same
 /// error code is only sent to the API once.
 /// </summary>
@@ -22,30 +22,15 @@ public static class DiagnosticService
 
     public static void Initialize()
     {
-        var configPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Resources", "openAiConfig.json");
+        var apiKey = Environment.GetEnvironmentVariable("MISTRAL_API_KEY");
 
-        if (!File.Exists(configPath))
+        if (string.IsNullOrWhiteSpace(apiKey))
         {
-            // Fallback: look relative to the working directory (useful in dev)
-            configPath = Path.Combine("Resources", "openAiConfig.json");
-        }
-
-        if (!File.Exists(configPath))
-        {
-            Console.Error.WriteLine("[DiagnosticService] openAiConfig.json not found – AI diagnostics disabled.");
+            Console.Error.WriteLine("[DiagnosticService] MISTRAL_API_KEY not set – AI diagnostics disabled.");
             return;
         }
 
-        var json   = File.ReadAllText(configPath);
-        var config = JsonConvert.DeserializeObject<OpenAiConfig>(json);
-
-        if (config is null || string.IsNullOrWhiteSpace(config.ApiKey))
-        {
-            Console.Error.WriteLine("[DiagnosticService] ApiKey is empty – AI diagnostics disabled.");
-            return;
-        }
-
-        _apiKey = config.ApiKey;
+        _apiKey = apiKey;
         Console.WriteLine("[DiagnosticService] initialised.");
     }
 
@@ -56,7 +41,7 @@ public static class DiagnosticService
     /// <summary>
     /// Returns a diagnosis for <paramref name="errorDescription"/>.
     /// First checks the static AlarmKnowledgeBase for known Sinexcel/Growatt alarms.
-    /// Falls back to in-memory cache, then calls OpenAI only for unknown alarms.
+    /// Falls back to in-memory cache, then calls Mistral AI only for unknown alarms.
     /// </summary>
     public static async Task<DiagnosticResponse?> DiagnoseAsync(Int64 installationId, string errorDescription)
     {
@@ -89,10 +74,10 @@ public static class DiagnosticService
             .Take(5)
             .ToList();
 
-        // 5. Build prompt and call OpenAI API (only for unknown alarms)
-        Console.WriteLine($"[DiagnosticService] Calling OpenAI for unknown alarm: {errorDescription}");
+        // 5. Build prompt and call Mistral API (only for unknown alarms)
+        Console.WriteLine($"[DiagnosticService] Calling Mistral for unknown alarm: {errorDescription}");
         var prompt   = BuildPrompt(errorDescription, productName, recentDescriptions);
-        var response = await CallOpenAiAsync(prompt);
+        var response = await CallMistralAsync(prompt);
 
         if (response is null) return null;
 
@@ -121,17 +106,17 @@ Reply with ONLY valid JSON, no markdown:
 ";
     }
 
-    // ── OpenAI HTTP call ────────────────────────────────────────────
+    // ── Mistral HTTP call ────────────────────────────────────────────
 
-    private static readonly string OpenAiUrl = "https://api.openai.com/v1/chat/completions";
+    private static readonly string MistralUrl = "https://api.mistral.ai/v1/chat/completions";
 
-    private static async Task<DiagnosticResponse?> CallOpenAiAsync(string userPrompt)
+    private static async Task<DiagnosticResponse?> CallMistralAsync(string userPrompt)
     {
         try
         {
             var requestBody = new
             {
-                model = "gpt-4o-mini",          // cost-efficient, fast; swap to "gpt-4" if quality needs tuning
+                model = "mistral-small-latest",  // cost-efficient, fast; swap to "mistral-large-latest" if quality needs tuning
                 messages = new[]
                 {
                     new { role = "user", content = userPrompt }
@@ -140,19 +125,19 @@ Reply with ONLY valid JSON, no markdown:
                 temperature = 0.2               // low temperature for factual consistency
             };
 
-            var responseText = await OpenAiUrl
+            var responseText = await MistralUrl
                 .SetHeader("Authorization", $"Bearer {_apiKey}")
                 .SetHeader("Content-Type", "application/json")
                 .PostJsonAsync(requestBody)
                 .ReceiveString();
 
-            // parse OpenAI envelope
+            // parse Mistral envelope (same structure as OpenAI)
             var envelope = JsonConvert.DeserializeObject<dynamic>(responseText);
             var content  = (string?) envelope?.choices?[0]?.message?.content;
 
             if (string.IsNullOrWhiteSpace(content))
             {
-                Console.Error.WriteLine("[DiagnosticService] OpenAI returned empty content.");
+                Console.Error.WriteLine("[DiagnosticService] Mistral returned empty content.");
                 return null;
             }
 
@@ -175,11 +160,6 @@ Reply with ONLY valid JSON, no markdown:
 
 // ── config / response models ────────────────────────────────────────────────
 
-public class OpenAiConfig
-{
-    public string ApiKey { get; set; } = "";
-}
-
 public class DiagnosticResponse
 {
     public string               Explanation { get; set; } = "";