[FA-misc] Translation engine work

Reviewed-on: #65

FictionArchive.Service.TranslationService.Tests/FictionArchive.Service.TranslationService.Tests.csproj

@@ -0,0 +1,29 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="FluentAssertions" Version="6.12.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="NSubstitute" Version="5.1.0" />
+    <PackageReference Include="xunit" Version="2.9.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+    <PackageReference Include="coverlet.collector" Version="6.0.2">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\FictionArchive.Service.TranslationService\FictionArchive.Service.TranslationService.csproj" />
+  </ItemGroup>
+
+</Project>

FictionArchive.Service.TranslationService.Tests/NanoGpt/NanoGptTranslationEngineTests.cs

@@ -0,0 +1,187 @@
+using System.Net;
+using System.Text;
+using System.Text.Json;
+using FictionArchive.Service.TranslationService.Models.Enums;
+using FictionArchive.Service.TranslationService.Services.TranslationEngines.NanoGpt;
+using FictionArchive.Service.TranslationService.Tests.TestSupport;
+using FluentAssertions;
+using Microsoft.Extensions.Logging.Abstractions;
+using Polly;
+using Xunit;
+using Language = FictionArchive.Common.Enums.Language;
+
+namespace FictionArchive.Service.TranslationService.Tests.NanoGpt;
+
+public class NanoGptTranslationEngineTests
+{
+    private static (NanoGptTranslationEngine engine, TestHttpMessageHandler handler)
+        BuildEngine(Func<HttpRequestMessage, HttpResponseMessage> responder, string modelKey = "nanogpt-test", string modelId = "test-model")
+    {
+        var handler = new TestHttpMessageHandler(responder);
+        var httpClient = new HttpClient(handler) { BaseAddress = new Uri("https://nano-gpt.test/api/") };
+        var apiClient = new NanoGptApiClient(httpClient, NullLogger<NanoGptApiClient>.Instance);
+        var options = new NanoGptModelOptions { Key = modelKey, DisplayName = "Test", Model = modelId };
+        var pipeline = new ResiliencePipelineBuilder().Build(); // no-retry pipeline for deterministic tests
+        var engine = new NanoGptTranslationEngine(apiClient, options, pipeline, NullLogger<NanoGptTranslationEngine>.Instance);
+        return (engine, handler);
+    }
+
+    private static HttpResponseMessage JsonResponse(HttpStatusCode status, string json)
+    {
+        return new HttpResponseMessage(status)
+        {
+            Content = new StringContent(json, Encoding.UTF8, "application/json")
+        };
+    }
+
+    private const string SuccessJson = """
+        {
+          "choices": [{"message": {"role":"assistant","content":"안녕, 세상."}}],
+          "usage": {"prompt_tokens": 10, "completion_tokens": 5, "total_tokens": 15}
+        }
+        """;
+
+    [Fact]
+    public void Descriptor_ReflectsConfiguredOptions()
+    {
+        var (engine, _) = BuildEngine(_ => JsonResponse(HttpStatusCode.OK, SuccessJson),
+            modelKey: "nanogpt-gpt-4o");
+
+        engine.Descriptor.Key.Should().Be("nanogpt-gpt-4o");
+        engine.Descriptor.DisplayName.Should().Be("Test");
+    }
+
+    [Fact]
+    public async Task GetTranslation_OnSuccess_ReturnsTranslatedTextAndUsage()
+    {
+        var (engine, _) = BuildEngine(_ => JsonResponse(HttpStatusCode.OK, SuccessJson));
+
+        var result = await engine.GetTranslation("Hello, world.", Language.En, Language.Kr);
+
+        result.Status.Should().Be(TranslationRequestStatus.Success);
+        result.TranslatedText.Should().Be("안녕, 세상.");
+        result.OriginalText.Should().Be("Hello, world.");
+        result.From.Should().Be(Language.En);
+        result.To.Should().Be(Language.Kr);
+        result.TranslationEngineKey.Should().Be("nanogpt-test");
+        result.BilledCharacterCount.Should().Be(15u);
+    }
+
+    [Fact]
+    public async Task GetTranslation_PostsToChatCompletionsEndpoint()
+    {
+        var (engine, handler) = BuildEngine(_ => JsonResponse(HttpStatusCode.OK, SuccessJson));
+
+        await engine.GetTranslation("Hello", Language.En, Language.Kr);
+
+        handler.Requests.Should().HaveCount(1);
+        var request = handler.Requests[0];
+        request.Method.Should().Be(HttpMethod.Post);
+        request.RequestUri!.AbsoluteUri.Should().Be("https://nano-gpt.test/api/v1/chat/completions");
+    }
+
+    [Fact]
+    public async Task GetTranslation_SendsConfiguredModelAndTemperature()
+    {
+        var (engine, handler) = BuildEngine(
+            _ => JsonResponse(HttpStatusCode.OK, SuccessJson),
+            modelId: "chatgpt-4o-latest");
+
+        await engine.GetTranslation("Hello", Language.En, Language.Kr);
+
+        var body = JsonDocument.Parse(handler.RequestBodies[0]).RootElement;
+        body.GetProperty("model").GetString().Should().Be("chatgpt-4o-latest");
+        body.GetProperty("temperature").GetDouble().Should().Be(0.2);
+    }
+
+    [Fact]
+    public async Task GetTranslation_WrapsSourceTextInDelimitersAndIncludesSystemPrompt()
+    {
+        var (engine, handler) = BuildEngine(_ => JsonResponse(HttpStatusCode.OK, SuccessJson));
+
+        await engine.GetTranslation("Hello", Language.En, Language.Kr);
+
+        var body = JsonDocument.Parse(handler.RequestBodies[0]).RootElement;
+        var messages = body.GetProperty("messages");
+        messages.GetArrayLength().Should().Be(2);
+
+        var system = messages[0];
+        system.GetProperty("role").GetString().Should().Be("system");
+        var systemContent = system.GetProperty("content").GetString()!;
+        systemContent.Should().Contain("English").And.Contain("Korean");
+        systemContent.Should().Contain("<source_text>").And.Contain("Output only the translated text");
+
+        var user = messages[1];
+        user.GetProperty("role").GetString().Should().Be("user");
+        user.GetProperty("content").GetString().Should().Be("<source_text>\nHello\n</source_text>");
+    }
+
+    [Theory]
+    [InlineData(Language.En, "English")]
+    [InlineData(Language.Kr, "Korean")]
+    [InlineData(Language.Ch, "Chinese")]
+    [InlineData(Language.Ja, "Japanese")]
+    public async Task GetTranslation_RendersExpectedLanguageNamesInSystemPrompt(Language to, string expectedName)
+    {
+        var (engine, handler) = BuildEngine(_ => JsonResponse(HttpStatusCode.OK, SuccessJson));
+
+        await engine.GetTranslation("Hello", Language.En, to);
+
+        var body = JsonDocument.Parse(handler.RequestBodies[0]).RootElement;
+        var systemContent = body.GetProperty("messages")[0].GetProperty("content").GetString()!;
+        systemContent.Should().Contain(expectedName);
+    }
+
+    [Fact]
+    public async Task GetTranslation_On4xx_ReturnsFailedResultWithoutThrowing()
+    {
+        var (engine, _) = BuildEngine(_ => JsonResponse(HttpStatusCode.BadRequest,
+            """{"error":"bad model"}"""));
+
+        var result = await engine.GetTranslation("Hello", Language.En, Language.Kr);
+
+        result.Status.Should().Be(TranslationRequestStatus.Failed);
+        result.TranslatedText.Should().BeNull();
+        result.TranslationEngineKey.Should().Be("nanogpt-test");
+        result.OriginalText.Should().Be("Hello");
+    }
+
+    [Fact]
+    public async Task GetTranslation_On5xx_ReturnsFailedResultWithoutThrowing()
+    {
+        var (engine, _) = BuildEngine(_ => JsonResponse(HttpStatusCode.InternalServerError, "{}"));
+
+        var result = await engine.GetTranslation("Hello", Language.En, Language.Kr);
+
+        result.Status.Should().Be(TranslationRequestStatus.Failed);
+        result.TranslatedText.Should().BeNull();
+    }
+
+    [Fact]
+    public async Task GetTranslation_OnMalformedJson_ReturnsFailedResult()
+    {
+        var (engine, _) = BuildEngine(_ => JsonResponse(HttpStatusCode.OK, "not json"));
+
+        var result = await engine.GetTranslation("Hello", Language.En, Language.Kr);
+
+        result.Status.Should().Be(TranslationRequestStatus.Failed);
+        result.TranslatedText.Should().BeNull();
+    }
+
+    [Fact]
+    public async Task GetTranslation_OnEmptyChoices_ReturnsFailedResult()
+    {
+        const string emptyChoicesJson = """
+            {
+              "choices": [],
+              "usage": {"prompt_tokens": 0, "completion_tokens": 0, "total_tokens": 0}
+            }
+            """;
+        var (engine, _) = BuildEngine(_ => JsonResponse(HttpStatusCode.OK, emptyChoicesJson));
+
+        var result = await engine.GetTranslation("Hello", Language.En, Language.Kr);
+
+        result.Status.Should().Be(TranslationRequestStatus.Failed);
+        result.TranslatedText.Should().BeNull();
+    }
+}

FictionArchive.Service.TranslationService.Tests/Resilience/TranslationResiliencePipelineTests.cs

@@ -0,0 +1,127 @@
+using DeepL;
+using FictionArchive.Service.TranslationService.Services.Resilience;
+using FluentAssertions;
+using Polly;
+using Xunit;
+
+namespace FictionArchive.Service.TranslationService.Tests.Resilience;
+
+public class TranslationResiliencePipelineTests
+{
+    [Fact]
+    public async Task RetriesTransientHttpRequestException_ThenSucceeds()
+    {
+        var pipeline = TranslationResiliencePipeline.Build();
+        var attempts = 0;
+
+        var result = await pipeline.ExecuteAsync(async _ =>
+        {
+            attempts++;
+            if (attempts < 3)
+            {
+                throw new HttpRequestException("transient");
+            }
+            return await ValueTask.FromResult("ok");
+        });
+
+        attempts.Should().Be(3);
+        result.Should().Be("ok");
+    }
+
+    [Fact]
+    public async Task RetriesDeepLConnectionException()
+    {
+        var pipeline = TranslationResiliencePipeline.Build();
+        var attempts = 0;
+
+        var result = await pipeline.ExecuteAsync(async _ =>
+        {
+            attempts++;
+            if (attempts < 2)
+            {
+                throw new ConnectionException("transient", new HttpRequestException("inner"));
+            }
+            return await ValueTask.FromResult("ok");
+        });
+
+        attempts.Should().Be(2);
+        result.Should().Be("ok");
+    }
+
+    [Fact]
+    public async Task RetriesDeepLTooManyRequestsException()
+    {
+        var pipeline = TranslationResiliencePipeline.Build();
+        var attempts = 0;
+
+        var result = await pipeline.ExecuteAsync(async _ =>
+        {
+            attempts++;
+            if (attempts < 2)
+            {
+                throw new TooManyRequestsException("rate limited");
+            }
+            return await ValueTask.FromResult("ok");
+        });
+
+        attempts.Should().Be(2);
+        result.Should().Be("ok");
+    }
+
+    [Fact]
+    public async Task DoesNotRetryNonTransientException()
+    {
+        var pipeline = TranslationResiliencePipeline.Build();
+        var attempts = 0;
+
+        var act = async () => await pipeline.ExecuteAsync(async _ =>
+        {
+            attempts++;
+            throw new ArgumentException("permanent");
+#pragma warning disable CS0162
+            return await ValueTask.FromResult("never");
+#pragma warning restore CS0162
+        });
+
+        await act.Should().ThrowAsync<ArgumentException>();
+        attempts.Should().Be(1);
+    }
+
+    [Fact]
+    public async Task DoesNotRetryDeepLAuthorizationException()
+    {
+        var pipeline = TranslationResiliencePipeline.Build();
+        var attempts = 0;
+
+        var act = async () => await pipeline.ExecuteAsync(async _ =>
+        {
+            attempts++;
+            throw new AuthorizationException("bad key");
+#pragma warning disable CS0162
+            return await ValueTask.FromResult("never");
+#pragma warning restore CS0162
+        });
+
+        await act.Should().ThrowAsync<AuthorizationException>();
+        attempts.Should().Be(1);
+    }
+
+    [Fact]
+    public async Task ExhaustsRetryBudget_ThenRethrows()
+    {
+        var pipeline = TranslationResiliencePipeline.Build();
+        var attempts = 0;
+
+        var act = async () => await pipeline.ExecuteAsync(async _ =>
+        {
+            attempts++;
+            throw new HttpRequestException("always transient");
+#pragma warning disable CS0162
+            return await ValueTask.FromResult("never");
+#pragma warning restore CS0162
+        });
+
+        await act.Should().ThrowAsync<HttpRequestException>();
+        attempts.Should().Be(4); // initial attempt + 3 retries
+    }
+}

FictionArchive.Service.TranslationService.Tests/TestSupport/TestHttpMessageHandler.cs

@@ -0,0 +1,25 @@
+namespace FictionArchive.Service.TranslationService.Tests.TestSupport;
+
+public sealed class TestHttpMessageHandler : HttpMessageHandler
+{
+    private readonly Func<HttpRequestMessage, HttpResponseMessage> _responder;
+
+    public List<HttpRequestMessage> Requests { get; } = new();
+    public List<string> RequestBodies { get; } = new();
+
+    public TestHttpMessageHandler(Func<HttpRequestMessage, HttpResponseMessage> responder)
+    {
+        _responder = responder;
+    }
+
+    protected override async Task<HttpResponseMessage> SendAsync(
+        HttpRequestMessage request, CancellationToken cancellationToken)
+    {
+        var bodyText = request.Content is null
+            ? string.Empty
+            : await request.Content.ReadAsStringAsync(cancellationToken);
+        Requests.Add(request);
+        RequestBodies.Add(bodyText);
+        return _responder(request);
+    }
+}

FictionArchive.Service.TranslationService/FictionArchive.Service.TranslationService.csproj

@@ -22,6 +22,7 @@
         </PackageReference>
         <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="9.0.4" />
         <PackageReference Include="DeepL.net" Version="1.17.0" />
+        <PackageReference Include="Polly" Version="8.6.5" />
         <PackageReference Include="Swashbuckle.AspNetCore" Version="6.6.2"/>
     </ItemGroup>
 

FictionArchive.Service.TranslationService/Program.cs

@@ -9,6 +9,10 @@ using FictionArchive.Service.TranslationService.Services;
 using FictionArchive.Service.TranslationService.Services.Database;
 using FictionArchive.Service.TranslationService.Services.TranslationEngines;
 using FictionArchive.Service.TranslationService.Services.TranslationEngines.DeepLTranslate;
+using System.Net.Http.Headers;
+using FictionArchive.Service.TranslationService.Services.Resilience;
+using FictionArchive.Service.TranslationService.Services.TranslationEngines.NanoGpt;
+using Polly;
 
 namespace FictionArchive.Service.TranslationService;
 
@@ -55,12 +59,44 @@ public class Program
         
         #region Translation Adapter
 
-        builder.Services.AddTransient<DeepLClient>(provider =>
-        {
-            return new DeepLClient(builder.Configuration["DeepL:ApiKey"]);
-        });
+        // Shared resilience pipeline used by both DeepL and NanoGPT engines.
+        builder.Services.AddSingleton(TranslationResiliencePipeline.Build());
+
+        // DeepL
+        builder.Services.AddTransient<DeepLClient>(_ => new DeepLClient(builder.Configuration["DeepL:ApiKey"]));
         builder.Services.AddTransient<ITranslationEngine, DeepLTranslationEngine>();
 
+        // NanoGPT — typed HttpClient (bearer auth + base address + 120s timeout).
+        builder.Services.AddHttpClient<NanoGptApiClient>(client =>
+        {
+            var baseAddress = builder.Configuration["NanoGpt:BaseAddress"];
+            if (!string.IsNullOrWhiteSpace(baseAddress))
+            {
+                client.BaseAddress = new Uri(baseAddress);
+            }
+
+            var apiKey = builder.Configuration["NanoGpt:ApiKey"];
+            if (!string.IsNullOrWhiteSpace(apiKey) && apiKey != "REPLACE_ME")
+            {
+                client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", apiKey);
+            }
+
+            client.Timeout = TimeSpan.FromSeconds(120);
+        });
+
+        // Register one ITranslationEngine per configured NanoGPT model.
+        var nanoGptModels = builder.Configuration
+            .GetSection("NanoGpt:Models")
+            .Get<NanoGptModelOptions[]>() ?? [];
+        foreach (var modelOptions in nanoGptModels)
+        {
+            builder.Services.AddTransient<ITranslationEngine>(sp => new NanoGptTranslationEngine(
+                sp.GetRequiredService<NanoGptApiClient>(),
+                modelOptions,
+                sp.GetRequiredService<ResiliencePipeline>(),
+                sp.GetRequiredService<ILogger<NanoGptTranslationEngine>>()));
+        }
+
         builder.Services.AddTransient<TranslationEngineService>();
 
         #endregion

FictionArchive.Service.TranslationService/Services/Resilience/TranslationResiliencePipeline.cs

@@ -0,0 +1,26 @@
+using DeepL;
+using Polly;
+using Polly.Retry;
+
+namespace FictionArchive.Service.TranslationService.Services.Resilience;
+
+public static class TranslationResiliencePipeline
+{
+    public static ResiliencePipeline Build()
+    {
+        return new ResiliencePipelineBuilder()
+            .AddRetry(new RetryStrategyOptions
+            {
+                ShouldHandle = new PredicateBuilder()
+                    .Handle<HttpRequestException>()
+                    .Handle<TaskCanceledException>(ex => ex.InnerException is TimeoutException)
+                    .Handle<ConnectionException>()
+                    .Handle<TooManyRequestsException>(),
+                MaxRetryAttempts = 3,
+                BackoffType = DelayBackoffType.Exponential,
+                Delay = TimeSpan.FromMilliseconds(500),
+                UseJitter = true
+            })
+            .Build();
+    }
+}

FictionArchive.Service.TranslationService/Services/TranslationEngines/DeepLTranslate/DeepLTranslationEngine.cs

@@ -2,6 +2,7 @@ using DeepL;
 using DeepL.Model;
 using FictionArchive.Service.TranslationService.Models;
 using FictionArchive.Service.TranslationService.Models.Enums;
+using Polly;
 using Language = FictionArchive.Common.Enums.Language;
 
 namespace FictionArchive.Service.TranslationService.Services.TranslationEngines.DeepLTranslate;
@@ -9,34 +10,38 @@ namespace FictionArchive.Service.TranslationService.Services.TranslationEngines.
 public class DeepLTranslationEngine : ITranslationEngine
 {
     private readonly DeepLClient _deepLClient;
+    private readonly ResiliencePipeline _pipeline;
     private readonly ILogger<DeepLTranslationEngine> _logger;
 
     private const string DisplayName = "DeepL";
     private const string Key = "deepl";
 
-    public DeepLTranslationEngine(DeepLClient deepLClient, ILogger<DeepLTranslationEngine> logger)
+    public DeepLTranslationEngine(
+        DeepLClient deepLClient,
+        ResiliencePipeline pipeline,
+        ILogger<DeepLTranslationEngine> logger)
     {
         _deepLClient = deepLClient;
+        _pipeline = pipeline;
         _logger = logger;
     }
 
-    public TranslationEngineDescriptor Descriptor
-    {
-        get
-        {
-            return new TranslationEngineDescriptor()
+    public TranslationEngineDescriptor Descriptor => new()
     {
         DisplayName = DisplayName,
         Key = Key,
     };
-        }
-    }
 
     public async Task<TranslationResult> GetTranslation(string body, Language from, Language to)
     {
-        TextResult translationResult = await _deepLClient.TranslateTextAsync(body, GetLanguageCode(from), GetLanguageCode(to));
-        _logger.LogInformation("Translated text. Usage statistics: CHARACTERS BILLED {TranslationResultBilledCharacters}", translationResult.BilledCharacters);
-        return new TranslationResult()
+        TextResult translationResult = await _pipeline.ExecuteAsync(
+            async _ => await _deepLClient.TranslateTextAsync(body, GetLanguageCode(from), GetLanguageCode(to)));
+
+        _logger.LogInformation(
+            "Translated text. Usage statistics: CHARACTERS BILLED {TranslationResultBilledCharacters}",
+            translationResult.BilledCharacters);
+
+        return new TranslationResult
         {
             OriginalText = body,
             From = from,

FictionArchive.Service.TranslationService/Services/TranslationEngines/NanoGpt/NanoGptApiClient.cs

@@ -0,0 +1,34 @@
+using System.Net.Http.Json;
+
+namespace FictionArchive.Service.TranslationService.Services.TranslationEngines.NanoGpt;
+
+public class NanoGptApiClient
+{
+    private readonly HttpClient _httpClient;
+    private readonly ILogger<NanoGptApiClient> _logger;
+
+    public NanoGptApiClient(HttpClient httpClient, ILogger<NanoGptApiClient> logger)
+    {
+        _httpClient = httpClient;
+        _logger = logger;
+    }
+
+    public async Task<NanoGptChatResponse> CompleteAsync(
+        string model,
+        IReadOnlyList<NanoGptMessage> messages,
+        double temperature,
+        CancellationToken ct = default)
+    {
+        var request = new NanoGptChatRequest(model, messages, temperature);
+
+        using var response = await _httpClient.PostAsJsonAsync("v1/chat/completions", request, ct);
+        response.EnsureSuccessStatusCode();
+
+        var body = await response.Content.ReadFromJsonAsync<NanoGptChatResponse>(ct);
+        if (body is null)
+        {
+            throw new InvalidOperationException("NanoGPT returned an empty response body.");
+        }
+        return body;
+    }
+}

FictionArchive.Service.TranslationService/Services/TranslationEngines/NanoGpt/NanoGptDtos.cs

@@ -0,0 +1,24 @@
+using System.Text.Json.Serialization;
+
+namespace FictionArchive.Service.TranslationService.Services.TranslationEngines.NanoGpt;
+
+public sealed record NanoGptMessage(
+    [property: JsonPropertyName("role")] string Role,
+    [property: JsonPropertyName("content")] string Content);
+
+public sealed record NanoGptChatRequest(
+    [property: JsonPropertyName("model")] string Model,
+    [property: JsonPropertyName("messages")] IReadOnlyList<NanoGptMessage> Messages,
+    [property: JsonPropertyName("temperature")] double Temperature);
+
+public sealed record NanoGptChatResponse(
+    [property: JsonPropertyName("choices")] IReadOnlyList<NanoGptChoice> Choices,
+    [property: JsonPropertyName("usage")] NanoGptUsage Usage);
+
+public sealed record NanoGptChoice(
+    [property: JsonPropertyName("message")] NanoGptMessage Message);
+
+public sealed record NanoGptUsage(
+    [property: JsonPropertyName("prompt_tokens")] int PromptTokens,
+    [property: JsonPropertyName("completion_tokens")] int CompletionTokens,
+    [property: JsonPropertyName("total_tokens")] int TotalTokens);

FictionArchive.Service.TranslationService/Services/TranslationEngines/NanoGpt/NanoGptModelOptions.cs

@@ -0,0 +1,8 @@
+namespace FictionArchive.Service.TranslationService.Services.TranslationEngines.NanoGpt;
+
+public sealed class NanoGptModelOptions
+{
+    public string Key { get; set; } = string.Empty;
+    public string DisplayName { get; set; } = string.Empty;
+    public string Model { get; set; } = string.Empty;
+}

FictionArchive.Service.TranslationService/Services/TranslationEngines/NanoGpt/NanoGptTranslationEngine.cs

@@ -0,0 +1,109 @@
+using FictionArchive.Service.TranslationService.Models;
+using FictionArchive.Service.TranslationService.Models.Enums;
+using Polly;
+using Language = FictionArchive.Common.Enums.Language;
+
+namespace FictionArchive.Service.TranslationService.Services.TranslationEngines.NanoGpt;
+
+public class NanoGptTranslationEngine : ITranslationEngine
+{
+    private const double Temperature = 0.2;
+
+    private const string SystemPromptTemplate =
+        "You are a professional translator. Translate the user's message from {0} to {1}. " +
+        "The source text is wrapped in <source_text> tags; translate only the contents of those tags. " +
+        "Preserve formatting (paragraphs, line breaks, punctuation). " +
+        "Do not add commentary, notes, or alternative translations. " +
+        "Output only the translated text, with no surrounding tags.";
+
+    private readonly NanoGptApiClient _apiClient;
+    private readonly NanoGptModelOptions _options;
+    private readonly ResiliencePipeline _pipeline;
+    private readonly ILogger<NanoGptTranslationEngine> _logger;
+
+    public NanoGptTranslationEngine(
+        NanoGptApiClient apiClient,
+        NanoGptModelOptions options,
+        ResiliencePipeline pipeline,
+        ILogger<NanoGptTranslationEngine> logger)
+    {
+        _apiClient = apiClient;
+        _options = options;
+        _pipeline = pipeline;
+        _logger = logger;
+    }
+
+    public TranslationEngineDescriptor Descriptor => new()
+    {
+        DisplayName = _options.DisplayName,
+        Key = _options.Key
+    };
+
+    public async Task<TranslationResult> GetTranslation(string body, Language from, Language to)
+    {
+        var systemPrompt = string.Format(SystemPromptTemplate, GetLanguageName(from), GetLanguageName(to));
+        var userPrompt = $"<source_text>\n{body}\n</source_text>";
+        var messages = new List<NanoGptMessage>
+        {
+            new("system", systemPrompt),
+            new("user", userPrompt)
+        };
+
+        try
+        {
+            var response = await _pipeline.ExecuteAsync(
+                async ct => await _apiClient.CompleteAsync(_options.Model, messages, Temperature, ct));
+
+            if (response.Choices.Count == 0)
+            {
+                _logger.LogWarning("NanoGPT returned no choices for model {Model}", _options.Model);
+                return Failed(body, from, to);
+            }
+
+            _logger.LogInformation(
+                "Translated text via {Model}. Tokens billed: {TotalTokens} (prompt {Prompt}, completion {Completion})",
+                _options.Model,
+                response.Usage.TotalTokens,
+                response.Usage.PromptTokens,
+                response.Usage.CompletionTokens);
+
+            return new TranslationResult
+            {
+                OriginalText = body,
+                From = from,
+                To = to,
+                TranslationEngineKey = _options.Key,
+                BilledCharacterCount = (uint)response.Usage.TotalTokens,
+                Status = TranslationRequestStatus.Success,
+                TranslatedText = response.Choices[0].Message.Content
+            };
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex,
+                "NanoGPT translation failed for model {Model} ({From} to {To})",
+                _options.Model, from, to);
+            return Failed(body, from, to);
+        }
+    }
+
+    private TranslationResult Failed(string body, Language from, Language to) => new()
+    {
+        OriginalText = body,
+        From = from,
+        To = to,
+        TranslationEngineKey = _options.Key,
+        Status = TranslationRequestStatus.Failed,
+        TranslatedText = null,
+        BilledCharacterCount = 0
+    };
+
+    private static string GetLanguageName(Language language) => language switch
+    {
+        Language.En => "English",
+        Language.Kr => "Korean",
+        Language.Ch => "Chinese",
+        Language.Ja => "Japanese",
+        _ => throw new ArgumentOutOfRangeException(nameof(language), language, null)
+    };
+}

FictionArchive.Service.TranslationService/appsettings.json

@@ -9,6 +9,11 @@
   "DeepL": {
     "ApiKey": "REPLACE_ME"
   },
+  "NanoGpt": {
+    "ApiKey": "REPLACE_ME",
+    "BaseAddress": "https://nano-gpt.com/api/",
+    "Models": []
+  },
   "ConnectionStrings": {
     "DefaultConnection": "Host=localhost;Database=FictionArchive_NovelService;Username=postgres;password=postgres"
   },

FictionArchive.sln

@@ -27,6 +27,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "FictionArchive.Service.Repo
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "FictionArchive.Service.ReportingService.Tests", "FictionArchive.Service.ReportingService.Tests\FictionArchive.Service.ReportingService.Tests.csproj", "{E704ACF1-2E1D-4A1C-BBCE-8FAE9F1A9944}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "FictionArchive.Service.TranslationService.Tests", "FictionArchive.Service.TranslationService.Tests\FictionArchive.Service.TranslationService.Tests.csproj", "{F57F475F-49C0-4454-966F-AB6A4199FF42}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -85,5 +87,9 @@ Global
 		{E704ACF1-2E1D-4A1C-BBCE-8FAE9F1A9944}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{E704ACF1-2E1D-4A1C-BBCE-8FAE9F1A9944}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{E704ACF1-2E1D-4A1C-BBCE-8FAE9F1A9944}.Release|Any CPU.Build.0 = Release|Any CPU
+		{F57F475F-49C0-4454-966F-AB6A4199FF42}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{F57F475F-49C0-4454-966F-AB6A4199FF42}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{F57F475F-49C0-4454-966F-AB6A4199FF42}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{F57F475F-49C0-4454-966F-AB6A4199FF42}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 EndGlobal