novelly/src/Novelly.Mcp/NovelApiClient.cs

using System.Net;
using System.Net.Http.Json;
using System.Text.Json;
using ModelContextProtocol.Protocol;

namespace Novelly.Mcp;

/// <summary>
/// Thin wrapper over the Novelly REST API. The MCP server deliberately owns no
/// domain logic of its own — it is a second front end onto the same API the web client
/// uses, so an edit made from Claude Code and one made in the browser are the same edit.
/// </summary>
public class NovelApiClient(HttpClient http)
{
    private static readonly JsonSerializerOptions Options = new(JsonSerializerDefaults.Web)
    {
        WriteIndented = true
    };

    public Task<CallToolResult> GetAsync(string path, CancellationToken ct = default) => SendAsync(new HttpRequestMessage(HttpMethod.Get, path), ct);

    public Task<CallToolResult> PostAsync(string path, object body, CancellationToken ct = default) =>
        SendAsync(new HttpRequestMessage(HttpMethod.Post, path)
        {
            Content = JsonContent.Create(body, options: Options)
        }, ct);

    public Task<CallToolResult> PatchAsync(string path, object body, CancellationToken ct = default) =>
        SendAsync(new HttpRequestMessage(HttpMethod.Patch, path)
        {
            Content = JsonContent.Create(body, options: Options)
        }, ct);

    public Task<CallToolResult> DeleteAsync(string path, CancellationToken ct = default) => SendAsync(new HttpRequestMessage(HttpMethod.Delete, path), ct);

    /// <summary>
    /// Sends the request and shapes the outcome as a tool result. Failures come back as
    /// `isError` results carrying the API's own message, rather than as exceptions the
    /// SDK would flatten into "an error occurred" — the model can act on the former.
    /// </summary>
    private async Task<CallToolResult> SendAsync(HttpRequestMessage request, CancellationToken ct)
    {
        HttpResponseMessage response;
        try
        {
            response = await http.SendAsync(request, ct);
        }
        catch (HttpRequestException ex)
        {
            // The API not being up is the most common failure here, and a bare connection
            // exception tells the model nothing actionable.
            return Error($"Could not reach the Novelly API at {http.BaseAddress}. Is it running? ({ex.Message})");
        }

        var body = await response.Content.ReadAsStringAsync(ct);

        if (response.IsSuccessStatusCode)
        {
            return Ok(string.IsNullOrWhiteSpace(body) ? "{\"ok\":true}" : Prettify(body));
        }

        var detail = TryReadProblemDetail(body) ?? body;
        return Error(response.StatusCode switch
        {
            HttpStatusCode.NotFound => $"Not found: {detail}",
            HttpStatusCode.BadRequest => $"Rejected: {detail}",
            _ => $"API returned {(int)response.StatusCode}: {detail}"
        });
    }

    private static CallToolResult Ok(string text) =>
        new() { Content = [new TextContentBlock { Text = text }] };

    private static CallToolResult Error(string message) =>
        new() { Content = [new TextContentBlock { Text = message }], IsError = true };

    /// <summary>Reformats the API's compact JSON so tool output reads well in a transcript.</summary>
    private static string Prettify(string json)
    {
        try
        {
            return JsonSerializer.Serialize(JsonSerializer.Deserialize<JsonElement>(json), Options);
        }
        catch (JsonException)
        {
            return json;
        }
    }

    private static string? TryReadProblemDetail(string body)
    {
        try
        {
            var problem = JsonSerializer.Deserialize<JsonElement>(body);
            return problem.TryGetProperty("detail", out var detail) ? detail.GetString() : null;
        }
        catch (JsonException)
        {
            return null;
        }
    }
}