feat(core): add JSON-backed config store

src/Vantage.Core/Configuration/IConfigStore.cs

@@ -0,0 +1,12 @@
+using Vantage.Core.Models;
+
+namespace Vantage.Core.Configuration;
+
+public interface IConfigStore
+{
+    string Path { get; }
+
+    Task<VantageConfig> LoadAsync(CancellationToken cancellationToken = default);
+
+    Task SaveAsync(VantageConfig config, CancellationToken cancellationToken = default);
+}

src/Vantage.Core/Configuration/JsonConfigStore.cs

@@ -0,0 +1,50 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Vantage.Core.Models;
+
+namespace Vantage.Core.Configuration;
+
+public sealed class JsonConfigStore : IConfigStore
+{
+    private static readonly JsonSerializerOptions SerializerOptions = new()
+    {
+        WriteIndented = true,
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+        Converters = { new JsonStringEnumConverter(JsonNamingPolicy.CamelCase) }
+    };
+
+    public JsonConfigStore(string path)
+    {
+        Path = path;
+    }
+
+    public string Path { get; }
+
+    public static string DefaultPath()
+    {
+        var root = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
+        return System.IO.Path.Combine(root, "vantage", "config.json");
+    }
+
+    public async Task<VantageConfig> LoadAsync(CancellationToken cancellationToken = default)
+    {
+        if (!File.Exists(Path))
+            return new VantageConfig();
+
+        await using var stream = File.OpenRead(Path);
+        var config = await JsonSerializer
+            .DeserializeAsync<VantageConfig>(stream, SerializerOptions, cancellationToken)
+            .ConfigureAwait(false);
+        return config ?? new VantageConfig();
+    }
+
+    public async Task SaveAsync(VantageConfig config, CancellationToken cancellationToken = default)
+    {
+        var directory = System.IO.Path.GetDirectoryName(Path);
+        if (!string.IsNullOrEmpty(directory))
+            Directory.CreateDirectory(directory);
+
+        await using var stream = File.Create(Path);
+        await JsonSerializer.SerializeAsync(stream, config, SerializerOptions, cancellationToken).ConfigureAwait(false);
+    }
+}