feat(utils): add JsonPathReader utility for JSON file path navigation (#841)

- Add JsonPathReader class for reading JSON files with property path navigation
- Add JsonPathValue class with indexer and TryGetPathValue<T> support
- Integrate with ImportDataViewModel for KonoAsset folder auto-detection
- Add documentation in docs/11-json-utilities.md

Author: puk06

AvatarExplorer.Core/Services/IO/JsonPathReader.cs

@@ -0,0 +1,142 @@
+using System.Text.Json;
+using System.Text.Json.Nodes;
+
+namespace AvatarExplorer.Core.Services.IO;
+
+/// <summary>
+/// JSON ファイルを読み込み、プロパティを簡単に辿れる値として公開します。
+/// </summary>
+public sealed class JsonPathReader(string path)
+{
+    /// <summary>このリーダーに関連付けられたパスを取得します。</summary>
+    public string Path { get; } = path ?? throw new ArgumentNullException(nameof(path));
+
+    /// <summary>
+    /// <see cref="Path"/> の JSON ファイルを読み込みます。
+    /// </summary>
+    /// <returns>読み込んだ値。不正な JSON の場合は null。</returns>
+    public JsonPathValue? Read()
+    {
+        try
+        {
+            var node = JsonNode.Parse(File.ReadAllText(Path));
+            return node is null ? null : new JsonPathValue(node);
+        }
+        catch (JsonException)
+        {
+            return null;
+        }
+    }
+}
+
+/// <summary>
+/// JSON の値をプロパティパスで読み取るための薄いラッパーです。
+/// </summary>
+public sealed class JsonPathValue
+{
+    private readonly JsonNode _node;
+
+    internal JsonPathValue(JsonNode node) => _node = node;
+
+    /// <summary>内部の <see cref="JsonNode"/> を取得します。</summary>
+    public JsonNode Node => _node;
+
+    /// <summary>
+    /// JSON オブジェクトのプロパティを取得します。値がプリミティブの場合は CLR 値を返します。
+    /// </summary>
+    /// <param name="propertyName">取得するプロパティ名。</param>
+    /// <returns>プロパティ値、または存在しない場合は null。</returns>
+    public dynamic? this[string propertyName]
+    {
+        get
+        {
+            if (_node is not JsonObject jsonObject || !jsonObject.TryGetPropertyValue(propertyName, out var value))
+            {
+                return null;
+            }
+
+            return Wrap(value);
+        }
+    }
+
+    /// <summary>
+    /// JSON 配列の要素を取得します。
+    /// </summary>
+    /// <param name="index">取得する配列インデックス。</param>
+    /// <returns>配列要素、または範囲外の場合は null。</returns>
+    public dynamic? this[int index]
+    {
+        get
+        {
+            if (_node is not JsonArray jsonArray || index < 0 || index >= jsonArray.Count)
+            {
+                return null;
+            }
+
+            return Wrap(jsonArray[index]);
+        }
+    }
+
+    /// <summary>
+    /// ドット区切りのプロパティパスから値を取得します。
+    /// 配列は数値のパス要素（例: <c>items.0.name</c>）で指定できます。
+    /// </summary>
+    public bool TryGetPathValue<T>(string path, out T? result)
+    {
+        ArgumentNullException.ThrowIfNull(path);
+
+        JsonNode? current = _node;
+        foreach (var part in path.Split('.', StringSplitOptions.RemoveEmptyEntries))
+        {
+            current = current switch
+            {
+                JsonObject obj when obj.TryGetPropertyValue(part, out var value) => value,
+                JsonArray array when int.TryParse(part, out var index) && index >= 0 && index < array.Count => array[index],
+                _ => null
+            };
+
+            if (current is null)
+            {
+                result = default;
+                return false;
+            }
+        }
+
+        try
+        {
+            result = current.Deserialize<T>(JsonManager.JsonSerializerOptions);
+            return true;
+        }
+        catch (JsonException)
+        {
+            result = default;
+            return false;
+        }
+    }
+
+    private static object? Wrap(JsonNode? node)
+    {
+        if (node is JsonObject or JsonArray)
+        {
+            return new JsonPathValue(node);
+        }
+
+        if (node is not JsonValue value)
+        {
+            return null;
+        }
+
+        using var document = JsonDocument.Parse(value.ToJsonString());
+        var element = document.RootElement;
+        return element.ValueKind switch
+        {
+            JsonValueKind.String => element.GetString(),
+            JsonValueKind.Number when element.TryGetInt64(out var integer) => integer,
+            JsonValueKind.Number when element.TryGetDecimal(out var decimalValue) => decimalValue,
+            JsonValueKind.Number => element.GetDouble(),
+            JsonValueKind.True => true,
+            JsonValueKind.False => false,
+            _ => null
+        };
+    }
+}

AvatarExplorer.UI/ViewModels/Overlays/ImportDataViewModel.cs

@@ -3,6 +3,7 @@
 using AvatarExplorer.Core.Extensions;
 using AvatarExplorer.Core.Localization;
 using AvatarExplorer.Core.Models.External;
+using AvatarExplorer.Core.Services.IO;
 using AvatarExplorer.UI.Interfaces;
 using AvatarExplorer.UI.Localization;
 using AvatarExplorer.UI.Services;
@@ -53,7 +54,18 @@ public ImportDataViewModel()
     public async Task Initialize()
     {
         this.WhenAnyValue(x => x.SelectedImportSourceIndex)
-            .Subscribe(_ => CanImportThumbnails = SelectedImportSource != DataImportType.Folder);
+            .Subscribe(_ =>
+            {
+                CanImportThumbnails = SelectedImportSource != DataImportType.Folder;
+                if (SelectedImportSource == DataImportType.KonoAsset && TryGetKonoAssetFolderPath(out var path))
+                {
+                    FolderPath = path;
+                }
+                else
+                {
+                    FolderPath = string.Empty;
+                }
+            });
 
         Localizer.Instance.LanguageChanged += OnLanguageChanged;
         OnLanguageChanged();
@@ -135,5 +147,27 @@ await NotificationManager.ShowWithProgress(
         }
     }
 
+    private static bool TryGetKonoAssetFolderPath(out string path)
+    {
+        path = string.Empty;
+
+        var appDataPath = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
+        var konoAssetFolderPath = Path.Combine(appDataPath, "dev.konoasset.app");
+        var preferenceFilePath = Path.Combine(konoAssetFolderPath, "preference.json");
+
+        if (!File.Exists(preferenceFilePath)) return false;
+
+        var reader = new JsonPathReader(preferenceFilePath);
+        var value = reader.Read();
+
+        if (value?.TryGetPathValue<string>("data.dataDirPath", out var dataDirPath) == true && !string.IsNullOrEmpty(dataDirPath))
+        {
+            path = dataDirPath;
+            return true;
+        }
+
+        return false;
+    }
+
     private void Close() => IsVisible = false;
 }