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src/WireMock.Net.Shared/Transformers/SystemTextJsonBodyTransformer.cs

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+// Copyright © WireMock.Net
+
+using System.Collections;
+using System.Text.Json;
+using System.Text.Json.Nodes;
+using HandlebarsDotNet.Helpers.Models;
+using JetBrains.Annotations;
+using JsonConverter.Abstractions;
+using JsonConverter.System.Text.Json;
+using WireMock.Settings;
+using WireMock.Types;
+using WireMock.Util;
+
+namespace WireMock.Transformers;
+
+/// <summary>
+/// JSON body transformer implementation based on System.Text.Json.
+/// </summary>
+/// <param name="settings">The server settings used to configure JSON transformation behavior.</param>
+[PublicAPI]
+public class SystemTextJsonBodyTransformer(WireMockServerSettings settings) : IJsonBodyTransformer
+{
+    private readonly IJsonConverter _jsonConverter = new SystemTextJsonConverter();
+
+    /// <inheritdoc />
+    public BodyData TransformBodyAsJson(
+        ITransformerContext transformerContext,
+        ReplaceNodeOptions options,
+        object model,
+        IBodyData original)
+    {
+        JsonNode? jsonNode = null;
+        switch (original.BodyAsJson)
+        {
+            case JsonObject bodyAsJsonObject:
+                jsonNode = CloneNode(bodyAsJsonObject);
+                jsonNode = WalkNode(transformerContext, options, jsonNode, model);
+                break;
+
+            case JsonArray bodyAsJsonArray:
+                jsonNode = CloneNode(bodyAsJsonArray);
+                jsonNode = WalkNode(transformerContext, options, jsonNode, model);
+                break;
+
+            case var bodyAsEnumerable when bodyAsEnumerable is IEnumerable and not string:
+                jsonNode = JsonSerializer.SerializeToNode(bodyAsEnumerable);
+                if (jsonNode != null)
+                {
+                    jsonNode = WalkNode(transformerContext, options, jsonNode, model);
+                }
+                break;
+
+            case string bodyAsString:
+                jsonNode = ReplaceSingleNode(transformerContext, options, bodyAsString, model);
+                break;
+
+            case not null:
+                jsonNode = JsonSerializer.SerializeToNode(original.BodyAsJson);
+                if (jsonNode != null)
+                {
+                    jsonNode = WalkNode(transformerContext, options, jsonNode, model);
+                }
+                break;
+        }
+
+        return new BodyData
+        {
+            Encoding = original.Encoding,
+            DetectedBodyType = original.DetectedBodyType,
+            DetectedBodyTypeFromContentType = original.DetectedBodyTypeFromContentType,
+            ProtoDefinition = original.ProtoDefinition,
+            ProtoBufMessageType = original.ProtoBufMessageType,
+            BodyAsJson = jsonNode
+        };
+    }
+
+    private JsonNode ParseAsJsonObject(string stringValue)
+    {
+        if (_jsonConverter.IsValidJson(stringValue))
+        {
+            try
+            {
+                var parsed = JsonNode.Parse(stringValue);
+                if (parsed is JsonObject)
+                {
+                    return parsed;
+                }
+            }
+            catch
+            {
+                // Ignore and return as string.
+            }
+        }
+
+        return JsonValue.Create(stringValue)!;
+    }
+
+    private JsonNode? ReplaceSingleNode(ITransformerContext transformerContext, ReplaceNodeOptions options, string stringValue, object model)
+    {
+        var transformedString = transformerContext.ParseAndRender(stringValue, model);
+
+        if (!string.Equals(stringValue, transformedString))
+        {
+            return ReplaceNodeValue(options, transformedString);
+        }
+
+        return JsonValue.Create(stringValue);
+    }
+
+    private JsonNode? WalkNode(ITransformerContext transformerContext, ReplaceNodeOptions options, JsonNode? node, object model)
+    {
+        switch (node)
+        {
+            case JsonObject jsonObject:
+                foreach (var property in jsonObject.ToArray())
+                {
+                    jsonObject[property.Key] = WalkNode(transformerContext, options, property.Value, model);
+                }
+                return jsonObject;
+
+            case JsonArray jsonArray:
+                for (var i = 0; i < jsonArray.Count; i++)
+                {
+                    jsonArray[i] = WalkNode(transformerContext, options, jsonArray[i], model);
+                }
+                return jsonArray;
+
+            case JsonValue jsonValue when jsonValue.TryGetValue<string>(out var stringValue):
+                if (string.IsNullOrEmpty(stringValue))
+                {
+                    return jsonValue;
+                }
+
+                var transformed = transformerContext.ParseAndEvaluate(stringValue!, model);
+                return !Equals(stringValue, transformed) ? ReplaceNodeValue(options, transformed) ?? jsonValue : jsonValue;
+
+            default:
+                return node;
+        }
+    }
+
+    private JsonNode? ReplaceNodeValue(ReplaceNodeOptions options, object? transformedValue)
+    {
+        switch (transformedValue)
+        {
+            case JsonNode jsonNode:
+                return CloneNode(jsonNode);
+
+            case string transformedString:
+                var (isConvertedFromString, convertedValueFromString) = TryConvert(options, transformedString);
+                return isConvertedFromString
+                    ? JsonSerializer.SerializeToNode(convertedValueFromString)
+                    : ParseAsJsonObject(transformedString);
+
+            case WireMockList<string> strings:
+                switch (strings.Count)
+                {
+                    case 1:
+                        return ParseAsJsonObject(strings[0]);
+
+                    case > 1:
+                        return JsonSerializer.SerializeToNode(strings.ToArray());
+                }
+                break;
+
+            case { }:
+                var (isConverted, convertedValue) = TryConvert(options, transformedValue);
+                if (isConverted)
+                {
+                    return JsonSerializer.SerializeToNode(convertedValue);
+                }
+                break;
+        }
+
+        return null;
+    }
+
+    private static JsonNode? CloneNode(JsonNode? node)
+    {
+#if NET8_0_OR_GREATER
+        return node?.DeepClone();
+#else
+        return node == null ? null : JsonNode.Parse(node.ToJsonString());
+#endif
+    }
+
+    private static (bool IsConverted, object ConvertedValue) TryConvert(ReplaceNodeOptions options, object value)
+    {
+        var valueAsString = value as string;
+
+        if (options == ReplaceNodeOptions.Evaluate)
+        {
+            if (valueAsString != null && WrappedString.TryDecode(valueAsString, out var decoded))
+            {
+                return (true, decoded);
+            }
+
+            return (false, value);
+        }
+
+        if (valueAsString != null)
+        {
+            return WrappedString.TryDecode(valueAsString, out var decoded)
+                ? (true, decoded)
+                : NewtonsoftJsonBodyTransformer.TryConvertToKnownType(valueAsString);
+        }
+
+        return (false, value);
+    }
+}