Implement diff-reporter PoC (#5)

src/Recordingtest.DiffReporter/JsonDiffer.cs

@@ -0,0 +1,77 @@
+using System.Text.Json;
+
+namespace Recordingtest.DiffReporter;
+
+internal static class JsonDiffer
+{
+    public static IReadOnlyList<Hunk> Diff(JsonElement a, JsonElement b)
+    {
+        var aMap = new SortedDictionary<string, string>(StringComparer.Ordinal);
+        var bMap = new SortedDictionary<string, string>(StringComparer.Ordinal);
+        Flatten("$", a, aMap);
+        Flatten("$", b, bMap);
+
+        var hunks = new List<Hunk>();
+        var allKeys = new SortedSet<string>(aMap.Keys, StringComparer.Ordinal);
+        foreach (var k in bMap.Keys) allKeys.Add(k);
+
+        int idx = 0;
+        foreach (var key in allKeys)
+        {
+            var hasA = aMap.TryGetValue(key, out var av);
+            var hasB = bMap.TryGetValue(key, out var bv);
+            if (hasA && hasB)
+            {
+                if (!string.Equals(av, bv, StringComparison.Ordinal))
+                    hunks.Add(new Hunk(idx, "changed", $"{key}={av}", $"{key}={bv}"));
+            }
+            else if (hasA)
+            {
+                hunks.Add(new Hunk(idx, "removed", $"{key}={av}", string.Empty));
+            }
+            else if (hasB)
+            {
+                hunks.Add(new Hunk(idx, "added", string.Empty, $"{key}={bv}"));
+            }
+            idx++;
+        }
+        return hunks;
+    }
+
+    private static void Flatten(string path, JsonElement el, IDictionary<string, string> map)
+    {
+        switch (el.ValueKind)
+        {
+            case JsonValueKind.Object:
+                foreach (var p in el.EnumerateObject())
+                    Flatten(path + "." + p.Name, p.Value, map);
+                break;
+            case JsonValueKind.Array:
+                int i = 0;
+                foreach (var item in el.EnumerateArray())
+                {
+                    Flatten(path + "[" + i + "]", item, map);
+                    i++;
+                }
+                break;
+            case JsonValueKind.String:
+                map[path] = "\"" + el.GetString() + "\"";
+                break;
+            case JsonValueKind.Number:
+                map[path] = el.GetRawText();
+                break;
+            case JsonValueKind.True:
+                map[path] = "true";
+                break;
+            case JsonValueKind.False:
+                map[path] = "false";
+                break;
+            case JsonValueKind.Null:
+                map[path] = "null";
+                break;
+            default:
+                map[path] = el.GetRawText();
+                break;
+        }
+    }
+}