🐍 Add JsonSnakeCaseNamingPolicy

- For the use of online configuration generation
- Source: dotnet/corefx#40003
- See also: dotnet/runtime#782

Author: database64128

shadowsocks-uri-generator/JsonSnakeCaseNamingPolicy.cs

@@ -0,0 +1,87 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Source: https://github.com/dotnet/corefx/pull/40003
+// See also: https://github.com/dotnet/runtime/issues/782
+
+using System;
+using System.Text;
+using System.Text.Json;
+
+namespace shadowsocks_uri_generator
+{
+    public class JsonSnakeCaseNamingPolicy : JsonNamingPolicy
+    {
+        internal enum SnakeCaseState
+        {
+            Start,
+            Lower,
+            Upper,
+            NewWord
+        }
+
+        public override string ConvertName(string name)
+        {
+            if (string.IsNullOrEmpty(name))
+            {
+                return name;
+            }
+
+            var sb = new StringBuilder();
+            var state = SnakeCaseState.Start;
+
+            var nameSpan = name.AsSpan();
+
+            for (int i = 0; i < nameSpan.Length; i++)
+            {
+                if (nameSpan[i] == ' ')
+                {
+                    if (state != SnakeCaseState.Start)
+                    {
+                        state = SnakeCaseState.NewWord;
+                    }
+                }
+                else if (char.IsUpper(nameSpan[i]))
+                {
+                    switch (state)
+                    {
+                        case SnakeCaseState.Upper:
+                            bool hasNext = (i + 1 < nameSpan.Length);
+                            if (i > 0 && hasNext)
+                            {
+                                char nextChar = nameSpan[i + 1];
+                                if (!char.IsUpper(nextChar) && nextChar != '_')
+                                {
+                                    sb.Append('_');
+                                }
+                            }
+                            break;
+                        case SnakeCaseState.Lower:
+                        case SnakeCaseState.NewWord:
+                            sb.Append('_');
+                            break;
+                    }
+                    sb.Append(char.ToLowerInvariant(nameSpan[i]));
+                    state = SnakeCaseState.Upper;
+                }
+                else if (nameSpan[i] == '_')
+                {
+                    sb.Append('_');
+                    state = SnakeCaseState.Start;
+                }
+                else
+                {
+                    if (state == SnakeCaseState.NewWord)
+                    {
+                        sb.Append('_');
+                    }
+
+                    sb.Append(nameSpan[i]);
+                    state = SnakeCaseState.Lower;
+                }
+            }
+
+            return sb.ToString();
+        }
+    }
+}