Initial commit to new repository

src/AxCopilot/Services/Agent/TextFileCodec.cs

@@ -0,0 +1,131 @@
+using System.IO;
+using System.Text;
+
+namespace AxCopilot.Services.Agent;
+
+/// <summary>
+/// 텍스트 파일 인코딩 감지/읽기/쓰기 유틸.
+/// - 읽기: BOM + UTF-8 유효성 검사 기반 자동 감지
+/// - 쓰기: 기존 파일 인코딩/UTF-8 BOM 여부를 최대한 보존
+/// </summary>
+public static class TextFileCodec
+{
+    public readonly record struct TextReadResult(string Text, Encoding Encoding, bool HasBom);
+
+    static TextFileCodec()
+    {
+        Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
+    }
+
+    public static TextReadResult ReadAllText(string path)
+    {
+        var bytes = File.ReadAllBytes(path);
+        return Decode(bytes);
+    }
+
+    public static async Task<TextReadResult> ReadAllTextAsync(string path, CancellationToken ct = default)
+    {
+        var bytes = await File.ReadAllBytesAsync(path, ct);
+        return Decode(bytes);
+    }
+
+    public static string[] SplitLines(string text)
+        => text.Split('\n');
+
+    public static Encoding ResolveWriteEncoding(Encoding sourceEncoding, bool sourceHasBom)
+    {
+        if (sourceEncoding.CodePage == Encoding.UTF8.CodePage)
+            return new UTF8Encoding(sourceHasBom);
+        return sourceEncoding;
+    }
+
+    public static async Task WriteAllTextAsync(string path, string content, Encoding encoding, CancellationToken ct = default)
+    {
+        var dir = Path.GetDirectoryName(path);
+        if (!string.IsNullOrWhiteSpace(dir))
+            Directory.CreateDirectory(dir);
+
+        await using var stream = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.Read, 4096, useAsync: true);
+        await using var writer = new StreamWriter(stream, encoding);
+        await writer.WriteAsync(content.AsMemory(), ct);
+        await writer.FlushAsync();
+    }
+
+    public static Encoding Utf8NoBom => new UTF8Encoding(encoderShouldEmitUTF8Identifier: false);
+
+    private static TextReadResult Decode(byte[] bytes)
+    {
+        var detected = DetectEncoding(bytes, out var bomLength, out var hasBom);
+        var payload = bomLength > 0 ? bytes[bomLength..] : bytes;
+        var text = detected.GetString(payload);
+        return new TextReadResult(text, detected, hasBom);
+    }
+
+    private static Encoding DetectEncoding(byte[] bytes, out int bomLength, out bool hasBom)
+    {
+        // UTF-8 BOM
+        if (bytes.Length >= 3 && bytes[0] == 0xEF && bytes[1] == 0xBB && bytes[2] == 0xBF)
+        {
+            bomLength = 3;
+            hasBom = true;
+            return Encoding.UTF8;
+        }
+
+        // UTF-16 LE BOM
+        if (bytes.Length >= 2 && bytes[0] == 0xFF && bytes[1] == 0xFE)
+        {
+            bomLength = 2;
+            hasBom = true;
+            return Encoding.Unicode;
+        }
+
+        // UTF-16 BE BOM
+        if (bytes.Length >= 2 && bytes[0] == 0xFE && bytes[1] == 0xFF)
+        {
+            bomLength = 2;
+            hasBom = true;
+            return Encoding.BigEndianUnicode;
+        }
+
+        bomLength = 0;
+        hasBom = false;
+
+        if (IsValidUtf8(bytes))
+            return new UTF8Encoding(encoderShouldEmitUTF8Identifier: false);
+
+        // 한국어 Windows 환경 호환 fallback
+        try { return Encoding.GetEncoding("euc-kr"); }
+        catch { return Encoding.Default; }
+    }
+
+    private static bool IsValidUtf8(byte[] bytes)
+    {
+        var i = 0;
+        while (i < bytes.Length)
+        {
+            if (bytes[i] <= 0x7F)
+            {
+                i++;
+                continue;
+            }
+
+            int extra;
+            if ((bytes[i] & 0xE0) == 0xC0) extra = 1;
+            else if ((bytes[i] & 0xF0) == 0xE0) extra = 2;
+            else if ((bytes[i] & 0xF8) == 0xF0) extra = 3;
+            else return false;
+
+            if (i + extra >= bytes.Length) return false;
+            for (var j = 1; j <= extra; j++)
+            {
+                if ((bytes[i + j] & 0xC0) != 0x80)
+                    return false;
+            }
+
+            i += extra + 1;
+        }
+
+        return true;
+    }
+}
+