using Microsoft.VisualStudio.TestTools.UnitTesting;

using System;

using System.IO;

using System.Text;

namespace ModerBox.Comtrade.Test {

/// <summary>

/// 编码自动检测测试

/// 测试 COMTRADE 库对不同文件编码的自动识别能力

/// </summary>

[TestClass]

public class EncodingDetectionTests {

private string _testDir;

[TestInitialize]

public void Setup() {

_testDir = Path.Combine(Path.GetTempPath(), "ComtradeEncodingTests_" + Guid.NewGuid().ToString("N"));

Directory.CreateDirectory(_testDir);

Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);

}

[TestCleanup]

public void Cleanup() {

if (Directory.Exists(_testDir)) {

Directory.Delete(_testDir, true);

}

}

#region BOM 检测测试

[TestMethod]

public void DetectEncoding_Utf8WithBom_ReturnsUtf8() {

// Arrange

string testFile = Path.Combine(_testDir, "utf8_bom.cfg");

byte[] bom = new byte[] { 0xEF, 0xBB, 0xBF };

byte[] content = Encoding.UTF8.GetBytes("Test content");

byte[] fileContent = new byte[bom.Length + content.Length];

bom.CopyTo(fileContent, 0);

content.CopyTo(fileContent, bom.Length);

File.WriteAllBytes(testFile, fileContent);

// Act

Encoding detected = Comtrade.DetectEncoding(testFile);

// Assert

Assert.AreEqual(Encoding.UTF8.CodePage, detected.CodePage, "Should detect UTF-8 with BOM");

}

[TestMethod]

public void DetectEncoding_Utf16LeBom_ReturnsUtf16Le() {

// Arrange

string testFile = Path.Combine(_testDir, "utf16_le.cfg");

File.WriteAllText(testFile, "Test content", Encoding.Unicode);

// Act

Encoding detected = Comtrade.DetectEncoding(testFile);

// Assert

Assert.AreEqual(Encoding.Unicode.CodePage, detected.CodePage, "Should detect UTF-16 LE");

}

[TestMethod]

public void DetectEncoding_Utf16BeBom_ReturnsUtf16Be() {

// Arrange

string testFile = Path.Combine(_testDir, "utf16_be.cfg");

File.WriteAllText(testFile, "Test content", Encoding.BigEndianUnicode);

// Act

Encoding detected = Comtrade.DetectEncoding(testFile);

// Assert

Assert.AreEqual(Encoding.BigEndianUnicode.CodePage, detected.CodePage, "Should detect UTF-16 BE");

}

#endregion

#region 无 BOM 编码检测测试

[TestMethod]

public void DetectEncoding_AsciiContent_ReturnsUtf8Compatible() {

// Arrange - 纯 ASCII 内容，UTF-8 和 GBK 都兼容

string testFile = Path.Combine(_testDir, "ascii.cfg");

File.WriteAllBytes(testFile, Encoding.ASCII.GetBytes("Station1,Device1,2013\n2,1A,1D\n"));

// Act

Encoding detected = Comtrade.DetectEncoding(testFile);

// Assert - 纯 ASCII 应该返回 UTF-8 (向前兼容)

Assert.AreEqual(Encoding.UTF8.CodePage, detected.CodePage, "Pure ASCII should return UTF-8");

}

[TestMethod]

public void DetectEncoding_Utf8WithoutBom_ChineseContent_ReturnsUtf8() {

// Arrange - UTF-8 without BOM with Chinese characters

string testFile = Path.Combine(_testDir, "utf8_no_bom.cfg");

// 使用 UTF-8 编码写入中文字符 (不带 BOM)

using (var writer = new StreamWriter(testFile, false, new UTF8Encoding(false))) {

writer.WriteLine("北京变电站,录波器A,2013");

writer.WriteLine("2,1A,1D");

}

// Act

Encoding detected = Comtrade.DetectEncoding(testFile);

// Assert

Assert.AreEqual(Encoding.UTF8.CodePage, detected.CodePage, "UTF-8 without BOM should be detected");

}

[TestMethod]

public void DetectEncoding_GbkContent_ReturnsGbk() {

// Arrange - GBK encoded Chinese content

string testFile = Path.Combine(_testDir, "gbk.cfg");

Encoding gbk = Encoding.GetEncoding("GBK");

string chineseContent = "北京变电站,录波器A,2013\n2,1A,1D\n";

File.WriteAllBytes(testFile, gbk.GetBytes(chineseContent));

// Act

Encoding detected = Comtrade.DetectEncoding(testFile);

// Assert - 如果不是有效的 UTF-8，应该检测为 GBK

Assert.AreEqual(gbk.CodePage, detected.CodePage, "GBK content should be detected as GBK");

}

#endregion

#region 边界情况测试

[TestMethod]

public void DetectEncoding_EmptyFile_ReturnsUtf8() {

// Arrange

string testFile = Path.Combine(_testDir, "empty.cfg");

File.WriteAllBytes(testFile, Array.Empty<byte>());

// Act

Encoding detected = Comtrade.DetectEncoding(testFile);

// Assert

Assert.AreEqual(Encoding.UTF8.CodePage, detected.CodePage, "Empty file should return UTF-8 as default");

}

[TestMethod]

public void DetectEncoding_SingleByteFile_ReturnsUtf8() {

// Arrange

string testFile = Path.Combine(_testDir, "single_byte.cfg");

File.WriteAllBytes(testFile, new byte[] { 0x41 }); // 'A'

// Act

Encoding detected = Comtrade.DetectEncoding(testFile);

// Assert

Assert.AreEqual(Encoding.UTF8.CodePage, detected.CodePage, "Single ASCII byte should return UTF-8");

}

#endregion

#region DetectEncodingFromBytes 测试

[TestMethod]

public void DetectEncodingFromBytes_Utf8Bom_ReturnsUtf8() {

// Arrange

byte[] buffer = new byte[] { 0xEF, 0xBB, 0xBF, 0x41, 0x42, 0x43 };

// Act

Encoding detected = Comtrade.DetectEncodingFromBytes(buffer, buffer.Length);

// Assert

Assert.AreEqual(Encoding.UTF8.CodePage, detected.CodePage);

}

[TestMethod]

public void DetectEncodingFromBytes_Utf16LeBom_ReturnsUtf16Le() {

// Arrange

byte[] buffer = new byte[] { 0xFF, 0xFE, 0x41, 0x00, 0x42, 0x00 };

// Act

Encoding detected = Comtrade.DetectEncodingFromBytes(buffer, buffer.Length);

// Assert

Assert.AreEqual(Encoding.Unicode.CodePage, detected.CodePage);

}

[TestMethod]

public void DetectEncodingFromBytes_Utf16BeBom_ReturnsUtf16Be() {

// Arrange

byte[] buffer = new byte[] { 0xFE, 0xFF, 0x00, 0x41, 0x00, 0x42 };

// Act

Encoding detected = Comtrade.DetectEncodingFromBytes(buffer, buffer.Length);

// Assert

Assert.AreEqual(Encoding.BigEndianUnicode.CodePage, detected.CodePage);

}

[TestMethod]

public void DetectEncodingFromBytes_ValidUtf8Multibyte_ReturnsUtf8() {

// Arrange - "中" in UTF-8 is E4 B8 AD

byte[] buffer = new byte[] { 0xE4, 0xB8, 0xAD };

// Act

Encoding detected = Comtrade.DetectEncodingFromBytes(buffer, buffer.Length);

// Assert

Assert.AreEqual(Encoding.UTF8.CodePage, detected.CodePage);

}

[TestMethod]

public void DetectEncodingFromBytes_InvalidUtf8_ReturnsGbk() {

// Arrange - Invalid UTF-8 sequence that looks like GBK

// GBK "中" is D6 D0

byte[] buffer = new byte[] { 0xD6, 0xD0 };

// Act

Encoding detected = Comtrade.DetectEncodingFromBytes(buffer, buffer.Length);

// Assert

Assert.AreEqual(Encoding.GetEncoding("GBK").CodePage, detected.CodePage);

}

#endregion

}

}