using System.Text;
using Serilog;
using YZWater.Core.Utils;

namespace YZWater.Core.Tests.Services;

/// <summary>
/// 文本文件编码的回归测试。
/// 背景：日志和 CSV 导出原先写成无 BOM 的 UTF-8，中文 Windows 上记事本、Excel、
/// PowerShell 5.1 的 Get-Content 都会按 GBK 解释，取证时看到的是乱码。
/// </summary>
public class FileEncodingTests : IDisposable
{
    private readonly string _dir = Path.Combine(
        Path.GetTempPath(), "yzwater-encoding-" + Guid.NewGuid().ToString("N"));

    public FileEncodingTests() => Directory.CreateDirectory(_dir);

    public void Dispose()
    {
        try { Directory.Delete(_dir, true); } catch (IOException) { }
    }

    [Fact]
    public void Utf8WithBom_Preamble_IsTheThreeUtf8SignatureBytes()
    {
        Assert.Equal(new byte[] { 0xEF, 0xBB, 0xBF }, FileTextEncoding.Utf8WithBom.Preamble.ToArray());
    }

    [Fact]
    public void SerilogFileSink_NewFile_StartsWithBomAndKeepsChineseReadable()
    {
        var previous = Serilog.Log.Logger;
        var path = Path.Combine(_dir, "log-encoding.txt");
        try
        {
            Log.Logger = new LoggerConfiguration()
                .WriteTo.File(path, encoding: FileTextEncoding.Utf8WithBom)
                .CreateLogger();
            Log.Information("集水池 {Level:F2} 米，泵已停止", 3.5f);
            Log.CloseAndFlush();

            var bytes = File.ReadAllBytes(path);
            Assert.Equal(new byte[] { 0xEF, 0xBB, 0xBF }, bytes.Take(3).ToArray());

            // 去 BOM 后必须是合法 UTF-8 且中文原样可读（乱码时这两条都会失败）
            var text = File.ReadAllText(path);
            Assert.Contains("集水池 3.50 米，泵已停止", text);
            Assert.DoesNotContain("", text);
        }
        finally
        {
            Log.Logger = previous;
        }
    }

    [Fact]
    public void AppendAllText_WritesBomOnlyOnce()
    {
        var path = Path.Combine(_dir, "crash-sim.log");

        File.AppendAllText(path, "第一段：集水池溢出\n", FileTextEncoding.Utf8WithBom);
        File.AppendAllText(path, "第二段：泵故障\n", FileTextEncoding.Utf8WithBom);

        var bytes = File.ReadAllBytes(path);
        Assert.Equal(1, CountOccurrences(bytes, new byte[] { 0xEF, 0xBB, 0xBF }));
        Assert.Contains("第二段：泵故障", File.ReadAllText(path));
    }

    private static int CountOccurrences(byte[] haystack, byte[] needle)
    {
        var count = 0;
        for (var i = 0; i <= haystack.Length - needle.Length; i++)
        {
            var match = true;
            for (var j = 0; j < needle.Length; j++)
                if (haystack[i + j] != needle[j]) { match = false; break; }
            if (match) count++;
        }
        return count;
    }
}