codeplay/CodePlay.Core/Pipeline/Converters/SwitchExpressionConverter.cs

using System;
using System.Text;
using System.Text.RegularExpressions;
using CodePlay.Core.Interfaces;

namespace CodePlay.Core.Pipeline.Converters;

/// <summary>
/// C# switch 表达式转换器
/// switch { pattern => expression, _ => default } → 嵌套 if-else
/// </summary>
public class SwitchExpressionConverter : ILineConverter
{
    public int Priority => 55;

    public string Convert(string line, ConversionContext context)
    {
        if (!line.Contains("switch") && !line.Contains("=>"))
            return line;

        // 检测 switch 表达式赋值: var x = expr switch { ... };
        var assignMatch = Regex.Match(line,
            @"(\w+)\s+(\w+)\s*=\s*(.+)\s+switch\s*\{");

        // 单行 switch 表达式: expr switch { pattern => val, _ => defVal }
        var singleLineMatch = Regex.Match(line,
            @"(.+?)\s+switch\s*\{\s*(.+?)\s*,\s*_\s*=>\s*(.+?)\s*\}");

        if (singleLineMatch.Success)
        {
            var expr = singleLineMatch.Groups[1].Value.Trim();
            var cases = singleLineMatch.Groups[2].Value.Trim();
            var defaultVal = singleLineMatch.Groups[3].Value.Trim();

            var parts = Regex.Split(cases, @"\s*,\s*(?=(?:(?:[^""]*""){2})*[^""]*$)(?![^()]*\))");
            var sb = new StringBuilder();

            sb.AppendLine("{");
            if (parts.Length > 0)
            {
                var firstCase = Regex.Match(parts[0], @"(.+?)\s*=>\s*(.+)");
                if (firstCase.Success)
                {
                    var pattern = firstCase.Groups[1].Value.Trim();
                    var value = firstCase.Groups[2].Value.Trim();
                    sb.AppendLine($"    if ({expr} == {pattern}) return {value};");
                }
            }
            for (var i = 1; i < parts.Length; i++)
            {
                var caseMatch = Regex.Match(parts[i], @"(.+?)\s*=>\s*(.+)");
                if (caseMatch.Success)
                {
                    var pattern = caseMatch.Groups[1].Value.Trim();
                    var value = caseMatch.Groups[2].Value.Trim();
                    sb.AppendLine($"    if ({expr} == {pattern}) return {value};");
                }
            }
            sb.AppendLine($"    return {defaultVal};");
            sb.Append("}");
            return sb.ToString();
        }

        // 多行 switch 表达式赋值: var x = expr switch { ... }
        if (assignMatch.Success && line.TrimEnd().EndsWith("{"))
        {
            var varType = assignMatch.Groups[1].Value;
            var varName = assignMatch.Groups[2].Value;
            var expr = assignMatch.Groups[3].Value.Trim();

            var sb = new StringBuilder();
            sb.AppendLine($"{varType} {varName};");
            sb.Append($"// switch expression for {varName} = {expr} switch {{...}}");
            return sb.ToString();
        }

        return line;
    }
}