poc-misc/FormulaEnginePoC/CSharpProvider/ExpressionCompiler.cs

using System;
using System.CodeDom.Compiler;
using System.Collections.Generic;
using System.Linq;

namespace FormulaEnginePoC.CSharpProvider
{
    public class ExpressionCompiler<TDelegate> where TDelegate : Delegate
    {
        private readonly string _expressionCode;
        private readonly string _baseClass;

        private readonly List<string> _assemblies = new List<string>();
        private readonly List<string> _namespaces = new List<string>();

        private CodeCompiler<TDelegate> _codeCompiler;
        private TDelegate _compiledDelegate;

        public CompilerError[] CompilerErrors => _codeCompiler.CompilerErrors.ToArray();

        public TDelegate CompiledDelegate => _compiledDelegate ?? throw new InvalidOperationException("No compiled yet");

        public ExpressionCompiler(string expressionCode, string baseClass = null)
        {
            _expressionCode = expressionCode;
            _baseClass = baseClass;

        }

        public void AddReferenceAssembly(params string[] assemblies)
        {
            _assemblies.AddRange(assemblies);
        }

        public void AddNamespace(params string[] namespaces)
        {
            _namespaces.AddRange(namespaces);
        }

        public void Compile()
        {
            _codeCompiler = new CodeCompiler<TDelegate>();


            var namespaceIncluding = string.Join(Environment.NewLine, _namespaces.Select(p => $"using {p};"));

            var typeName = $"ClassOnTheFly_{string.Join("", Guid.NewGuid().ToByteArray().Select(p => $"{p:X2}"))}";
            var methodName = $"MethodOnTheFly_{string.Join("", Guid.NewGuid().ToByteArray().Select(p => $"{p:X2}"))}";

            var delegateMethod = typeof(TDelegate).GetMethod("Invoke") ?? throw new MissingMethodException("Can not find method `Invoke' from Delegate");
            var returnType = delegateMethod.ReturnType;
            var paramList = string.Join(",", delegateMethod.GetParameters().Select((p, i) => p.ParameterType.FullName + (i == 0 ? " p" : $" arg{i - 1}")));

            var preCompileCode =
                $"{namespaceIncluding}" +
                $"public class {typeName} {(string.IsNullOrWhiteSpace(_baseClass) ? "" : $":{_baseClass}")}" +
                $"{{ public static {returnType.FullName} {methodName}({paramList})" +
                $" {{" +
                $" return {_expressionCode};" +
                $" }}" +
                $"}}";

            _codeCompiler.Compile(typeName, methodName, preCompileCode, _assemblies.ToArray());
            _compiledDelegate = _codeCompiler.CompiledDelegate;
        }
    }
}