Cis/EC.Helper/RabbitFunc/Expressions/ExpressionCompiler.cs

using EC.Helper.RabbitFunc.Runtime;

namespace EC.Helper.RabbitFunc.Expressions;

internal class ExpressionCompiler
{
    private readonly Dictionary<string, LambdaCompiler> lambdas = new Dictionary<string, LambdaCompiler>();

    private LambdaCompiler GetLambdaCompiler(LambdaExpression expression)
    {
        if (!lambdas.TryGetValue(expression.Name, out var lambda))
        {
            lambda = new LambdaCompiler(this, expression);
            lambdas.Add(expression.Name, lambda);
        }
        return lambda;
    }

    public Delegate Compile(LambdaExpression expression, Type delegateType = null)
    {
        var lambda = new LambdaCompiler(this, expression);
        lambdas.Add(lambda.Name, lambda);
        return lambda.Compile(delegateType);
    }

    private sealed class LambdaCompiler
    {
        private readonly ExpressionCompiler compiler;
        private readonly LambdaExpression expression;
        private readonly List<System.Linq.Expressions.ParameterExpression> parameters;

        public LambdaCompiler(ExpressionCompiler compiler, LambdaExpression expression)
        {
            this.compiler = compiler;
            this.expression = expression;
            this.parameters = new List<System.Linq.Expressions.ParameterExpression>();
            foreach (var parameter in expression.Parameters)
            {
                parameters.Add(System.Linq.Expressions.Expression.Parameter(parameter.Type, parameter.Name));
            }
        }

        public string Name => expression.Name;

        private System.Linq.Expressions.Expression EmitExpression(Expression expression)
        {
            switch (expression)
            {
                case ConditionalExpression conditionExpression:
                    {
                        var test = EmitExpression(conditionExpression.Test);
                        var trueExpression = EmitExpression(conditionExpression.TrueExpression);
                        var falseExpression = EmitExpression(conditionExpression.FalseExpression);
                        return System.Linq.Expressions.Expression.Condition(test, trueExpression, falseExpression);
                    }
                case BinaryExpression binaryExpression:
                    {
                        var left = EmitExpression(binaryExpression.Left);
                        var right = EmitExpression(binaryExpression.Right);
                        return expression.NodeType switch
                        {
                            ExpressionType.Add => System.Linq.Expressions.Expression.Add(left, right),
                            ExpressionType.Subtract => System.Linq.Expressions.Expression.Subtract(left, right),
                            ExpressionType.Multiply => System.Linq.Expressions.Expression.Multiply(left, right),
                            ExpressionType.Divide => System.Linq.Expressions.Expression.Divide(left, right),
                            ExpressionType.Modulo => System.Linq.Expressions.Expression.Modulo(left, right),
                            ExpressionType.Power => System.Linq.Expressions.Expression.Power(left, right),
                            ExpressionType.LessThan => System.Linq.Expressions.Expression.LessThan(left, right),
                            ExpressionType.LessThanOrEqual => System.Linq.Expressions.Expression.LessThanOrEqual(left, right),
                            ExpressionType.Equal => System.Linq.Expressions.Expression.Equal(left, right),
                            ExpressionType.GreaterThanOrEqual => System.Linq.Expressions.Expression.GreaterThanOrEqual(left, right),
                            ExpressionType.GreaterThan => System.Linq.Expressions.Expression.GreaterThan(left, right),
                            ExpressionType.NotEqual => System.Linq.Expressions.Expression.NotEqual(left, right),
                            _ => throw new LambdaCompilerException("unknown operator char:" + expression.NodeType.ToString()),
                        };
                    }
                case ConstantExpression constantExpression:
                    return System.Linq.Expressions.Expression.Constant(constantExpression.Value);

                case MethodCallExpression methodCallExpression:
                    {
                        var lambda = methodCallExpression.GetLambda(this.expression.Domain);
                        if (lambda == null) throw new LambdaCompilerException(string.Format("missing method:{0}", methodCallExpression.MethodName));
                        if (lambda is SystemLambdaExpression systemLambda)
                        {
                            var arguments = new List<System.Linq.Expressions.Expression>();
                            foreach (var argument in methodCallExpression.Arguments)
                            {
                                arguments.Add(EmitExpression(argument));
                            }
                            return System.Linq.Expressions.Expression.Call(null, systemLambda.Method, arguments);
                        }
                        else
                        {
                            var elementType = typeof(object);
                            var customLambda = compiler.GetLambdaCompiler(lambda);
                            var arguments = new System.Linq.Expressions.Expression[customLambda.parameters.Count];
                            for (var i = 0; i < arguments.Length; i++)
                            {
                                var parameter = customLambda.parameters[i];
                                var argument = EmitExpression(methodCallExpression.Arguments[i]);
                                arguments[i] = parameter.Type != elementType
                                    ? System.Linq.Expressions.Expression.Convert(argument, elementType)
                                    : argument;
                            }

                            var custom = customLambda.Compile();
                            return System.Linq.Expressions.Expression.Convert(
                                System.Linq.Expressions.Expression.Call(
                                    System.Linq.Expressions.Expression.Constant(custom),
                                    typeof(Delegate).GetMethod(nameof(Delegate.DynamicInvoke)),
                                    System.Linq.Expressions.Expression.NewArrayInit(elementType, arguments)),
                                lambda.Type);
                        }
                    }
                case ParameterExpression parameterExpression:
                    {
                        var parameter = parameters.Find(p => p.Name == parameterExpression.Name);
                        if (parameter == null) throw new RuntimeException("Missing member:" + parameterExpression.Name);
                        return parameter;
                    }
                case UnaryExpression unaryExpression:
                    {
                        var operand = EmitExpression(unaryExpression.Operand);
                        return unaryExpression.NodeType switch
                        {
                            ExpressionType.Negate => System.Linq.Expressions.Expression.Negate(operand),
                            ExpressionType.Not => System.Linq.Expressions.Expression.Not(operand),
                            _ => throw new RuntimeException("unknown NodeType:" + unaryExpression.NodeType.ToString()),
                        };
                    }
                default:
                    return null;
            }
        }

        public Delegate Compile(Type delegateType = null)
        {
            var body = EmitExpression(this.expression.Body);
            var lambda = delegateType == null
                ? System.Linq.Expressions.Expression.Lambda(body, this.expression.Name, parameters)
                : System.Linq.Expressions.Expression.Lambda(delegateType, body, this.expression.Name, parameters);
            return lambda.Compile();
        }
    }
}