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

using EC.Helper.RabbitFunc.Runtime;
using System.Collections.ObjectModel;
using System.Text;

namespace EC.Helper.RabbitFunc.Expressions;

public class LambdaExpression : Expression
{
    internal LambdaExpression(string name, Expression body, params ParameterExpression[] parameters)
        : base(ExpressionType.Lambda)
    {
        Name = name;
        Parameters = new ReadOnlyCollection<ParameterExpression>(parameters);
        Body = body;
    }

    public RabbitDomain Domain { get; internal set; }

    public string Name { get; }

    public ReadOnlyCollection<ParameterExpression> Parameters { get; }

    public Expression Body { get; }

    public override Type Type => typeof(double);

    public Delegate Compile(Type deletageType = null)
    {
        var lambdaCompiler = new ExpressionCompiler();
        return lambdaCompiler.Compile(this, deletageType);
    }

    public T Compile<T>()
    {
        return (T)(object)Compile(typeof(T));
    }

    public override object Eval(RuntimeContext context)
    {
        if (context == null)
            throw new ArgumentNullException(nameof(context));

        var lambdaContext = new RuntimeContext(context);
        lambdaContext.Domain = Domain;
        for (int i = 0; i < Parameters.Count; i++)
        {
            var parameter = Parameters[i];
            var value = parameter.Eval(context);
            lambdaContext.Variable(parameter.Name, value);
        }

        return Body.Eval(lambdaContext);
    }

    public override string ToString()
    {
        var sb = new StringBuilder();
        sb.Append(Name).Append('(');
        using (var e = Parameters.GetEnumerator())
        {
            if (e.MoveNext())
            {
                sb.Append(e.Current.Name);
                while (e.MoveNext())
                {
                    sb.Append(',');
                    sb.Append(e.Current.Name);
                }
            }
        }

        sb.Append(")=").Append(Body.ToString());
        return sb.ToString();
    }
}