TypeExtensions.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Threading;

namespace ServiceStack;

public delegate object ObjectActivator(params object[] args);

public delegate object MethodInvoker(object instance, params object[] args);
    
public delegate object StaticMethodInvoker(params object[] args);
    
public delegate void ActionInvoker(object instance, params object[] args);
    
public delegate void StaticActionInvoker(params object[] args);

/// <summary>
/// Delegate to return a different value from an instance (e.g. member accessor)
/// </summary>
public delegate object InstanceMapper(object instance);


public static class TypeExtensions
{
    public static Type[] GetReferencedTypes(this Type type)
    {
        var refTypes = new HashSet<Type> { type };

        AddReferencedTypes(type, refTypes);

        return refTypes.ToArray();
    }

    public static void AddReferencedTypes(Type type, HashSet<Type> refTypes)
    {
        if (type.BaseType != null)
        {
            if (!refTypes.Contains(type.BaseType))
            {
                refTypes.Add(type.BaseType);
                AddReferencedTypes(type.BaseType, refTypes);
            }

            if (!type.BaseType.GetGenericArguments().IsEmpty())
            {
                foreach (var arg in type.BaseType.GetGenericArguments())
                {
                    if (!refTypes.Contains(arg))
                    {
                        refTypes.Add(arg);
                        AddReferencedTypes(arg, refTypes);
                    }
                }
            }
        }

        foreach (var iface in type.GetInterfaces())
        {
            if (iface.IsGenericType && !iface.IsGenericTypeDefinition)
            {
                foreach (var arg in iface.GetGenericArguments())
                {
                    if (!refTypes.Contains(arg))
                    {
                        refTypes.Add(arg);
                        AddReferencedTypes(arg, refTypes);
                    }
                }
            }
        }

        var properties = type.GetProperties();
        if (!properties.IsEmpty())
        {
            foreach (var p in properties)
            {
                if (!refTypes.Contains(p.PropertyType))
                {
                    refTypes.Add(p.PropertyType);
                    AddReferencedTypes(type, refTypes);
                }

                var args = p.PropertyType.GetGenericArguments();
                if (!args.IsEmpty())
                {
                    foreach (var arg in args)
                    {
                        if (!refTypes.Contains(arg))
                        {
                            refTypes.Add(arg);
                            AddReferencedTypes(arg, refTypes);
                        }
                    }
                }
                else if (p.PropertyType.IsArray)
                {
                    var elType = p.PropertyType.GetElementType();
                    if (!refTypes.Contains(elType))
                    {
                        refTypes.Add(elType);
                        AddReferencedTypes(elType, refTypes);
                    }
                }
            }
        }
    }

    public static ObjectActivator GetActivatorToCache(ConstructorInfo ctor)
    {
        var pi = ctor.GetParameters();
        var paramArgs = Expression.Parameter(typeof(object[]), "args");
        var exprArgs = new Expression[pi.Length];

        var convertFromMethod = typeof(TypeExtensions).GetStaticMethod(nameof(ConvertFromObject));

        for (int i = 0; i < pi.Length; i++)
        {
            var index = Expression.Constant(i);
            var paramType = pi[i].ParameterType;
            var paramAccessorExp = Expression.ArrayIndex(paramArgs, index);
            var paramCastExp = Expression.Convert(paramAccessorExp, paramType);
            var convertParam = convertFromMethod.MakeGenericMethod(paramType);
            exprArgs[i] = Expression.Call(convertParam, paramAccessorExp);
        }

        var newExp = Expression.New(ctor, exprArgs);
        var lambda = Expression.Lambda(typeof(ObjectActivator), 
            Expression.Convert(newExp, typeof(object)), 
            paramArgs);

        var ctorFn = (ObjectActivator)lambda.Compile();
        return ctorFn;
    }

    static Dictionary<ConstructorInfo, ObjectActivator> activatorCache = new();

    public static ObjectActivator GetActivator(this ConstructorInfo ctor)
    {
        if (activatorCache.TryGetValue(ctor, out var fn))
            return fn;

        fn = GetActivatorToCache(ctor);

        Dictionary<ConstructorInfo, ObjectActivator> snapshot, newCache;
        do
        {
            snapshot = activatorCache;
            newCache = new Dictionary<ConstructorInfo, ObjectActivator>(activatorCache) { [ctor] = fn };

        } while (!ReferenceEquals(
                     Interlocked.CompareExchange(ref activatorCache, newCache, snapshot), snapshot));

        return fn;
    }

    private static Expression[] CreateInvokerParamExpressions(MethodInfo method, ParameterExpression paramArgs)
    {
        var convertFromMethod = typeof(TypeExtensions).GetStaticMethod(nameof(ConvertFromObject));

        var pi = method.GetParameters();
        var exprArgs = new Expression[pi.Length];
        for (int i = 0; i < pi.Length; i++)
        {
            var index = Expression.Constant(i);
            var paramType = pi[i].ParameterType;
            var paramAccessorExp = Expression.ArrayIndex(paramArgs, index);
            var convertParam = convertFromMethod.MakeGenericMethod(paramType);
            exprArgs[i] = Expression.Call(convertParam, paramAccessorExp);
        }

        return exprArgs;
    }

    private static string UseCorrectInvokerErrorMessage(MethodInfo method)
    {
        var invokerName = method.ReturnType == typeof(void) 
            ? (method.IsStatic ? nameof(GetStaticActionInvoker) : nameof(GetActionInvoker)) 
            : (method.IsStatic ? nameof(GetStaticInvoker) : nameof(GetInvoker));
        var invokerType = method.ReturnType == typeof(void) 
            ? (method.IsStatic ? nameof(StaticMethodInvoker) : nameof(MethodInvoker)) 
            : (method.IsStatic ? nameof(StaticActionInvoker) : nameof(ActionInvoker));
        var methodType = method.ReturnType == typeof(void)
            ? (method.IsStatic ? "static void methods" : "instance void methods")
            : (method.IsStatic ? "static methods" : "instance methods"); 
        return $"Use {invokerName} to create a {invokerType} for invoking {methodType}";
    }

    public static MethodInvoker GetInvokerToCache(MethodInfo method)
    {
        if (method.IsStatic)
            throw new NotSupportedException(UseCorrectInvokerErrorMessage(method));
            
        var paramInstance = Expression.Parameter(typeof(object), "instance");
        var paramArgs = Expression.Parameter(typeof(object[]), "args");

        var exprArgs = CreateInvokerParamExpressions(method, paramArgs);
            
        var methodCall = method.DeclaringType.IsValueType 
            ? Expression.Call(Expression.Convert(paramInstance, method.DeclaringType), method, exprArgs)
            : Expression.Call(Expression.TypeAs(paramInstance, method.DeclaringType), method, exprArgs);

        var convertToMethod = typeof(TypeExtensions).GetStaticMethod(nameof(ConvertToObject));
        var convertReturn = convertToMethod.MakeGenericMethod(method.ReturnType);
            
        var lambda = Expression.Lambda(typeof(MethodInvoker), 
            Expression.Call(convertReturn, methodCall), 
            paramInstance, 
            paramArgs);

        var fn = (MethodInvoker)lambda.Compile();
        return fn;
    }

    public static StaticMethodInvoker GetStaticInvokerToCache(MethodInfo method)
    {
        if (!method.IsStatic || method.ReturnType == typeof(void))
            throw new NotSupportedException(UseCorrectInvokerErrorMessage(method));
            
        var paramArgs = Expression.Parameter(typeof(object[]), "args");

        var exprArgs = CreateInvokerParamExpressions(method, paramArgs);

        var methodCall = Expression.Call(method, exprArgs);

        var convertToMethod = typeof(TypeExtensions).GetStaticMethod(nameof(ConvertToObject));
        var convertReturn = convertToMethod.MakeGenericMethod(method.ReturnType);
            
        var lambda = Expression.Lambda(typeof(StaticMethodInvoker), 
            Expression.Call(convertReturn, methodCall), 
            paramArgs);

        var fn = (StaticMethodInvoker)lambda.Compile();
        return fn;
    }

    public static ActionInvoker GetActionInvokerToCache(MethodInfo method)
    {
        if (method.IsStatic || method.ReturnType != typeof(void))
            throw new NotSupportedException(UseCorrectInvokerErrorMessage(method));

        var paramInstance = Expression.Parameter(typeof(object), "instance");
        var paramArgs = Expression.Parameter(typeof(object[]), "args");

        var exprArgs = CreateInvokerParamExpressions(method, paramArgs);
            
        var methodCall = method.DeclaringType.IsValueType 
            ? Expression.Call(Expression.Convert(paramInstance, method.DeclaringType), method, exprArgs)
            : Expression.Call(Expression.TypeAs(paramInstance, method.DeclaringType), method, exprArgs);

        var lambda = Expression.Lambda(typeof(ActionInvoker), 
            methodCall, 
            paramInstance, 
            paramArgs);

        var fn = (ActionInvoker)lambda.Compile();
        return fn;
    }

    public static StaticActionInvoker GetStaticActionInvokerToCache(MethodInfo method)
    {
        if (!method.IsStatic || method.ReturnType != typeof(void))
            throw new NotSupportedException(UseCorrectInvokerErrorMessage(method));

        var paramArgs = Expression.Parameter(typeof(object[]), "args");

        var exprArgs = CreateInvokerParamExpressions(method, paramArgs);
            
        var methodCall = Expression.Call(method, exprArgs);

        var lambda = Expression.Lambda(typeof(StaticActionInvoker), 
            methodCall, 
            paramArgs);

        var fn = (StaticActionInvoker)lambda.Compile();
        return fn;
    }
        
    static Dictionary<MethodInfo, MethodInvoker> invokerCache = new();

    /// <summary>
    /// Create the correct Invoker Delegate Type based on the type of Method
    /// </summary>
    public static Delegate GetInvokerDelegate(this MethodInfo method)
    {
        if (!method.IsStatic)
        {
            if (method.ReturnType != typeof(void))
                return method.GetInvoker();
                
            return method.GetActionInvoker();
        }

        if (method.ReturnType != typeof(void))
            return method.GetStaticInvoker();
            
        return method.GetStaticActionInvoker();
    }

    /// <summary>
    /// Create an Invoker for public instance methods
    /// </summary>
    public static MethodInvoker GetInvoker(this MethodInfo method)
    {
        if (invokerCache.TryGetValue(method, out var fn))
            return fn;

        fn = GetInvokerToCache(method);

        Dictionary<MethodInfo, MethodInvoker> snapshot, newCache;
        do
        {
            snapshot = invokerCache;
            newCache = new Dictionary<MethodInfo, MethodInvoker>(invokerCache) { [method] = fn };

        } while (!ReferenceEquals(
                     Interlocked.CompareExchange(ref invokerCache, newCache, snapshot), snapshot));

        return fn;
    }
        
    static Dictionary<MethodInfo, StaticMethodInvoker> staticInvokerCache = new();

    /// <summary>
    /// Create an Invoker for public static methods
    /// </summary>
    public static StaticMethodInvoker GetStaticInvoker(this MethodInfo method)
    {
        if (staticInvokerCache.TryGetValue(method, out var fn))
            return fn;

        fn = GetStaticInvokerToCache(method);

        Dictionary<MethodInfo, StaticMethodInvoker> snapshot, newCache;
        do
        {
            snapshot = staticInvokerCache;
            newCache = new Dictionary<MethodInfo, StaticMethodInvoker>(staticInvokerCache) { [method] = fn };

        } while (!ReferenceEquals(
                     Interlocked.CompareExchange(ref staticInvokerCache, newCache, snapshot), snapshot));

        return fn;
    }
        
    static Dictionary<MethodInfo, ActionInvoker> actionInvokerCache = new();

    /// <summary>
    /// Create an Invoker for public instance void methods
    /// </summary>
    public static ActionInvoker GetActionInvoker(this MethodInfo method)
    {
        if (actionInvokerCache.TryGetValue(method, out var fn))
            return fn;

        fn = GetActionInvokerToCache(method);

        Dictionary<MethodInfo, ActionInvoker> snapshot, newCache;
        do
        {
            snapshot = actionInvokerCache;
            newCache = new Dictionary<MethodInfo, ActionInvoker>(actionInvokerCache) { [method] = fn };

        } while (!ReferenceEquals(
                     Interlocked.CompareExchange(ref actionInvokerCache, newCache, snapshot), snapshot));

        return fn;
    }
        
    static Dictionary<MethodInfo, StaticActionInvoker> staticActionInvokerCache = new();

    /// <summary>
    /// Create an Invoker for public static void methods
    /// </summary>
    public static StaticActionInvoker GetStaticActionInvoker(this MethodInfo method)
    {
        if (staticActionInvokerCache.TryGetValue(method, out var fn))
            return fn;

        fn = GetStaticActionInvokerToCache(method);

        Dictionary<MethodInfo, StaticActionInvoker> snapshot, newCache;
        do
        {
            snapshot = staticActionInvokerCache;
            newCache = new Dictionary<MethodInfo, StaticActionInvoker>(staticActionInvokerCache) { [method] = fn };

        } while (!ReferenceEquals(
                     Interlocked.CompareExchange(ref staticActionInvokerCache, newCache, snapshot), snapshot));

        return fn;
    }

    public static T ConvertFromObject<T>(object value)
    {
        if (value == null)
            return default(T);
            
        if (value is T variable)
            return variable;

        if (typeof(T) == typeof(string) && value is IRawString rs)
            return (T)(object)rs.ToRawString();

        return value.ConvertTo<T>();
    }

    public static object ConvertToObject<T>(T value) => value;

    public static Func<object,object> GetPropertyAccessor(this Type type, PropertyInfo forProperty)
    {
        var lambda = CreatePropertyAccessorExpression(type, forProperty);
        var fn = (Func<object,object>)lambda.Compile();
        return fn;
    }

    public static LambdaExpression CreatePropertyAccessorExpression(Type type, PropertyInfo forProperty)
    {
        var paramInstance = Expression.Parameter(typeof(object), "instance");

        var castToType = type.IsValueType
            ? Expression.Convert(paramInstance, type)
            : Expression.TypeAs(paramInstance, type);

        var propExpr = Expression.Property(castToType, forProperty);

        var lambda = Expression.Lambda(typeof(Func<object, object>),
            propExpr,
            paramInstance);
        return lambda;
    }
}