//-----------------------------------------------------------------------------
// Copyright (c) Microsoft Corporation.  All rights reserved.
//-----------------------------------------------------------------------------

namespace System.Activities.Runtime
{
    using System;
    using System.Reflection;
    using System.Runtime.Serialization;
    using System.Diagnostics.CodeAnalysis;
    using System.Runtime;
    using System.Security;
    using System.Security.Permissions;
    using System.Threading;

    [DataContract]
    class CallbackWrapper
    {
        static BindingFlags bindingFlags = BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.DeclaredOnly | BindingFlags.Static;

        static PermissionSet ReflectionMemberAccessPermissionSet = null;

        string callbackName;

        string declaringAssemblyName;

        string declaringTypeName;

        Delegate callback;

        ActivityInstance activityInstance;

        public CallbackWrapper(Delegate callback, ActivityInstance owningInstance)
        {
            this.ActivityInstance = owningInstance;
            this.callback = callback;
        }
        
        public ActivityInstance ActivityInstance
        {
            get
            {
                return this.activityInstance;
            }
            private set
            {
                this.activityInstance = value;
            }
        }

        protected bool IsCallbackNull
        {
            get
            {
                return this.callback == null && this.callbackName == null;
            }
        }

        protected Delegate Callback
        {
            get
            {
                return this.callback;
            }
        }

        [DataMember(Name = "callbackName")]
        internal string SerializedCallbackName
        {
            get { return this.callbackName; }
            set { this.callbackName = value; }
        }

        [DataMember(EmitDefaultValue = false, Name = "declaringAssemblyName")]
        internal string SerializedDeclaringAssemblyName
        {
            get { return this.declaringAssemblyName; }
            set { this.declaringAssemblyName = value; }
        }

        [DataMember(EmitDefaultValue = false, Name = "declaringTypeName")]
        internal string SerializedDeclaringTypeName
        {
            get { return this.declaringTypeName; }
            set { this.declaringTypeName = value; }
        }

        [DataMember(Name = "ActivityInstance")]
        internal ActivityInstance SerializedActivityInstance
        {
            get { return this.ActivityInstance; }
            set { this.ActivityInstance = value; }
        }

        public static bool IsValidCallback(Delegate callback, ActivityInstance owningInstance)
        {
            Fx.Assert(callback != null, "This should only be called with non-null callbacks");

            object target = callback.Target;

            // if the target is null, it is static 
            if (target == null)
            {
                Fx.Assert(callback.Method.IsStatic, "This method should be static when target is null");
                return true;
            }

            // its owner's activity
            if (object.ReferenceEquals(target, owningInstance.Activity))
            {
                return true;
            }

            return false;
        }

        // Special note about establishing callbacks:
        //
        // When establising a callback, we need to Assert ReflectionPermission(MemberAccess) because the callback
        // method will typically be a private method within a class that derives from Activity. Activity authors need
        // to be aware that their callback may be invoked with different permissions than were present when the Activity
        // was originally executed and perform appropriate security checks.
        //
        // We ensure that the declaring type of the callback method derives from Activity. This check is made in RecreateCallback.
        //
        // The classes that derive from CallbackWrapper and call EnsureCallback do an explicit cast of the returned delegate
        // to the delegate type that they expect before calling thru to the delegate. This cast is done in SecuritySafeCritical code.
        //
        // These checks are both made in Security[Safe]Critical code.

        [Fx.Tag.SecurityNote(Critical = "Because we are calling GenerateCallback, which are SecurityCritical.")]
        [SecurityCritical]
        protected void EnsureCallback(Type delegateType, Type[] parameterTypes, Type genericParameter)
        {
            // We were unloaded and have some work to do to rebuild the callback
            if (this.callback == null)
            {
                this.callback = GenerateCallback(delegateType, parameterTypes, genericParameter);
                Fx.Assert(this.callback != null, "GenerateCallback should have been able to produce a non-null callback.");
            }
        }

        [Fx.Tag.SecurityNote(Critical = "Because we are calling GenerateCallback, which are SecurityCritical.",
            Safe = "Because the delegate is not leaked out of this routine. It is only validated.")]
        [SecuritySafeCritical]
        protected void ValidateCallbackResolution(Type delegateType, Type[] parameterTypes, Type genericParameter)
        {
            Fx.Assert(this.callback != null && this.callbackName != null, "We must have a callback and a callback name");
            
            if (!this.callback.Equals(GenerateCallback(delegateType, parameterTypes, genericParameter)))
            {
                throw FxTrace.Exception.AsError(new InvalidOperationException(SR.InvalidExecutionCallback(this.callback.Method, null)));
            }
        }

        MethodInfo FindMatchingGenericMethod(Type declaringType, Type[] parameterTypes, Type genericParameter)
        {
            MethodInfo[] potentialMatches = declaringType.GetMethods(bindingFlags);
            for (int i = 0; i < potentialMatches.Length; i++)
            {
                MethodInfo potentialMatch = potentialMatches[i];

                if (potentialMatch.IsGenericMethod && potentialMatch.Name == this.callbackName)
                {
                    Fx.Assert(potentialMatch.IsGenericMethodDefinition, "We should be getting the generic method definition here.");

                    Type[] genericArguments = potentialMatch.GetGenericArguments();

                    if (genericArguments.Length == 1)
                    {
                        potentialMatch = potentialMatch.MakeGenericMethod(genericParameter);

                        ParameterInfo[] parameters = potentialMatch.GetParameters();

                        bool match = true;
                        for (int parameterIndex = 0; parameterIndex < parameters.Length; parameterIndex++)
                        {
                            ParameterInfo parameter = parameters[parameterIndex];

                            if (parameter.IsOut || parameter.IsOptional || parameter.ParameterType != parameterTypes[parameterIndex])
                            {
                                match = false;
                                break;
                            }
                        }

                        if (match)
                        {
                            return potentialMatch;
                        }
                    }
                }
            }
            return null;
        }

        [Fx.Tag.SecurityNote(Critical = "Because we are calling RecreateCallback, which is SecurityCritical.")]
        [SecurityCritical]
        Delegate GenerateCallback(Type delegateType, Type[] parameterTypes, Type genericParameter)
        {
            Type declaringType;
            MethodInfo methodInfo = GetMatchingMethod(parameterTypes, out declaringType);

            if (methodInfo == null)
            {
                Fx.Assert(declaringType != null, "We must have found the declaring type.");
                methodInfo = FindMatchingGenericMethod(declaringType, parameterTypes, genericParameter);
            }

            if (methodInfo == null)
            {
                return null;
            }
            
            return RecreateCallback(delegateType, methodInfo);
        }

        [Fx.Tag.SecurityNote(Critical = "Because we are calling RecreateCallback, which is SecurityCritical.")]
        [SecurityCritical]
        protected void EnsureCallback(Type delegateType, Type[] parameters)
        {
            // We were unloaded and have some work to do to rebuild the callback
            if (this.callback == null)
            {
                Type unusedDeclaringType;
                MethodInfo methodInfo = GetMatchingMethod(parameters, out unusedDeclaringType);

                Fx.Assert(methodInfo != null, "We must have a method info by now");

                this.callback = RecreateCallback(delegateType, methodInfo);
            }
        }

        MethodInfo GetMatchingMethod(Type[] parameters, out Type declaringType)
        {
            Fx.Assert(this.callbackName != null, "This should only be called when there is actually a callback to run.");

            object targetInstance = this.ActivityInstance.Activity;

            if (this.declaringTypeName == null)
            {
                declaringType = targetInstance.GetType();
            }
            else
            {
                // make a MethodInfo since it's not hanging directly off of our activity type
                Assembly callbackAssembly;
                if (this.declaringAssemblyName != null)
                {
                    callbackAssembly = Assembly.Load(this.declaringAssemblyName);
                }
                else
                {
                    callbackAssembly = targetInstance.GetType().Assembly;
                }

                declaringType = callbackAssembly.GetType(this.declaringTypeName);
            }

            Fx.Assert(declaringType != null, "declaring type should be re-constructable from our serialized components");

            return declaringType.GetMethod(this.callbackName, bindingFlags, null, parameters, null);
        }

        // The MethodInfo passed to this method must be derived
        [Fx.Tag.SecurityNote(Critical = "Because we are Asserting ReflectionPermission(MemberAccess) in order to get at private callback methods.")]
        [SecurityCritical]
        Delegate RecreateCallback(Type delegateType, MethodInfo callbackMethod)
        {
            object targetInstance = null;

            // If the declaring type does not derive from Activity, somebody has manipulated the callback in the persistece store.
            if (!typeof(Activity).IsAssignableFrom(callbackMethod.DeclaringType))
            {
                return null;
            }

            if (!callbackMethod.IsStatic)
            {
                targetInstance = this.ActivityInstance.Activity;
            }

            // Asserting ReflectionPermission.MemberAccess because the callback method is most likely internal or private
            if (ReflectionMemberAccessPermissionSet == null)
            {
                PermissionSet myPermissionSet = new PermissionSet(PermissionState.None);
                myPermissionSet.AddPermission(new ReflectionPermission(ReflectionPermissionFlag.MemberAccess));
                Interlocked.CompareExchange(ref ReflectionMemberAccessPermissionSet, myPermissionSet, null);
            }
            ReflectionMemberAccessPermissionSet.Assert();
            try
            {
                return Delegate.CreateDelegate(delegateType, targetInstance, callbackMethod);
            }
            finally
            {
                CodeAccessPermission.RevertAssert();
            }
        }

        [OnSerializing]
        [SuppressMessage(FxCop.Category.Usage, FxCop.Rule.ReviewUnusedParameters)]
        [SuppressMessage(FxCop.Category.Usage, "CA2238:ImplementSerializationMethodsCorrectly",
            Justification = "Needs to be internal for serialization in partial trust. We have set InternalsVisibleTo(System.Runtime.Serialization) to allow this.")]
        internal void OnSerializing(StreamingContext context)
        {
            if (this.callbackName == null && !this.IsCallbackNull)
            {
                MethodInfo method = this.callback.Method;
                this.callbackName = method.Name;
                Type declaringType = method.DeclaringType;
                Type activityType = this.ActivityInstance.Activity.GetType();

                if (declaringType != activityType)
                {
                    // If we're not directly off of the Activity type being used,
                    // then we need to store the declaringType's name.
                    this.declaringTypeName = declaringType.FullName;

                    if (declaringType.Assembly != activityType.Assembly)
                    {
                        this.declaringAssemblyName = declaringType.Assembly.FullName;
                    }
                }
                
                if (method.IsGenericMethod)
                {
                    OnSerializingGenericCallback();
                }
            }
        }
        
        protected virtual void OnSerializingGenericCallback()
        {
            // Generics are invalid by default
            throw FxTrace.Exception.AsError(new InvalidOperationException(SR.InvalidExecutionCallback(this.callback.Method, null)));
        }
    }
}