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Create EventEmitter.cs
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‎ModFramework/Emitters/EventEmitter.cs‎

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/*
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Copyright (C) 2024 DeathCradle
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This file is part of Open Terraria API v3 (OTAPI)
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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using Mono.Cecil;
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using Mono.Cecil.Cil;
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using System;
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using System.Linq;
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namespace ModFramework;
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[MonoMod.MonoModIgnore]
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public static class EventEmitter
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{
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/// <summary>
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/// Creates a new event based upon the source definition
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/// </summary>
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/// <param name="sourceDefinition">The method to base the even upon</param>
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/// <param name="containingType">The type to create the event in</param>
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/// <param name="eventArgsType">The event args to use</param>
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/// <param name="name">Optional desired name for the event</param>
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/// <returns>A tuple of the field and event definitions</returns>
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public static (FieldDefinition fieldDefinition, EventDefinition eventDefinition) CreateEvent(this MethodDefinition sourceDefinition, TypeDefinition containingType, TypeDefinition eventArgsType, string? name = null)
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{
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// Define the event backing field
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var fieldName = name ?? $"{sourceDefinition.Name}Event";
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FieldDefinition eventField = new(
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fieldName,
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FieldAttributes.Private | FieldAttributes.Static,
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new GenericInstanceType(sourceDefinition.Module.ImportReference(typeof(EventHandler<>)))
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{
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GenericArguments = { eventArgsType }
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}
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);
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containingType.Fields.Add(eventField);
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// Define the event itself
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EventDefinition eventDefinition = new(
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fieldName,
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EventAttributes.None,
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eventField.FieldType
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);
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containingType.Events.Add(eventDefinition);
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// Create the `add` method
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MethodDefinition addMethod = new(
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$"add_{fieldName}",
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MethodAttributes.Public | MethodAttributes.HideBySig | MethodAttributes.Static | MethodAttributes.SpecialName,
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containingType.Module.TypeSystem.Void
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);
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ParameterDefinition parameter = new("value", ParameterAttributes.None, eventField.FieldType);
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addMethod.Parameters.Add(parameter);
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var ilAdd = addMethod.Body.GetILProcessor();
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GenericInstanceMethod methodInterlockedCompareExchange = new(containingType.Module.ImportReference(typeof(System.Threading.Interlocked)
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.GetMethods()
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.Single(m => m.Name == "CompareExchange" && m.IsGenericMethodDefinition)));
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methodInterlockedCompareExchange.GenericArguments.Add(eventField.FieldType);
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VariableDefinition v0 = new(eventField.FieldType);
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VariableDefinition v1 = new(eventField.FieldType);
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VariableDefinition v2 = new(eventField.FieldType);
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addMethod.Body.Variables.Add(v0);
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addMethod.Body.Variables.Add(v1);
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addMethod.Body.Variables.Add(v2);
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ilAdd.Emit(OpCodes.Ldsfld, eventField); // Load static field
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ilAdd.Emit(OpCodes.Stloc_0); // Store into local v0
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var loopStart = ilAdd.Create(OpCodes.Ldloc_0);
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ilAdd.Append(loopStart);
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ilAdd.Emit(OpCodes.Stloc_1); // Store into local v1
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ilAdd.Emit(OpCodes.Ldloc_1); // Load local v1
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ilAdd.Emit(OpCodes.Ldarg_0); // Load the parameter value
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ilAdd.Emit(OpCodes.Call, containingType.Module.ImportReference(typeof(Delegate).GetMethods().Single(x => x.Name == "Combine" && x.GetParameters().Length == 2)));
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ilAdd.Emit(OpCodes.Castclass, eventField.FieldType);
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ilAdd.Emit(OpCodes.Stloc_2); // Store into local v2
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ilAdd.Emit(OpCodes.Ldsflda, eventField);
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ilAdd.Emit(OpCodes.Ldloc_2);
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ilAdd.Emit(OpCodes.Ldloc_1);
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ilAdd.Emit(OpCodes.Call, methodInterlockedCompareExchange);
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ilAdd.Emit(OpCodes.Stloc_0); // Update v0
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ilAdd.Emit(OpCodes.Ldloc_0);
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ilAdd.Emit(OpCodes.Ldloc_1);
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ilAdd.Emit(OpCodes.Bne_Un_S, loopStart); // If not equal, loop back
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ilAdd.Emit(OpCodes.Ret);
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containingType.Methods.Add(addMethod);
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// Create the `remove` method
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MethodDefinition removeMethod = new(
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$"remove_{fieldName}",
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MethodAttributes.Public | MethodAttributes.HideBySig | MethodAttributes.Static | MethodAttributes.SpecialName,
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containingType.Module.TypeSystem.Void
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);
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removeMethod.Parameters.Add(parameter);
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v0 = new(eventField.FieldType);
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v1 = new(eventField.FieldType);
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v2 = new(eventField.FieldType);
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removeMethod.Body.Variables.Add(v0);
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removeMethod.Body.Variables.Add(v1);
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removeMethod.Body.Variables.Add(v2);
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var ilRemove = removeMethod.Body.GetILProcessor();
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ilRemove.Emit(OpCodes.Ldsfld, eventField); // Load static field
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ilRemove.Emit(OpCodes.Stloc_0); // Store into local v0
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loopStart = ilRemove.Create(OpCodes.Ldloc_0);
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ilRemove.Append(loopStart);
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ilRemove.Emit(OpCodes.Stloc_1); // Store into local v1
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ilRemove.Emit(OpCodes.Ldloc_1); // Load local v1
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ilRemove.Emit(OpCodes.Ldarg_0); // Load the parameter value
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ilRemove.Emit(OpCodes.Call, containingType.Module.ImportReference(typeof(Delegate).GetMethod("Remove")));
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ilRemove.Emit(OpCodes.Castclass, eventField.FieldType);
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ilRemove.Emit(OpCodes.Stloc_2); // Store into local v2
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ilRemove.Emit(OpCodes.Ldsflda, eventField);
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ilRemove.Emit(OpCodes.Ldloc_2);
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ilRemove.Emit(OpCodes.Ldloc_1);
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ilRemove.Emit(OpCodes.Call, methodInterlockedCompareExchange);
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ilRemove.Emit(OpCodes.Stloc_0); // Update v0
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ilRemove.Emit(OpCodes.Ldloc_0);
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ilRemove.Emit(OpCodes.Ldloc_1);
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ilRemove.Emit(OpCodes.Bne_Un_S, loopStart); // If not equal, loop back
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ilRemove.Emit(OpCodes.Ret);
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containingType.Methods.Add(removeMethod);
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// add compiler generated attribute
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addMethod.CustomAttributes.Add(new(containingType.Module.ImportReference(typeof(System.Runtime.CompilerServices.CompilerGeneratedAttribute).GetConstructor(Type.EmptyTypes))));
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removeMethod.CustomAttributes.Add(new(containingType.Module.ImportReference(typeof(System.Runtime.CompilerServices.CompilerGeneratedAttribute).GetConstructor(Type.EmptyTypes))));
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eventField.CustomAttributes.Add(new(containingType.Module.ImportReference(typeof(System.Runtime.CompilerServices.CompilerGeneratedAttribute).GetConstructor(Type.EmptyTypes))));
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// Link the add/remove methods to the event
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eventDefinition.AddMethod = addMethod;
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eventDefinition.RemoveMethod = removeMethod;
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return (eventField, eventDefinition);
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}
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}

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