ModernUO/Scripts/Commands/Generic/Extensions/Compilers/SortCompiler.cs

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;

namespace Server.Commands.Generic
{
  public sealed class OrderInfo
  {
    private int m_Order;

    public OrderInfo(Property property, bool isAscending)
    {
      Property = property;

      IsAscending = isAscending;
    }

    public Property Property{ get; set; }

    public bool IsAscending
    {
      get => m_Order > 0;
      set => m_Order = value ? +1 : -1;
    }

    public bool IsDescending
    {
      get => m_Order < 0;
      set => m_Order = value ? -1 : +1;
    }

    public int Sign
    {
      get => Math.Sign(m_Order);
      set
      {
        m_Order = Math.Sign(value);

        if (m_Order == 0)
          throw new InvalidOperationException("Sign cannot be zero.");
      }
    }
  }

  public static class SortCompiler
  {
    public static IComparer<T> Compile<T>(AssemblyEmitter assembly, Type objectType, OrderInfo[] orders)
    {
      TypeBuilder typeBuilder = assembly.DefineType(
        "__sort",
        TypeAttributes.Public,
        typeof(T)
      );

      #region Constructor

      {
        ConstructorBuilder ctor = typeBuilder.DefineConstructor(
          MethodAttributes.Public,
          CallingConventions.Standard,
          Type.EmptyTypes
        );

        ILGenerator il = ctor.GetILGenerator();

        // : base()
        il.Emit(OpCodes.Ldarg_0);
        il.Emit(OpCodes.Call, typeof(T).GetConstructor(Type.EmptyTypes) ??
                              throw new Exception($"Could not find empty constructor for type {typeof(T).FullName}"));

        // return;
        il.Emit(OpCodes.Ret);
      }

      #endregion

      #region IComparer

      typeBuilder.AddInterfaceImplementation(typeof(IComparer<T>));

      #region Compare
      {
        MethodEmitter emitter = new MethodEmitter(typeBuilder);

        emitter.Define(
          /*  name  */ "Compare",
          /*  attr  */ MethodAttributes.Public | MethodAttributes.Virtual,
          /* return */ typeof(int),
          /* params */ new[] { typeof(T), typeof(T) });

        LocalBuilder a = emitter.CreateLocal(objectType);
        LocalBuilder b = emitter.CreateLocal(objectType);

        LocalBuilder v = emitter.CreateLocal(typeof(int));

        emitter.LoadArgument(1);
        emitter.CastAs(objectType);
        emitter.StoreLocal(a);

        emitter.LoadArgument(2);
        emitter.CastAs(objectType);
        emitter.StoreLocal(b);

        emitter.Load(0);
        emitter.StoreLocal(v);

        Label end = emitter.CreateLabel();

        for (int i = 0; i < orders.Length; ++i)
        {
          if (i > 0)
          {
            emitter.LoadLocal(v);
            emitter.BranchIfTrue(end); // if ( v != 0 ) return v;
          }

          OrderInfo orderInfo = orders[i];

          Property prop = orderInfo.Property;
          int sign = orderInfo.Sign;

          emitter.LoadLocal(a);
          emitter.Chain(prop);

          bool couldCompare =
            emitter.CompareTo(sign, delegate
            {
              emitter.LoadLocal(b);
              emitter.Chain(prop);
            });

          if (!couldCompare)
            throw new InvalidOperationException("Property is not comparable.");

          emitter.StoreLocal(v);
        }

        emitter.MarkLabel(end);

        emitter.LoadLocal(v);
        emitter.Return();

        typeBuilder.DefineMethodOverride(
          emitter.Method,
          typeof(IComparer<T>).GetMethod(
            "Compare",
            new[]
            {
              typeof(T),
              typeof(T)
            }
          ) ?? throw new Exception($"No Compare method found for type {typeof(T).FullName}")
        );
      }

      #endregion

      #endregion

      Type comparerType = typeBuilder.CreateType();
      return (IComparer<T>)Activator.CreateInstance(comparerType);
    }
  }
}