using System;
using System.Collections.Generic;
using System.Reflection.Emit;
using System.Text;
using Sunweaver.DataPrototypes;

namespace Sunweaver.Commands.Abstracts
{
    /// <summary>
    /// An abstract class that handles the fizzle behavior for binary math operations
    /// </summary>
    abstract public class BinaryOperation : BasePair
    {
        protected VirtualMachine VM = null;

        public override void Implementation(VirtualMachine VM)
        {
            //fizzles if there aren't enough values
            if (VM.Stack.Count() < 2)
                return;

            long b = VM.Stack.Pop();
            long a = VM.Stack.Pop();

            this.VM = VM;
            Operation(a, b);
        }

        internal override void Compile(ILGenerator il, Locals locals)
        {
            var cont = il.DefineLabel();

            il.Emit(OpCodes.Ldloc, locals[typeof(VirtualMachine)]);
            il.Emit(OpCodes.Ldfld, typeof(VirtualMachine).GetField("Stack"));
            il.Emit(OpCodes.Call, typeof(IntStack).GetMethod("Count"));
            il.Emit(OpCodes.Ldc_I4_2);
            il.Emit(OpCodes.Blt_S, cont); // We dont return, just go the end of this method

            il.Emit(OpCodes.Ldloc, locals[typeof(VirtualMachine)]);
            il.Emit(OpCodes.Ldfld, typeof(VirtualMachine).GetField("Stack"));
            il.Emit(OpCodes.Call, typeof(IntStack).GetMethod("Pop"));
            il.Emit(OpCodes.Conv_I8);
            il.Emit(OpCodes.Stloc, locals[typeof(long), 1]);

            il.Emit(OpCodes.Ldloc, locals[typeof(VirtualMachine)]);
            il.Emit(OpCodes.Ldfld, typeof(VirtualMachine).GetField("Stack"));
            il.Emit(OpCodes.Call, typeof(IntStack).GetMethod("Pop"));
            il.Emit(OpCodes.Conv_I8);
            il.Emit(OpCodes.Stloc, locals[typeof(long), 0]);

            CompileOperation(il, locals);

            il.MarkLabel(cont);         
        }

        /// <summary>
        /// Child members implement this with their specifics
        /// </summary>
        /// <param name="a">top value on the int stack</param>
        /// <param name="b">second to top value on the int stack</param>
        public abstract void Operation(long a, long b);

        /// <summary>
        /// Abstract interface that child classes implement
        /// </summary>
        /// <remarks>
        /// The long variables for the operation are stored in long0 and long1 of locals.
        /// </remarks>
        public abstract void CompileOperation(ILGenerator il, Locals locals);
    }
}