using System;
using System.Collections.Generic;
using TLang.BytecodeCompiler;
using TLang.Common;
namespace TLang.VM
{
    public class ChunkExecuter
    {
        public string ClassName {get;set;}="";
        public ChunkExecuter(TVMFile file,Chunk chunk,TLangEnvironment env)
        {
            File =file;
            Chunk = chunk;
            Environment = env;
        }
        public TLangEnvironment Environment {get;set;}
        public TVMFile File {get;}

        public Chunk Chunk {get;}
        public int IP {get;set;}=0;
        public Stack<TObject> Stack {get;}=new Stack<TObject>();


        public TObject Execute(params TObject[] args)
        {
            var env=Environment.GetSubEnvironment();
            for(int i = 0;i< args.Length;i++)
            {
                if(i<Chunk.Arguments.Count)
                {
                    env.SetObject(Chunk.Arguments[i],args[i]);
                }
            }
            while(IP < Chunk.Code.Length)
            {
                var instruction = Chunk.Code[IP++];
                switch(instruction)
                {
                    case Instruction.ADD:
                        Stack.Push(Add(Stack.Pop(),Stack.Pop()));
                        break;
                    case Instruction.SUB:
                        Stack.Push(Sub(Stack.Pop(),Stack.Pop()));
                        break;
                    case Instruction.TIMES:
                        Stack.Push(Times(Stack.Pop(),Stack.Pop()));
                        break;
                    case Instruction.DIVIDE:
                        Stack.Push(Divide(Stack.Pop(),Stack.Pop()));
                        break;
                    case Instruction.MOD:
                        Stack.Push(Mod(Stack.Pop(),Stack.Pop()));
                        break;
                    case Instruction.RET:
                        return Stack.Pop();
                    
                    case Instruction.SCOPE_BEGIN:
                        env = Environment.GetSubEnvironment();
                        break;
                    case Instruction.SCOPE_END:
                        env = Environment.GetParentEnvironment();
                        break;
                    case Instruction.PUSH_DOUBLE:
                        Stack.Push(new TNumber(ReadDouble()));
                        break;
                    case Instruction.PUSH_CLOSURE:
                        int closureId = ReadInt();
                        if(closureId >= File.Chunks.Count) throw new IndexOutOfRangeException($"No chunk with id {closureId}");
                        Stack.Push(new TClosure(File,File.Chunks[closureId],env));
                        break;
                    case Instruction.PUSH_STRING:
                        Stack.Push(new TString(ReadString()));
                        break;
                    case Instruction.PUSH_VARIABLE_VALUE:
                    {
                        var res=EnsurePop<TString>();
                        Stack.Push(env.GetObject(res.Value));
                    }
                    break;
                    case Instruction.POP_VARIABLE_VALUE:
                    {
                        var res=EnsurePop<TString>();
                        env.SetObject(res.Value,Stack.Pop());
                    }
                    break;
                    case Instruction.CALL_FUNC:
                    {
                        var argC = (int)EnsurePop<TNumber>().Value;
                        TObject[] argV = new TObject[argC];
                        for(int i = argC;i>0;i--)
                        {
                            argV[i] = Stack.Pop();
                        }
                        var name = EnsurePop<TString>();
                        var callable=env.GetObject(name.Value) as TCallable;
                        if(callable != null)
                        {
                            Stack.Push(callable.Execute(argV));
                        }else{
                            Stack.Push(new TUndefined());
                        }
                    }
                    break;
                    case Instruction.CALL_METHOD:
                    {
                        var argC = (int)EnsurePop<TNumber>().Value;
                        TObject[] argV = new TObject[argC];
                        for(int i = argC;i>0;i--)
                        {
                            argV[i] = Stack.Pop();
                        }
                        var name = EnsurePop<TString>();
                        var symbol = Stack.Pop();

                        Stack.Push(ExecuteMethod(symbol,name.Value,argV));
                    }
                    break;
                }
            }
            if(Stack.Count > 0)
            return Stack.Pop();
            return new TNull();
        }

        private TObject ExecuteMethod(TObject symbol, string name, params TObject[] argV)
        {
            
        }

        private T EnsurePop<T>() where T : TObject
        {
            var item = Stack.Pop() as T;
            if(item == null) throw new Exception("Pop failed");
            return item;
        }   

        private double ReadDouble()
        {
            if(IP + 8 < Chunk.Code.Length)
            {
                byte[] data =new byte[8];
                Array.Copy(Chunk.Code,IP,data,0,8);
                IP += 8;
                if(BitConverter.IsLittleEndian) Array.Reverse(data);
                return BitConverter.ToDouble(data,0);
            }
            throw new Exception("Malformed binary");
        }
        private int ReadInt()
        {
            if(IP + 4 < Chunk.Code.Length)
            {
                byte[] data =new byte[4];
                Array.Copy(Chunk.Code,IP,data,0,4);
                IP += 4;
                if(BitConverter.IsLittleEndian) Array.Reverse(data);
                return BitConverter.ToInt32(data,0);
            }
            throw new Exception("Malformed binary");
        }
        private string ReadString()
        {
            int strLen = ReadInt();
            if(IP + strLen < Chunk.Code.Length)
            {
                var str=System.Text.Encoding.UTF8.GetString(Chunk.Code,IP,strLen);
                IP += strLen;
                return str;
            }
            throw new Exception("Malformed binary");
        }
        private TObject Mod(TObject object1, TObject object2)
        {
            throw new NotImplementedException();
        }

        private TObject Divide(TObject object1, TObject object2)
        {
            throw new NotImplementedException();
        }

        private TObject Times(TObject object1, TObject object2)
        {
            throw new NotImplementedException();
        }

        private TObject Sub(TObject object2, TObject object1)
        {
            throw new NotImplementedException();
        }

        private TObject Add(TObject object2, TObject object1)
        {
            var left = object2 as TNumber;
            var right = object1 as TNumber;
            var lStr = object2 as TString;
            var rStr = object1 as TString;
            if(left != null && right != null)
            {
                return new TNumber(left.Value + right.Value);
            }
            if(lStr != null && rStr != null)
            {
                return new TString(lStr.Value + rStr.Value);
            }
            return new TNumber(0);
        }
    }

    
}