/*
 * MIT License
 * 
 * Copyright (c) 2017 Michael VanOverbeek and ShiftOS devs
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ShiftOS.Engine
{
    /// <summary>
    /// Receives events from the interpreter.
    /// </summary>
    public interface IBFListener
    {
        void PointerMoved(ushort newval);
        void IPtrMoved(int newval);
        void MemChanged(ushort pos, byte newval);
        void MemReset();
    }
    /// <summary>
    /// Interprets Brainfuck code.
    /// </summary>
    public class BFInterpreter
    {
        private byte[] mem;
        private ushort ptr;
        private string prg;
        private object lck;
        private Stream str;

        public IBFListener lst = null;

        private static byte[] newline = Encoding.UTF8.GetBytes(Environment.NewLine);

        public BFInterpreter(Stream io, IBFListener listener = null, string program = "")
        {
            lck = new object();
            prg = program;
            str = io;
            Reset();
            lst = listener;
        }
        public void Execute(string program, int offset = 0)
        {
            int c = 0;
            lock (lck)
                while (c < program.Length)
                {
                    switch (program[c++])
                    {
                        case '<':
                            ptr--;
                            if (lst != null)
                                lst.PointerMoved(ptr);
                            break;
                        case '>':
                            ptr++;
                            if (lst != null)
                                lst.PointerMoved(ptr);
                            break;
                        case '+':
                            mem[ptr]++;
                            if (lst != null)
                                lst.MemChanged(ptr, mem[ptr]);
                            break;
                        case '-':
                            mem[ptr]--;
                            if (lst != null)
                                lst.MemChanged(ptr, mem[ptr]);
                            break;
                        case '.':
                            if (mem[ptr] == 10)
                                str.Write(newline, 0, newline.Length); // normalise newline
                            else
                                str.WriteByte(mem[ptr]);
                            break;
                        case ',':
                            mem[ptr] = (byte)str.ReadByte();
                            if (mem[ptr] == 13)
                                mem[ptr] = 10; // normalise newline
                            if (lst != null)
                                lst.MemChanged(ptr, mem[ptr]);
                            break;
                        case '[':
                            int b;
                            int oldc = c;
                            for (b = 1; b != 0 && c < program.Length; c++)
                            {
                                if (program[c] == '[')
                                    b++;
                                else if (program[c] == ']')
                                    b--;
                            }
                            if (b == 0)
                            {
                                string block = program.Substring(oldc, c - oldc - 1);
                                while (mem[ptr] != 0)
                                    Execute(block, offset + oldc);
                            }
                            break;
                        case ']':
                            throw new Exception("Unbalanced brackets");
                    }
                    if (lst != null)
                        lst.IPtrMoved(offset + c);
                }
        }
        public void Execute()
        {
            Execute(prg);
        }
        public void Reset()
        {
            lock (lck)
            {
                mem = new byte[30000];
                ptr = 0;
                if (lst != null)
                {
                    lst.MemReset();
                    lst.PointerMoved(0);
                }
            }
        }
    }
}