// This file is part of the Noddybox.Emulation C# suite.
//
// Noddybox.Emulation is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Noddybox.Emulation is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
//
// Copyright (c) 2012 Ian Cowburn
//
using System;

namespace Noddybox.Emulation.EightBit.Z80
{
    /// <summary>
    /// Provides an implementation of a Zilog Z80 processor.
    /// </summary>
    public partial class Z80Cpu : ICpu
    {
        #region Private types

        [Flags]
        private enum Z80Flags
        {
            None        = 0x00,
            Carry       = 0x01,
            Neg		    = 0x02,
            PV		    = 0x04,
            Hidden3	    = 0x08,
            HalfCarry   = 0x10,
            Hidden5     = 0x20,
            Zero		= 0x40,
            Sign		= 0x80,
            Hidden      = Hidden3 | Hidden5
        };

        #endregion

        #region Private data

        // Lookup tables
        //
        private Z80Flags[] PSZtable = new Z80Flags[512];
        private Z80Flags[] SZtable = new Z80Flags[512];
        private Z80Flags[] Ptable = new Z80Flags[512];
        private Z80Flags[] Stable = new Z80Flags[512];
        private Z80Flags[] Ztable = new Z80Flags[512];
        private Z80Flags[] H35table = new Z80Flags[512];

        // Machine accessors
        //
        private IMemory memory;
        private IDevice device;
        private Clock   clock;

        // Main registers
        //
        private byte        A;
        private Z80Flags    F;
        private Register16  BC = new Register16(0);
        private Register16  DE = new Register16(0);
        private Register16  HL = new Register16(0);
        private Register16  IX = new Register16(0);
        private Register16  IY = new Register16(0);
        private ushort      SP;
        private ushort      PC;

        // Alternate registers
        //
        private Register16  AF_ = new Register16(0);
        private Register16  BC_ = new Register16(0);
        private Register16  DE_ = new Register16(0);
        private Register16  HL_ = new Register16(0);

        // Auxilliary registers and flags
        //
        private ushort      I;
        private byte        R;
        private bool        IFF1;
        private bool        IFF2;
        private bool        raise;
        private bool        nmi;
        private byte        devbyte;
        private int         IM;
        private bool        HALT;
        private int         shift;

        #endregion

        #region Private members

        private void CheckInterrupts()
        {
            if (raise)
            {
                if (nmi)
                {
                    if (HALT)
                    {
                        HALT = false;
                        PC++;
                    }

                    clock.Add(2);
                    IFF1 = false;
                    nmi = false;
                    PUSH(PC);
                    PC = 0x66;
                }
                else if (IFF1)
                {
                    if (HALT)
                    {
                        HALT = false;
                        PC++;
                    }

                    clock.Add(2);
                    IFF1 = false;
                    IFF2 = false;

                    switch(IM)
                    {
                        case 1:
                            PUSH(PC);
                            PC = 0x38;
                            break;

                        case 2:
                            PUSH(PC);
                            PC = (ushort)((I << 8) + devbyte);
                            break;

                        default:
                            DecodeByte(devbyte);
                            break;
                    }
                }

                raise = false;
            }
        }

        #endregion

        #region ICpu Members

        public void Initialise(IMemory memory, IDevice device, Clock clock)
        {
            this.memory = memory;
            this.device = device;
            this.clock = clock;

            Reset();
        }

        public void Reset()
        {
            PC = 0;
            A = 0xff;
            F = (Z80Flags)0xff;

            BC.reg = 0xffff;
            DE.reg = 0xffff;
            HL.reg = 0xffff;
            AF_.reg = 0xffff;
            BC_.reg = 0xffff;
            DE_.reg = 0xffff;
            HL_.reg = 0xffff;

            IX.reg = 0xffff;
            IY.reg = 0xffff;

            SP = 0xffff;

            IFF1 = false;
            IFF2 = false;
            IM = 0;
            I = 0;
            R = 0;
            HALT = false;
            shift = 0;
            raise = false;
            nmi = false;
            devbyte = 0;
        }

        public void Step()
        {
            CheckInterrupts();
            AddR(1);
            shift = 0;
            DecodeByte(memory.Read(PC++));
        }

        public void Run()
        {
            while(!clock.FrameDone)
            {
                Step();
            }
        }

        public void MaskableInterrupt(byte value)
        {
            raise = true;
            devbyte = value;
            nmi = false;
        }

        public void NonMaskableInterrupt(byte value)
        {
            raise = true;
            nmi = true;
        }

        #endregion

        #region Constructors

        public Z80Cpu()
        {
            // Verify runtime
            //
            Register16.Verify();

            // Setup lookup tables
            //
            for(int f = 0; f < 256; f++)
            {
                Z80Flags p = Z80Flags.None;
                Z80Flags z = Z80Flags.None;
                Z80Flags s = Z80Flags.None;
                Z80Flags h3 = Z80Flags.None;
                Z80Flags h5 = Z80Flags.None;

                int parity = 0;

                for(int b=0; b < 8; b++)
                {
                    if ((f & (1<<b)) == (1<<b))
                    {
                        parity++;
                    }
                }

                if ((parity & 1) == 1)
                {
                    p = Z80Flags.PV;
                }

                if (f == 0)
                {
                    z = Z80Flags.Zero;
                }

                if ((f & 0x80) == 0x80)
                {
                    s = Z80Flags.Sign;
                }

                if ((f & (int)Z80Flags.Hidden3) == (int)Z80Flags.Hidden3)
                {
                    h3 = Z80Flags.Hidden3;
                }

                if ((f & (int)Z80Flags.Hidden5) == (int)Z80Flags.Hidden5)
                {
                    h5 = Z80Flags.Hidden5;
                }

                Ptable[f] = p;
                Stable[f] = s;
                Ztable[f] = z;
                SZtable[f] =z | s;
                PSZtable[f] = z | s | p;
                H35table[f] = h3 | h5;

                Ptable[f+256] = Ptable[f] | Z80Flags.Carry;
                Stable[f+256] = Stable[f] | Z80Flags.Carry;
                Ztable[f+256] = Ztable[f] | Z80Flags.Carry;
                SZtable[f+256] = SZtable[f] | Z80Flags.Carry;
                PSZtable[f+256] = PSZtable[f] | Z80Flags.Carry;
                H35table[f+256] = h3 | h5;
            }

            Reset();
        }

        #endregion
    }
}