// 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 Noddybox.Emulation.  If not, see <http://www.gnu.org/licenses/>.
//
// Copyright (c) 2012 Ian Cowburn
//
// Some of the concepts and code in here are taken from FUSE, the open source UNIX
// Spectrum emulator Copyright (c) 1999-2003 Philip Kendall.
// See <http://fuse-emulator.sourceforge.net/>
//
// Any introduced bugs in that code are mine, and not the original authors.
//
using System;

namespace Noddybox.Emulation.EightBit.Z80
{
    public partial class Z80Cpu
    {
        #region Fetch and helper operations

        /// <summary>
        /// Fetch the next word from the PC.
        /// </summary>
        /// <returns>The word.</returns>
        ushort FetchWord()
        {
            Register16 r = new Register16(0);

            r.low = memory.Read(PC++);
            r.high = memory.Read(PC++);

            return r.reg;
        }

        /// <summary>
        /// Swap two 16-bit registers.
        /// </summary>
        /// <param name="a">The first register.</param>
        /// <param name="b">The second register.</param>
        void Swap(ref Register16 a, ref Register16 b)
        {
            Register16 t = a;
            a = b;
            b = t;
        }

        /// <summary>
        /// Fetch the offset if the current opcode is shifted.
        /// </summary>
        /// <returns>The offset, or zero if the current opcode is not shifted.</returns>
        sbyte Offset()
        {
            if (shift == 0xdd || shift == 0xfd)
            {
                clock.Add(8);
                byte b = memory.Read(PC++);
                return (sbyte)b;
            }
            else
            {
                return 0;
            }
        }
        
        #endregion

        #region Status/special register helpers
        
        /// <summary>
        /// Set a flag in the status register.
        /// </summary>
        /// <param name="flag">The flag.</param>
        private void SetFlag(Z80Flags flag)
        {
            F |= flag;
        }

        /// <summary>
        /// Clear a flag in the status register.
        /// </summary>
        /// <param name="flag">The flag.</param>
        private void ClearFlag(Z80Flags flag)
        {
            F &= ~flag;
        }

        /// <summary>
        /// Add a value to the R (refresh) register.
        /// </summary>
        /// <param name="v">The value.</param>
        private void AddR(byte v)
        {
            R = (byte)((R & 0x80) | (R + v) & 0x7f);
        }

        #endregion

        #region Stack commands

        /// <summary>
        /// Push a value on the stack.
        /// </summary>
        /// <param name="val">The value.</param>
        private void PUSH(ushort val)
        {
            Register16 r = new Register16(val);
            memory.Write(--SP, r.high);
            memory.Write(--SP, r.low);
        }

        /// <summary>
        /// Pop a value from the stack.
        /// </summary>
        /// <returns></returns>
        private ushort POP()
        {
            Register16 r = new Register16(0);

            r.low = memory.Read(SP++);
            r.high = memory.Read(SP++);

            return r.reg;
        }

        #endregion

        #region ALU arithmetic and comparison

        /// <summary>
        /// Add an 8-bit value to the accumulator without carry.
        /// </summary>
        /// <param name="b">The vakue.</param>
        private void ADD8(byte b)
        {
            int w = A + b;
            int lookup = ((A & 0x88) >> 3) | ((b & 0x88) >> 2) | ((w & 0x88) >> 1);

            F = SZtable[w] | H35table[w & 0xff] |
                halfcarry_add_table[lookup & 0x07] | overflow_add_table[lookup >> 4];

            A = (byte)(w & 0xff);
        }

        /// <summary>
        /// Add an 8-bit value to the accumulator with carry.
        /// </summary>
        /// <param name="b">The vakue.</param>
        private void ADC8(byte b)
        {
            int w = A + b + (int)(F & Z80Flags.Carry);
            int lookup = ((A & 0x88) >> 3) | ((b  & 0x88) >> 2) | ((w & 0x88) >> 1);

            F = SZtable[w] | H35table[w & 0xff] |
                halfcarry_add_table[lookup & 0x07] | overflow_add_table[lookup >> 4];

            A = (byte)(w & 0xff);
        }

        /// <summary>
        /// Subtract an 8-bit value from the accumulator without carry.
        /// </summary>
        /// <param name="b">The vakue.</param>
        private void SUB8(byte b)
        {
            int w = A - b;

            if (w < 0)
            {
                w += 0x200;
            }

            int lookup = ((A & 0x88) >> 3) | ((b & 0x88) >> 2) | ((w & 0x88) >> 1);

            F = SZtable[w] | H35table[w] | Z80Flags.Neg |
                halfcarry_sub_table[lookup & 0x07] | overflow_sub_table[lookup >> 4];

            A = (byte)(w & 0xff);
        }

        /// <summary>
        /// Compare an 8-bit value with the accumulator.
        /// </summary>
        /// <param name="b">The vakue.</param>
        private void CP(byte b)
        {
            int w = A - b;

            if (w < 0)
            {
                w += 0x200;
            }

            int lookup = ((A & 0x88) >> 3) | ((b & 0x88) >> 2) | ((w & 0x88) >> 1);

            F = SZtable[w] | H35table[b] | Z80Flags.Neg |
                halfcarry_sub_table[lookup & 0x07] | overflow_sub_table[lookup >> 4];
        }

        /// <summary>
        /// Subtract an 8-bit value from the accumulator with carry.
        /// </summary>
        /// <param name="b">The vakue.</param>
        private void SBC8(byte b)
        {
            int w = A - b - (int)(F & Z80Flags.Carry);

            if (w < 0)
            {
                w += 0x200;
            }

            int lookup = ((A & 0x88) >> 3) | ((b & 0x88) >> 2) | ((w & 0x88) >> 1);

            F = SZtable[w] | H35table[w & 0xff] | Z80Flags.Neg |
                halfcarry_sub_table[lookup & 0x07] | overflow_sub_table[lookup >> 4];

            A = (byte)(w & 0xff);
        }

        /// <summary>
        /// Add a 16-bit value to a register without carry.
        /// </summary>
        /// <param name="b">The vakue.</param>
        private void ADD16(ref ushort reg, ushort b)
        {
            int w = reg + b;

            F &= Z80Flags.Sign | Z80Flags.Zero | Z80Flags.PV;

            if (w > 0xffff)
            {
                F |= Z80Flags.Carry;
            }

            int lookup = ((reg & 0x8800) >> 11) |
                         ((b & 0x8800) >> 10) |
                         ((w & 0x8800) >> 9);

            reg = (ushort)(w & 0xffff);

            F |= halfcarry_add_table[lookup & 0x07] | H35table[reg >> 8];
        }

        /// <summary>
        /// Add a 16-bit value to a register with carry.
        /// </summary>
        /// <param name="b">The vakue.</param>
        private void ADC16(ref ushort reg, ushort b)
        {
            int w = reg + b + (int)(F & Z80Flags.Carry);

            F = Z80Flags.None;

            if ((w & 0xffff) == 0)
            {
                F |= Z80Flags.Zero;
            }

            if ((w & 0x8000) == 0x8000)
            {
                F |= Z80Flags.Sign;
            }

            if (w > 0xffff)
            {
                F |= Z80Flags.Carry;
            }

            int lookup = ((reg & 0x8800) >> 11) |
                         ((b & 0x8800) >> 10) |
                         ((w & 0x8800) >> 9);

            reg = (ushort)(w & 0xffff);

            F |= halfcarry_add_table[lookup & 0x07] | overflow_add_table[lookup >> 4] |
                 H35table[reg >> 8];
        }


        /// <summary>
        /// Subtract a 16-bit value from a register with carry.
        /// </summary>
        /// <param name="b">The vakue.</param>
        private void SBC(ref ushort reg, ushort b)
        {
            int w = reg - b - (int)(F & Z80Flags.Carry);

            F = Z80Flags.Neg;

            if (w < 0)
            {
                w += 0x10000;
                F |= Z80Flags.Carry;
            }

            if ((w & 0xffff) == 0)
            {
                F |= Z80Flags.Zero;
            }

            if ((w & 0x8000) == 0x8000)
            {
                F |= Z80Flags.Sign;
            }

            int lookup = ((reg & 0x8800) >> 11) |
                         ((b & 0x8800) >> 10) |
                         ((w & 0x8800) >> 9);

            reg = (ushort)(w & 0xffff);

            F |= halfcarry_sub_table[lookup & 0x07] | overflow_sub_table[lookup >> 4] |
                 H35table[reg >> 8];
        }

        /// <summary>
        /// Increment an 8-bit register.
        /// </summary>
        /// <param name="reg">The register to increment.</param>
        void INC8(ref byte reg)
        {
            reg++;

            F &= Z80Flags.Carry;

            if (reg == 0x80)
            {
                F |= Z80Flags.PV;
            }

            if ((reg & 0x0f) == 0x00)
            {
                F |= Z80Flags.HalfCarry;
            }

            F |= SZtable[reg] | H35table[reg];
        }

        /// <summary>
        /// Decrement an 8-bit register.
        /// </summary>
        /// <param name="reg">The register to decrement.</param>
        void DEC8(ref byte reg)
        {
            reg--;

            F &= Z80Flags.Carry;
            F |= Z80Flags.Neg;

            if (reg == 0x7f)
            {
                F |= Z80Flags.PV;
            }

            if ((reg & 0x0f) == 0x0f)
            {
                F |= Z80Flags.HalfCarry;
            }

            F |= SZtable[reg] | H35table[reg];
        }

        /// <summary>
        /// Decimally adjust the accumulator.  A bugger of an opcode.
        /// Based on info from http://www.worldofspectrum.org/faq/reference/z80reference.htm
        /// </summary>
        void DAA()
        {
            byte add = 0;
            Z80Flags carry = Z80Flags.None;
            Z80Flags nf = F & Z80Flags.Neg;
            byte acc = A;

            if (acc>0x99 || (F & Z80Flags.Carry) == Z80Flags.Carry)
            {
                add |= 0x60;
                carry = Z80Flags.Carry;
            }

            if ((acc & 0xf) > 0x9 || (F & Z80Flags.HalfCarry) == Z80Flags.HalfCarry)
            {
                add|=0x06;
            }

            if (nf == Z80Flags.Neg)
            {
                A -= add;
            }
            else
            {
                A += add;
            }

            F = PSZtable[A]
                    | carry
                    | nf
                    | H35table[A];

            if (((A ^ acc) & 0x10) == 0x10)
            {
                F |= Z80Flags.HalfCarry;
            }
        }

        #endregion

        #region ALU rotate and shift operations

        /// <summary>
        /// Do RRCA.
        /// </summary>
        private void RRCA()
        {
            F &= Z80Flags.Sign | Z80Flags.Zero | Z80Flags.PV;
            F |= (Z80Flags)(A & 1);
            A = (byte)(Binary.ShiftRight(A, 1) | Binary.ShiftLeft(A, 7));
            F |= H35table[A];
        }

        /// <summary>
        /// Do RRA.
        /// </summary>
        private void RRA()
        {
            byte carry = (byte)(F & Z80Flags.Carry);
            F &= Z80Flags.Sign | Z80Flags.Zero | Z80Flags.PV;
            F |= (Z80Flags)(A & 1);
            A = (byte)(Binary.ShiftRight(A, 1) | Binary.ShiftLeft(carry, 7));
            F |= H35table[A];
        }

        /// <summary>
        /// Do RRC.
        /// </summary>
        /// <param name="reg">The register to operate on.</param>
        private void RRC(ref byte reg)
        {
            F = (Z80Flags)(reg & (int)Z80Flags.Carry);
            reg = (byte)(Binary.ShiftRight(reg, 1) | Binary.ShiftLeft(reg, 7));
            F |= PSZtable[reg] | H35table[reg];
        }

        /// <summary>
        /// Do RR.
        /// </summary>
        /// <param name="reg">The register to operate on.</param>
        private void RR(ref byte reg)
        {
            byte carry = (byte)(F & Z80Flags.Carry);
            F = (Z80Flags)(reg & (int)Z80Flags.Carry);
            reg = (byte)(Binary.ShiftRight(reg, 1) | Binary.ShiftLeft(carry, 7));
            F |= PSZtable[reg] | H35table[reg];
        }

        /// <summary>
        /// Do RLCA.
        /// </summary>
        private void RLCA()
        {
            F = (F & (Z80Flags.PV | Z80Flags.Sign | Z80Flags.Zero))
                     | (Z80Flags)Binary.ShiftRight(A, 7);

            A = (byte)(Binary.ShiftLeft(A, 1) | Binary.ShiftRight(A, 7));

            F |= H35table[A];
        }

        /// <summary>
        /// Do RLA.
        /// </summary>
        private void RLA()
        {
            byte carry = (byte)(F & Z80Flags.Carry);
            F = (F & (Z80Flags.PV | Z80Flags.Sign | Z80Flags.Zero))
                     | (Z80Flags)Binary.ShiftRight(A, 7);
            A = (byte)(Binary.ShiftLeft(A, 1) | carry);
            F |= H35table[A];
        }

        /// <summary>
        /// Do RLC.
        /// </summary>
        /// <param name="reg">The register to operate on.</param>
        private void RLC(ref byte reg)
        {
            byte carry = Binary.ShiftRight(reg, 7);
            reg = (byte)(Binary.ShiftLeft(reg, 1) | carry);
            F = PSZtable[reg] | (Z80Flags)carry | H35table[reg];
        }

        /// <summary>
        /// Do RL.
        /// </summary>
        /// <param name="reg">The register to operate on.</param>
        private void RL(ref byte reg)
        {
            byte carry = Binary.ShiftRight(reg, 7);
            reg = (byte)(Binary.ShiftLeft(reg, 1) | (int)(F & Z80Flags.Carry));
            F = PSZtable[reg] | (Z80Flags)carry | H35table[reg];
        }

        /// <summary>
        /// Do SRL.
        /// </summary>
        /// <param name="reg">The register to operate on.</param>
        private void SRL(ref byte reg)
        {
            byte carry = (byte)(reg & 1);
            reg = Binary.ShiftRight(reg, 1);
            F = PSZtable[reg] | (Z80Flags)carry | H35table[reg];
        }

        /// <summary>
        /// Do SRA.
        /// </summary>
        /// <param name="reg">The register to operate on.</param>
        private void SRA(ref byte reg)
        {
            byte carry = (byte)(reg & 1);
            reg = (byte)(Binary.ShiftRight(reg, 1) | (reg & 0x80));
            F = PSZtable[reg] | (Z80Flags)carry | H35table[reg];
        }

        /// <summary>
        /// Do SLL.
        /// </summary>
        /// <param name="reg">The register to operate on.</param>
        private void SLL(ref byte reg)
        {
            byte carry = Binary.ShiftRight(reg, 7);
            reg = (byte)(Binary.ShiftLeft(reg, 1) | 0x01);
            F = PSZtable[reg] | (Z80Flags)carry | H35table[reg];
        }

        /// <summary>
        /// Do SLA.
        /// </summary>
        /// <param name="reg">The register to operate on.</param>
        private void SLA(ref byte reg)
        {
            byte carry = Binary.ShiftRight(reg, 7);
            reg = Binary.ShiftLeft(reg, 1);
            F = PSZtable[reg] | (Z80Flags)carry | H35table[reg];
        }

        #endregion

        #region ALU boolean operations

        /// <summary>
        /// AND a value with the accumulator.
        /// </summary>
        /// <param name="val">The value.</param>
        void AND(byte val)
        {
            A &= val;
            F = PSZtable[A] | Z80Flags.HalfCarry | H35table[A];
        }

        /// <summary>
        /// OR a value with the accumulator.
        /// </summary>
        /// <param name="val">The value.</param>
        void OR(byte val)
        {
            A |= val;
            F = PSZtable[A] | H35table[A];
        }

        /// <summary>
        /// XOR a value with the accumulator.
        /// </summary>
        /// <param name="val">The value.</param>
        void XOR(byte val)
        {
            A ^= val;
            F = PSZtable[A] | H35table[A];
        }

        /// <summary>
        /// Perform the BIT operation.
        /// </summary>
        /// <param name="reg">The register to operate on.</param>
        /// <param name="bit">The bit to test.</param>
        void BIT(ref byte reg, int bit)
        {
            F &= Z80Flags.Carry;
            F |= Z80Flags.HalfCarry | H35table[reg];

            if ((reg & (1 << bit)) != 0)
            {
                if (bit == 7 && (reg & (int)Z80Flags.Sign) != 0)
                {
                    F |= Z80Flags.Sign;
                }
            }
            else
            {
                F |= Z80Flags.Zero | Z80Flags.PV;
            }
        }

        /// <summary>
        /// Perform the BIT operation on an indexed location.
        /// </summary>
        /// <param name="reg">The register to operate on.</param>
        /// <param name="bit">The bit to test.</param>
        /// <param name="addr">The address being checked.</param>
        void BIT(ref byte reg, int bit, ushort addr)
        {
            F &= Z80Flags.Carry;
            F |= Z80Flags.HalfCarry | H35table[addr>>8];

            if ((reg & (1 << bit)) != 0)
            {
                if (bit == 7 && (reg & (int)Z80Flags.Sign) != 0)
                {
                    F |= Z80Flags.Sign;
                }
            }
            else
            {
                F |= Z80Flags.Zero | Z80Flags.PV;
            }
        }

        /// <summary>
        /// Perform the bit set operation.
        /// </summary>
        /// <param name="reg">The register to operate on.</param>
        /// <param name="bit">The bit to test.</param>
        void BIT_SET(ref byte reg, int bit)
        {
            reg |= (byte)(1 << bit);
        }

        /// <summary>
        /// Perform the bit clear operation.
        /// </summary>
        /// <param name="reg">The register to operate on.</param>
        /// <param name="bit">The bit to test.</param>
        void BIT_RES(ref byte reg, int bit)
        {
            reg &= (byte)~(1 << bit);
        }

        #endregion

        #region Jump operations

        /// <summary>
        /// The call operation.
        /// </summary>
        private void CALL()
        {
            PUSH((ushort)(PC + 2));
            PC = FetchWord();
        }

        /// <summary>
        /// The jump operation.
        /// </summary>
        private void JP()
        {
            PC = FetchWord();
        }

        /// <summary>
        /// The jump relative operation.
        /// </summary>
        private void JR()
        {
            PC = (ushort)(PC + (sbyte)memory.Read(PC) + 1);
        }

        /// <summary>
        /// Jump relative if the passed condition flag ANDed with the flag
        /// register equals the passed check value.
        /// </summary>
        /// <param name="cond">The condition flag.</param>
        /// <param name="val">The check value.</param>
        private void JR_COND(Z80Flags cond, Z80Flags val)
        {
            if ((F & cond) == val)
            {
                clock.Add(12);
                JR();
            }
            else
            {
                clock.Add(7);
                PC++;
            }
        }

        /// <summary>
        /// Jump if the passed condition flag ANDed with the flag
        /// register equals the passed check value.
        /// </summary>
        /// <param name="cond">The condition flag.</param>
        /// <param name="val">The check value.</param>
        private void JP_COND(Z80Flags cond, Z80Flags val)
        {
            clock.Add(10);

            if ((F & cond) == val)
            {
                JP();
            }
            else
            {
                PC+=2;
            }
        }

        /// <summary>
        /// Call if the passed condition flag ANDed with the flag
        /// register equals the passed check value.
        /// </summary>
        /// <param name="cond">The condition flag.</param>
        /// <param name="val">The check value.</param>
        private void CALL_COND(Z80Flags cond, Z80Flags val)
        {
            if ((F & cond) == val)
            {
                clock.Add(17);
                CALL();
            }
            else
            {
                clock.Add(10);
                PC+=2;
            }
        }

        /// <summary>
        /// Return if the passed condition flag ANDed with the flag
        /// register equals the passed check value.
        /// </summary>
        /// <param name="cond">The condition flag.</param>
        /// <param name="val">The check value.</param>
        private void RET_COND(Z80Flags cond, Z80Flags val)
        {
            if ((F & cond) == val)
            {
                clock.Add(11);
                PC = POP();
            }
            else
            {
                clock.Add(5);
            }
        }

        /// <summary>
        /// Reset the PC to an address.
        /// </summary>
        /// <param name="addr">The address.</param>
        private void RST(ushort addr)
        {
            clock.Add(11);
            PUSH(PC);
            PC = addr;
        }

        #endregion

        #region Block operations

        /// <summary>
        /// LDI instruction.
        /// </summary>
        private void LDI()
        {
            byte b = memory.Read(HL.reg);
            memory.Write(DE.reg, b);
            DE.reg++;
            HL.reg++;
            BC.reg--;

            if (BC.reg != 0)
            {
                ClearFlag(Z80Flags.HalfCarry | Z80Flags.Neg);
                SetFlag(Z80Flags.PV);
            }
            else
            {
                ClearFlag(Z80Flags.HalfCarry | Z80Flags.Neg | Z80Flags.PV);
            }

            F |= H35table[A + b];
        }

        /// <summary>
        /// LDD instruction.
        /// </summary>
        private void LDD()
        {
            byte b = memory.Read(HL.reg);
            memory.Write(DE.reg, b);
            DE.reg--;
            HL.reg--;
            BC.reg--;

            if (BC.reg != 0)
            {
                ClearFlag(Z80Flags.HalfCarry | Z80Flags.Neg);
                SetFlag(Z80Flags.PV);
            }
            else
            {
                ClearFlag(Z80Flags.HalfCarry | Z80Flags.Neg | Z80Flags.PV);
            }

            F |= H35table[A + b];
        }

        /// <summary>
        /// CPI instruction.
        /// </summary>
        private void CPI()
        {
            Z80Flags c = F & Z80Flags.Carry;
            byte b = memory.Read(HL.reg);

            CP(b);
            F |= c;

            HL.reg++;
            BC.reg--;

            if (BC.reg != 0)
            {
                SetFlag(Z80Flags.PV);
            }
            else
            {
                ClearFlag(Z80Flags.PV);
            }
        }

        /// <summary>
        /// CPD instruction.
        /// </summary>
        private void CPD()
        {
            Z80Flags c = F & Z80Flags.Carry;
            byte b = memory.Read(HL.reg);

            CP(b);
            F |= c;

            HL.reg--;
            BC.reg--;

            if (BC.reg != 0)
            {
                SetFlag(Z80Flags.PV);
            }
            else
            {
                ClearFlag(Z80Flags.PV);
            }
        }

        /// <summary>
        /// INI instruction.
        /// </summary>
        private void INI()
        {
            int w;
            byte b = device.Read(BC.reg);
            memory.Write(HL.reg, b);

            BC.high--;
            HL.reg++;

            F = SZtable[BC.high] | H35table[BC.high];

            w = BC.low + b;

            if ((w & 0x80) == 0x80)
            {
                SetFlag(Z80Flags.Neg);
            }

            if ((w & 0x100) == 0x100)
            {
                SetFlag(Z80Flags.Carry | Z80Flags.HalfCarry);
            }
            else
            {
                ClearFlag(Z80Flags.Carry | Z80Flags.HalfCarry);
            }
        }

        /// <summary>
        /// IND instruction.
        /// </summary>
        private void IND()
        {
            int w;
            byte b = device.Read(BC.reg);
            memory.Write(HL.reg, b);

            BC.high--;
            HL.reg--;

            F = SZtable[BC.high] | H35table[BC.high];

            w = BC.low + b;

            if ((w & 0x80) == 0x80)
            {
                SetFlag(Z80Flags.Neg);
            }

            if ((w & 0x100) == 0x100)
            {
                SetFlag(Z80Flags.Carry | Z80Flags.HalfCarry);
            }
            else
            {
                ClearFlag(Z80Flags.Carry | Z80Flags.HalfCarry);
            }
        }

        /// <summary>
        /// OUTI instruction.
        /// </summary>
        private void OUTI()
        {
            device.Write(BC.reg, memory.Read(HL.reg));

            HL.reg++;
            BC.high--;

            F = SZtable[BC.high] | H35table[BC.high];
        }

        /// <summary>
        /// OUTD instruction.
        /// </summary>
        private void OUTD()
        {
            device.Write(BC.reg, memory.Read(HL.reg));

            HL.reg--;
            BC.high--;

            F = SZtable[BC.high] | H35table[BC.high] | Z80Flags.Neg;
        }

        #endregion
    }
}