#include "stdafx.h"
#include "LR35902.h"

// based on http://www.z80.info/decoding.htm
// Half carry flag help from https://github.com/oubiwann/z80

EightBit::LR35902::LR35902(Bus& memory)
: IntelProcessor(memory),
  m_ime(false),
  m_prefixCB(false) {
}

void EightBit::LR35902::reset() {
	IntelProcessor::reset();
	sp.word = 0xfffe;
	di();
}

void EightBit::LR35902::initialise() {

	IntelProcessor::initialise();

	AF().word = 0xffff;

	BC().word = 0xffff;
	DE().word = 0xffff;
	HL().word = 0xffff;

	m_prefixCB = false;
}

#pragma region Interrupt routines

void EightBit::LR35902::di() {
	IME() = false;
}

void EightBit::LR35902::ei() {
	IME() = true;
}

int EightBit::LR35902::interrupt(uint8_t value) {
	cycles = 0;
	di();
	restart(value);
	return 4;
}

#pragma endregion Interrupt routines

#pragma region Flag manipulation helpers

void EightBit::LR35902::adjustZero(uint8_t& f, uint8_t value) {
	clearFlag(f, ZF, value);
}

void EightBit::LR35902::postIncrement(uint8_t& f, uint8_t value) {
	adjustZero(f, value);
	clearFlag(f, NF);
	clearFlag(f, HC, lowNibble(value));
}

void EightBit::LR35902::postDecrement(uint8_t& f, uint8_t value) {
	adjustZero(f, value);
	setFlag(f, NF);
	clearFlag(f, HC, lowNibble(value + 1));
}

#pragma endregion Flag manipulation helpers

#pragma region PC manipulation: call/ret/jp/jr

bool EightBit::LR35902::jrConditionalFlag(int flag) {
	switch (flag) {
	case 0:	// NZ
		return jrConditional(!(F() & ZF));
	case 1:	// Z
		return jrConditional(F() & ZF);
	case 2:	// NC
		return jrConditional(!(F() & CF));
	case 3:	// C
		return jrConditional(F() & CF);
	}
	throw std::logic_error("Unhandled JR conditional");
}

bool EightBit::LR35902::jumpConditionalFlag(int flag) {
	switch (flag) {
	case 0:	// NZ
		return jumpConditional(!(F() & ZF));
	case 1:	// Z
		return jumpConditional(F() & ZF);
	case 2:	// NC
		return jumpConditional(!(F() & CF));
	case 3:	// C
		return jumpConditional(F() & CF);
	}
	throw std::logic_error("Unhandled JP conditional");
}

void EightBit::LR35902::reti() {
	ret();
	ei();
}

bool EightBit::LR35902::returnConditionalFlag(int flag) {
	switch (flag) {
	case 0:	// NZ
		return returnConditional(!(F() & ZF));
	case 1:	// Z
		return returnConditional(F() & ZF);
	case 2:	// NC
		return returnConditional(!(F() & CF));
	case 3:	// C
		return returnConditional(F() & CF);
	}
	throw std::logic_error("Unhandled RET conditional");
}

bool EightBit::LR35902::callConditionalFlag(int flag) {
	switch (flag) {
	case 0:	// NZ
		return callConditional(!(F() & ZF));
	case 1:	// Z
		return callConditional(F() & ZF);
	case 2:	// NC
		return callConditional(!(F() & CF));
	case 3:	// C
		return callConditional(F() & CF);
	}
	throw std::logic_error("Unhandled CALL conditional");
}

#pragma endregion PC manipulation: call/ret/jp/jr

#pragma region 16-bit arithmetic

void EightBit::LR35902::sbc(register16_t& operand, register16_t value) {

	auto before = operand;

	auto result = before.word - value.word - (F() & CF);
	operand.word = result;

	auto& f = F();
	clearFlag(f, ZF, operand.word);
	adjustHalfCarrySub(f, before.high, value.high, operand.high);
	setFlag(f, NF);
	setFlag(f, CF, result & Bit16);
}

void EightBit::LR35902::adc(register16_t& operand, register16_t value) {

	auto before = operand;

	auto result = before.word + value.word + (F() & CF);
	operand.word = result;

	auto& f = F();
	clearFlag(f, ZF, result);
	adjustHalfCarryAdd(f, before.high, value.high, operand.high);
	clearFlag(f, NF);
	setFlag(f, CF, result & Bit16);
}

void EightBit::LR35902::add(register16_t& operand, register16_t value) {

	auto before = operand;

	auto result = before.word + value.word;

	operand.word = result;

	auto& f = F();
	clearFlag(f, NF);
	setFlag(f, CF, result & Bit16);
	adjustHalfCarryAdd(f, before.high, value.high, operand.high);
}

#pragma endregion 16-bit arithmetic

#pragma region ALU

void EightBit::LR35902::add(uint8_t& operand, uint8_t value, int carry) {

	auto& f = F();

	register16_t result;
	result.word = operand + value + carry;

	adjustHalfCarryAdd(f, operand, value, result.low);

	operand = result.low;

	clearFlag(f, NF);
	setFlag(f, CF, result.word & Bit8);
	adjustZero(f, operand);
}

void EightBit::LR35902::adc(uint8_t& operand, uint8_t value) {
	add(operand, value, F() & CF);
}

void EightBit::LR35902::sub(uint8_t& operand, uint8_t value, int carry) {

	auto& f = F();

	register16_t result;
	result.word = operand - value - carry;

	adjustHalfCarrySub(f, operand, value, result.low);

	operand = result.low;

	setFlag(f, NF);
	setFlag(f, CF, result.word & Bit8);
	adjustZero(f, operand);
}

void EightBit::LR35902::sbc(uint8_t& operand, uint8_t value) {
	sub(operand, value, F() & CF);
}

void EightBit::LR35902::andr(uint8_t& operand, uint8_t value) {
	auto& f = F();
	operand &= value;
	setFlag(f, HC);
	clearFlag(f, CF | NF);
	adjustZero(f, operand);
}

void EightBit::LR35902::xorr(uint8_t& operand, uint8_t value) {
	auto& f = F();
	operand ^= value;
	clearFlag(f, HC | CF | NF);
	adjustZero(f, operand);
}

void EightBit::LR35902::orr(uint8_t& operand, uint8_t value) {
	auto& f = F();
	operand |= value;
	clearFlag(f, HC | CF | NF);
	adjustZero(f, operand);
}

void EightBit::LR35902::compare(uint8_t value) {
	auto check = A();
	sub(check, value);
}

#pragma endregion ALU

#pragma region Shift and rotate

void EightBit::LR35902::rlc(uint8_t& operand) {
	auto& f = F();
	auto carry = operand & Bit7;
	operand <<= 1;
	setFlag(f, CF, carry);
	carry ? operand |= Bit0 : operand &= ~Bit0;
	clearFlag(f, NF | HC);
	adjustZero(f, operand);
}

void EightBit::LR35902::rrc(uint8_t& operand) {
	auto& f = F();
	auto carry = operand & Bit0;
	operand >>= 1;
	carry ? operand |= Bit7 : operand &= ~Bit7;
	setFlag(f, CF, carry);
	clearFlag(f, NF | HC);
	adjustZero(f, operand);
}

void EightBit::LR35902::rl(uint8_t& operand) {
	auto& f = F();
	auto oldCarry = f & CF;
	auto newCarry = operand & Bit7;
	operand <<= 1;
	oldCarry ? operand |= Bit0 : operand &= ~Bit0;
	setFlag(f, CF, newCarry);
	clearFlag(f, NF | HC);
	adjustZero(f, operand);
}

void EightBit::LR35902::rr(uint8_t& operand) {
	auto& f = F();
	auto oldCarry = f & CF;
	auto newCarry = operand & Bit0;
	operand >>= 1;
	operand |= oldCarry << 7;
	setFlag(f, CF, newCarry);
	clearFlag(f, NF | HC);
	adjustZero(f, operand);
}

//

void EightBit::LR35902::sla(uint8_t& operand) {
	auto& f = F();
	auto newCarry = operand & Bit7;
	operand <<= 1;
	setFlag(f, CF, newCarry);
	clearFlag(f, NF | HC);
	adjustZero(f, operand);
}

void EightBit::LR35902::sra(uint8_t& operand) {
	auto& f = F();
	auto new7 = operand & Bit7;
	auto newCarry = operand & Bit0;
	operand >>= 1;
	operand |= new7;
	setFlag(f, CF, newCarry);
	clearFlag(f, NF | HC);
	adjustZero(f, operand);
}

void EightBit::LR35902::srl(uint8_t& operand) {
	auto& f = F();
	auto newCarry = operand & Bit0;
	operand >>= 1;
	operand &= ~Bit7;	// clear bit 7
	setFlag(f, CF, newCarry);
	clearFlag(f, NF | HC);
	adjustZero(f, operand);
}

#pragma endregion Shift and rotate

#pragma region BIT/SET/RES

void EightBit::LR35902::bit(int n, uint8_t& operand) {
	auto& f = F();
	auto carry = f & CF;
	uint8_t discarded = operand;
	andr(discarded, 1 << n);
	setFlag(f, CF, carry);
}

void EightBit::LR35902::res(int n, uint8_t& operand) {
	auto bit = 1 << n;
	operand &= ~bit;
}

void EightBit::LR35902::set(int n, uint8_t& operand) {
	auto bit = 1 << n;
	operand |= bit;
}

#pragma endregion BIT/SET/RES

#pragma region Miscellaneous instructions

void EightBit::LR35902::daa() {

	auto& f = F();

	uint8_t a = A();

	auto lowAdjust = (f & HC) | ((A() & Mask4) > 9);
	auto highAdjust = (f & CF) | (A() > 0x99);

	if (F() & NF) {
		if (lowAdjust)
			a -= 6;
		if (highAdjust)
			a -= 0x60;
	} else {
		if (lowAdjust)
			a += 6;
		if (highAdjust)
			a += 0x60;
	}

	f = (f & (CF | NF)) | (A() > 0x99) | ((A() ^ a) & HC);

	adjustZero(f, a);

	A() = a;
}

void EightBit::LR35902::cpl() {
	A() = ~A();
	auto& f = F();
	setFlag(f, HC | NF);
}

void EightBit::LR35902::scf() {
	auto& f = F();
	setFlag(f, CF);
	clearFlag(f, HC | NF);
}

void EightBit::LR35902::ccf() {
	auto& f = F();
	auto carry = f & CF;
	clearFlag(f, CF, carry);
	clearFlag(f, NF | HC);
}

void EightBit::LR35902::swap(uint8_t& operand) {
	auto& f = F();
	auto low = lowNibble(operand);
	auto high = highNibble(operand);
	operand = promoteNibble(low) | demoteNibble(high);
	adjustZero(f, operand);
	clearFlag(f, NF | HC | CF);
}

#pragma endregion Miscellaneous instructions

int EightBit::LR35902::step() {
	ExecutingInstruction.fire(*this);
	m_prefixCB = false;
	cycles = 0;
	return fetchExecute();
}

int EightBit::LR35902::execute(uint8_t opcode) {

	auto x = (opcode & 0b11000000) >> 6;
	auto y = (opcode & 0b111000) >> 3;
	auto z = (opcode & 0b111);

	auto p = (y & 0b110) >> 1;
	auto q = (y & 1);

	if (m_prefixCB)
		executeCB(x, y, z, p, q);
	else
		executeOther(x, y, z, p, q);

	if (cycles == 0)
		throw std::logic_error("Unhandled opcode");

	return cycles * 4;
}

void EightBit::LR35902::executeCB(int x, int y, int z, int p, int q) {
	switch (x) {
	case 0:	// rot[y] r[z]
		switch (y) {
		case 0:
			rlc(R(z));
			break;
		case 1:
			rrc(R(z));
			break;
		case 2:
			rl(R(z));
			break;
		case 3:
			rr(R(z));
			break;
		case 4:
			sla(R(z));
			break;
		case 5:
			sra(R(z));
			break;
		case 6:
			swap(R(z));
			break;
		case 7:
			srl(R(z));
			break;
		}
		adjustZero(F(), R(z));
		cycles += 2;
		if (z == 6)
			cycles += 2;
		break;
	case 1: // BIT y, r[z]
			bit(y, R(z));
			cycles += 2;
			if (z == 6)
				cycles += 2;
		break;
	case 2:	// RES y, r[z]
		res(y, R(z));
		cycles += 2;
		if (z == 6)
			cycles += 2;
		break;
	case 3:	// SET y, r[z]
		set(y, R(z));
		cycles += 2;
		if (z == 6)
			cycles += 2;
		break;
	}
}

void EightBit::LR35902::executeOther(int x, int y, int z, int p, int q) {
	switch (x) {
	case 0:
		switch (z) {
		case 0:	// Relative jumps and assorted ops
			switch (y) {
			case 0:	// NOP
				cycles++;
				break;
			case 1:	// GB: LD (nn),SP
				fetchWord();
				m_memory.setWord(MEMPTR().word, sp);
				cycles += 5;
				break;
			case 2:	// GB: STOP
				stop();
				cycles++;
				break;
			case 3:	// JR d
				jr(fetchByte());
				cycles += 4;
				break;
			default: {	// JR cc,d
					auto condition = y - 4;
					if (condition < 4) {
						if (jrConditionalFlag(condition))
							cycles++;
						cycles += 2;
					}
				}
				break;
			}
			break;
		case 1:	// 16-bit load immediate/add
			switch (q) {
			case 0:	// LD rp,nn
				Processor::fetchWord(RP(p));
				cycles += 3;
				break;
			case 1:	// ADD HL,rp
				add(HL(), RP(p));
				cycles += 2;
				break;
			}
			break;
		case 2:	// Indirect loading
			switch (q) {
			case 0:
				switch (p) {
				case 0:	// LD (BC),A
					MEMPTR() = BC();
					MEMPTR().high = memptrReference() = A();
					cycles += 2;
					break;
				case 1:	// LD (DE),A
					MEMPTR() = DE();
					MEMPTR().high = memptrReference() = A();
					cycles += 2;
					break;
				case 2:	// GB: LDI (HL),A
					MEMPTR().word = HL().word++;
					MEMPTR().high = memptrReference() = A();
					cycles += 2;
					break;
				case 3: // GB: LDD (HL),A
					MEMPTR().word = HL().word--;
					MEMPTR().high = memptrReference() = A();
					cycles += 2;
					break;
				}
				break;
			case 1:
				switch (p) {
				case 0:	// LD A,(BC)
					MEMPTR() = BC();
					A() = memptrReference();
					cycles += 2;
					break;
				case 1:	// LD A,(DE)
					MEMPTR() = DE();
					A() = memptrReference();
					cycles += 2;
					break;
				case 2:	// GB: LDI A,(HL)
					MEMPTR().word = HL().word++;
					A() = m_memory.reference();
					cycles += 2;
					break;
				case 3:	// GB: LDD A,(HL)
					MEMPTR().word = HL().word--;
					A() = m_memory.reference();
					cycles += 2;
					break;
				}
				break;
			}
			break;
		case 3:	// 16-bit INC/DEC
			switch (q) {
			case 0:	// INC rp
				++RP(p).word;
				break;
			case 1:	// DEC rp
				--RP(p).word;
				break;
			}
			cycles += 2;
			break;
		case 4:	// 8-bit INC
			postIncrement(F(), ++R(y));	// INC r
			cycles++;
			if (y == 6)
				cycles += 2;
			break;
		case 5:	// 8-bit DEC
			postDecrement(F(), --R(y));	// DEC r
			cycles++;
			if (y == 6)
				cycles += 2;
			break;
		case 6: // 8-bit load immediate
			R(y) = fetchByte();
			cycles += 2;
			break;
		case 7:	// Assorted operations on accumulator/flags
			switch (y) {
			case 0:
				rlc(A());
				break;
			case 1:
				rrc(A());
				break;
			case 2:
				rl(A());
				break;
			case 3:
				rr(A());
				break;
			case 4:
				daa();
				break;
			case 5:
				cpl();
				break;
			case 6:
				scf();
				break;
			case 7:
				ccf();
				break;
			}
			cycles++;
			break;
		}
		break;
	case 1:	// 8-bit loading
		if (z == 6 && y == 6) { 	// Exception (replaces LD (HL), (HL))
			halt();
		} else {
			R(y) = R(z);
			if ((y == 6) || (z == 6))	// M operations
				cycles++;
		}
		cycles++;
		break;
	case 2:	// Operate on accumulator and register/memory location
		switch (y) {
		case 0:	// ADD A,r
			add(A(), R(z));
			break;
		case 1:	// ADC A,r
			adc(A(), R(z));
			break;
		case 2:	// SUB r
			sub(A(), R(z));
			break;
		case 3:	// SBC A,r
			sbc(A(), R(z));
			break;
		case 4:	// AND r
			andr(A(), R(z));
			break;
		case 5:	// XOR r
			xorr(A(), R(z));
			break;
		case 6:	// OR r
			orr(A(), R(z));
			break;
		case 7:	// CP r
			compare(R(z));
			break;
		}
		cycles++;
		if (z == 6)
			cycles++;
		break;
	case 3:
		switch (z) {
		case 0:	// Conditional return
			if (y < 4) {
				if (returnConditionalFlag(y))
					cycles += 3;
				cycles += 2;
			} else {
				switch (y) {
				case 4:	// GB: LD (FF00 + n),A
					m_memory.set(0xff00 + fetchByte(), A());
					cycles += 3;
					break;
				case 5: { // GB: ADD SP,dd
						auto& f = F();
						auto before = sp;
						auto value = fetchByte();
						sp.word += (int8_t)value;
						clearFlag(f, ZF | NF);
						setFlag(f, CF, sp.word & Bit16);
						adjustHalfCarryAdd(f, before.high, value, sp.high);
					}
					cycles += 4;
					break;
				case 6:	// GB: LD A,(FF00 + n)
					A() = m_memory.get(0xff00 + fetchByte());
					cycles += 3;
					break;
				case 7: { // GB: LD HL,SP + dd
						auto& f = F();
						auto before = sp;
						auto value = fetchByte();
						HL().word = before.word + (int8_t)value;
						clearFlag(f, ZF | NF);
						setFlag(f, CF, HL().word & Bit16);
						adjustHalfCarryAdd(f, before.high, value, HL().high);
					}
					cycles += 3;
					break;
				}
			}
			break;
		case 1:	// POP & various ops
			switch (q) {
			case 0:	// POP rp2[p]
				popWord(RP2(p));
				cycles += 3;
				break;
			case 1:
				switch (p) {
				case 0:	// RET
					ret();
					cycles += 4;
					break;
				case 1:	// GB: RETI
					reti();
					cycles += 4;
					break;
				case 2:	// JP HL
					pc = HL();
					cycles += 1;
					break;
				case 3:	// LD SP,HL
					sp = HL();
					cycles += 2;
					break;
				}
			}
			break;
		case 2:	// Conditional jump
			if (y < 4) {
				jumpConditionalFlag(y);
				cycles += 3;
			} else {
				switch (y) {
				case 4:	// GB: LD (FF00 + C),A
					m_memory.set(0xff00 + C(), A());
					cycles += 2;
					break;
				case 5:	// GB: LD (nn),A
					fetchWord();
					m_memory.ADDRESS() = MEMPTR();
					m_memory.reference() = A();
					cycles += 4;
					break;
				case 6:	// GB: LD A,(FF00 + C)
					m_memory.ADDRESS().word = 0xff00 + C();
					A() = m_memory.reference();
					cycles += 2;
					break;
				case 7:	// GB: LD A,(nn)
					fetchWord();
					m_memory.ADDRESS() = MEMPTR();
					A() = m_memory.reference();
					cycles += 4;
					break;
				}
			}
			break;
		case 3:	// Assorted operations
			switch (y) {
			case 0:	// JP nn
				fetchWord();
				jump();
				cycles += 4;
				break;
			case 1:	// CB prefix
				m_prefixCB = true;
				fetchExecute();
				break;
			case 6:	// DI
				di();
				cycles++;
				break;
			case 7:	// EI
				ei();
				cycles++;
				break;
			}
			break;
		case 4:	// Conditional call: CALL cc[y], nn
			if (callConditionalFlag(y))
				cycles += 3;
			cycles += 3;
			break;
		case 5:	// PUSH & various ops
			switch (q) {
			case 0:	// PUSH rp2[p]
				pushWord(RP2(p));
				cycles += 4;
				break;
			case 1:
				switch (p) {
				case 0:	// CALL nn
					fetchWord();
					call();
					cycles += 6;
					break;
				}
			}
			break;
		case 6:	// Operate on accumulator and immediate operand: alu[y] n
			switch (y) {
			case 0:	// ADD A,n
				add(A(), fetchByte());
				break;
			case 1:	// ADC A,n
				adc(A(), fetchByte());
				break;
			case 2:	// SUB n
				sub(A(), fetchByte());
				break;
			case 3:	// SBC A,n
				sbc(A(), fetchByte());
				break;
			case 4:	// AND n
				andr(A(), fetchByte());
				break;
			case 5:	// XOR n
				xorr(A(), fetchByte());
				break;
			case 6:	// OR n
				orr(A(), fetchByte());
				break;
			case 7:	// CP n
				compare(fetchByte());
				break;
			}
			cycles += 2;
			break;
		case 7:	// Restart: RST y * 8
			restart(y << 3);
			cycles += 4;
			break;
		}
		break;
	}
}