#include "CPU.hpp"


void CPU::Implicit()
{
	pc += 1;

	// Do nothing
	fetchedByte = acc;
}

void CPU::Immediate()
{
	pc += 2;

	fetchedAddress = pc - 1;
	fetchedByte = ReadMemory(fetchedAddress);
}

void CPU::ZeroPage()
{
	pc += 2;

	fetchedAddress = ReadMemory(pc - 1);
	fetchedByte = ReadMemory(fetchedAddress);
}

void CPU::ZeroPageX()
{
	pc += 2;

	uint8_t operand = ReadMemory(pc - 1);
	fetchedAddress = (operand + x) & 0xFFu;
	fetchedByte = ReadMemory(fetchedAddress);
}

void CPU::ZeroPageY()
{
	pc += 2;

	uint8_t operand = ReadMemory(pc - 1);
	fetchedAddress = (operand + y) & 0xFFu;
	fetchedByte = ReadMemory(fetchedAddress);
}

void CPU::Absolute()
{
	pc += 3;

	uint8_t addressLsb = ReadMemory(pc - 2);
	uint8_t addressMsb = ReadMemory(pc - 1);

	fetchedAddress = ComposeAddress(addressMsb, addressLsb);
	fetchedByte = ReadMemory(fetchedAddress);
}

void CPU::AbsoluteX()
{
	pc += 3;

	uint8_t addressLsb = ReadMemory(pc - 2);
	uint8_t addressMsb = ReadMemory(pc - 1);

	uint16_t preAddress = ComposeAddress(addressMsb, addressLsb);
	fetchedAddress = preAddress + x;
	fetchedByte = ReadMemory(fetchedAddress);

	pageBoundaryCrossed = IsPageBoundaryCrossed(preAddress, fetchedAddress);
}

void CPU::AbsoluteY()
{
	pc += 3;

	uint8_t addressLsb = ReadMemory(pc - 2);
	uint8_t addressMsb = ReadMemory(pc - 1);

	uint16_t preAddress = ComposeAddress(addressMsb, addressLsb);
	fetchedAddress = preAddress + y;
	fetchedByte = ReadMemory(fetchedAddress);

	pageBoundaryCrossed = IsPageBoundaryCrossed(preAddress, fetchedAddress);
}

void CPU::Indirect()
{
	pc += 3;

	uint8_t indirectLsb = ReadMemory(pc - 2);
	uint8_t indirectMsb = ReadMemory(pc - 1);

	// NOTE: 6502 BUG - indirect address wraps
	// $02FF + 1 = $0200

	uint16_t addressIndirect = ComposeAddress(indirectMsb, indirectLsb);
	uint8_t addressLsb = ReadMemory(addressIndirect);

	// Increment LSB to read second byte - it will wrap
	++indirectLsb;

	addressIndirect = ComposeAddress(indirectMsb, indirectLsb);
	uint8_t addressMsb = ReadMemory(addressIndirect);

	fetchedAddress = ComposeAddress(addressMsb, addressLsb);
	fetchedByte = ReadMemory(fetchedAddress);
}

void CPU::IndirectX()
{
	pc += 2;

	uint8_t addressIndirect = ReadMemory(pc - 1) + x;

	// Modulo to keep within zero-page
	uint16_t addressLsb = ReadMemory((addressIndirect % 0x100));
	uint16_t addressMsb = ReadMemory((addressIndirect + 1) % 0x100);

	fetchedAddress = ComposeAddress(addressMsb, addressLsb);
	fetchedByte = ReadMemory(fetchedAddress);
}

void CPU::IndirectY()
{
	pc += 2;

	uint8_t addressIndirect = ReadMemory(pc - 1);

	// Modulo to keep within zero-page
	uint8_t addressLsb = ReadMemory(addressIndirect % 0x100);
	uint8_t addressMsb = ReadMemory((addressIndirect + 1) % 0x100);

	uint16_t preAddress = ComposeAddress(addressMsb, addressLsb);
	fetchedAddress = preAddress + y;
	fetchedByte = ReadMemory(fetchedAddress);

	pageBoundaryCrossed = IsPageBoundaryCrossed(preAddress, fetchedAddress);
}

void CPU::Relative()
{
	pc += 2;

	int8_t operand = ReadMemory(pc - 1);

	uint16_t oldPc = pc;

	fetchedAddress = pc + operand;
	fetchedByte = ReadMemory(fetchedAddress);

	pageBoundaryCrossed = IsPageBoundaryCrossed(oldPc, fetchedAddress);
}