#include <stdint.h>
#include <stdio.h>
#include <string.h>

// DO NOT ENABLE FOR NES!!!!!
// #define ENABLE_DECIMAL_MODE

#define PAGE_CROSSED(base, addr) (((base ^ addr) > 0xff))

static inline uint8_t pack_flags(struct cpu_state *cpu) {
	return (cpu->n << 7) | (cpu->v << 6) | (1 << 5) | (cpu->d << 3) | (cpu->i << 2) | (cpu->z << 1) | cpu->c;
}

static inline void unpack_flags(struct cpu_state *cpu, uint8_t value) {
	cpu->n = (value >> 7) & 1;
	cpu->v = (value >> 6) & 1;
	cpu->d = (value >> 3) & 1;
	cpu->i = (value >> 2) & 1;
	cpu->z = (value >> 1) & 1;
	cpu->c = value & 1;
}

static inline void update_zn(struct cpu_state *cpu, uint8_t result) {
	cpu->z = (result == 0);
	cpu->n = (result & 0x80) != 0;
}

static void (*opcode_lut[256*2])(struct nes_state *) __attribute__((aligned(4096)));

#include "cpu_opcodes.c"
#include "cpu_opcodes_ud.c"

static inline void do_nmi(struct nes_state *state) {
	struct cpu_state * restrict cpu = &state->cpu;

	memory_read_dummy(state, cpu->pc);		// T1: dummy read (fetch suppressed)

	uint8_t pcl = cpu->pc & 0xff;
	uint8_t pch = cpu->pc >> 8;

	memory_write(state, 0x0100 + cpu->sp--, pch);	// T2
	memory_write(state, 0x0100 + cpu->sp--, pcl);	// T3
	memory_write(state, 0x0100 + cpu->sp--, pack_flags(cpu) & ~0x10);	// T4: push P (B flag clear)

	uint8_t lo = memory_read(state, 0xfffa);	// T5
	uint8_t hi = memory_read(state, 0xfffb);	// T6

	cpu->pc = lo | (hi << 8);			// T7
	cpu->i = 1;
}

static inline void do_irq(struct nes_state *state) {
	struct cpu_state * restrict cpu = &state->cpu;

	memory_read_dummy(state, cpu->pc);		// T1: dummy read (fetch suppressed)

	uint8_t pcl = cpu->pc & 0xff;
	uint8_t pch = cpu->pc >> 8;

	memory_write(state, 0x0100 + cpu->sp--, pch);	// T2
	memory_write(state, 0x0100 + cpu->sp--, pcl);	// T3
	memory_write(state, 0x0100 + cpu->sp--, pack_flags(cpu) & ~0x10);	// T4: push P (B flag clear)

	uint8_t lo = memory_read(state, 0xfffe);	// T5
	uint8_t hi = memory_read(state, 0xffff);	// T6

	cpu->pc = lo | (hi << 8);			// T7
	cpu->i = 1;
}

static inline void check_interrupts(struct nes_state *state) {
	struct cpu_state * restrict cpu = &state->cpu;

	if(state->cpu.nmi_pending) {
		state->cpu.nmi_pending = 0;
		do_nmi(state);
	} else if(state->cpu.irq_pending && cpu->i == 0) {
		state->cpu.irq_pending = 0;
		do_irq(state);
	}
}

static inline void cpu_tick(struct nes_state *state) {
	struct cpu_state * restrict cpu = &state->cpu;
	check_interrupts(state);

	// printf("%4.4x: ", cpu->pc);
	uint8_t opcode = memory_read(state, cpu->pc++);
	// printf("%2.2x   a:%2.2x x:%2.2x y:%2.2x p:%2.2x sp:%2.2x  cycle: %ld\n", opcode, cpu->a, cpu->x, cpu->y, pack_flags(cpu), cpu->sp, state->cycles);
	opcode_lut[opcode](state);
}