#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <termios.h>
#include <time.h>
#include <unistd.h>

#include "cpu.h"
#include "ram.h"
#include "rom.h"

#define MACHINE_SPEED_HZ 1000000ULL // 1 MHz;
#define SYNC_CYCLES 100

struct termios orig_termios;
struct timespec emulationStart;

uint64_t totalCycles = 0;
uint64_t lastSyncCycles = 0;

void restore_terminal(void) { tcsetattr(STDIN_FILENO, TCSANOW, &orig_termios); }

void set_nonblocking_input(void) {
  struct termios raw;

  tcgetattr(STDIN_FILENO, &orig_termios);
  atexit(restore_terminal);

  raw = orig_termios;
  raw.c_lflag &= ~(ICANON | ECHO); // disable line buffering, echo
  /* Ctrl+C becomes ordinary input byte 0x03 */
  raw.c_cc[VINTR] = _POSIX_VDISABLE;
  raw.c_cc[VMIN] = 0; // don't block waiting for input
  raw.c_cc[VTIME] = 0;
  tcsetattr(STDIN_FILENO, TCSANOW, &raw);

  // make stdin reads non-blocking too
  int flags = fcntl(STDIN_FILENO, F_GETFL, 0);
  fcntl(STDIN_FILENO, F_SETFL, flags | O_NONBLOCK);
}

int main(void) {
  uint8_t *ram = NULL;
  CPU cpu;

  printf("6502PC Emulator with MS Basic\n");
  printf("CTRL + G to exit\n");

  clock_gettime(CLOCK_MONOTONIC, &emulationStart);

  set_nonblocking_input();

  initRom(rom);

  if (createRAM(&ram) != 0) {
    printf("Could not create RAM\n");
    exit(EXIT_FAILURE);
  }

  initCPU(&cpu);
  resetCPU(&cpu, rom);

  while (1) {
    uint8_t cycles = runCycle(&cpu, ram, rom);
    totalCycles += cycles;

    // No 1 cycle instruction exists
    if (cycles == 1) {
      printf("Illegal opcode $%02X at $%04X "
             "A=$%02X X=$%02X Y=$%02X SP=$%02X\n",
             ram[cpu.ProgrammeCounter - 1], cpu.ProgrammeCounter - 1, cpu.Accumulator, cpu.X, cpu.Y, cpu.StackPointer);
      exit(EXIT_FAILURE);
    }

    // Sleep if batch is full
    if (totalCycles - lastSyncCycles >= SYNC_CYCLES) {
      struct timespec now;
      clock_gettime(CLOCK_MONOTONIC, &now);

      uint64_t elapsed_ns =
          (uint64_t)(now.tv_sec - emulationStart.tv_sec) * 1000000000ULL + (uint64_t)(now.tv_nsec - emulationStart.tv_nsec);
      uint64_t target_ns = totalCycles * 1000000000ULL / MACHINE_SPEED_HZ;

      if (target_ns > elapsed_ns) {
        uint64_t wait_ns = target_ns - elapsed_ns;

        struct timespec wait = {.tv_sec = wait_ns / 1000000000ULL, .tv_nsec = wait_ns % 1000000000ULL};

        nanosleep(&wait, NULL);
      }

      lastSyncCycles = totalCycles;
    }
  }

  destroyRAM(ram);

  return 0;
}