#ifndef GB_H
#define GB_H

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */

#include <stdint.h>

typedef enum {
  GB_CPU_STATE_RUN,
  GB_CPU_STATE_STOP,
  GB_CPU_STATE_HALT,
  GB_CPU_STATE_INVALID,
  GB_CPU_STATE_NOT_IMPLEMENTED,
  GB_CPU_STATE_LAST,
} gb_cpu_state_t;

#define GB_BTN_UP     1
#define GB_BTN_DOWN   (1 << 1)
#define GB_BTN_LEFT   (1 << 2)
#define GB_BTN_RIGHT  (1 << 3)
#define GB_BTN_A      (1 << 4)
#define GB_BTN_B      (1 << 5)
#define GB_BTN_SELECT (1 << 6)
#define GB_BTN_START  (1 << 7)

// frame buffer size, in bytes
#define GB_FB_SIZE (3 * 160 * 144)

typedef struct gb_t_ gb_t;

typedef struct {
  void (*on_set_rom_bank)(const gb_t *, const uint16_t);
  void (*on_set_ram_bank)(const gb_t *, const uint16_t);
  void (*on_vblank)(const gb_t *);
  void (*on_hblank)(const gb_t *);
  void (*on_set_cpu_state)(const gb_t *, const gb_cpu_state_t);
  void (*on_timer)(const gb_t *);
  void (*on_gpu_step)(const gb_t *);
  void (*on_gpu_set_mode)(const gb_t *, const uint8_t);
  void (*on_rst)(const gb_t *, const uint16_t);
  void (*on_mmu_rb)(const gb_t *, const uint16_t, const uint8_t);
  void (*on_mmu_wb)(const gb_t *, const uint16_t, const uint8_t);
  void (*on_oam_wb)(const gb_t *, const uint16_t, const uint8_t);
  void *cb_data;
} gb_config_t;

struct gb_t_ {
  const gb_config_t *config;

  struct {
    // _Bool in_bios;

    // FIXME: combine these?
    uint8_t ram[0x2000]; // working ram (8k)
    uint8_t eram[0x10000]; // external ram (banked, up to 64k)
    uint8_t vram[0x2000]; // vram (8k)
    uint8_t oam[0xA0]; // oam (160 bytes)
    uint8_t zram[0x80]; // zram (128 bytes)

    // rom (at least 32k)
    const uint8_t *rom;
    uint32_t rom_size;

    union {
      struct {
        // current rom bank (5 bits); see note about
        // rom_ram_mode below
        uint8_t rom_bank;

        // is external ram enabled?
        _Bool ram_enable;

        // ram bank
        // rom_ram_mode == 0: high two bits of rom bank
        // rom_ram_mode == 1: ram bank
        uint8_t ram_bank;

        // set interpretation of ram_bank
        _Bool rom_ram_mode;
      } mbc1;

      struct {
        // current rom bank (4 bits)
        uint8_t rom_bank;

        // is eram enabled?
        _Bool ram_enable;
      } mbc2;
    };

    // interrupts
    // ie: interrupt enable (addr: 0xFFFF)
    // iv: interrupt vector (addr: 0xFF0F)
    // (gb-manual, p26)
    uint8_t ie;
    uint8_t iv;

    // buttons (addr: 0xFF00)
    // gb-manual, p23
    uint8_t p1_mode;
    uint8_t btns;
  } mmu;

  struct {
    uint16_t clock;
    uint8_t mode,
            lcdc,
            stat,
            scy,
            scx,
            wy,
            wx,
            bgp,
            obp0,
            obp1,
            line,
            lyc;

    // frame buffer
    uint8_t fb[GB_FB_SIZE];

    // frame counter
    uint32_t frame;

    struct {
      int16_t x, y;
      uint8_t tile;
      bool priority,
           y_flip,
           x_flip,
           palette;
    } oam_cache[40];

    bool oam_dirty;
  } gpu;

  struct {
    uint16_t div;
    uint32_t tima; // NOTE: cannot be uint16_t because of 10-bit shift
    uint8_t tma,
            tac;
  } timer;

  struct {
    uint16_t rs[6 /* RW_LAST */];
    uint32_t clock; /* FIXME: uint16_t? */
    gb_cpu_state_t state;

    // interrupt master enable
    _Bool ime;
  } cpu;
};

void gb_init(
  gb_t * const ctx,
  const gb_config_t * const config,
  const uint8_t *rom,
  const uint32_t rom_size
);

void gb_set_buttons(gb_t * const, const uint8_t);
void gb_frame(gb_t * const);
void gb_step(gb_t * const);
_Bool gb_disasm(gb_t * const, char * const, size_t * const);
const uint8_t *gb_get_frame(const gb_t * const);

#ifdef __cplusplus
};
#endif /* __cplusplus */

#endif /* GB_H */