#include "display.h"
#include <stdint.h>
#include <string.h>

#define WIDTH 640
#define HEIGHT 480
#define MODE_VGA_320_200_8 0x13
#define MODE_VESA_640_480_8 0x101

// 8-color VGA palette gradient, lighter shades of lavender to pink
#define COLOR_OFFSET 0x50
#define COLOR_NUM 8
#define COLOR_STEP (HEIGHT / COLOR_NUM)

/* https://wiki.osdev.org/VESA_Video_Modes */
_Packed struct VbeInfoBlock {
  char VbeSignature[4];     // == "VESA"
  uint16_t VbeVersion;      // == 0x0300 for VBE 3.0
  uint16_t OemStringPtr[2]; // isa vbeFarPtr
  uint8_t Capabilities[4];
  uint16_t VideoModePtr[2]; // isa vbeFarPtr
  uint16_t TotalMemory;     // as # of 64KB blocks
  uint8_t Reserved[492];
};

_Packed struct ModeInfoBlock {
  uint16_t
      attributes; // deprecated, only bit 7 should be of interest to you, and it
                  // indicates the mode supports a linear frame buffer.
  uint8_t window_a;     // deprecated
  uint8_t window_b;     // deprecated
  uint16_t granularity; // deprecated; used while calculating bank numbers
  uint16_t window_size;
  uint16_t segment_a;
  uint16_t segment_b;
  uint32_t win_func_ptr; // deprecated; used to switch banks from protected mode
                         // without returning to real mode
  uint16_t pitch;        // number of bytes per horizontal line
  uint16_t width;        // width in pixels
  uint16_t height;       // height in pixels
  uint8_t w_char;        // unused...
  uint8_t y_char;        // ...
  uint8_t planes;
  uint8_t bpp;   // bits per pixel in this mode
  uint8_t banks; // deprecated; total number of banks in this mode
  uint8_t memory_model;
  uint8_t bank_size; // deprecated; size of a bank, almost always 64 KB but may
                     // be 16 KB...
  uint8_t image_pages;
  uint8_t reserved0;

  uint8_t red_mask;
  uint8_t red_position;
  uint8_t green_mask;
  uint8_t green_position;
  uint8_t blue_mask;
  uint8_t blue_position;
  uint8_t reserved_mask;
  uint8_t reserved_position;
  uint8_t direct_color_attributes;

  uint32_t framebuffer; // physical address of the linear frame buffer; write
                        // here to draw to the screen
  uint32_t off_screen_mem_off;
  uint16_t off_screen_mem_size; // size of memory in the framebuffer but not
                                // being displayed on the screen
  uint8_t reserved1[206];
};

static char get_video_mode();
#pragma aux get_video_mode = "mov ah, 0x0f"                                    \
                             "int 0x10" value[al] modify[ah];

static void set_video_mode(unsigned char);
#pragma aux set_video_mode = "mov ah, 0x00"                                    \
                             "int 0x10" parm[al] modify[ah];

static void set_vesa_video_mode(unsigned short);
#pragma aux set_vesa_video_mode = "mov ax, 0x4f02"                             \
                                  "int 0x10" parm[bx] modify[ah];

static void wait_for_key();
#pragma aux wait_for_key = "mov ah, 0x00"                                      \
                           "int 0x16" modify[ah];

static short get_vesa_controller_info(struct VbeInfoBlock *);
#pragma aux get_vesa_controller_info = "mov ax, 0x4f00"                        \
                                       "int 0x10" parm[es di] value[ax];

static short get_vesa_mode_info(uint16_t mode, struct ModeInfoBlock *);
#pragma aux get_vesa_mode_info = "mov ax, 0x4F01"                              \
                                 "int 0x10" parm[cx][es di] value[ax];

/* https://wiki.osdev.org/User:Omarrx024/VESA_Tutorial*/
static char *find_display_memory(void) {
  struct VbeInfoBlock *ctrl = (struct VbeInfoBlock *)0x2000;
  struct ModeInfoBlock *inf = (struct ModeInfoBlock *)0x3000;
  uint16_t *modes;
  int i;

  strncpy(ctrl->VbeSignature, "VBE2", 4);
  if (get_vesa_controller_info(ctrl) != 0x004F)
    return NULL;

  modes = (uint16_t *)(ctrl->VideoModePtr);
  for (i = 0; modes[i] != 0xFFFF; ++i) {
    if (get_vesa_mode_info(modes[i], inf) != 0x004F)
      continue;

    // Check if this is a graphics mode with linear frame buffer support
    if ((inf->attributes & 0x80) != 0x80)
      continue;

    // Check if this is a packed pixel or direct color mode
    if (inf->memory_model != 4 && inf->memory_model != 6)
      continue;

    // Check if this is exactly the mode we're looking for
    if (WIDTH == inf->width && HEIGHT == inf->height && 256 == inf->pitch)
      return (char *)inf->framebuffer;
  }

  return NULL;
}

extern int plr_display_dos_main(int argc, char *argv[]) {
  char far *buf = (char far *)0xA0000; // VGA memory address
  int x, y;

  unsigned char saved_mode = get_video_mode(); // Save original mode
  set_vesa_video_mode(MODE_VESA_640_480_8);    // Set our VGA mode

  buf = find_display_memory();

  /* TODO: Fetch info about the mode, to know the availability */
  /*       as well as base address in memory */
  /*       https://wiki.osdev.org/VESA_Video_Modes */

  // Now draw. We draw pixel-by-pixel by directly setting the video memory like
  // it was an array. We step the color every 25 pixels so that we have 8 bands
  // of even height.
  for (y = 0; y < HEIGHT; y++) {
    for (x = 0; x < WIDTH; x++) {
      buf[y * WIDTH + x] = COLOR_OFFSET + y / COLOR_STEP;
    }
  }

  wait_for_key();
  set_video_mode(saved_mode); // Restore original mode

  return 0;
}