#include "vga.h"

#include <stdbool.h>

#include "string.h"
#include "stdlib.h"

static bool params_ok( vga_t *vga, const int x, const int y );
static int calculate_offset( vga_t *vga );
static uint8_t calculate_color_cell( vga_t *vga );
static void scroll_screen( vga_t *vga );

void vga_init( vga_t *vga )
{
	memset( vga, 0, sizeof( vga_t ) );

	vga->res_x = VGA_DEFAULT_RES_X;
	vga->res_y = VGA_DEFAULT_RES_Y;
	vga->color = VGA_COLOR_DARK_GREY;
	vga->background_color = VGA_COLOR_BLACK;

	// make sure we use the 0x3dx VGA ports, is done
	// in assembly in stage 2 too
	port8_init( &vga->crtc_misc_port, 0x3d2 );
	port8_write( &vga->crtc_misc_port, 1 );

	// set up VGA ports
	port8_init( &vga->crtc_index_port, 0x3d4 );
	port8_init( &vga->crtc_data_port, 0x3d5 );
	
	vga_set_cursor_from_hardware( vga );	
};

void vga_clear_screen( vga_t *vga )
{
	volatile uint8_t *VIDEO_MEMORY = (uint8_t *)0xb8000;

	for( int i = 0; i < 2 * ( vga->res_x * vga->res_y ); i += 2 ) {
		*(VIDEO_MEMORY+i) = ' ';
		*(VIDEO_MEMORY+i+1) = calculate_color_cell( vga );
	}
	
	vga_set_cursor( vga, 0, 0 );
}

void vga_set_cursor( vga_t *vga, const int x, const int y )
{
	// TODO: PANIC? OUT OF BOUND ACCESS
	if( !params_ok( vga, x, y ) ) return;

	vga->cursor_x = x;
	vga->cursor_y = y;
	
	// TODO: have a silent mode where we don't update the cursor
	vga_set_cursor_on_hardware( vga );
}

void vga_set_cursor_from_hardware( vga_t *vga )
{
	uint16_t hw_cursor_pos;
	
	port8_write( &vga->crtc_index_port, 14 );
	uint8_t data = port8_read( &(vga->crtc_data_port ) );
	hw_cursor_pos = data << 8;
 
	port8_write( &vga->crtc_index_port, 15 );
	data = port8_read( &(vga->crtc_data_port ) );

	hw_cursor_pos |= data;
	
	vga->cursor_x = hw_cursor_pos % vga->res_x;
	vga->cursor_y = hw_cursor_pos / vga->res_x;
	
	// reset to sane values if we get funny values from the VGA card
	if( vga->cursor_x < 0 || vga->cursor_x > vga->res_x ||
		vga->cursor_y < 0 || vga->cursor_y > vga->res_y ) {
		vga->cursor_x = 0;
		vga->cursor_y = 0;
	}
}

void vga_set_cursor_on_hardware( vga_t *vga )
{
    uint16_t hw_cursor_pos = vga->cursor_x + vga->cursor_y * vga->res_x;

    port8_write( &vga->crtc_index_port, 15 );
    port8_write( &vga->crtc_data_port, hw_cursor_pos & 0xff );
    port8_write( &vga->crtc_index_port, 14 );
    port8_write( &vga->crtc_data_port, hw_cursor_pos >> 8 );
}

int vga_get_cursor_x( vga_t *vga )
{
	return vga->cursor_x;
}

int vga_get_cursor_y( vga_t *vga )
{
	return vga->cursor_y;
}

void vga_set_color( vga_t *vga, const vga_color_t color )
{
	vga->color = color;
}

void vga_set_background_color( vga_t *vga, const vga_color_t color )
{
	vga->background_color = color;
}

static int calculate_offset( vga_t *vga )
{
	int offset = ( vga->res_x * vga->cursor_y + vga->cursor_x ) * 2;
	
	return offset;
}

static void scroll_screen( vga_t *vga )
{
	volatile uint8_t *VIDEO_MEMORY = (uint8_t *)0xb8000;

	memmove( (void *)VIDEO_MEMORY, (const void *)VIDEO_MEMORY + 2 * vga->res_x, 2 * ( vga->res_y - 1 ) * vga->res_x );

	for( int i = 2 * ( vga->res_x * ( vga->res_y - 1 ) ); i < 2 * ( vga->res_x * vga->res_y ); i += 2 ) {
		*(VIDEO_MEMORY+i) = ' ';
		*(VIDEO_MEMORY+i+1) = calculate_color_cell( vga );
	}
	
	vga->cursor_y = vga->res_y - 1;
}

static uint8_t calculate_color_cell( vga_t *vga )
{
	uint8_t cell;
	
	cell = ( vga->background_color << 4 ) | vga->color;
	
	return cell;
}

static bool params_ok( vga_t *vga, const int x, const int y )
{
	if( x > vga->res_x || y > vga->res_y ) return false;

	return true;
}

void vga_put_char_at( vga_t *vga, const int x, const int y, const char c )
{
	vga_set_cursor( vga, x, y );
	vga_put_char( vga, c );
}


void vga_put_string_at( vga_t *vga, const int x, const int y, const char *s )
{
	vga_set_cursor( vga, x, y );
	vga_put_string( vga, s );	
}

void vga_put_char( vga_t *vga, const char c )
{		
	int offset = calculate_offset( vga );

	volatile uint8_t *VIDEO_MEMORY = (uint8_t *)0xb8000;
	*(VIDEO_MEMORY+offset) = (uint8_t)c;
	*(VIDEO_MEMORY+offset+1) = calculate_color_cell( vga );	

	vga->cursor_x++;
	if( vga->cursor_x >= vga->res_x ) {
		vga->cursor_x = 0;
		vga->cursor_y++;
		if( vga->cursor_y >= vga->res_y ) {
			scroll_screen( vga );
		}
	}

	vga_set_cursor_on_hardware( vga );
}

void vga_put_string( vga_t *vga, const char *s )
{
	for( size_t i = 0; i < strlen( s ); i++ ) {
		vga_put_char( vga, s[i] );
	}
}

void vga_put_hex( vga_t *vga, const uint32_t v )
{
	char buf[9];
	
	vga_put_string( vga, "0x" );
	itoa( v, (char *)buf, 16 );
	vga_put_string( vga, (const char *)buf );
}

void vga_put_newline( vga_t *vga )
{
	vga->cursor_x = 0;
	vga->cursor_y++;
	if( vga->cursor_y >= vga->res_y ) {
		scroll_screen( vga );
	}

	vga_set_cursor_on_hardware( vga );
}