#include <system.h>

/*
 * Text pointer, background, foreground
 */
unsigned short * textmemptr;
int attrib = 0x0F;
int csr_x = 0, csr_y = 0;

/*
 * scroll
 * Scroll the screen
 */
void
scroll() {
	unsigned blank, temp;
	blank = 0x20 | (attrib << 8);
	if (csr_y >= 25) {
		/*
		 * Move the current text chunk that makes up the screen
		 * back in the buffer by one line.
		 */
		temp = csr_y - 25 + 1;
		memcpy(textmemptr, textmemptr + temp * 80, (25 - temp) * 80 * 2);
		/*
		 * Set the chunk of memory that occupies
		 * the last line of text to the blank character
		 */
		memsetw(textmemptr + (25 - temp) * 80, blank, 80);
		csr_y = 25 - 1;
	}
}

/*
 * move_csr
 * Update the hardware cursor
 */
void
move_csr() {
	unsigned temp;
	temp = csr_y * 80 + csr_x;
	
	/*
	 * Write stuff out.
	 */
	outportb(0x3D4, 14);
	outportb(0x3D5, temp >> 8);
	outportb(0x3D4, 15);
	outportb(0x3D5, temp);
}

/*
 * cls
 * Clear the screen
 */
void
cls() {
	unsigned blank;
	int i;
	blank = 0x20 | (attrib << 8);
	for (i = 0; i < 25; ++i) {
		memsetw(textmemptr + i * 80, blank, 80);
	}
	csr_x = 0;
	csr_y = 0;
	move_csr();
}

/*
 * putch
 * Puts a character to the screen
 */
void
putch(
		unsigned char c
	 ) {
	unsigned short *where;
	unsigned att = attrib << 8;
	if (c == 0x08) {
		/* Backspace */
		if (csr_x != 0) csr_x--;
	} else if (c == 0x09) {
		/* Tab */
		csr_x = (csr_x + 8) & ~(8 - 1);
	} else if (c == '\r') {
		/* Carriage return */
		csr_x = 0;
	} else if (c == '\n') {
		/* New line */
		csr_x = 0;
		csr_y++;
	} else if (c >= ' ') {
		where = textmemptr + (csr_y * 80 + csr_x);
		*where = c | att;
		csr_x++;
	}

	if (csr_x >= 80) {
		csr_x = 0;
		csr_y++;
	}
	scroll();
	move_csr();
}

/*
 * puts
 * Put string to screen
 */
void
puts(
		unsigned char * text
	){ 
	int i;
	int len = strlen(text);
	for (i = 0; i < len; ++i) {
		putch(text[i]);
	}
}

/*
 * settextcolor
 * Sets the foreground and background color
 */
void
settextcolor(
		unsigned char forecolor,
		unsigned char backcolor
		) {
	attrib = (backcolor << 4) | (forecolor & 0x0F);
}

/*
 * init_video
 * Initialize the VGA driver.
 */
void init_video() {
	textmemptr = (unsigned short *)0xB8000;
	cls();
}