#include "vga.h"
#define VGA_WIDTH 80
#define VGA_HEIGHT 25
#define VGA_MEM_ADDR 0xb8000
#define CURSOR_HOME (VGA_HEIGHT-1)*VGA_WIDTH
#define CURSOR_CHR  177;

unsigned int cursor_loc = CURSOR_HOME;
unsigned char fgcolor;
unsigned char bgcolor;
unsigned short blank;

static unsigned char vga_entry_color(enum vga_color fg, enum vga_color bg) {
    return fg | bg << 4;
}
unsigned short vga_blank_entry() {
    return vga_entry_color(fgcolor, bgcolor) << 8;
}
void draw_cursor(void) {
    *((unsigned char *)VGA_MEM_ADDR + cursor_loc * 2) = CURSOR_CHR;
    *((unsigned char *)VGA_MEM_ADDR+1 + cursor_loc * 2) = vga_entry_color(fgcolor, bgcolor);
}

void vga_set_color(enum vga_color fg, enum vga_color bg) {
    fgcolor = fg;
    bgcolor = bg;
}
void vga_init(enum vga_color fg, enum vga_color bg) {
    vga_set_color(fg, bg);
    blank = vga_blank_entry();
    cls();
}
void cls(void) {
    int i;
    for (i=0; i<VGA_HEIGHT*VGA_WIDTH;i++) {
        *((unsigned short *) VGA_MEM_ADDR+i) = blank;
    }
}
void scroll(void) {
    int y;
    int x;
    *((unsigned short *) VGA_MEM_ADDR+cursor_loc) = blank;
    for (y=0;y<VGA_HEIGHT;y++) {
        for (x = 0;x<VGA_WIDTH;x++) {
            *((unsigned short *) VGA_MEM_ADDR+y*VGA_WIDTH+x) = *((unsigned short *) VGA_MEM_ADDR+(y+1)*VGA_WIDTH+x);
        }
    }
    for (x=0;x<VGA_WIDTH;x++) {
        *((unsigned short *) VGA_MEM_ADDR+CURSOR_HOME+x) = blank;
    }
    cursor_loc = CURSOR_HOME;
    draw_cursor();
}
void putchar(unsigned char chr) {
    if (chr == '\n') {
        scroll();
        return;
    }
    *((unsigned char *) VGA_MEM_ADDR+cursor_loc * 2) = chr;
    *((unsigned char *) VGA_MEM_ADDR+1+cursor_loc * 2) = vga_entry_color(fgcolor, bgcolor);
    cursor_loc++;
    if (cursor_loc >= VGA_HEIGHT*VGA_WIDTH) {
        scroll();
    }
    draw_cursor();
}

void vga_write(const char* text) {
    int i = 0;
    while(text[i]) {
        putchar(text[i]);
        i++;
    }
}
void vga_write_color( const char* text, enum vga_color fg, enum vga_color bg) {
    unsigned char prevfg = fgcolor;
    unsigned char prevbg = bgcolor;
    vga_set_color(fg, bg);
    vga_write(text);
    fgcolor = prevfg;
    bgcolor = prevbg;
}
void vga_write_line(const char* text) {
    if (cursor_loc != CURSOR_HOME) {
        scroll();
    }
    vga_write(text);
    scroll();
}
void vga_write_line_color(const char* text, enum vga_color fg, enum vga_color bg) {
    unsigned char prevfg = fgcolor;
    unsigned char prevbg = bgcolor;
    vga_set_color(fg, bg);
    vga_write_line(text);
    fgcolor = prevfg;
    bgcolor = prevbg;
}