/**
 * @file vga.c
 * @brief Basic functions for interacting with the CRTC controller in VGA text-mode.
 * @author rami
 * @version 0.1
 * @date 2024-02-03
 */

#include <vga.h>
#include <io.h>
#include <printf.h>

uint16_t get_cursor_pos() {
    uint16_t pos = 0;

    /* Tell CRTC controller we want the low cursor position */
    outportb(CRTC_ADDR_PORT, CRTC_CURSOR_LO_REGISTER);
    /* Read it through the data port */
    pos = inportb(CRTC_DATA_PORT);
    
    /* Repeat with high position */
    outportb(CRTC_ADDR_PORT, CRTC_CURSOR_HI_REGISTER);
    uint16_t hi_pos = 0;
    hi_pos = inportb(CRTC_DATA_PORT);
    pos |= hi_pos << 8;

    return pos;
}

void set_cursor_pos(uint16_t pos) {
    /* Tell CRTC controller we want the low cursor position */
    outportb(CRTC_ADDR_PORT, CRTC_CURSOR_LO_REGISTER);
    outportb(CRTC_DATA_PORT, (uint8_t)(pos & 0xFF));
    /* Repeat with high position */
    outportb(CRTC_ADDR_PORT, CRTC_CURSOR_HI_REGISTER);
    outportb(CRTC_DATA_PORT, (uint8_t)((pos >> 8) & 0xFF));
}

void clear_screen(void) {
    char *video_memory = (char *)VGA_MEMORY_ADDR;
    for (int i = 0; i < VGA_MAX_COLS * VGA_MAX_ROWS; i++) {
       video_memory[i * 2] = 0;
    }

    set_cursor_pos(0);
}

/* Implementation of _putchar. Function is defined in print.h */
void _putchar(char character) {
    uint16_t pos = get_cursor_pos();
    char *video_memory = (char *)VGA_MEMORY_ADDR + pos * 2;

    if (character == '\n') {
        uint16_t next_line = VGA_MAX_COLS * (pos / VGA_MAX_COLS + 1);
        set_cursor_pos(next_line);
    } else {
        video_memory[0] = character;
        video_memory[1] = WHITE_ON_BLACK;
        set_cursor_pos(pos + 1);
    }
}

void popchar() {
    uint16_t pos = get_cursor_pos();
    if (pos == 0) return;
    char *video_memory = (char *)(VGA_MEMORY_ADDR + (pos - 1) * 2);
    video_memory[0] = 0;
    set_cursor_pos(pos - 1);
}