#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

#include <sys/video.h>

typedef struct {
    uint8_t magic[2];
    uint8_t mode;
    uint8_t charsz;
} psf_hdr_t;

typedef struct {
    int fd;
    psf_hdr_t hdr;
    void* glyphs;
} psf_font_t;

psf_font_t* load_font(const char* path);
void free_font(psf_font_t* font);

void term_write_char(char c);
void render_char(char c);
void clear(uint32_t color);
void spawn_shell();

void start_terminal();

static int ptys;
static int ptym;
static int vga_fd;

static void* fb = NULL;
static fb_info_t fb_info;

static uint32_t console_row = 0;
static uint32_t console_col = 0;
static uint32_t console_width = 0;
static uint32_t console_height = 0;
static uint32_t console_text_color = 0;
static uint32_t console_backgrnd_color = 0;

static int shell_pid;

psf_font_t* terminal_font = NULL;

int main(int argc, char *argv[]) {
    (void)argc;
    (void)argv;

    ptym = pty(&ptys);

    vga_fd = open("/dev/vga");
    if (vga_fd == -1) return 1;

    int res = ioctl(vga_fd, FBIOGET_INFO, &fb_info);
    if (!res) {
        return 1;
    }

    fb = mmap(vga_fd);

    terminal_font = load_font("/usr/fonts/kernel_font.psf");
    if (!terminal_font) {
        return 1;
    }

    console_height = fb_info.height / terminal_font->hdr.charsz;
    console_width = fb_info.width / 8;
    console_text_color = 0xFFFFFFFF;
    console_backgrnd_color = 0xFF6c7482;

    start_terminal();

    free_font(terminal_font);
    close(vga_fd);
    close(ptym);

    return 0;
}

void render_char(char c) {
    if (!terminal_font) return;
    uint32_t vga_pitch = fb_info.pitch;
    uint8_t* glyph = (uint8_t*)terminal_font->glyphs + (c * terminal_font->hdr.charsz);

    uint32_t pixel_y_start = console_row * terminal_font->hdr.charsz;
    uint32_t pixel_x_start = console_col * 8;

    for (uint32_t y = 0; y < terminal_font->hdr.charsz; y++) {
        uint8_t bits = glyph[y];
        uint8_t* row_bytes = (uint8_t*)fb + ((pixel_y_start + y) * vga_pitch);
        uint32_t* pixel_row = (uint32_t*)row_bytes;

        for (int x = 0; x < 8; x++) {
            if (bits & (0b10000000 >> x)) {
                pixel_row[pixel_x_start + x] = console_text_color;
            } else {
                pixel_row[pixel_x_start + x] = console_backgrnd_color;
            }
        }
    }
}     

void spawn_shell() {
    if ((shell_pid = fork()) == 0) {
        close(ptym);
        close(vga_fd);

        dup2(ptys, 0);
        dup2(0, 1);
        dup2(0, 2);
        if (!exec("/usr/bin/rocksh")) exit(1);
    }

    close(ptys);
    dup2(ptym, 0);
    dup2(0, 1);
    dup2(0, 2);
}

void clear(uint32_t color) {
    for (uint32_t i = 0; i < fb_info.fb_size; i++) {
        ((uint32_t*)fb)[i] = color;
    }
}

psf_font_t* load_font(const char* path) {
    int fd = open(path);
    if (fd == -1) {
        return NULL;
    }

    psf_hdr_t header;
    int rd = read(fd, &header, sizeof(psf_hdr_t));
    if (rd <= 0) {
        return NULL;
    }

    uint32_t num_glyphs = (header.mode & (1 << 0)) ? 512 : 256;
    uint32_t glyph_sz = header.charsz;
    size_t glyph_buf_sz = num_glyphs * glyph_sz;

    void* glyphs = malloc(glyph_buf_sz);

    rd = 0;
    rd = read(fd, glyphs, glyph_buf_sz);
    if (rd <= 0) {
        free(glyphs);
        return NULL;
    }

    psf_font_t* font = (psf_font_t*)malloc(sizeof(psf_font_t));
    font->fd = fd;
    font->hdr = header;
    font->glyphs = glyphs;
    return font;
}

void free_font(psf_font_t* font) {
    close(font->fd);
    free(font->glyphs);
    free(font);
}

void term_write_char(char c) {
    if (!terminal_font) return;

    if (c == '\n') {
        console_col = 0;
        console_row++;
        if (console_row >= console_height) {
            console_row = 0;
        }
        return;
    }
    
    render_char(c);
    
    console_col++;
    if (console_col >= console_width) {
        console_col = 0;
        console_row++;
    }

    if (console_row >= console_height) {
        console_row = 0;
    }
}

void start_terminal() {
    spawn_shell();

    clear(console_backgrnd_color);
    
    int kbd_fd = open("/dev/kbd"); 
    if (kbd_fd == -1) return;

    while (1) {
        char c;
        int rd = read(STDIN_FILENO, &c, 1);
        if (rd > 0) {
            term_write_char(c);
            continue;
        }
        
        rd = 0;
        c = 0;
        rd = read(kbd_fd, &c, 1);
        if (rd > 0) {
            write(STDOUT_FILENO, &c, 1);
        }
    }
}