lc3_vm 0.1.0

extern crate termios;

use libc::STDIN_FILENO;
use signal_hook::{iterator::Signals, SIGINT};
use std::process;
use std::{error::Error, thread};
use termios::*;

fn handle_control_c(sig: i32) {
    restore_terminal_settings();
    println!("\n\n");
    println!("The LC3 VM received Ctrl-C interrupt signal (= {}).", sig);
    println!("So, exiting the process with exit code = 128 + 2 = 130.\n");
    //read http://tldp.org/LDP/abs/html/exitcodes.html for linux exit codes.
    //Control-C is fatal error with signal = 2,
    //code 128+n is for Fatal error signal = "n"
    //so recommanded code for Control-C is 130.
    process::exit(130);
}

pub fn restore_terminal_settings() {
    let mut term: Termios = Termios::from_fd(STDIN_FILENO).unwrap();
    //turn on canonical mode and echo mode
    term.c_lflag |= ICANON | ECHO;
    tcsetattr(STDIN_FILENO, TCSANOW, &term).unwrap();
}

pub fn turn_off_canonical_and_echo_modes() {
    let mut term: Termios = Termios::from_fd(STDIN_FILENO).unwrap();
    //turn off canonical mode and echo mode
    term.c_lflag &= !(ICANON | ECHO);
    tcsetattr(STDIN_FILENO, TCSANOW, &term).unwrap();
}

/// When the program is interrupted (with pressing `Control-C` keys), we want to restore the terminal settings back to normal.
/// `spawn_control_c_handler` function will spawn a thread to handle `Control-C` (interrupt signal).
/// When user presses `Control-C` keys, it restores terminal to its original, i.e. it turns value of `ICANON` and `ECHO` modes to 1.
/// And exists the process with process code = 130 (as mentioned here, http://tldp.org/LDP/abs/html/exitcodes.html).
pub fn spawn_control_c_handler() -> Result<(), Box<Error>> {
    //setup for interrupt handling.
    let signals = Signals::new(&[SIGINT])?;
    thread::spawn(move || {
        for sig in signals.forever() {
            //Interrupt (Ctrl + C) is handled as follows...
            //Terminal is restored to its original configuration
            //Process is exited with (130)
            handle_control_c(sig);
        }
    });
    Ok(())
}