use clap::Parser;
use std::fs;
use std::fs::File;
use std::io::BufReader;
use std::io::prelude::*;
use std::process;

#[derive(Parser, Debug)]
#[clap(author, version, about, long_about = None)]
struct Args {
    /// file A
    file_a: String,

    /// file B
    file_b: String,
}

fn main() {
    let args = Args::parse();

    let size_a = fs::metadata(&args.file_a).unwrap().len();
    let size_b = fs::metadata(&args.file_b).unwrap().len();

    if size_a != size_b {
        println!("Files have different sizes.");
        process::exit(1);
    }

    let handle_a = File::open(&args.file_a).unwrap();
    let handle_b = File::open(&args.file_b).unwrap();

    let mut reader_a = BufReader::new(handle_a);
    let mut reader_b = BufReader::new(handle_b);

    let mut buf_a = [0; 1024];
    let mut buf_b = [0; 1024];

    loop {
        let len_a = reader_a.read(&mut buf_a).unwrap();
        let len_b = reader_b.read(&mut buf_b).unwrap();

        if len_a == 0 && len_b == 0 {
            break;
        }

        if len_a != len_b {
            println!("Files are NOT equal.");
            process::exit(2);
        }

        if buf_a != buf_b {
            println!("Files are NOT equal.");
            process::exit(3);
        }
    }

    println!("Files are equal.");
    process::exit(0);
}