use std::env;
use std::error::Error;
use std::fs::OpenOptions;
use std::io::stdin;
use std::os::windows::fs::FileExt;
use std::process::{Command, exit};

fn pause() {
    // call pause command to keep the console open, so the user can read infos/errors
    Command::new("cmd").args(&["/C", "pause"]).spawn().expect("failed to execute pause command");
}

fn abort(message: &str, error: Option<&dyn Error>) -> ! {
    if let Some(error) = error {
        println!("{:}", error);
    }
    println!("{}. Abort!", message);
    pause();
    exit(1);
}

fn main() {
    const IMAGE_FILE_LARGE_ADDRESS_AWARE: u8 = 0x20;
    let mut buffer2 = [0u8; 2];
    let mut buffer4 = [0u8; 4];
    let args= env::args().collect::<Vec<String>>();
    let path = match args.get(1) {
        None => abort("Didn't receive path to EXE as argument", None),
        Some(path) => path
    };
    if !path.to_lowercase().ends_with(".exe") {
        abort("Argument is not an EXE", None);
    }
    println!("Working on: {}", path);
    let file = match OpenOptions::new().read(true).write(true).open(path) {
        Ok(file) => file,
        Err(error) => abort("Failed to open EXE in read/write mode", Some(&error))
    };
    if let Err(error) = file.seek_read(&mut buffer4, 0x3C) {
        abort("Failed to read e_lfanew of MS-DOS stub", Some(&error));
    }
    let address_coff_characteristics = (u32::from_le_bytes(buffer4) + 0x4 + 0x12) as u64; // real data starts after "PE\0\0" string (first 4 Bytes)
    if let Err(error) = file.seek_read(&mut buffer2, address_coff_characteristics) {
        abort("Failed to read Characteristics from COFF file header", Some(&error));
    }
    let is_laa_enabled = buffer2[0] & IMAGE_FILE_LARGE_ADDRESS_AWARE != 0;
    println!("LAA currently enabled: {}\nDo you want to change that [y/n]?", is_laa_enabled);
    let mut input = String::new();
    if let Err(error) = stdin().read_line(&mut input) {
        abort("Failed to read user input from stdin", Some(&error));
    }
    match input.to_lowercase().trim() {
        "y" => {},
        "n" => return,
        _ => abort("Invalid input", None)
    }
    buffer2[0] ^= IMAGE_FILE_LARGE_ADDRESS_AWARE; // flip bit
    if let Err(error) = file.seek_write(buffer2.as_slice(), address_coff_characteristics) {
        abort("Failed to write modification back to file", Some(&error));
    }
    println!("Modification written to disk.");
    pause();
}