const HELP_FLAG:              &str = "help h";
const VERSION_FLAG:           &str = "version v";
const DONT_PERSIST:           &str = "d";


pub struct Flags {
    pub help: bool,
    pub version: bool,
    pub dont_persist: bool,
    pub arg_count: usize
}


/// Parses an list of String arguments into a set of flags that can be used by crab
/// #### Arguments
/// * `args` - The list of String arguments
/// #### Returns
/// * `None` - If there is an invalid argument in the list
/// * `Some(Flags)` - If the arguments were secussfully parsed, returning the flags
pub fn parse(args: &[String]) -> Option<Flags> {
    let mut flags = Flags { 
        help: false, 
        version: false,
        dont_persist: false, 
        arg_count: 0 
    };
    for arg in args {
        if !is_arg(&arg) { break; }
        flags.arg_count += 1;
        if arg.starts_with("--") {
            let flag = &arg[2..];
            if !set_flag(&flag, &mut flags) {
                eprintln!("Invalid argument: {}", arg);
                return None
            }
        } else {
            let flag = &arg[1..];
            for char in flag.chars() {
                if !set_flag(&char.to_string(), &mut flags) {
                    eprintln!("Invalid argument: {}", arg);
                    return None
                }
            }
        }
    }
    Some(flags)
}


/// Checks if a given string is a given argument
fn is_arg(arg: &str) -> bool {
  return arg.starts_with("-");
}


/// Sets a flag in a `Flags` struct
/// #### Arguments
/// * `arg` - The argument to check
/// * `flags` - The `Flags` stuct to update
/// #### Returns
/// * `true` - If the argument passed is a valid flag
/// * `false` - If the argument passed is not a valid flag
fn set_flag(arg: &str, flags: &mut Flags) -> bool {
    if has_flag_set(&arg, HELP_FLAG) {
        flags.help = true;
        return true
    } else if has_flag_set(&arg, VERSION_FLAG) {
        flags.version = true;
        return true
    } else if has_flag_set(&arg, DONT_PERSIST) {
        flags.dont_persist = true;
        return true
    }
    false
}


/// Returns if a given argument is a certain flag
/// #### Arguments
/// * `arg` - The arch to check
/// #### Returns
/// * `true` - If the argument matches the flag
/// * `false` - If the argument doesn't match the flag
fn has_flag_set(arg: &str, check: &str) -> bool {
    for check_arg in check.split(" ") {
        if check_arg == arg {
            return true
        }
    }
    return false
}