use std::env;

type Error = &'static str;

fn query_only_excluded(_: &[String]) -> Result<Vec<String>, Error> { Ok(vec![]) }
fn query_no_required  (_: &[String], _: &[String]) -> Result<Vec<String>, Error> { Ok(vec![]) }
fn query_with_required(_: &[String], _: &[String], _: &[String]) -> Result<Vec<String>, Error> { Ok(vec![]) }

fn query_tags() -> Result<Vec<String>, Error> {
  let mut excluded_tags = vec![];
  let mut required_tags = vec![];
  let mut prefered_tags = vec![];

  for arg in env::args() {
    match (arg.get(..1), arg.get(1..)) {
      (Some("-"), Some(rst)) => excluded_tags.push(rst.to_string()),
      (Some("+"), Some(rst)) => required_tags.push(rst.to_string()),
      _                      => prefered_tags.push(arg),
    }
  }

  match (&required_tags[..], &prefered_tags[..], &excluded_tags[..]) {
    ([], [], []) => Err("No Input"),
    ([], [], ex) => Ok(query_only_excluded(        ex)?),
    ([], pr, ex) => Ok(query_no_required  (    pr, ex)?),
    (re, pr, ex) => Ok(query_with_required(re, pr, ex)?),
  }
}

fn main() -> Result<(), Error> {
  let files = query_tags()?;
  println!("{:?}", files);
  Ok(())
}