use regex::{Captures, Regex};

fn compile_pattern(pattern: &str) -> Regex {
    let mut result = String::new();
    for c in pattern.chars() {
        match c {
            // This is a nightmare, because we're escaping for regex syntax before we put
            // things into result.

            // We don't end with a backslash, so this is an unescaped wildcard.
            '%' if !result.ends_with(r"\\") => {
                result.push_str(r"(\w*)");
            }

            // We end with two backslashes, so this is an escaped backslash and then an
            // unescaped wildcard.
            '%' if result.ends_with(r"\\\\") => {
                result = result.strip_suffix(r"\\\\").unwrap().to_string();
                result.push_str(r"\\(\w*)");
            }

            // We end with one backslash, so this is an escaped wildcard.
            '%' if result.ends_with(r"\\") => {
                result = result.strip_suffix(r"\\").unwrap().to_string();
                result.push('%');
            }
            _ => result.push_str(&regex::escape(&c.to_string())),
        }
    }
    Regex::new(&result).expect("built invalid regex!")
}

pub(crate) fn r#match<'a>(pattern: &str, text: &'a str) -> Option<Captures<'a>> {
    compile_pattern(pattern).captures(text)
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn pattern_backslashes() {
        let test_case = compile_pattern(r"the\%weird\\%pattern\\");
        assert_eq!(test_case.to_string(), r"the%weird\\(\w*)pattern\\\\");

        let hell = compile_pattern(r"\\\\%");
        assert_eq!(hell.to_string(), r"\\\\\\(\w*)");
    }
}