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use proc_macro2::Span;
use syn::parse::{self, Parse, ParseStream};

mod kw {
    syn::custom_keyword!(when);
    syn::custom_keyword!(then);
    syn::custom_keyword!(given);
    syn::custom_keyword!(case);
    syn::custom_keyword!(section);
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum SectionKeyword {
    When,
    Then,
    Given,
    Case,
    Section,
}

impl SectionKeyword {
    pub fn to_name(&self) -> String {
        match self {
            Self::When => "when".to_string(),
            Self::Then => "then".to_string(),
            Self::Given => "given".to_string(),
            Self::Case => "case".to_string(),
            Self::Section => "section".to_string(),
        }
    }
}

impl SectionKeyword {
    pub fn peek(i: ParseStream) -> bool {
        let lk = i.lookahead1();

        let mut test = false;

        test |= lk.peek(kw::when);
        test |= lk.peek(kw::given);
        test |= lk.peek(kw::section);
        test |= lk.peek(kw::then);
        test |= lk.peek(kw::case);

        test
    }
}

impl Parse for SectionKeyword {
    fn parse(input: ParseStream) -> parse::Result<Self> {
        let lk = input.lookahead1();

        if lk.peek(kw::when) {
            input.parse::<kw::when>()?;

            Ok(Self::When)
        } else if lk.peek(kw::then) {
            input.parse::<kw::then>()?;

            Ok(Self::Then)
        } else if lk.peek(kw::given) {
            input.parse::<kw::given>()?;

            Ok(Self::Given)
        } else if lk.peek(kw::case) {
            input.parse::<kw::case>()?;

            Ok(Self::Case)
        } else if lk.peek(kw::section) {
            input.parse::<kw::section>()?;

            Ok(Self::Section)
        } else {
            Err(parse::Error::new(
                Span::call_site(),
                "Invalid section keyword",
            ))
        }
    }
}

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

    #[test_case("when"      => SectionKeyword::When     ; "when")]
    #[test_case("given"     => SectionKeyword::Given    ; "given")]
    #[test_case("section"   => SectionKeyword::Section  ; "section")]
    #[test_case("then"      => SectionKeyword::Then     ; "then")]
    #[test_case("case"      => SectionKeyword::Case     ; "case")]
    fn parse(s: &str) -> SectionKeyword {
        syn::parse_str(s).unwrap()
    }

    #[test_case(SectionKeyword::When,    "when"     ; "when")]
    #[test_case(SectionKeyword::Given,   "given"    ; "given")]
    #[test_case(SectionKeyword::Section, "section"  ; "section")]
    #[test_case(SectionKeyword::Then,    "then"     ; "then")]
    #[test_case(SectionKeyword::Case,    "case"     ; "case")]
    fn to_name(kw: SectionKeyword, exp: &str) {
        assert_eq!(&kw.to_name(), exp);
    }
}