#[cfg(feature = "parsing")]
use crate::lookahead;
#[cfg(feature = "parsing")]
use crate::parse::{ParseStream, Result};
use core::cmp::Ordering;
use core::fmt::{self, Display};
use core::hash::{Hash, Hasher};
use proc_macro2::{Ident, Span};

/// A Rust lifetime: `'a`.
///
/// Lifetime names must conform to the following rules:
///
/// - Must start with an apostrophe.
/// - Must not consist of just an apostrophe: `'`.
/// - Character after the apostrophe must be `_` or a Unicode code point with
///   the XID_Start property.
/// - All following characters must be Unicode code points with the XID_Continue
///   property.
pub struct Lifetime {
    pub apostrophe: Span,
    pub ident: Ident,
}

impl Lifetime {
    /// # Panics
    ///
    /// Panics if the lifetime does not conform to the bulleted rules above.
    ///
    /// # Invocation
    ///
    /// ```
    /// # use proc_macro2::Span;
    /// # use syn::Lifetime;
    /// #
    /// # fn f() -> Lifetime {
    /// Lifetime::new("'a", Span::call_site())
    /// # }
    /// ```
    pub fn new(symbol: &str, span: Span) -> Self {
        let ident = match symbol.strip_prefix('\'') {
            Some(ident) => ident,
            None => panic!(
                "lifetime name must start with apostrophe as in \"'a\", got {:?}",
                symbol,
            ),
        };

        let unraw = ident.strip_prefix("r#");
        let validate = unraw.unwrap_or(ident);
        if validate.is_empty() {
            panic!("lifetime name must not be empty");
        }
        if !crate::ident::xid_ok(validate) {
            panic!("{:?} is not a valid lifetime name", symbol);
        }

        Lifetime {
            apostrophe: span,
            ident: match unraw {
                Some(unraw) => Ident::new_raw(unraw, span),
                None => Ident::new(ident, span),
            },
        }
    }

    pub fn span(&self) -> Span {
        self.apostrophe
            .join(self.ident.span())
            .unwrap_or(self.apostrophe)
    }

    pub fn set_span(&mut self, span: Span) {
        self.apostrophe = span;
        self.ident.set_span(span);
    }

    #[cfg(feature = "parsing")]
    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
    pub fn parse_any(input: ParseStream) -> Result<Self> {
        input.step(|cursor| match cursor.lifetime() {
            Some((lifetime, rest)) => Ok((lifetime, rest)),
            None => Err(cursor.error("expected lifetime")),
        })
    }
}

impl Display for Lifetime {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        "'".fmt(formatter)?;
        self.ident.fmt(formatter)
    }
}

impl Clone for Lifetime {
    fn clone(&self) -> Self {
        Lifetime {
            apostrophe: self.apostrophe,
            ident: self.ident.clone(),
        }
    }
}

impl PartialEq for Lifetime {
    fn eq(&self, other: &Lifetime) -> bool {
        self.ident.eq(&other.ident)
    }
}

impl Eq for Lifetime {}

impl PartialOrd for Lifetime {
    fn partial_cmp(&self, other: &Lifetime) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for Lifetime {
    fn cmp(&self, other: &Lifetime) -> Ordering {
        self.ident.cmp(&other.ident)
    }
}

impl Hash for Lifetime {
    fn hash<H: Hasher>(&self, h: &mut H) {
        self.ident.hash(h);
    }
}

#[cfg(feature = "parsing")]
pub_if_not_doc! {
    #[doc(hidden)]
    #[allow(non_snake_case)]
    pub fn Lifetime(marker: lookahead::TokenMarker) -> Lifetime {
        match marker {}
    }
}

#[cfg(feature = "parsing")]
pub(crate) mod parsing {
    use crate::error::Result;
    use crate::ident;
    use crate::lifetime::Lifetime;
    use crate::parse::{Parse, ParseStream};
    use alloc::string::ToString;

    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
    impl Parse for Lifetime {
        fn parse(input: ParseStream) -> Result<Self> {
            input.step(|cursor| {
                if let Some((lifetime, rest)) = cursor.lifetime() {
                    let repr = lifetime.ident.to_string();
                    if ident::parsing::accept_as_ident(&repr) || repr == "static" || repr == "_" {
                        Ok((lifetime, rest))
                    } else {
                        Err(cursor
                            .error(format_args!("unexpected keyword lifetime \"{}\"", lifetime)))
                    }
                } else {
                    Err(cursor.error("expected lifetime"))
                }
            })
        }
    }

    impl Lifetime {
        #[cfg(any(feature = "full", feature = "derive"))]
        pub(crate) fn parse_optional_any(input: ParseStream) -> Option<Self> {
            input
                .step(|cursor| match cursor.lifetime() {
                    Some((lifetime, rest)) => Ok((Some(lifetime), rest)),
                    None => Ok((None, *cursor)),
                })
                .unwrap()
        }
    }
}

#[cfg(feature = "printing")]
mod printing {
    use crate::ext::PunctExt as _;
    use crate::lifetime::Lifetime;
    use proc_macro2::{Punct, Spacing, TokenStream};
    use quote::{ToTokens, TokenStreamExt as _};

    #[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
    impl ToTokens for Lifetime {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            tokens.append(Punct::new_spanned('\'', Spacing::Joint, self.apostrophe));
            self.ident.to_tokens(tokens);
        }
    }
}