// Copyright 2018 Syn Developers
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use std::borrow::Cow;
use std::cmp::Ordering;
use std::fmt::{self, Display};
use std::hash::{Hash, Hasher};

use proc_macro2::Term;
use unicode_xid::UnicodeXID;

use proc_macro2::Span;

/// A word of Rust code, such as a keyword or variable name.
///
/// An identifier consists of at least one Unicode code point, the first of
/// which has the XID_Start property and the rest of which have the XID_Continue
/// property. An underscore may be used as the first character as long as it is
/// not the only character.
///
/// - The empty string is not an identifier. Use `Option<Ident>`.
/// - An underscore by itself is not an identifier. Use
///   `Token![_]` instead.
/// - A lifetime is not an identifier. Use `syn::Lifetime` instead.
///
/// An identifier constructed with `Ident::new` is permitted to be a Rust
/// keyword, though parsing one through its [`Synom`] implementation rejects
/// Rust keywords.
///
/// [`Synom`]: synom/trait.Synom.html
///
/// # Examples
///
/// A new ident can be created from a string using the `Ident::from` function.
///
/// ```rust
/// extern crate syn;
/// use syn::Ident;
/// #
/// # fn main() {
///
/// let ident = Ident::from("another_identifier");
///
/// # }
/// ```
///
/// When the ident is used in Macros 1.1 output, it needs to be turned into
/// a token stream. This is easy to do using the `quote!` macro from the `quote`
/// crate.
///
/// ```rust
/// # #[macro_use]
/// # extern crate quote;
/// # extern crate syn;
/// # use syn::Ident;
/// # fn main() {
/// # let ident = Ident::from("another_identifier");
/// #
/// // Create tokens using the ident.
/// let expanded = quote! { let #ident = 10; };
///
/// // Derive a new ident from the existing one.
/// let temp_ident = Ident::from(format!("new_{}", ident));
/// let expanded = quote! { let $temp_ident = 10; };
///
/// # }
/// ```
///
/// If `syn` is used to parse existing Rust source code, it is often useful to
/// convert the `Ident` to a more generic string data type at some point. The
/// methods `as_ref()` and `to_string()` achieve this.
///
/// ```rust
/// # use syn::Ident;
/// # let ident = Ident::from("another_identifier");
/// #
/// // Examine the ident as a &str.
/// let ident_str = ident.as_ref();
/// if ident_str.len() > 60 {
///     println!("Very long identifier: {}", ident_str)
/// }
///
/// // Create a String from the ident.
/// let ident_string = ident.to_string();
/// give_away(ident_string);
///
/// fn give_away(s: String) { /* ... */ }
/// ```
#[derive(Copy, Clone, Debug)]
pub struct Ident {
    term: Term,
    pub span: Span,
}

impl Ident {
    /// Creates a new `Ident` from the structured items. This is mainly used
    /// by the parser to create `Ident`s from existing Rust source code.
    ///
    /// Creating new `Ident`s programmatically is easier with `Ident::from`.
    pub fn new(s: &str, span: Span) -> Self {
        if s.is_empty() {
            panic!("ident is not allowed to be empty; use Option<Ident>");
        }

        if s.starts_with('\'') {
            panic!("ident is not allowed to be a lifetime; use syn::Lifetime");
        }

        if s == "_" {
            panic!("`_` is not a valid ident; use syn::token::Underscore");
        }

        if s.bytes().all(|digit| digit >= b'0' && digit <= b'9') {
            panic!("ident cannot be a number, use syn::Index instead");
        }

        fn xid_ok(s: &str) -> bool {
            let mut chars = s.chars();
            let first = chars.next().unwrap();
            if !(UnicodeXID::is_xid_start(first) || first == '_') {
                return false;
            }
            for ch in chars {
                if !UnicodeXID::is_xid_continue(ch) {
                    return false;
                }
            }
            true
        }

        if !xid_ok(s) {
            panic!("{:?} is not a valid ident", s);
        }

        Ident {
            term: Term::intern(s),
            span: span,
        }
    }
}

impl<'a> From<&'a str> for Ident {
    fn from(s: &str) -> Self {
        Ident::new(s, Span::def_site())
    }
}

impl From<Token![self]> for Ident {
    fn from(tok: Token![self]) -> Self {
        Ident::new("self", tok.0)
    }
}

impl From<Token![Self]> for Ident {
    fn from(tok: Token![Self]) -> Self {
        Ident::new("Self", tok.0)
    }
}

impl From<Token![super]> for Ident {
    fn from(tok: Token![super]) -> Self {
        Ident::new("super", tok.0)
    }
}

impl From<Token![crate]> for Ident {
    fn from(tok: Token![crate]) -> Self {
        Ident::new("crate", tok.0)
    }
}

impl<'a> From<Cow<'a, str>> for Ident {
    fn from(s: Cow<'a, str>) -> Self {
        Ident::new(&s, Span::def_site())
    }
}

impl From<String> for Ident {
    fn from(s: String) -> Self {
        Ident::new(&s, Span::def_site())
    }
}

impl AsRef<str> for Ident {
    fn as_ref(&self) -> &str {
        self.term.as_str()
    }
}

impl Display for Ident {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        self.term.as_str().fmt(formatter)
    }
}

impl<T: ?Sized> PartialEq<T> for Ident
where
    T: AsRef<str>,
{
    fn eq(&self, other: &T) -> bool {
        self.as_ref() == other.as_ref()
    }
}

impl Eq for Ident {}

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

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

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

#[cfg(feature = "parsing")]
pub mod parsing {
    use super::*;
    use synom::Synom;
    use buffer::Cursor;
    use parse_error;
    use synom::PResult;

    impl Synom for Ident {
        fn parse(input: Cursor) -> PResult<Self> {
            let (span, term, rest) = match input.term() {
                Some(term) => term,
                _ => return parse_error(),
            };
            if term.as_str().starts_with('\'') {
                return parse_error();
            }
            match term.as_str() {
                // From https://doc.rust-lang.org/grammar.html#keywords
                "abstract" | "alignof" | "as" | "become" | "box" | "break" | "const"
                | "continue" | "crate" | "do" | "else" | "enum" | "extern" | "false" | "final"
                | "fn" | "for" | "if" | "impl" | "in" | "let" | "loop" | "macro" | "match"
                | "mod" | "move" | "mut" | "offsetof" | "override" | "priv" | "proc" | "pub"
                | "pure" | "ref" | "return" | "Self" | "self" | "sizeof" | "static" | "struct"
                | "super" | "trait" | "true" | "type" | "typeof" | "unsafe" | "unsized" | "use"
                | "virtual" | "where" | "while" | "yield" => return parse_error(),
                _ => {}
            }

            Ok((
                Ident {
                    span: span,
                    term: term,
                },
                rest,
            ))
        }

        fn description() -> Option<&'static str> {
            Some("identifier")
        }
    }
}

#[cfg(feature = "printing")]
mod printing {
    use super::*;
    use quote::{ToTokens, Tokens};
    use proc_macro2::{TokenNode, TokenTree};

    impl ToTokens for Ident {
        fn to_tokens(&self, tokens: &mut Tokens) {
            tokens.append(TokenTree {
                span: self.span,
                kind: TokenNode::Term(self.term),
            })
        }
    }
}
