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use std::borrow::Borrow;
use std::fmt;
use std::hash::{Hash, Hasher};
use std::ops::{Add, Deref};

pub type RcStr = std::rc::Rc<str>;

/// Used to hold an immutable string.
///
/// It can construct as a const (by Str::ever).
#[derive(Debug, Clone, Eq)]
pub enum Str {
    Rc(RcStr),
    Static(&'static str),
}

impl PartialEq for Str {
    #[inline]
    fn eq(&self, other: &Str) -> bool {
        self[..] == other[..]
    }
}

impl Add<&str> for Str {
    type Output = Str;
    #[inline]
    fn add(self, other: &str) -> Str {
        Str::from(&format!("{self}{other}"))
    }
}

impl Hash for Str {
    fn hash<H: Hasher>(&self, state: &mut H) {
        match self {
            Str::Rc(s) => (s[..]).hash(state),
            Str::Static(s) => s.hash(state),
        }
    }
}

impl fmt::Display for Str {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Str::Rc(s) => write!(f, "{s}"),
            Str::Static(s) => write!(f, "{s}"),
        }
    }
}

// &'static str -> &strになってしまわないように
// あえて`impl<S: Into<Str>> From<S> for Str { ... }`はしない
impl From<&'static str> for Str {
    #[inline]
    fn from(s: &'static str) -> Self {
        Str::ever(s)
    }
}

impl From<&String> for Str {
    #[inline]
    fn from(s: &String) -> Self {
        Str::Rc((s[..]).into())
    }
}

impl From<String> for Str {
    #[inline]
    fn from(s: String) -> Self {
        Str::Rc((s[..]).into())
    }
}

impl From<&RcStr> for Str {
    #[inline]
    fn from(s: &RcStr) -> Self {
        Str::Rc(s.clone())
    }
}

impl From<RcStr> for Str {
    #[inline]
    fn from(s: RcStr) -> Self {
        Str::Rc(s)
    }
}

impl From<&Str> for Str {
    #[inline]
    fn from(s: &Str) -> Self {
        match s {
            Str::Rc(s) => Str::Rc(s.clone()),
            Str::Static(s) => Str::Static(s),
        }
    }
}

impl Deref for Str {
    type Target = str;
    fn deref(&self) -> &Self::Target {
        self.borrow()
    }
}

impl Borrow<str> for Str {
    #[inline]
    fn borrow(&self) -> &str {
        match self {
            Str::Rc(s) => s.borrow(),
            Str::Static(s) => s,
        }
    }
}

impl Str {
    pub const fn ever(s: &'static str) -> Self {
        Str::Static(s)
    }

    pub fn rc(s: &str) -> Self {
        Str::Rc(s.into())
    }

    pub fn as_ref(&self) -> &str {
        self.borrow()
    }

    pub fn into_rc(self) -> RcStr {
        match self {
            Str::Rc(s) => s,
            Str::Static(s) => RcStr::from(s),
        }
    }

    pub fn is_uppercase(&self) -> bool {
        self.chars()
            .next()
            .map(|c| c.is_uppercase())
            .unwrap_or(false)
    }
}