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// License: see LICENSE file at root directory of `master` branch

//! # Case-insensitive string

use std::{
    borrow::Cow,
    cmp::Ordering,
    convert::TryFrom,
    fmt,
    hash::{Hash, Hasher},
    io::{self, Error, ErrorKind},
};

/// # Case-insensitive string
///
/// ## Notes
///
/// This struct is intended for sorting in lists, or to be used in sets, so it _generates_ a lower-case form of source string and stores it
/// inside. That might look like a waste of memory, but it helps with performance. For example when you call [`Vec::sort()`][r://Vec/sort()] or
/// when you insert it into a [`HashSet`][r://HashSet], it doesn't have to generate any string again and again...
///
/// ## Examples
///
/// ```
/// use std::collections::HashSet;
/// use std::convert::TryFrom;
/// use sub_strs::CainStr;
///
/// let wild_data: HashSet<_> = vec!["swift", "C++", "rust", "SWIFT"].into_iter().collect();
/// assert_eq!(wild_data.len(), 4);
///
/// let data: HashSet<_> = wild_data.into_iter().map(|s| CainStr::from(s)).collect();
/// assert_eq!(data.len(), 3);
///
/// let mut data: Vec<_> = data.into_iter().collect();
/// data.sort();
/// let data: Vec<_> = data.iter().map(|cs| cs.as_ref()).collect();
/// assert_eq!(&data[..2], &["C++", "rust"]);
/// assert!(data[2].eq_ignore_ascii_case("swift"));
/// ```
///
/// [r://HashSet]: https://doc.rust-lang.org/std/collections/struct.HashSet.html
/// [r://Vec/sort()]: https://doc.rust-lang.org/std/vec/struct.Vec.html#method.sort
#[derive(Debug, Eq)]
pub struct CainStr<'a> {

    /// # Source string
    src: Cow<'a, str>,

    /// # Lower-case form of source string
    lowercase_src: String,

}

impl PartialEq for CainStr<'_> {

    fn eq(&self, other: &Self) -> bool {
        self.lowercase_src.eq(&other.lowercase_src)
    }

}

impl Ord for CainStr<'_> {

    fn cmp(&self, other: &Self) -> Ordering {
        self.lowercase_src.cmp(&other.lowercase_src)
    }

}

impl PartialOrd for CainStr<'_> {

    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }

}

impl Hash for CainStr<'_> {

    fn hash<H>(&self, h: &mut H) where H: Hasher {
        self.lowercase_src.hash(h);
    }

}

impl fmt::Display for CainStr<'_> {

    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        f.write_str(&self.src)
    }

}

impl<'a> From<&'a str> for CainStr<'a> {

    fn from(src: &'a str) -> Self {
        Self {
            src: src.into(),
            lowercase_src: src.to_lowercase(),
        }
    }

}

impl<'a> From<&'a String> for CainStr<'a> {

    fn from(src: &'a String) -> Self {
        Self {
            src: src.into(),
            lowercase_src: src.to_lowercase(),
        }
    }

}

impl From<String> for CainStr<'_> {

    fn from(src: String) -> Self {
        let lowercase_src = src.to_lowercase();
        Self {
            src: src.into(),
            lowercase_src,
        }
    }

}

impl<'a> TryFrom<CainStr<'a>> for &'a str {

    type Error = Error;

    fn try_from(cain_str: CainStr<'a>) -> io::Result<&'a str> {
        match cain_str.src {
            Cow::Borrowed(s) => Ok(s),
            Cow::Owned(_) => Err(Error::new(ErrorKind::InvalidData, "CainStr is borrowed, not owned")),
        }
    }

}

impl<'a> TryFrom<CainStr<'a>> for String {

    type Error = Error;

    fn try_from(cain_str: CainStr<'a>) -> io::Result<String> {
        match cain_str.src {
            Cow::Owned(s) => Ok(s),
            Cow::Borrowed(_) => Err(Error::new(ErrorKind::InvalidData, "CainStr is owned, not borrowed")),
        }
    }

}

impl AsRef<str> for CainStr<'_> {

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

}

#[test]
fn test_cain_str() {
    let s = "UPPER-CASE";
    assert_eq!(s.to_lowercase(), CainStr::from(s).lowercase_src);
}