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//! With this crate, you can conveniently chip pieces off a [slice] or [`str`] to use elsewhere.
//!
//! # Example
//!
//! ```rust
//! use gnaw::{Drain as _, Pop as _, Unshift as _};
//!
//! let mut text = "abcdefg";
//!
//! assert_eq!(text.unshift(), Some('a'));
//! assert_eq!(text.pop(), Some('g'));
//!
//! let mut drain = text.drain();
//! assert_eq!(drain.next(), Some('b'));
//! assert_eq!(drain.next(), Some('c'));
//! assert_eq!(drain.next_back(), Some('f'));
//! assert_eq!(drain.next_back(), Some('e'));
//! drop(drain);
//!
//! //TODO: Why isn't the mutable borrow released here?
//! //assert_eq!(text, "d");
//! ```

#![warn(clippy::pedantic)]

mod drains;
use drains::{SliceDrain, StrDrain};

pub trait Drain<'a, T> {
	type Target: DoubleEndedIterator<Item = T> + 'a;
	fn drain(&'a mut self) -> Self::Target;
}

pub trait Pop<T> {
	fn pop(&mut self) -> Option<T>;
}

pub trait Unshift<T> {
	fn unshift(&mut self) -> Option<T>;
}

impl<'a, T: 'a> Drain<'a, &'a T> for &'a [T] {
	type Target = SliceDrain<'a, T>;
	fn drain(&'a mut self) -> Self::Target {
		SliceDrain(self)
	}
}

// TODO
// impl<'a, T: 'a> Drain<'a, &'a mut T> for &'a mut [T] {
//     type Target = MutSliceDrain<'a, T>;
//     fn drain(&'a mut self) -> Self::Target {
//         MutSliceDrain(self)
//     }
// }

impl<'a> Drain<'a, char> for &'a str {
	type Target = StrDrain<'a>;
	fn drain(&'a mut self) -> Self::Target {
		StrDrain(self)
	}
}

// TODO: This method doesn't compile as-is, but there should be a way to do this.
// impl<'a, T> Pop<&'a mut T> for &'a mut [T] {
//     fn pop(&mut self) -> Option<&'a mut T> {
//         self.split_last_mut().map(|(t, rest)| -> &'a mut T {
//             *self = rest;
//             t
//         })
//     }
// }

impl<'a, T> Pop<&'a T> for &'a [T] {
	fn pop(&mut self) -> Option<&'a T> {
		self.split_last().map(|(t, rest)| {
			*self = rest;
			t
		})
	}
}

impl Pop<char> for &str {
	fn pop(&mut self) -> Option<char> {
		let c = self.chars().last();
		if let Some(c) = c {
			*self = &self[..self.len() - c.len_utf8()];
		}
		c
	}
}

// TODO: This method doesn't compile as-is, but there should be a way to do this.
// impl<'a, T> Unshift<&'a mut T> for &'a mut [T] {
//     fn unshift(&mut self) -> Option<&'a mut T> {
//         self.split_first_mut().map(|(t, rest)| -> &'a mut T {
//             *self = rest;
//             t
//         })
//     }
// }

impl<'a, T> Unshift<&'a T> for &'a [T] {
	fn unshift(&mut self) -> Option<&'a T> {
		self.split_first().map(|(t, rest)| {
			*self = rest;
			t
		})
	}
}

impl Unshift<char> for &str {
	fn unshift(&mut self) -> Option<char> {
		let c = self.chars().next();
		if let Some(c) = c {
			*self = &self[c.len_utf8()..];
		}
		c
	}
}