tinylog 4.0.2

use std::{cell::Cell, fmt};

/// Operate on an empty, reused, thread-local string. Falls back to a new one if it isn't available.
pub(super) fn with_local_string<F, R>(f: F) -> R
where
	F: FnOnce(&mut String) -> R,
{
	// I'd use RefCell, but lifetimes are hard when you're trying to avoid all panics.
	thread_local! {
		static GLOBAL_STR: Cell<Option<String>> = const { Cell::new(Some(String::new())) };
	}

	if let Some(mut s) = GLOBAL_STR.try_with(Cell::take).ok().flatten() {
		let result = f(&mut s);

		// If this fails, then our thread is probably shutting down.
		// In that case it's fine for the shared string to be lost.
		let _ = GLOBAL_STR.try_with(move |cell| {
			s.clear();
			cell.set(Some(s));
		});

		result
	} else {
		f(&mut String::new())
	}
}

/// Similar to [`std::fmt::Write`], but with infallible methods.
pub(super) trait StringLike {
	/// Append a single character.
	fn push(&mut self, c: char);
	/// Append a string slice.
	fn push_str(&mut self, s: &str);
	/// Reserve capacity for `additional` more bytes.
	fn reserve(&mut self, additional: usize);
}

impl<T: StringLike> StringLike for &mut T {
	fn push(&mut self, c: char) {
		(**self).push(c);
	}

	fn push_str(&mut self, s: &str) {
		(**self).push_str(s);
	}

	fn reserve(&mut self, additional: usize) {
		(**self).reserve(additional);
	}
}

impl StringLike for String {
	fn push(&mut self, c: char) {
		self.push(c);
	}

	fn push_str(&mut self, s: &str) {
		self.push_str(s);
	}

	fn reserve(&mut self, additional: usize) {
		self.reserve(additional);
	}
}

/// Indents all text written to it by a certain amount.
#[non_exhaustive]
pub(super) struct Indented<T> {
	pub output: T,

	/// How many spaces to indent by.
	pub indent: usize,
}

impl<T> Indented<T> {
	pub fn new(output: T, indent: usize) -> Self {
		Self { output, indent }
	}
}

impl<T: StringLike> StringLike for Indented<T> {
	fn push(&mut self, c: char) {
		if c == '\n' {
			self.output.reserve(1 + self.indent);
			self.output.push('\n');
			for _ in 0..self.indent {
				self.output.push(' ');
			}
		} else {
			self.output.push(c);
		}
	}

	fn push_str(&mut self, s: &str) {
		let mut lines = s.split('\n');
		if let Some(first_line) = lines.next() {
			self.output.push_str(first_line);
			for line in lines {
				self.output.reserve(1 + self.indent + line.len());
				self.output.push('\n');
				for _ in 0..self.indent {
					self.output.push(' ');
				}
				self.output.push_str(line);
			}
		}
	}

	fn reserve(&mut self, additional: usize) {
		self.output.reserve(additional);
	}
}

impl<T: StringLike> fmt::Write for Indented<T> {
	fn write_char(&mut self, c: char) -> std::fmt::Result {
		self.push(c);
		Ok(())
	}

	fn write_str(&mut self, s: &str) -> std::fmt::Result {
		self.push_str(s);
		Ok(())
	}
}