use std::fmt;

pub struct HelpMessage {
	title: &'static str,
	segments: Vec<HelpSegment>,
}

impl fmt::Display for HelpMessage {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		writeln!(f, "{}", self.title.to_uppercase())?;

		for seg in &self.segments {
			write!(f, "{seg}")?;
		}

		Ok(())
	}
}

pub struct HelpSegment {
	head: &'static str,
	body: &'static str,
}

impl fmt::Display for HelpSegment {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		writeln!(f, "{}:", self.head)?;

		const INDENT: IndentStr<4> = IndentStr::new();
		const LINE_LEN: usize = 80 - INDENT.len();

		let mut curr = self.body;
		loop {
			let line_len = curr.len().min(LINE_LEN);
			let line = &curr[..line_len];
			curr = &curr[line_len..];

			writeln!(f, "{INDENT}{line}")?;

			if curr.len() == 0 {
				break Ok(());
			}
		}
	}
}

struct IndentStr<const N: usize> {
	arr: [u8; N],
}

impl<const N: usize> IndentStr<N> {
	pub const fn new() -> Self {
		IndentStr {
			arr: [' ' as u8; N],
		}
	}

	pub const fn len(&self) -> usize {
		N
	}

	pub const fn as_str(&self) -> &str {
		unsafe { std::str::from_utf8_unchecked(&self.arr) }
	}
}

impl<const N: usize> Default for IndentStr<N> {
	fn default() -> Self {
		Self::new()
	}
}

impl<const N: usize> fmt::Display for IndentStr<N> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		let ident = unsafe { std::str::from_utf8_unchecked(&self.arr) };
		write!(f, "{ident}")
	}
}

#[cfg(test)]
mod test {
	use crate::helpgen::HelpSegment;

	#[test]
	fn segment() {
		let segment = HelpSegment {
			head: "head",
			body: "body of the help string",
		};

		let expected = "head:\n    body of the help string\n";

		assert_eq!(segment.to_string(), expected)
	}

	#[test]
	fn segment_longline() {
		let segment = HelpSegment {
			head: "head",
			body: "01234567890123456789012345678901234567890123456789012345678901234567890123456789",
		};
		let expected = "head:\n    0123456789012345678901234567890123456789012345678901234567890123456789012345\n    6789\n";

		assert_eq!(segment.to_string(), expected)
	}
}