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use std::hash::Hash;

use static_regular_grammar::RegularGrammar;

use crate::utils::{self, str_eq};

/// Single variant subtag.
///
/// Variant subtags are used to indicate additional, well-recognized
/// variations that define a language or its dialects that are not
/// covered by other available subtags.
#[derive(RegularGrammar)]
#[grammar(file = "src/grammar.abnf", entry_point = "variant")]
#[grammar(sized(
	VariantBuf,
	derive(Debug, Display, PartialEq, Eq, PartialOrd, Ord, Hash)
))]
#[cfg_attr(feature = "serde", grammar(serde))]
pub struct Variant(str);

impl PartialEq for Variant {
	fn eq(&self, other: &Self) -> bool {
		utils::case_insensitive_eq(self.as_bytes(), other.as_bytes())
	}
}

impl Eq for Variant {}

str_eq!(Variant);
str_eq!(VariantBuf);

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

impl Ord for Variant {
	fn cmp(&self, other: &Self) -> std::cmp::Ordering {
		utils::case_insensitive_cmp(self.as_bytes(), other.as_bytes())
	}
}

impl Hash for Variant {
	fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
		utils::case_insensitive_hash(self.as_bytes(), state)
	}
}

/// List of variant subtags.
///
/// Represents a list of variant subtags separated by a `-` character
/// as found in a language tag.
///
/// ```abnf
/// variants = [ variant *("-" variant) ]
///
/// variant  = 5*8alphanum       ; registered variants
///          / (DIGIT 3alphanum)
///
/// alphanum = (ALPHA / DIGIT)   ; letters and numbers
/// ```
#[derive(RegularGrammar)]
#[grammar(sized(
	VariantsBuf,
	derive(Debug, Display, PartialEq, Eq, PartialOrd, Ord, Hash)
))]
#[cfg_attr(feature = "serde", grammar(serde))]
pub struct Variants(str);

impl Variants {
	pub fn iter(&self) -> VariantsIter {
		VariantsIter::new(&self.0)
	}

	pub fn first(&self) -> Option<&Variant> {
		self.iter().next()
	}

	pub fn last(&self) -> Option<&Variant> {
		self.iter().next_back()
	}
}

impl PartialEq for Variants {
	fn eq(&self, other: &Self) -> bool {
		utils::case_insensitive_eq(self.as_bytes(), other.as_bytes())
	}
}

impl Eq for Variants {}

str_eq!(Variants);
str_eq!(VariantsBuf);

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

impl Ord for Variants {
	fn cmp(&self, other: &Self) -> std::cmp::Ordering {
		utils::case_insensitive_cmp(self.as_bytes(), other.as_bytes())
	}
}

impl Hash for Variants {
	fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
		utils::case_insensitive_hash(self.as_bytes(), state)
	}
}

#[derive(Default)]
pub struct VariantsIter<'a> {
	data: &'a str,
	offset: usize,
	end: usize,
}

impl<'a> VariantsIter<'a> {
	fn new(data: &'a str) -> Self {
		Self {
			data,
			offset: 0,
			end: data.len(),
		}
	}

	pub fn empty() -> Self {
		Self::default()
	}
}

impl<'a> Iterator for VariantsIter<'a> {
	type Item = &'a Variant;

	fn next(&mut self) -> Option<Self::Item> {
		if self.offset < self.end {
			let end = super::find_segment_end(self.data, self.offset);
			let item = unsafe { Variant::new_unchecked(&self.data[self.offset..end]) };
			self.offset = end + 1;
			Some(item)
		} else {
			None
		}
	}
}

impl<'a> DoubleEndedIterator for VariantsIter<'a> {
	fn next_back(&mut self) -> Option<Self::Item> {
		if self.end > self.offset {
			let start = super::find_segment_start(self.data, self.end);
			let item = unsafe { Variant::new_unchecked(&self.data[start..self.end]) };

			self.end = if start > 0 { start - 1 } else { 0 };

			Some(item)
		} else {
			None
		}
	}
}