use ArgdataRef;
use ReadError;

/// An argdata value representing a sequence.
pub trait Seq<'d> {
	/// Iterate to the next element, returning None if the end is reached.
	///
	/// You probably want to use `iter_seq` instead, which gives you a normal Iterator.
	///
	/// `cookie` should be 0 for the first element, and is modified by this method to refer to the
	/// next element on each call. The value of the `cookie` is implementation-specific. It might
	/// for example be the index into a vector, or the byte-offset into an encoded argdata value.
	///
	/// Might panic if you give it an invalid `cookie`.
	fn iter_seq_next<'a>(
		&'a self,
		cookie: &mut usize,
	) -> Option<Result<ArgdataRef<'a, 'd>, ReadError>>
	where
		'd: 'a;
}

impl<'a, 'd: 'a> Seq<'d> + 'a {
	/// Get an iterator to the elements of the sequence.
	pub fn iter_seq(&'a self) -> SeqIterator<'a, 'd> {
		SeqIterator {
			seq: self,
			cookie: 0,
		}
	}
}

/// An iterator of a sequence, returned by `Seq::iter_seq()`.
pub struct SeqIterator<'a, 'd: 'a> {
	seq: &'a (Seq<'d> + 'a),
	cookie: usize,
}

impl<'a, 'd: 'a> Iterator for SeqIterator<'a, 'd> {
	type Item = Result<ArgdataRef<'a, 'd>, ReadError>;
	fn next(&mut self) -> Option<Self::Item> {
		self.seq.iter_seq_next(&mut self.cookie)
	}
}