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//! Implements methods to create an `Element`
//! from a stream of characters.
use core::iter::Peekable;
use crate::Element;
impl Element {
/// Creates an `Element` from a peekable stream of characters.
///
/// # Arguments
///
/// * `stream` - A mutable reference to a peekable iterator over characters.
///
/// # Returns
///
/// * `Ok(Some(Element))` if an element symbol was successfully parsed.
/// * `Ok(None)` if the stream is exhausted (no character at all to parse).
///
/// # Errors
///
/// * If the parsing fails, it returns the consumed character that caused
/// the failure.
///
/// # Examples
///
/// ```
/// use elements_rs::Element;
///
/// let mut stream = "He".chars().peekable();
/// assert_eq!(Element::try_from_stream(&mut stream), Ok(Some(Element::He)));
///
/// let mut stream = "H".chars().peekable();
/// assert_eq!(Element::try_from_stream(&mut stream), Ok(Some(Element::H)));
///
/// let mut stream = "Hz".chars().peekable();
/// assert_eq!(Element::try_from_stream(&mut stream), Ok(Some(Element::H)));
/// assert_eq!(stream.next(), Some('z'));
///
/// let mut stream = "!".chars().peekable();
/// assert_eq!(Element::try_from_stream(&mut stream), Err('!'));
///
/// let mut stream = "".chars().peekable();
/// assert_eq!(Element::try_from_stream(&mut stream), Ok(None));
/// ```
pub fn try_from_stream<I>(stream: &mut Peekable<I>) -> Result<Option<Self>, char>
where
I: Iterator<Item = char>,
{
let Some(character) = stream.next() else {
return Ok(None);
};
if let Some(peak) = stream.peek().copied()
&& let Ok(element) = Element::try_from([character, peak])
{
stream.next();
Ok(Some(element))
} else if let Ok(element) = Element::try_from(character) {
Ok(Some(element))
} else {
Err(character)
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_try_from_stream() {
// Empty stream
let mut stream = "".chars().peekable();
assert_eq!(Element::try_from_stream(&mut stream), Ok(None));
// Valid 1-char element
let mut stream = "H".chars().peekable();
assert_eq!(Element::try_from_stream(&mut stream), Ok(Some(Element::H)));
assert_eq!(stream.next(), None);
// Valid 2-char element
let mut stream = "He".chars().peekable();
assert_eq!(Element::try_from_stream(&mut stream), Ok(Some(Element::He)));
assert_eq!(stream.next(), None);
// Valid 1-char element followed by char making invalid 2-char
let mut stream = "Hz".chars().peekable();
assert_eq!(Element::try_from_stream(&mut stream), Ok(Some(Element::H)));
assert_eq!(stream.next(), Some('z'));
// Valid 2-char element (greedy match over 1-char)
// 'C' is Carbon, 'Co' is Cobalt. Should match Cobalt.
let mut stream = "Co".chars().peekable();
assert_eq!(Element::try_from_stream(&mut stream), Ok(Some(Element::Co)));
assert_eq!(stream.next(), None);
// Invalid character
let mut stream = "!".chars().peekable();
assert_eq!(Element::try_from_stream(&mut stream), Err('!'));
assert_eq!(stream.next(), None);
// Invalid 2-char, but first char is invalid too
let mut stream = "!H".chars().peekable();
assert_eq!(Element::try_from_stream(&mut stream), Err('!'));
assert_eq!(stream.next(), Some('H'));
}
}