libversion 0.3.3

Advanced version string comparison algorithm
Documentation 
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// SPDX-FileCopyrightText: Copyright 2024 Dmitry Marakasov <amdmi3@amdmi3.ru>
// SPDX-License-Identifier: Apache-2.0 OR MIT

use std::cmp::Ordering;

#[derive(Debug, PartialEq, Eq)]
pub(crate) enum Component<'a> {
    LowerBound,
    PreRelease(u8),
    Zero,
    PostRelease(u8),
    NonZero(&'a str),
    LetterSuffix(u8),
    UpperBound,
}

impl Component<'_> {
    fn discriminant(&self) -> u8 {
        match self {
            Self::LowerBound => 0,
            Self::PreRelease(_) => 1,
            Self::Zero => 2,
            Self::PostRelease(_) => 3,
            Self::NonZero(_) => 4,
            Self::LetterSuffix(_) => 5,
            Self::UpperBound => 6,
        }
    }
}

impl Ord for Component<'_> {
    fn cmp(&self, other: &Self) -> Ordering {
        self.discriminant()
            .cmp(&other.discriminant())
            .then_with(|| match (self, other) {
                (Component::PreRelease(a), Component::PreRelease(b)) => a.cmp(b),
                (Component::PostRelease(a), Component::PostRelease(b)) => a.cmp(b),
                (Component::NonZero(a), Component::NonZero(b)) => {
                    a.len().cmp(&b.len()).then_with(|| a.cmp(b))
                }
                (Component::LetterSuffix(a), Component::LetterSuffix(b)) => a.cmp(b),
                _ => Ordering::Equal,
            })
    }
}

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

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_component_order() {
        let ordered = [
            Component::LowerBound,
            Component::PreRelease(b'a'),
            Component::PreRelease(b'b'),
            Component::PreRelease(b'z'),
            Component::Zero,
            Component::PostRelease(b'a'),
            Component::PostRelease(b'b'),
            Component::PostRelease(b'z'),
            Component::NonZero("0"),
            Component::NonZero("1"),
            Component::NonZero("9"),
            Component::NonZero("10"),
            Component::NonZero("99"),
            Component::NonZero("100"),
            Component::LetterSuffix(b'a'),
            Component::LetterSuffix(b'b'),
            Component::LetterSuffix(b'z'),
            Component::UpperBound,
        ];

        for (lhs_index, lhs) in ordered.iter().enumerate() {
            for (rhs_index, rhs) in ordered.iter().enumerate() {
                let expected_ordering = lhs_index.cmp(&rhs_index);
                assert!(
                    lhs.cmp(rhs) == expected_ordering,
                    "Component Ord violation, expected {lhs:?} {expected_ordering:?} {rhs:?}"
                );
                assert!(
                    lhs.partial_cmp(rhs) == Some(expected_ordering),
                    "Component PartialOrd violation, expected {lhs:?} {expected_ordering:?} {rhs:?}"
                );
            }
        }
    }
}