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    //! This module implements support for preferring some versions of a package
    //! over other versions.

    use std::cmp::Ordering;
    use std::collections::{HashMap, HashSet};

    use cargo_util_schemas::manifest::RustVersion;

    use crate::core::{Dependency, PackageId, Summary};
    use crate::util::interning::InternedString;

    /// A collection of preferences for particular package versions.
    ///
    /// This is built up with [`Self::prefer_package_id`] and [`Self::prefer_dependency`], then used to sort the set of
    /// summaries for a package during resolution via [`Self::sort_summaries`].
    ///
    /// As written, a version is either "preferred" or "not preferred".  Later extensions may
    /// introduce more granular preferences.
    #[derive(Default)]
    pub struct VersionPreferences {
        try_to_use: HashSet<PackageId>,
        prefer_patch_deps: HashMap<InternedString, HashSet<Dependency>>,
        version_ordering: VersionOrdering,
        max_rust_version: Option<RustVersion>,
    }

    #[derive(Copy, Clone, Default, PartialEq, Eq, Hash, Debug)]
    pub enum VersionOrdering {
        #[default]
        MaximumVersionsFirst,
        MinimumVersionsFirst,
    }

    impl VersionPreferences {
        /// Indicate that the given package (specified as a [`PackageId`]) should be preferred.
        pub fn prefer_package_id(&mut self, pkg_id: PackageId) {
            self.try_to_use.insert(pkg_id);
        }

        /// Indicate that the given package (specified as a [`Dependency`])  should be preferred.
        pub fn prefer_dependency(&mut self, dep: Dependency) {
            self.prefer_patch_deps
                .entry(dep.package_name())
                .or_insert_with(HashSet::new)
                .insert(dep);
        }

        pub fn version_ordering(&mut self, ordering: VersionOrdering) {
            self.version_ordering = ordering;
        }

        pub fn max_rust_version(&mut self, ver: Option<RustVersion>) {
            self.max_rust_version = ver;
        }

        /// Sort (and filter) the given vector of summaries in-place
        ///
        /// Note: all summaries presumed to be for the same package.
        ///
        /// Sort order:
        /// 1. Preferred packages
        /// 2. [`VersionPreferences::max_rust_version`]
        /// 3. `first_version`, falling back to [`VersionPreferences::version_ordering`] when `None`
        ///
        /// Filtering:
        /// - `first_version`
        pub fn sort_summaries(
            &self,
            summaries: &mut Vec<Summary>,
            first_version: Option<VersionOrdering>,
        ) {
            let should_prefer = |pkg_id: &PackageId| {
                self.try_to_use.contains(pkg_id)
                    || self
                        .prefer_patch_deps
                        .get(&pkg_id.name())
                        .map(|deps| deps.iter().any(|d| d.matches_id(*pkg_id)))
                        .unwrap_or(false)
            };
            summaries.sort_unstable_by(|a, b| {
                let prefer_a = should_prefer(&a.package_id());
                let prefer_b = should_prefer(&b.package_id());
                let previous_cmp = prefer_a.cmp(&prefer_b).reverse();
                if previous_cmp != Ordering::Equal {
                    return previous_cmp;
                }

                if let Some(max_rust_version) = &self.max_rust_version {
                    match (a.rust_version(), b.rust_version()) {
                        // Fallback
                        (None, None) => {}
                        (Some(a), Some(b)) if a == b => {}
                        // Primary comparison
                        (Some(a), Some(b)) => {
                            let a_is_compat = a <= max_rust_version;
                            let b_is_compat = b <= max_rust_version;
                            match (a_is_compat, b_is_compat) {
                                (true, true) => {}   // fallback
                                (false, false) => {} // fallback
                                (true, false) => return Ordering::Less,
                                (false, true) => return Ordering::Greater,
                            }
                        }
                        // Prioritize `None` over incompatible
                        (None, Some(b)) => {
                            if b <= max_rust_version {
                                return Ordering::Greater;
                            } else {
                                return Ordering::Less;
                            }
                        }
                        (Some(a), None) => {
                            if a <= max_rust_version {
                                return Ordering::Less;
                            } else {
                                return Ordering::Greater;
                            }
                        }
                    }
                }

                let cmp = a.version().cmp(b.version());
                match first_version.unwrap_or(self.version_ordering) {
                    VersionOrdering::MaximumVersionsFirst => cmp.reverse(),
                    VersionOrdering::MinimumVersionsFirst => cmp,
                }
            });
            if first_version.is_some() && !summaries.is_empty() {
                let _ = summaries.split_off(1);
            }
        }
    }

    #[cfg(test)]
    mod test {
        use super::*;
        use crate::core::SourceId;
        use std::collections::BTreeMap;

        fn pkgid(name: &str, version: &str) -> PackageId {
            let src_id =
                SourceId::from_url("registry+https://github.com/rust-lang/crates.io-index").unwrap();
            PackageId::try_new(name, version, src_id).unwrap()
        }

        fn dep(name: &str, version: &str) -> Dependency {
            let src_id =
                SourceId::from_url("registry+https://github.com/rust-lang/crates.io-index").unwrap();
            Dependency::parse(name, Some(version), src_id).unwrap()
        }

        fn summ(name: &str, version: &str, msrv: Option<&str>) -> Summary {
            let pkg_id = pkgid(name, version);
            let features = BTreeMap::new();
            Summary::new(
                pkg_id,
                Vec::new(),
                &features,
                None::<&String>,
                msrv.map(|m| m.parse().unwrap()),
            )
            .unwrap()
        }

        fn describe(summaries: &Vec<Summary>) -> String {
            let strs: Vec<String> = summaries
                .iter()
                .map(|summary| format!("{}/{}", summary.name(), summary.version()))
                .collect();
            strs.join(", ")
        }

        #[test]
        fn test_prefer_package_id() {
            let mut vp = VersionPreferences::default();
            vp.prefer_package_id(pkgid("foo", "1.2.3"));

            let mut summaries = vec![
                summ("foo", "1.2.4", None),
                summ("foo", "1.2.3", None),
                summ("foo", "1.1.0", None),
                summ("foo", "1.0.9", None),
            ];

            vp.version_ordering(VersionOrdering::MaximumVersionsFirst);
            vp.sort_summaries(&mut summaries, None);
            assert_eq!(
                describe(&summaries),
                "foo/1.2.3, foo/1.2.4, foo/1.1.0, foo/1.0.9".to_string()
            );

            vp.version_ordering(VersionOrdering::MinimumVersionsFirst);
            vp.sort_summaries(&mut summaries, None);
            assert_eq!(
                describe(&summaries),
                "foo/1.2.3, foo/1.0.9, foo/1.1.0, foo/1.2.4".to_string()
            );
        }

        #[test]
        fn test_prefer_dependency() {
            let mut vp = VersionPreferences::default();
            vp.prefer_dependency(dep("foo", "=1.2.3"));

            let mut summaries = vec![
                summ("foo", "1.2.4", None),
                summ("foo", "1.2.3", None),
                summ("foo", "1.1.0", None),
                summ("foo", "1.0.9", None),
            ];

            vp.version_ordering(VersionOrdering::MaximumVersionsFirst);
            vp.sort_summaries(&mut summaries, None);
            assert_eq!(
                describe(&summaries),
                "foo/1.2.3, foo/1.2.4, foo/1.1.0, foo/1.0.9".to_string()
            );

            vp.version_ordering(VersionOrdering::MinimumVersionsFirst);
            vp.sort_summaries(&mut summaries, None);
            assert_eq!(
                describe(&summaries),
                "foo/1.2.3, foo/1.0.9, foo/1.1.0, foo/1.2.4".to_string()
            );
        }

        #[test]
        fn test_prefer_both() {
            let mut vp = VersionPreferences::default();
            vp.prefer_package_id(pkgid("foo", "1.2.3"));
            vp.prefer_dependency(dep("foo", "=1.1.0"));

            let mut summaries = vec![
                summ("foo", "1.2.4", None),
                summ("foo", "1.2.3", None),
                summ("foo", "1.1.0", None),
                summ("foo", "1.0.9", None),
            ];

            vp.version_ordering(VersionOrdering::MaximumVersionsFirst);
            vp.sort_summaries(&mut summaries, None);
            assert_eq!(
                describe(&summaries),
                "foo/1.2.3, foo/1.1.0, foo/1.2.4, foo/1.0.9".to_string()
            );

            vp.version_ordering(VersionOrdering::MinimumVersionsFirst);
            vp.sort_summaries(&mut summaries, None);
            assert_eq!(
                describe(&summaries),
                "foo/1.1.0, foo/1.2.3, foo/1.0.9, foo/1.2.4".to_string()
            );
        }

        #[test]
        fn test_max_rust_version() {
            let mut vp = VersionPreferences::default();
            vp.max_rust_version(Some("1.50".parse().unwrap()));

            let mut summaries = vec![
                summ("foo", "1.2.4", None),
                summ("foo", "1.2.3", Some("1.60")),
                summ("foo", "1.2.2", None),
                summ("foo", "1.2.1", Some("1.50")),
                summ("foo", "1.2.0", None),
                summ("foo", "1.1.0", Some("1.40")),
                summ("foo", "1.0.9", None),
            ];

            vp.version_ordering(VersionOrdering::MaximumVersionsFirst);
            vp.sort_summaries(&mut summaries, None);
            assert_eq!(
                describe(&summaries),
                "foo/1.2.1, foo/1.1.0, foo/1.2.4, foo/1.2.2, foo/1.2.0, foo/1.0.9, foo/1.2.3"
                    .to_string()
            );

            vp.version_ordering(VersionOrdering::MinimumVersionsFirst);
            vp.sort_summaries(&mut summaries, None);
            assert_eq!(
                describe(&summaries),
                "foo/1.1.0, foo/1.2.1, foo/1.0.9, foo/1.2.0, foo/1.2.2, foo/1.2.4, foo/1.2.3"
                    .to_string()
            );
        }

        #[test]
        fn test_empty_summaries() {
            let vp = VersionPreferences::default();
            let mut summaries = vec![];

            vp.sort_summaries(&mut summaries, Some(VersionOrdering::MaximumVersionsFirst));
            assert_eq!(summaries, vec![]);
        }
    }