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    use super::dep_cache::RegistryQueryer;
    use super::errors::ActivateResult;
    use super::types::{ConflictMap, ConflictReason, FeaturesSet, ResolveOpts};
    use super::RequestedFeatures;
    use crate::core::{Dependency, PackageId, SourceId, Summary};
    use crate::util::interning::InternedString;
    use crate::util::Graph;
    use anyhow::format_err;
    use log::debug;
    use std::collections::HashMap;
    use std::num::NonZeroU64;

    pub use super::encode::Metadata;
    pub use super::encode::{EncodableDependency, EncodablePackageId, EncodableResolve};
    pub use super::resolve::Resolve;

    // A `Context` is basically a bunch of local resolution information which is
    // kept around for all `BacktrackFrame` instances. As a result, this runs the
    // risk of being cloned *a lot* so we want to make this as cheap to clone as
    // possible.
    #[derive(Clone)]
    pub struct Context {
        pub age: ContextAge,
        pub activations: Activations,
        /// list the features that are activated for each package
        pub resolve_features: im_rc::HashMap<PackageId, FeaturesSet>,
        /// get the package that will be linking to a native library by its links attribute
        pub links: im_rc::HashMap<InternedString, PackageId>,
        /// for each package the list of names it can see,
        /// then for each name the exact version that name represents and whether the name is public.
        pub public_dependency: Option<PublicDependency>,

        /// a way to look up for a package in activations what packages required it
        /// and all of the exact deps that it fulfilled.
        pub parents: Graph<PackageId, im_rc::HashSet<Dependency>>,
    }

    /// When backtracking it can be useful to know how far back to go.
    /// The `ContextAge` of a `Context` is a monotonically increasing counter of the number
    /// of decisions made to get to this state.
    /// Several structures store the `ContextAge` when it was added,
    /// to be used in `find_candidate` for backtracking.
    pub type ContextAge = usize;

    /// Find the activated version of a crate based on the name, source, and semver compatibility.
    /// By storing this in a hash map we ensure that there is only one
    /// semver compatible version of each crate.
    /// This all so stores the `ContextAge`.
    pub type ActivationsKey = (InternedString, SourceId, SemverCompatibility);
    pub type Activations = im_rc::HashMap<ActivationsKey, (Summary, ContextAge)>;

    /// A type that represents when cargo treats two Versions as compatible.
    /// Versions `a` and `b` are compatible if their left-most nonzero digit is the
    /// same.
    #[derive(Clone, Copy, Eq, PartialEq, Hash, Debug, PartialOrd, Ord)]
    pub enum SemverCompatibility {
        Major(NonZeroU64),
        Minor(NonZeroU64),
        Patch(u64),
    }

    impl From<&semver::Version> for SemverCompatibility {
        fn from(ver: &semver::Version) -> Self {
            if let Some(m) = NonZeroU64::new(ver.major) {
                return SemverCompatibility::Major(m);
            }
            if let Some(m) = NonZeroU64::new(ver.minor) {
                return SemverCompatibility::Minor(m);
            }
            SemverCompatibility::Patch(ver.patch)
        }
    }

    impl PackageId {
        pub fn as_activations_key(self) -> ActivationsKey {
            (self.name(), self.source_id(), self.version().into())
        }
    }

    impl Context {
        pub fn new(check_public_visible_dependencies: bool) -> Context {
            Context {
                age: 0,
                resolve_features: im_rc::HashMap::new(),
                links: im_rc::HashMap::new(),
                public_dependency: if check_public_visible_dependencies {
                    Some(PublicDependency::new())
                } else {
                    None
                },
                parents: Graph::new(),
                activations: im_rc::HashMap::new(),
            }
        }

        /// Activate this summary by inserting it into our list of known activations.
        ///
        /// The `parent` passed in here is the parent summary/dependency edge which
        /// cased `summary` to get activated. This may not be present for the root
        /// crate, for example.
        ///
        /// Returns `true` if this summary with the given features is already activated.
        pub fn flag_activated(
            &mut self,
            summary: &Summary,
            opts: &ResolveOpts,
            parent: Option<(&Summary, &Dependency)>,
        ) -> ActivateResult<bool> {
            let id = summary.package_id();
            let age: ContextAge = self.age;
            match self.activations.entry(id.as_activations_key()) {
                im_rc::hashmap::Entry::Occupied(o) => {
                    debug_assert_eq!(
                        &o.get().0,
                        summary,
                        "cargo does not allow two semver compatible versions"
                    );
                }
                im_rc::hashmap::Entry::Vacant(v) => {
                    if let Some(link) = summary.links() {
                        if self.links.insert(link, id).is_some() {
                            return Err(format_err!(
                                "Attempting to resolve a dependency with more than \
                                 one crate with links={}.\nThis will not build as \
                                 is. Consider rebuilding the .lock file.",
                                &*link
                            )
                            .into());
                        }
                    }
                    v.insert((summary.clone(), age));

                    // If we've got a parent dependency which activated us, *and*
                    // the dependency has a different source id listed than the
                    // `summary` itself, then things get interesting. This basically
                    // means that a `[patch]` was used to augment `dep.source_id()`
                    // with `summary`.
                    //
                    // In this scenario we want to consider the activation key, as
                    // viewed from the perspective of `dep.source_id()`, as being
                    // fulfilled. This means that we need to add a second entry in
                    // the activations map for the source that was patched, in
                    // addition to the source of the actual `summary` itself.
                    //
                    // Without this it would be possible to have both 1.0.0 and
                    // 1.1.0 "from crates.io" in a dependency graph if one of those
                    // versions came from a `[patch]` source.
                    if let Some((_, dep)) = parent {
                        if dep.source_id() != id.source_id() {
                            let key = (id.name(), dep.source_id(), id.version().into());
                            let prev = self.activations.insert(key, (summary.clone(), age));
                            if let Some((previous_summary, _)) = prev {
                                return Err(
                                    (previous_summary.package_id(), ConflictReason::Semver).into()
                                );
                            }
                        }
                    }

                    return Ok(false);
                }
            }
            debug!("checking if {} is already activated", summary.package_id());
            match &opts.features {
                // This returns `false` for CliFeatures just for simplicity. It
                // would take a bit of work to compare since they are not in the
                // same format as DepFeatures (and that may be expensive
                // performance-wise). Also, it should only occur once for a root
                // package. The only drawback is that it may re-activate a root
                // package again, which should only affect performance, but that
                // should be rare. Cycles should still be detected since those
                // will have `DepFeatures` edges.
                RequestedFeatures::CliFeatures(_) => Ok(false),
                RequestedFeatures::DepFeatures {
                    features,
                    uses_default_features,
                } => {
                    let has_default_feature = summary.features().contains_key("default");
                    Ok(match self.resolve_features.get(&id) {
                        Some(prev) => {
                            features.is_subset(prev)
                                && (!uses_default_features
                                    || prev.contains("default")
                                    || !has_default_feature)
                        }
                        None => features.is_empty() && (!uses_default_features || !has_default_feature),
                    })
                }
            }
        }

        /// If the package is active returns the `ContextAge` when it was added
        pub fn is_active(&self, id: PackageId) -> Option<ContextAge> {
            self.activations
                .get(&id.as_activations_key())
                .and_then(|(s, l)| if s.package_id() == id { Some(*l) } else { None })
        }

        /// If the conflict reason on the package still applies returns the `ContextAge` when it was added
        pub fn still_applies(&self, id: PackageId, reason: &ConflictReason) -> Option<ContextAge> {
            self.is_active(id).and_then(|mut max| {
                match reason {
                    ConflictReason::PublicDependency(name) => {
                        if &id == name {
                            return Some(max);
                        }
                        max = std::cmp::max(max, self.is_active(*name)?);
                        max = std::cmp::max(
                            max,
                            self.public_dependency
                                .as_ref()
                                .unwrap()
                                .can_see_item(*name, id)?,
                        );
                    }
                    ConflictReason::PubliclyExports(name) => {
                        if &id == name {
                            return Some(max);
                        }
                        max = std::cmp::max(max, self.is_active(*name)?);
                        max = std::cmp::max(
                            max,
                            self.public_dependency
                                .as_ref()
                                .unwrap()
                                .publicly_exports_item(*name, id)?,
                        );
                    }
                    _ => {}
                }
                Some(max)
            })
        }

        /// Checks whether all of `parent` and the keys of `conflicting activations`
        /// are still active.
        /// If so returns the `ContextAge` when the newest one was added.
        pub fn is_conflicting(
            &self,
            parent: Option<PackageId>,
            conflicting_activations: &ConflictMap,
        ) -> Option<usize> {
            let mut max = 0;
            if let Some(parent) = parent {
                max = std::cmp::max(max, self.is_active(parent)?);
            }

            for (id, reason) in conflicting_activations.iter() {
                max = std::cmp::max(max, self.still_applies(*id, reason)?);
            }
            Some(max)
        }

        pub fn resolve_replacements(
            &self,
            registry: &RegistryQueryer<'_>,
        ) -> HashMap<PackageId, PackageId> {
            self.activations
                .values()
                .filter_map(|(s, _)| registry.used_replacement_for(s.package_id()))
                .collect()
        }

        pub fn graph(&self) -> Graph<PackageId, std::collections::HashSet<Dependency>> {
            let mut graph: Graph<PackageId, std::collections::HashSet<Dependency>> = Graph::new();
            self.activations
                .values()
                .for_each(|(r, _)| graph.add(r.package_id()));
            for i in self.parents.iter() {
                graph.add(*i);
                for (o, e) in self.parents.edges(i) {
                    let old_link = graph.link(*o, *i);
                    assert!(old_link.is_empty());
                    *old_link = e.iter().cloned().collect();
                }
            }
            graph
        }
    }

    impl Graph<PackageId, im_rc::HashSet<Dependency>> {
        pub fn parents_of(&self, p: PackageId) -> impl Iterator<Item = (PackageId, bool)> + '_ {
            self.edges(&p)
                .map(|(grand, d)| (*grand, d.iter().any(|x| x.is_public())))
        }
    }

    #[derive(Clone, Debug, Default)]
    pub struct PublicDependency {
        /// For each active package the set of all the names it can see,
        /// for each name the exact package that name resolves to,
        ///     the `ContextAge` when it was first visible,
        ///     and the `ContextAge` when it was first exported.
        inner: im_rc::HashMap<
            PackageId,
            im_rc::HashMap<InternedString, (PackageId, ContextAge, Option<ContextAge>)>,
        >,
    }

    impl PublicDependency {
        fn new() -> Self {
            PublicDependency {
                inner: im_rc::HashMap::new(),
            }
        }
        fn publicly_exports(&self, candidate_pid: PackageId) -> Vec<PackageId> {
            self.inner
                .get(&candidate_pid) // if we have seen it before
                .iter()
                .flat_map(|x| x.values()) // all the things we have stored
                .filter(|x| x.2.is_some()) // as publicly exported
                .map(|x| x.0)
                .chain(Some(candidate_pid)) // but even if not we know that everything exports itself
                .collect()
        }
        fn publicly_exports_item(
            &self,
            candidate_pid: PackageId,
            target: PackageId,
        ) -> Option<ContextAge> {
            debug_assert_ne!(candidate_pid, target);
            let out = self
                .inner
                .get(&candidate_pid)
                .and_then(|names| names.get(&target.name()))
                .filter(|(p, _, _)| *p == target)
                .and_then(|(_, _, age)| *age);
            debug_assert_eq!(
                out.is_some(),
                self.publicly_exports(candidate_pid).contains(&target)
            );
            out
        }
        pub fn can_see_item(&self, candidate_pid: PackageId, target: PackageId) -> Option<ContextAge> {
            self.inner
                .get(&candidate_pid)
                .and_then(|names| names.get(&target.name()))
                .filter(|(p, _, _)| *p == target)
                .map(|(_, age, _)| *age)
        }
        pub fn add_edge(
            &mut self,
            candidate_pid: PackageId,
            parent_pid: PackageId,
            is_public: bool,
            age: ContextAge,
            parents: &Graph<PackageId, im_rc::HashSet<Dependency>>,
        ) {
            // one tricky part is that `candidate_pid` may already be active and
            // have public dependencies of its own. So we not only need to mark
            // `candidate_pid` as visible to its parents but also all of its existing
            // publicly exported dependencies.
            for c in self.publicly_exports(candidate_pid) {
                // for each (transitive) parent that can newly see `t`
                let mut stack = vec![(parent_pid, is_public)];
                while let Some((p, public)) = stack.pop() {
                    match self.inner.entry(p).or_default().entry(c.name()) {
                        im_rc::hashmap::Entry::Occupied(mut o) => {
                            // the (transitive) parent can already see something by `c`s name, it had better be `c`.
                            assert_eq!(o.get().0, c);
                            if o.get().2.is_some() {
                                // The previous time the parent saw `c`, it was a public dependency.
                                // So all of its parents already know about `c`
                                // and we can save some time by stopping now.
                                continue;
                            }
                            if public {
                                // Mark that `c` has now bean seen publicly
                                let old_age = o.get().1;
                                o.insert((c, old_age, if public { Some(age) } else { None }));
                            }
                        }
                        im_rc::hashmap::Entry::Vacant(v) => {
                            // The (transitive) parent does not have anything by `c`s name,
                            // so we add `c`.
                            v.insert((c, age, if public { Some(age) } else { None }));
                        }
                    }
                    // if `candidate_pid` was a private dependency of `p` then `p` parents can't see `c` thru `p`
                    if public {
                        // if it was public, then we add all of `p`s parents to be checked
                        stack.extend(parents.parents_of(p));
                    }
                }
            }
        }
        pub fn can_add_edge(
            &self,
            b_id: PackageId,
            parent: PackageId,
            is_public: bool,
            parents: &Graph<PackageId, im_rc::HashSet<Dependency>>,
        ) -> Result<
            (),
            (
                ((PackageId, ConflictReason), (PackageId, ConflictReason)),
                Option<(PackageId, ConflictReason)>,
            ),
        > {
            // one tricky part is that `candidate_pid` may already be active and
            // have public dependencies of its own. So we not only need to check
            // `b_id` as visible to its parents but also all of its existing
            // publicly exported dependencies.
            for t in self.publicly_exports(b_id) {
                // for each (transitive) parent that can newly see `t`
                let mut stack = vec![(parent, is_public)];
                while let Some((p, public)) = stack.pop() {
                    // TODO: don't look at the same thing more than once
                    if let Some(o) = self.inner.get(&p).and_then(|x| x.get(&t.name())) {
                        if o.0 != t {
                            // the (transitive) parent can already see a different version by `t`s name.
                            // So, adding `b` will cause `p` to have a public dependency conflict on `t`.
                            return Err((
                                (o.0, ConflictReason::PublicDependency(p)), // p can see the other version and
                                (parent, ConflictReason::PublicDependency(p)), // p can see us
                            ))
                            .map_err(|e| {
                                if t == b_id {
                                    (e, None)
                                } else {
                                    (e, Some((t, ConflictReason::PubliclyExports(b_id))))
                                }
                            });
                        }
                        if o.2.is_some() {
                            // The previous time the parent saw `t`, it was a public dependency.
                            // So all of its parents already know about `t`
                            // and we can save some time by stopping now.
                            continue;
                        }
                    }
                    // if `b` was a private dependency of `p` then `p` parents can't see `t` thru `p`
                    if public {
                        // if it was public, then we add all of `p`s parents to be checked
                        stack.extend(parents.parents_of(p));
                    }
                }
            }
            Ok(())
        }
    }