//! Name resolution algorithm. The end result of the algorithm is an `ItemMap`:
//! a map which maps each module to its scope: the set of items visible in the
//! module. That is, we only resolve imports here, name resolution of item
//! bodies will be done in a separate step.
//!
//! Like Rustc, we use an interactive per-crate algorithm: we start with scopes
//! containing only directly defined items, and then iteratively resolve
//! imports.
//!
//! To make this work nicely in the IDE scenario, we place `InputModuleItems`
//! in between raw syntax and name resolution. `InputModuleItems` are computed
//! using only the module's syntax, and it is all directly defined items plus
//! imports. The plan is to make `InputModuleItems` independent of local
//! modifications (that is, typing inside a function should not change IMIs),
//! so that the results of name resolution can be preserved unless the module
//! structure itself is modified.
pub(crate) mod lower;

use std::sync::Arc;

use ra_db::CrateId;
use test_utils::tested_by;
use rustc_hash::{FxHashMap, FxHashSet};

use crate::{
    Module, ModuleDef,
    Path, PathKind,
    HirDatabase, Crate,
    Name,
    module_tree::{ModuleId, ModuleTree},
//FIXME: deglobify
    nameres::lower::*,
};

/// `ItemMap` is the result of name resolution. It contains, for each
/// module, the set of visible items.
// FIXME: currenty we compute item map per source-root. We should do it per crate instead.
#[derive(Default, Debug, PartialEq, Eq)]
pub struct ItemMap {
    pub per_module: FxHashMap<ModuleId, ModuleScope>,
}

#[derive(Debug, Default, PartialEq, Eq, Clone)]
pub struct ModuleScope {
    items: FxHashMap<Name, Resolution>,
}

impl ModuleScope {
    pub fn entries<'a>(&'a self) -> impl Iterator<Item = (&'a Name, &'a Resolution)> + 'a {
        self.items.iter()
    }
    pub fn get(&self, name: &Name) -> Option<&Resolution> {
        self.items.get(name)
    }
}

/// `Resolution` is basically `DefId` atm, but it should account for stuff like
/// multiple namespaces, ambiguity and errors.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Resolution {
    /// None for unresolved
    pub def_id: PerNs<ModuleDef>,
    /// ident by which this is imported into local scope.
    pub import: Option<ImportId>,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum Namespace {
    Types,
    Values,
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub struct PerNs<T> {
    pub types: Option<T>,
    pub values: Option<T>,
}

impl<T> PerNs<T> {
    pub fn none() -> PerNs<T> {
        PerNs {
            types: None,
            values: None,
        }
    }

    pub fn values(t: T) -> PerNs<T> {
        PerNs {
            types: None,
            values: Some(t),
        }
    }

    pub fn types(t: T) -> PerNs<T> {
        PerNs {
            types: Some(t),
            values: None,
        }
    }

    pub fn both(types: T, values: T) -> PerNs<T> {
        PerNs {
            types: Some(types),
            values: Some(values),
        }
    }

    pub fn is_none(&self) -> bool {
        self.types.is_none() && self.values.is_none()
    }

    pub fn take(self, namespace: Namespace) -> Option<T> {
        match namespace {
            Namespace::Types => self.types,
            Namespace::Values => self.values,
        }
    }

    pub fn take_types(self) -> Option<T> {
        self.take(Namespace::Types)
    }

    pub fn take_values(self) -> Option<T> {
        self.take(Namespace::Values)
    }

    pub fn get(&self, namespace: Namespace) -> Option<&T> {
        self.as_ref().take(namespace)
    }

    pub fn as_ref(&self) -> PerNs<&T> {
        PerNs {
            types: self.types.as_ref(),
            values: self.values.as_ref(),
        }
    }

    pub fn and_then<U>(self, f: impl Fn(T) -> Option<U>) -> PerNs<U> {
        PerNs {
            types: self.types.and_then(&f),
            values: self.values.and_then(&f),
        }
    }

    pub fn map<U>(self, f: impl Fn(T) -> U) -> PerNs<U> {
        PerNs {
            types: self.types.map(&f),
            values: self.values.map(&f),
        }
    }
}

pub(crate) struct Resolver<'a, DB> {
    db: &'a DB,
    input: &'a FxHashMap<ModuleId, Arc<LoweredModule>>,
    krate: CrateId,
    module_tree: Arc<ModuleTree>,
    processed_imports: FxHashSet<(ModuleId, ImportId)>,
    result: ItemMap,
}

impl<'a, DB> Resolver<'a, DB>
where
    DB: HirDatabase,
{
    pub(crate) fn new(
        db: &'a DB,
        input: &'a FxHashMap<ModuleId, Arc<LoweredModule>>,
        krate: CrateId,
    ) -> Resolver<'a, DB> {
        let module_tree = db.module_tree(krate);
        Resolver {
            db,
            input,
            krate,
            module_tree,
            processed_imports: FxHashSet::default(),
            result: ItemMap::default(),
        }
    }

    pub(crate) fn resolve(mut self) -> ItemMap {
        for (&module_id, items) in self.input.iter() {
            self.populate_module(module_id, Arc::clone(items));
        }

        loop {
            let processed_imports_count = self.processed_imports.len();
            for &module_id in self.input.keys() {
                self.db.check_canceled();
                self.resolve_imports(module_id);
            }
            if processed_imports_count == self.processed_imports.len() {
                // no new imports resolved
                break;
            }
        }
        self.result
    }

    fn populate_module(&mut self, module_id: ModuleId, input: Arc<LoweredModule>) {
        let mut module_items = ModuleScope::default();

        // Populate extern crates prelude
        {
            let root_id = module_id.crate_root(&self.module_tree);
            let file_id = root_id.source(&self.module_tree).file_id;
            let crate_graph = self.db.crate_graph();
            if let Some(crate_id) = crate_graph.crate_id_for_crate_root(file_id.as_original_file())
            {
                let krate = Crate::new(crate_id);
                for dep in krate.dependencies(self.db) {
                    if let Some(module) = dep.krate.root_module(self.db) {
                        let def_id = module.into();
                        self.add_module_item(
                            &mut module_items,
                            dep.name.clone(),
                            PerNs::types(def_id),
                        );
                    }
                }
            };
        }
        for (import_id, import_data) in input.imports.iter() {
            if let Some(segment) = import_data.path.segments.iter().last() {
                if !import_data.is_glob {
                    module_items.items.insert(
                        segment.name.clone(),
                        Resolution {
                            def_id: PerNs::none(),
                            import: Some(import_id),
                        },
                    );
                }
            }
        }
        // Populate explicitly declared items, except modules
        for (name, &def_id) in input.declarations.iter() {
            let resolution = Resolution {
                def_id,
                import: None,
            };
            module_items.items.insert(name.clone(), resolution);
        }

        // Populate modules
        for (name, module_id) in module_id.children(&self.module_tree) {
            let module = Module {
                module_id,
                krate: self.krate,
            };
            self.add_module_item(&mut module_items, name, PerNs::types(module.into()));
        }

        self.result.per_module.insert(module_id, module_items);
    }

    fn add_module_item(
        &self,
        module_items: &mut ModuleScope,
        name: Name,
        def_id: PerNs<ModuleDef>,
    ) {
        let resolution = Resolution {
            def_id,
            import: None,
        };
        module_items.items.insert(name, resolution);
    }

    fn resolve_imports(&mut self, module_id: ModuleId) {
        for (import_id, import_data) in self.input[&module_id].imports.iter() {
            if self.processed_imports.contains(&(module_id, import_id)) {
                // already done
                continue;
            }
            if self.resolve_import(module_id, import_id, import_data) == ReachedFixedPoint::Yes {
                log::debug!("import {:?} resolved (or definite error)", import_id);
                self.processed_imports.insert((module_id, import_id));
            }
        }
    }

    fn resolve_import(
        &mut self,
        module_id: ModuleId,
        import_id: ImportId,
        import: &ImportData,
    ) -> ReachedFixedPoint {
        log::debug!("resolving import: {:?}", import);
        if import.is_glob {
            return ReachedFixedPoint::Yes;
        };
        let original_module = Module {
            krate: self.krate,
            module_id,
        };
        let (def_id, reached_fixedpoint) =
            self.result
                .resolve_path_fp(self.db, original_module, &import.path);

        if reached_fixedpoint == ReachedFixedPoint::Yes {
            let last_segment = import.path.segments.last().unwrap();
            self.update(module_id, |items| {
                let res = Resolution {
                    def_id,
                    import: Some(import_id),
                };
                items.items.insert(last_segment.name.clone(), res);
            });
            log::debug!(
                "resolved import {:?} ({:?}) cross-source root to {:?}",
                last_segment.name,
                import,
                def_id,
            );
        }
        reached_fixedpoint
    }

    fn update(&mut self, module_id: ModuleId, f: impl FnOnce(&mut ModuleScope)) {
        let module_items = self.result.per_module.get_mut(&module_id).unwrap();
        f(module_items)
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum ReachedFixedPoint {
    Yes,
    No,
}

impl ItemMap {
    pub(crate) fn resolve_path(
        &self,
        db: &impl HirDatabase,
        original_module: Module,
        path: &Path,
    ) -> PerNs<ModuleDef> {
        self.resolve_path_fp(db, original_module, path).0
    }

    // returns true if we are sure that additions to `ItemMap` wouldn't change
    // the result. That is, if we've reached fixed point at this particular
    // import.
    fn resolve_path_fp(
        &self,
        db: &impl HirDatabase,
        original_module: Module,
        path: &Path,
    ) -> (PerNs<ModuleDef>, ReachedFixedPoint) {
        let mut curr_per_ns: PerNs<ModuleDef> = PerNs::types(match path.kind {
            PathKind::Crate => original_module.crate_root(db).into(),
            PathKind::Self_ | PathKind::Plain => original_module.into(),
            PathKind::Super => {
                if let Some(p) = original_module.parent(db) {
                    p.into()
                } else {
                    log::debug!("super path in root module");
                    return (PerNs::none(), ReachedFixedPoint::Yes);
                }
            }
            PathKind::Abs => {
                // TODO: absolute use is not supported
                return (PerNs::none(), ReachedFixedPoint::Yes);
            }
        });

        for (i, segment) in path.segments.iter().enumerate() {
            let curr = match curr_per_ns.as_ref().take_types() {
                Some(r) => r,
                None => {
                    // we still have path segments left, but the path so far
                    // didn't resolve in the types namespace => no resolution
                    // (don't break here because curr_per_ns might contain
                    // something in the value namespace, and it would be wrong
                    // to return that)
                    return (PerNs::none(), ReachedFixedPoint::No);
                }
            };
            // resolve segment in curr

            curr_per_ns = match curr {
                ModuleDef::Module(module) => {
                    if module.krate != original_module.krate {
                        let path = Path {
                            segments: path.segments[i..].iter().cloned().collect(),
                            kind: PathKind::Crate,
                        };
                        log::debug!("resolving {:?} in other crate", path);
                        let def_id = module.resolve_path(db, &path);
                        return (def_id, ReachedFixedPoint::Yes);
                    }

                    match self.per_module[&module.module_id].items.get(&segment.name) {
                        Some(res) if !res.def_id.is_none() => res.def_id,
                        _ => {
                            log::debug!("path segment {:?} not found", segment.name);
                            return (PerNs::none(), ReachedFixedPoint::No);
                        }
                    }
                }
                ModuleDef::Enum(e) => {
                    // enum variant
                    tested_by!(item_map_enum_importing);
                    let matching_variant = e
                        .variants(db)
                        .into_iter()
                        .find(|(n, _variant)| n == &segment.name);

                    match matching_variant {
                        Some((_n, variant)) => PerNs::both(variant.into(), (*e).into()),
                        None => PerNs::none(),
                    }
                }
                _ => {
                    // could be an inherent method call in UFCS form
                    // (`Struct::method`), or some other kind of associated
                    // item... Which we currently don't handle (TODO)
                    log::debug!(
                        "path segment {:?} resolved to non-module {:?}, but is not last",
                        segment.name,
                        curr,
                    );
                    return (PerNs::none(), ReachedFixedPoint::Yes);
                }
            };
        }
        (curr_per_ns, ReachedFixedPoint::Yes)
    }
}

#[cfg(test)]
mod tests;