//! Helper functions for working with def, which don't need to be a separate
//! query, but can't be computed directly from `*Data` (ie, which need a `db`).
use std::sync::Arc;

use hir_def::{
    adt::VariantData,
    db::DefDatabase,
    resolver::{HasResolver, TypeNs},
    type_ref::TypeRef,
    TraitId, TypeAliasId, VariantId,
};
use hir_expand::name::{self, Name};

// FIXME: this is wrong, b/c it can't express `trait T: PartialEq<()>`.
// We should return a `TraitREf` here.
fn direct_super_traits(db: &impl DefDatabase, trait_: TraitId) -> Vec<TraitId> {
    let resolver = trait_.resolver(db);
    // returning the iterator directly doesn't easily work because of
    // lifetime problems, but since there usually shouldn't be more than a
    // few direct traits this should be fine (we could even use some kind of
    // SmallVec if performance is a concern)
    db.generic_params(trait_.into())
        .where_predicates
        .iter()
        .filter_map(|pred| match &pred.type_ref {
            TypeRef::Path(p) if p.as_ident() == Some(&name::SELF_TYPE) => pred.bound.as_path(),
            _ => None,
        })
        .filter_map(|path| match resolver.resolve_path_in_type_ns_fully(db, path) {
            Some(TypeNs::TraitId(t)) => Some(t),
            _ => None,
        })
        .collect()
}

/// Returns an iterator over the whole super trait hierarchy (including the
/// trait itself).
pub(super) fn all_super_traits(db: &impl DefDatabase, trait_: TraitId) -> Vec<TraitId> {
    // we need to take care a bit here to avoid infinite loops in case of cycles
    // (i.e. if we have `trait A: B; trait B: A;`)
    let mut result = vec![trait_];
    let mut i = 0;
    while i < result.len() {
        let t = result[i];
        // yeah this is quadratic, but trait hierarchies should be flat
        // enough that this doesn't matter
        for tt in direct_super_traits(db, t) {
            if !result.contains(&tt) {
                result.push(tt);
            }
        }
        i += 1;
    }
    result
}

pub(super) fn associated_type_by_name_including_super_traits(
    db: &impl DefDatabase,
    trait_: TraitId,
    name: &Name,
) -> Option<TypeAliasId> {
    all_super_traits(db, trait_)
        .into_iter()
        .find_map(|t| db.trait_data(t).associated_type_by_name(name))
}

pub(super) fn variant_data(db: &impl DefDatabase, var: VariantId) -> Arc<VariantData> {
    match var {
        VariantId::StructId(it) => db.struct_data(it).variant_data.clone(),
        VariantId::UnionId(it) => db.union_data(it).variant_data.clone(),
        VariantId::EnumVariantId(it) => {
            db.enum_data(it.parent).variants[it.local_id].variant_data.clone()
        }
    }
}

/// Helper for mutating `Arc<[T]>` (i.e. `Arc::make_mut` for Arc slices).
/// The underlying values are cloned if there are other strong references.
pub(crate) fn make_mut_slice<T: Clone>(a: &mut Arc<[T]>) -> &mut [T] {
    if Arc::get_mut(a).is_none() {
        *a = a.iter().cloned().collect();
    }
    Arc::get_mut(a).unwrap()
}