//! Id handling for rustdoc-json.
//!
//! Manages the creation of [`rustdoc_json_types::Id`] and the
//! fact that these don't correspond exactly to [`DefId`], because
//! [`rustdoc_json_types::Item`] doesn't correspond exactly to what
//! other phases think of as an "item".

use rustc_data_structures::fx::FxHashMap;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::DefId;
use rustc_span::{Symbol, sym};
use rustdoc_json_types as types;

use super::JsonRenderer;
use crate::clean;

pub(super) type IdInterner = FxHashMap<FullItemId, types::Id>;

#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
/// An uninterned id.
///
/// Each one corresponds to exactly one of both:
/// 1. [`rustdoc_json_types::Item`].
/// 2. [`rustdoc_json_types::Id`] transitively (as each `Item` has an `Id`).
///
/// It's *broadly* equivalent to a [`DefId`], but needs slightly more information
/// to fully disambiguate items, because sometimes we choose to split a single HIR
/// item into multiple JSON items, or have items with no corresponding HIR item.
pub(super) struct FullItemId {
    /// The "main" id of the item.
    ///
    /// In most cases this uniquely identifies the item, the other fields are just
    /// used for edge-cases.
    def_id: DefId,

    /// An extra [`DefId`], which we need for:
    ///
    /// 1. Auto-trait impls synthesized by rustdoc.
    /// 2. Blanket impls synthesized by rustdoc.
    /// 3. Splitting of reexports of multiple items.
    ///
    ///    E.g:
    ///
    ///    ```rust
    ///    mod module {
    ///        pub struct Foo {} // Exists in type namespace
    ///        pub fn Foo(){} // Exists in value namespace
    ///    }
    ///
    ///    pub use module::Foo; // Imports both items
    ///    ```
    ///
    ///    In HIR, the `pub use` is just 1 item, but in rustdoc-json it's 2, so
    ///    we need to disambiguate.
    extra_id: Option<DefId>,

    /// Needed for `#[rustc_doc_primitive]` modules.
    ///
    /// For these, 1 [`DefId`] is used for both the primitive and the fake-module
    /// that holds its docs.
    ///
    /// N.B. This only matters when documenting the standard library with
    /// `--document-private-items`. Maybe we should delete that module, and
    /// remove this.
    name: Option<Symbol>,
}

impl JsonRenderer<'_> {
    pub(crate) fn id_from_item_default(&self, item_id: clean::ItemId) -> types::Id {
        self.id_from_item_inner(item_id, None, None)
    }

    fn id_from_item_inner(
        &self,
        item_id: clean::ItemId,
        name: Option<Symbol>,
        imported_id: Option<DefId>,
    ) -> types::Id {
        let (def_id, extra_id) = match item_id {
            clean::ItemId::DefId(did) => (did, imported_id),
            clean::ItemId::Blanket { for_, impl_id } => (for_, Some(impl_id)),
            clean::ItemId::Auto { for_, trait_ } => (for_, Some(trait_)),
        };

        let name = match name {
            Some(name) => Some(name),
            None => {
                // We need this workaround because primitive types' DefId actually refers to
                // their parent module, which isn't present in the output JSON items. So
                // instead, we directly get the primitive symbol
                if matches!(self.tcx.def_kind(def_id), DefKind::Mod)
                    && let Some(prim) = self
                        .tcx
                        .get_attrs(def_id, sym::rustc_doc_primitive)
                        .find_map(|attr| attr.value_str())
                {
                    Some(prim)
                } else {
                    self.tcx.opt_item_name(def_id)
                }
            }
        };

        let key = FullItemId { def_id, extra_id, name };

        let mut interner = self.id_interner.borrow_mut();
        let len = interner.len();
        *interner
            .entry(key)
            .or_insert_with(|| types::Id(len.try_into().expect("too many items in a crate")))
    }

    pub(crate) fn id_from_item(&self, item: &clean::Item) -> types::Id {
        match item.kind {
            clean::ItemKind::ImportItem(ref import) => {
                let imported_id = import.source.did;
                self.id_from_item_inner(item.item_id, item.name, imported_id)
            }
            _ => self.id_from_item_inner(item.item_id, item.name, None),
        }
    }
}