// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Server-side handles and storage for per-handle data.

use std::collections::{BTreeMap, HashMap};
use std::hash::Hash;
use std::num::NonZeroU32;
use std::ops::{Index, IndexMut};
use std::sync::atomic::{AtomicUsize, Ordering};

pub(super) type Handle = NonZeroU32;

pub(super) struct OwnedStore<T: 'static> {
    counter: &'static AtomicUsize,
    data: BTreeMap<Handle, T>,
}

impl<T> OwnedStore<T> {
    pub(super) fn new(counter: &'static AtomicUsize) -> Self {
        // Ensure the handle counter isn't 0, which would panic later,
        // when `NonZeroU32::new` (aka `Handle::new`) is called in `alloc`.
        assert_ne!(counter.load(Ordering::SeqCst), 0);

        OwnedStore {
            counter,
            data: BTreeMap::new(),
        }
    }
}

impl<T> OwnedStore<T> {
    pub(super) fn alloc(&mut self, x: T) -> Handle {
        let counter = self.counter.fetch_add(1, Ordering::SeqCst);
        let handle = Handle::new(counter as u32).expect("`proc_macro` handle counter overflowed");
        assert!(self.data.insert(handle, x).is_none());
        handle
    }

    pub(super) fn take(&mut self, h: Handle) -> T {
        self.data
            .remove(&h)
            .expect("use-after-free in `proc_macro` handle")
    }
}

impl<T> Index<Handle> for OwnedStore<T> {
    type Output = T;
    fn index(&self, h: Handle) -> &T {
        self.data
            .get(&h)
            .expect("use-after-free in `proc_macro` handle")
    }
}

impl<T> IndexMut<Handle> for OwnedStore<T> {
    fn index_mut(&mut self, h: Handle) -> &mut T {
        self.data
            .get_mut(&h)
            .expect("use-after-free in `proc_macro` handle")
    }
}

pub(super) struct InternedStore<T: 'static> {
    owned: OwnedStore<T>,
    interner: HashMap<T, Handle>,
}

impl<T: Copy + Eq + Hash> InternedStore<T> {
    pub(super) fn new(counter: &'static AtomicUsize) -> Self {
        InternedStore {
            owned: OwnedStore::new(counter),
            interner: HashMap::new(),
        }
    }

    pub(super) fn alloc(&mut self, x: T) -> Handle {
        let owned = &mut self.owned;
        *self.interner.entry(x).or_insert_with(|| owned.alloc(x))
    }

    pub(super) fn copy(&mut self, h: Handle) -> T {
        self.owned[h]
    }
}
