#![allow(dead_code)] // not used on all platforms

use crate::collections::BTreeMap;
use crate::ptr;
use crate::sync::atomic::{AtomicUsize, Ordering};
use crate::sys_common::mutex::Mutex;

pub type Key = usize;

type Dtor = unsafe extern "C" fn(*mut u8);

static NEXT_KEY: AtomicUsize = AtomicUsize::new(0);

static mut KEYS: *mut BTreeMap<Key, Option<Dtor>> = ptr::null_mut();
static KEYS_LOCK: Mutex = Mutex::new();

#[thread_local]
static mut LOCALS: *mut BTreeMap<Key, *mut u8> = ptr::null_mut();

unsafe fn keys() -> &'static mut BTreeMap<Key, Option<Dtor>> {
    if KEYS == ptr::null_mut() {
        KEYS = Box::into_raw(Box::new(BTreeMap::new()));
    }
    &mut *KEYS
}

unsafe fn locals() -> &'static mut BTreeMap<Key, *mut u8> {
    if LOCALS == ptr::null_mut() {
        LOCALS = Box::into_raw(Box::new(BTreeMap::new()));
    }
    &mut *LOCALS
}

#[inline]
pub unsafe fn create(dtor: Option<Dtor>) -> Key {
    let key = NEXT_KEY.fetch_add(1, Ordering::SeqCst);
    let _guard = KEYS_LOCK.lock();
    keys().insert(key, dtor);
    key
}

#[inline]
pub unsafe fn get(key: Key) -> *mut u8 {
    if let Some(&entry) = locals().get(&key) { entry } else { ptr::null_mut() }
}

#[inline]
pub unsafe fn set(key: Key, value: *mut u8) {
    locals().insert(key, value);
}

#[inline]
pub unsafe fn destroy(key: Key) {
    keys().remove(&key);
}

#[inline]
pub fn requires_synchronized_create() -> bool {
    false
}