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use std::cell::RefCell;
use std::os::raw::{c_int, c_void};
use std::rc::Rc;
use std::{fmt, mem, ptr};

#[cfg(feature = "async")]
use futures_core::future::LocalBoxFuture;

use crate::error::Result;
use crate::ffi;
use crate::lua::Lua;
use crate::util::{assert_stack, StackGuard};
use crate::value::MultiValue;

/// Type of Lua integer numbers.
pub type Integer = ffi::lua_Integer;
/// Type of Lua floating point numbers.
pub type Number = ffi::lua_Number;

/// A "light" userdata value. Equivalent to an unmanaged raw pointer.
#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub struct LightUserData(pub *mut c_void);

pub(crate) type Callback<'lua, 'a> =
    Box<dyn Fn(&'lua Lua, MultiValue<'lua>) -> Result<MultiValue<'lua>> + 'a>;

#[cfg(feature = "async")]
pub(crate) type AsyncCallback<'lua, 'a> =
    Box<dyn Fn(&'lua Lua, MultiValue<'lua>) -> LocalBoxFuture<'lua, Result<MultiValue<'lua>>> + 'a>;

/// An auto generated key into the Lua registry.
///
/// This is a handle to a value stored inside the Lua registry.  It is not automatically
/// garbage collected on Drop, but it can be removed with [`Lua::remove_registry_value`],
/// and instances not manually removed can be garbage collected with [`Lua::expire_registry_values`].
///
/// Be warned, If you place this into Lua via a `UserData` type or a rust callback, it is *very
/// easy* to accidentally cause reference cycles that the Lua garbage collector cannot resolve.
/// Instead of placing a `RegistryKey` into a `UserData` type, prefer instead to use
/// [`UserData::set_user_value`] / [`UserData::get_user_value`].
///
/// [`Lua::remove_registry_value`]: struct.Lua.html#method.remove_registry_value
/// [`Lua::expire_registry_values`]: struct.Lua.html#method.expire_registry_values
/// [`UserData::set_user_value`]: struct.UserData.html#method.set_user_value
/// [`UserData::get_user_value`]: struct.UserData.html#method.get_user_value
pub struct RegistryKey {
    pub(crate) registry_id: c_int,
    pub(crate) unref_list: Rc<RefCell<Option<Vec<c_int>>>>,
}

impl fmt::Debug for RegistryKey {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "RegistryKey({})", self.registry_id)
    }
}

impl Drop for RegistryKey {
    fn drop(&mut self) {
        let mut unref_list = mlua_expect!(self.unref_list.try_borrow_mut(), "unref list borrowed");
        if let Some(list) = unref_list.as_mut() {
            list.push(self.registry_id);
        }
    }
}

impl RegistryKey {
    // Destroys the RegistryKey without adding to the drop list
    pub(crate) fn take(self) -> c_int {
        let registry_id = self.registry_id;
        unsafe {
            ptr::read(&self.unref_list);
            mem::forget(self);
        }
        registry_id
    }
}

pub(crate) struct LuaRef<'lua> {
    pub(crate) lua: &'lua Lua,
    pub(crate) index: c_int,
}

impl<'lua> fmt::Debug for LuaRef<'lua> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Ref({})", self.index)
    }
}

impl<'lua> Clone for LuaRef<'lua> {
    fn clone(&self) -> Self {
        self.lua.clone_ref(self)
    }
}

impl<'lua> Drop for LuaRef<'lua> {
    fn drop(&mut self) {
        self.lua.drop_ref(self)
    }
}

impl<'lua> PartialEq for LuaRef<'lua> {
    fn eq(&self, other: &Self) -> bool {
        let lua = self.lua;
        unsafe {
            let _sg = StackGuard::new(lua.state);
            assert_stack(lua.state, 2);
            lua.push_ref(&self);
            lua.push_ref(&other);
            ffi::lua_rawequal(lua.state, -1, -2) == 1
        }
    }
}