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// Copyright 2020 Shin Yoshida
//
// "LGPL-3.0-or-later OR Apache-2.0"
//
// This is part of rust-bulk-allocator
//
//  rust-bulk-allocator is free software: you can redistribute it and/or modify
//  it under the terms of the GNU Lesser General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  rust-bulk-allocator is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU Lesser General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public License
//  along with rust-bulk-allocator.  If not, see <http://www.gnu.org/licenses/>.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use core::alloc::{AllocErr, AllocRef, Layout};
use core::ptr::NonNull;
use core::result::Result;

pub enum Backend<'a, B: AllocRef> {
    Borrowed(&'a mut B),
    Owned(B),
}

unsafe impl<B> AllocRef for Backend<'_, B>
where
    B: AllocRef,
{
    fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
        match self {
            Self::Borrowed(b) => b.alloc(layout),
            Self::Owned(b) => b.alloc(layout),
        }
    }

    unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
        match self {
            Self::Borrowed(b) => b.dealloc(ptr, layout),
            Self::Owned(b) => b.dealloc(ptr, layout),
        }
    }
}

impl<B> Default for Backend<'static, B>
where
    B: AllocRef + Default,
{
    fn default() -> Self {
        Self::Owned(Default::default())
    }
}

impl<B: AllocRef> From<B> for Backend<'static, B> {
    fn from(backend: B) -> Self {
        Self::Owned(backend)
    }
}

impl<'a, B: 'a + AllocRef> From<&'a mut B> for Backend<'a, B> {
    fn from(backend: &'a mut B) -> Self {
        Self::Borrowed(backend)
    }
}