/*
MIT License

Copyright (c) 2022 Philipp Schuster

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/
//! Module for [`GlobalChunkAllocator`].

use crate::{ChunkAllocator, DEFAULT_CHUNK_SIZE};
use core::alloc::{AllocError, Allocator, GlobalAlloc, Layout};
use core::ptr::NonNull;

/// The default number of chunks. If the default chunk size of [`DEFAULT_CHUNK_SIZE`] gets
/// used then this equals to 1MiB of memory.
pub const DEFAULT_CHUNK_AMOUNT: usize = 4096;

/// Synchronized high-level wrapper around [`ChunkAllocator`] that implements the Rust traits
/// [`GlobalAlloc`] which enables the usage as global allocator. The method
/// [`GlobalChunkAllocator::allocator_api_glue`] returns an object of type [`AllocatorApiGlue`]
/// which can be used with the `allocator_api` feature.
///
/// ```rust
/// #![feature(const_mut_refs)]
///
/// use simple_chunk_allocator::{heap, heap_bitmap, GlobalChunkAllocator, PageAligned};
///
/// // The macros help to get a correctly sized arrays types.
/// // I page-align them for better caching and to improve the availability of
/// // page-aligned addresses.
///
/// /// Backing storage for heap (1Mib). (read+write) static memory in final executable.
/// static mut HEAP: PageAligned<[u8; 1048576]> = heap!();
/// /// Backing storage for heap bookkeeping bitmap. (read+write) static memory in final executable.
/// static mut HEAP_BITMAP: PageAligned<[u8; 512]> = heap_bitmap!();
///
/// #[global_allocator]
/// static ALLOCATOR: GlobalChunkAllocator =
///     unsafe { GlobalChunkAllocator::new(HEAP.deref_mut_const(), HEAP_BITMAP.deref_mut_const()) };
/// ```
#[derive(Debug)]
pub struct GlobalChunkAllocator<'a, const CHUNK_SIZE: usize = DEFAULT_CHUNK_SIZE>(
    spin::Mutex<ChunkAllocator<'a, CHUNK_SIZE>>,
);

impl<'a, const CHUNK_SIZE: usize> GlobalChunkAllocator<'a, CHUNK_SIZE> {
    /// High-level constructor around [`ChunkAllocator::<CHUNK_SIZE>::new_const`].
    ///
    /// It is recommended that the heap and the bitmap both start at page-aligned addresses for
    /// better performance and to enable a faster search for correctly aligned addresses.
    #[inline]
    pub const fn new(heap: &'a mut [u8], bitmap: &'a mut [u8]) -> Self {
        let inner_alloc = ChunkAllocator::<CHUNK_SIZE>::new_const(heap, bitmap);
        let inner_alloc = spin::Mutex::new(inner_alloc);
        Self(inner_alloc)
    }

    /// Returns the usage of the allocator in percentage.
    #[inline]
    pub fn usage(&self) -> f32 {
        self.0.lock().usage()
    }

    /// Returns an instance of [`AllocatorApiGlue`].
    #[inline]
    pub const fn allocator_api_glue<'b>(&'b self) -> AllocatorApiGlue<'a, 'b, CHUNK_SIZE> {
        AllocatorApiGlue(self)
    }
}

unsafe impl<'a, const CHUNK_SIZE: usize> GlobalAlloc for GlobalChunkAllocator<'a, CHUNK_SIZE> {
    #[inline]
    #[must_use = "The pointer must be used and freed eventually to prevent memory leaks."]
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        self.0.lock().allocate(layout).unwrap().as_mut_ptr()
    }

    #[inline]
    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
        self.0.lock().deallocate(NonNull::new(ptr).unwrap(), layout)
    }
}

/// Helper struct generated by [`GlobalChunkAllocator`] that can be used in structs that accept
/// a custom instance of a specific allocator implementation.
///
/// This is mainly relevant for testing the allocator. In a real environment, an instance of
/// [`GlobalChunkAllocator`] is likely registered a global allocator for Rust. Thus, `Vec` and
/// others default to the `Global` allocator, which will use [`GlobalChunkAllocator`].
///
/// # Example
/// ```ignore
/// // ...
/// ALLOCATOR.init(HEAP_MEM.as_mut_slice(), BITMAP_MEM.as_mut_slice()).unwrap()
///
/// // Vector from the standard library will use my custom allocator instead.
/// let vec = Vec::<u8, _>::with_capacity_in(123, ALLOCATOR.allocator_api_glue());
/// ```
#[derive(Debug)]
pub struct AllocatorApiGlue<'a, 'b, const CHUNK_SIZE: usize>(
    &'a GlobalChunkAllocator<'b, CHUNK_SIZE>,
);

unsafe impl<'a, 'b, const CHUNK_SIZE: usize> Allocator for AllocatorApiGlue<'a, 'b, CHUNK_SIZE> {
    #[inline]
    #[must_use = "The pointer must be used and freed eventually to prevent memory leaks."]
    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
        self.0 .0.lock().allocate(layout)
    }

    #[inline]
    unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
        self.0 .0.lock().deallocate(ptr, layout)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::vec::Vec;

    /// Uses [`GlobalChunkAllocator`] against the Rust Allocator API to test
    /// the underlying [`ChunkAllocator`]. This is like an "integration" test
    /// whereas the other tests in the other module are unit tests.
    #[test]
    fn test_allocator_with_allocator_api() {
        const HEAP_SIZE: usize = DEFAULT_CHUNK_SIZE * 8;
        const CHUNK_COUNT: usize = HEAP_SIZE / DEFAULT_CHUNK_SIZE;
        const BITMAP_SIZE: usize = CHUNK_COUNT / 8;

        static mut HEAP_MEM: [u8; HEAP_SIZE] = [0; HEAP_SIZE];
        static mut BITMAP_MEM: [u8; BITMAP_SIZE] = [0; BITMAP_SIZE];
        static ALLOCATOR: GlobalChunkAllocator =
            GlobalChunkAllocator::new(unsafe { &mut HEAP_MEM }, unsafe { &mut BITMAP_MEM });

        assert_eq!(0.0, ALLOCATOR.usage());
        let vec1 =
            Vec::<u8, _>::with_capacity_in(DEFAULT_CHUNK_SIZE * 2, ALLOCATOR.allocator_api_glue());
        assert_eq!(25.0, ALLOCATOR.usage());
        let vec2 =
            Vec::<u8, _>::with_capacity_in(DEFAULT_CHUNK_SIZE * 6, ALLOCATOR.allocator_api_glue());
        assert_eq!(100.0, ALLOCATOR.usage());

        // I can't test it like this :( Because of the design of the types of the Rust standard library,
        // they fail if an allocation can't be satisfied. However, they do not throw a normal kind
        // of panic but trigger the "rust alloc error" hook, which terminates the program in a
        // different manner.
        //let alloc_res = std::panic::catch_unwind(|| {
        //    let _vec = Vec::<u8, _>::with_capacity_in(1, ALLOCATOR.allocator_api_glue());
        //});
        //assert!(panic_oom.is_err(), "allocator is out of memory");

        drop(vec1);
        assert_eq!(75.0, ALLOCATOR.usage());
        let vec3 =
            Vec::<u8, _>::with_capacity_in(DEFAULT_CHUNK_SIZE * 1, ALLOCATOR.allocator_api_glue());
        assert_eq!(87.5, ALLOCATOR.usage());

        drop(vec2);
        drop(vec3);
        assert_eq!(0.0, ALLOCATOR.usage());
    }
}