use crate::alloc::{GlobalAlloc, Layout, System};
use crate::ptr;
use crate::sys_common::alloc::{realloc_fallback, MIN_ALIGN};

#[stable(feature = "alloc_system_type", since = "1.28.0")]
unsafe impl GlobalAlloc for System {
    #[inline]
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        // jemalloc provides alignment less than MIN_ALIGN for small allocations.
        // So only rely on MIN_ALIGN if size >= align.
        // Also see <https://github.com/rust-lang/rust/issues/45955> and
        // <https://github.com/rust-lang/rust/issues/62251#issuecomment-507580914>.
        if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
            libc::malloc(layout.size()) as *mut u8
        } else {
            #[cfg(target_os = "macos")]
            {
                if layout.align() > (1 << 31) {
                    return ptr::null_mut();
                }
            }
            aligned_malloc(&layout)
        }
    }

    #[inline]
    unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
        // See the comment above in `alloc` for why this check looks the way it does.
        if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
            libc::calloc(layout.size(), 1) as *mut u8
        } else {
            let ptr = self.alloc(layout);
            if !ptr.is_null() {
                ptr::write_bytes(ptr, 0, layout.size());
            }
            ptr
        }
    }

    #[inline]
    unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
        libc::free(ptr as *mut libc::c_void)
    }

    #[inline]
    unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
        if layout.align() <= MIN_ALIGN && layout.align() <= new_size {
            libc::realloc(ptr as *mut libc::c_void, new_size) as *mut u8
        } else {
            realloc_fallback(self, ptr, layout, new_size)
        }
    }
}

cfg_if::cfg_if! {
    if #[cfg(any(
        target_os = "android",
        target_os = "illumos",
        target_os = "redox",
        target_os = "solaris"
    ))] {
        #[inline]
        unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
            // On android we currently target API level 9 which unfortunately
            // doesn't have the `posix_memalign` API used below. Instead we use
            // `memalign`, but this unfortunately has the property on some systems
            // where the memory returned cannot be deallocated by `free`!
            //
            // Upon closer inspection, however, this appears to work just fine with
            // Android, so for this platform we should be fine to call `memalign`
            // (which is present in API level 9). Some helpful references could
            // possibly be chromium using memalign [1], attempts at documenting that
            // memalign + free is ok [2] [3], or the current source of chromium
            // which still uses memalign on android [4].
            //
            // [1]: https://codereview.chromium.org/10796020/
            // [2]: https://code.google.com/p/android/issues/detail?id=35391
            // [3]: https://bugs.chromium.org/p/chromium/issues/detail?id=138579
            // [4]: https://chromium.googlesource.com/chromium/src/base/+/master/
            //                                       /memory/aligned_memory.cc
            libc::memalign(layout.align(), layout.size()) as *mut u8
        }
    } else if #[cfg(target_os = "wasi")] {
        #[inline]
        unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
            libc::aligned_alloc(layout.align(), layout.size()) as *mut u8
        }
    } else {
        #[inline]
        unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
            let mut out = ptr::null_mut();
            // posix_memalign requires that the alignment be a multiple of `sizeof(void*)`.
            // Since these are all powers of 2, we can just use max.
            let align = layout.align().max(crate::mem::size_of::<usize>());
            let ret = libc::posix_memalign(&mut out, align, layout.size());
            if ret != 0 { ptr::null_mut() } else { out as *mut u8 }
        }
    }
}