use super::{MIN_ALIGN, realloc_fallback};
use crate::alloc::Layout;
use crate::ptr;

// Used by rustc for checking the definitions of other function with the same symbol names
//
// See the `invalid_runtime_symbols_definitions` lint.
#[cfg(not(test))]
mod runtime_symbols {
    use core::ffi::{c_size_t, c_void};

    unsafe extern "C" {
        #[rustc_canonical_symbol]
        fn malloc(size: c_size_t) -> *mut c_void;

        #[rustc_canonical_symbol]
        fn realloc(ptr: *mut c_void, size: c_size_t) -> *mut c_void;

        #[rustc_canonical_symbol]
        fn free(ptr: *mut c_void);
    }
}

#[inline]
pub unsafe fn alloc(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() {
        unsafe { libc::malloc(layout.size()) as *mut u8 }
    } else {
        // `posix_memalign` returns a non-aligned value if supplied a very
        // large alignment on older versions of Apple's platforms (unknown
        // exactly which version range, but the issue is definitely
        // present in macOS 10.14 and iOS 13.3).
        //
        // <https://github.com/rust-lang/rust/issues/30170>
        #[cfg(target_vendor = "apple")]
        {
            if layout.align() > (1 << 31) {
                return ptr::null_mut();
            }
        }
        unsafe { aligned_malloc(&layout) }
    }
}

#[inline]
pub unsafe fn alloc_zeroed(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() {
        unsafe { libc::calloc(layout.size(), 1) as *mut u8 }
    } else {
        let ptr = unsafe { alloc(layout) };
        if !ptr.is_null() {
            unsafe { ptr::write_bytes(ptr, 0, layout.size()) };
        }
        ptr
    }
}

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

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

cfg_select! {
    // We use posix_memalign wherever possible, but some targets have very incomplete POSIX coverage
    // so we need a fallback for those.
    any(target_os = "horizon", target_os = "vita") => {
        #[inline]
        unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
            unsafe { libc::memalign(layout.align(), layout.size()) as *mut u8 }
        }
    }
    _ => {
        #[inline]
        #[cfg_attr(target_os = "vxworks", allow(unused_unsafe))]
        unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
            let mut out = ptr::null_mut();
            // We prefer posix_memalign over aligned_alloc since it is more widely available, and
            // since with aligned_alloc, implementations are making almost arbitrary choices for
            // which alignments are "supported", making it hard to use. For instance, some
            // implementations require the size to be a multiple of the alignment (wasi emmalloc),
            // while others require the alignment to be at least the pointer size (Illumos, macOS).
            // posix_memalign only has one, clear requirement: 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(size_of::<usize>());
            let ret = unsafe { libc::posix_memalign(&mut out, align, layout.size()) };
            if ret != 0 { ptr::null_mut() } else { out as *mut u8 }
        }
    }
}