// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you 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::ptr;

/// A safe interface to `memchr`.
///
/// Returns the index corresponding to the first occurrence of `needle` in
/// `haystack`, or `None` if one is not found.
///
// #[inline]
// pub fn memchr(needle: u8, haystack: &[u8]) -> Option<usize> {
//     ::sys::memchr::memchr(needle, haystack)
// }

/// A safe interface to `memrchr`.
///
/// Returns the index corresponding to the last occurrence of `needle` in
/// `haystack`, or `None` if one is not found.
///
// #[inline]
// pub fn memrchr(needle: u8, haystack: &[u8]) -> Option<usize> {
//     ::sys::memchr::memrchr(needle, haystack)
// }

pub fn memchr(needle: u8, haystack: &[u8]) -> Option<usize> {
    let p = unsafe {
        memchr_impl(
            haystack.as_ptr(),
            needle,
            haystack.len())
    };
    if p.is_null() {
        None
    } else {
        Some(p as usize - (haystack.as_ptr() as usize))
    }
}

unsafe fn memchr_impl(s: *const u8, c: u8, n: usize) -> *const u8 {
    let mut ret = ptr::null();
    let mut p = s;
    for _ in 0..n {
        if *p == c {
            ret = p;
            break;
        }
        p = p.offset(1);
    }
    ret
}

pub fn memrchr(needle: u8, haystack: &[u8]) -> Option<usize> {
    fn memrchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
        // GNU's memrchr() will - unlike memchr() - error if haystack is empty.
        if haystack.is_empty() {
            return None;
        }
        let p = unsafe {
            memrchr_impl(
                haystack.as_ptr(),
                needle,
                haystack.len(),
            )
        };
        if p.is_null() { None } else { Some(p as usize - (haystack.as_ptr() as usize)) }
    }

    memrchr_specific(needle, haystack)
}

unsafe fn memrchr_impl(s: *const u8, c: u8, n: usize) -> *const u8 {
    if n == 0 {
        return ptr::null();
    }
    let mut ret = ptr::null();
    let mut p: *const u8 = (s as usize + (n - 1)) as *const u8;
    for _ in 0..n {
        if *p == c {
            ret = p;
            break;
        }
        p = p.offset(-1);
    }
    ret
}