//! `strings.h` implementation.
//!
//! See <https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/strings.h.html>.

// TODO: set this for entire crate when possible
#![deny(unsafe_op_in_unsafe_fn)]

use core::{
    arch,
    iter::{once, zip},
    ptr,
};

use crate::{
    header::{ctype, string},
    iter::NulTerminated,
    platform::types::*,
};

/// See <https://pubs.opengroup.org/onlinepubs/009695399/functions/bcmp.html>.
///
/// # Deprecation
/// The `bcmp()` function was marked legacy in the Open Group Base
/// Specifications Issue 6, and removed in Issue 7.
#[deprecated]
#[unsafe(no_mangle)]
pub unsafe extern "C" fn bcmp(first: *const c_void, second: *const c_void, n: size_t) -> c_int {
    unsafe { string::memcmp(first, second, n) }
}

/// See <https://pubs.opengroup.org/onlinepubs/009695399/functions/bcopy.html>.
///
/// # Deprecation
/// The `bcopy()` function was marked legacy in the Open Group Base
/// Specifications Issue 6, and removed in Issue 7.
#[deprecated]
#[unsafe(no_mangle)]
pub unsafe extern "C" fn bcopy(src: *const c_void, dst: *mut c_void, n: size_t) {
    unsafe {
        ptr::copy(src as *const u8, dst as *mut u8, n);
    }
}

/// See <https://pubs.opengroup.org/onlinepubs/009695399/functions/bzero.html>.
///
/// # Deprecation
/// The `bzero()` function was marked legacy in the Open Group Base
/// Specifications Issue 6, and removed in Issue 7.
#[deprecated]
#[unsafe(no_mangle)]
pub unsafe extern "C" fn bzero(dst: *mut c_void, n: size_t) {
    unsafe {
        ptr::write_bytes(dst as *mut u8, 0, n);
    }
}

/// Non-POSIX, see <https://man7.org/linux/man-pages/man3/bzero.3.html>.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn explicit_bzero(s: *mut c_void, n: size_t) {
    for i in 0..n {
        unsafe {
            *(s as *mut u8).add(i) = 0 as u8;
        }
    }
    unsafe {
        arch::asm!("");
    }
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/ffs.html>.
#[unsafe(no_mangle)]
pub extern "C" fn ffs(i: c_int) -> c_int {
    if i == 0 {
        return 0;
    }
    1 + i.trailing_zeros() as c_int
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/ffs.html>.
#[unsafe(no_mangle)]
pub extern "C" fn ffsl(i: c_long) -> c_int {
    if i == 0 {
        return 0;
    }
    1 + i.trailing_zeros() as c_int
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/ffs.html>.
#[unsafe(no_mangle)]
pub extern "C" fn ffsll(i: c_longlong) -> c_int {
    if i == 0 {
        return 0;
    }
    1 + i.trailing_zeros() as c_int
}

/// See <https://pubs.opengroup.org/onlinepubs/009695399/functions/index.html>.
///
/// # Deprecation
/// The `index()` function was marked legacy in the Open Group Base
/// Specifications Issue 6, and removed in Issue 7.
#[deprecated]
#[unsafe(no_mangle)]
pub unsafe extern "C" fn index(s: *const c_char, c: c_int) -> *mut c_char {
    unsafe { string::strchr(s, c) }
}

/// See <https://pubs.opengroup.org/onlinepubs/009695399/functions/rindex.html>.
///
/// # Deprecation
/// The `rindex()` function was marked legacy in the Open Group Base
/// Specifications Issue 6, and removed in Issue 7.
#[deprecated]
#[unsafe(no_mangle)]
pub unsafe extern "C" fn rindex(s: *const c_char, c: c_int) -> *mut c_char {
    unsafe { string::strrchr(s, c) }
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strcasecmp.html>.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn strcasecmp(s1: *const c_char, s2: *const c_char) -> c_int {
    // SAFETY: the caller must ensure that s1 and s2 point to nul-terminated buffers.
    let s1_iter = unsafe { NulTerminated::new(s1).unwrap() }.chain(once(&0));
    let s2_iter = unsafe { NulTerminated::new(s2).unwrap() }.chain(once(&0));

    let zipped = zip(s1_iter, s2_iter);
    inner_casecmp(zipped)
}

// TODO: needs locale_t
// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strcasecmp.html>.
// #[unsafe(no_mangle)]
/*pub extern "C" fn strcasecmp_l(s1: *const c_char, s2: *const c_char, locale: locale_t) -> c_int {
    unimplemented!();
}*/

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strcasecmp.html>.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn strncasecmp(s1: *const c_char, s2: *const c_char, n: size_t) -> c_int {
    // SAFETY: the caller must ensure that s1 and s2 point to nul-terminated buffers.
    let s1_iter = unsafe { NulTerminated::new(s1).unwrap() }.chain(once(&0));
    let s2_iter = unsafe { NulTerminated::new(s2).unwrap() }.chain(once(&0));

    let zipped = zip(s1_iter, s2_iter).take(n);
    inner_casecmp(zipped)
}

// TODO: needs locale_t
// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strcasecmp.html>.
// #[unsafe(no_mangle)]
/*pub extern "C" fn strncasecmp_l(s1: *const c_char, s2: *const c_char, n: size_t, locale: locale_t) -> c_int {
    unimplemented!();
}*/

/// Given two zipped `&c_char` iterators, either find the first comparison != 0, or return 0.
fn inner_casecmp<'a>(iterator: impl Iterator<Item = (&'a c_char, &'a c_char)>) -> c_int {
    let mut cmp_iter =
        iterator.map(|(&c1, &c2)| ctype::tolower(c1.into()) - ctype::tolower(c2.into()));
    let mut skip_iter = cmp_iter.skip_while(|&cmp| cmp == 0);
    skip_iter.next().or(Some(0)).unwrap()
}