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

use core::{
    ptr, slice,
    str::{self, FromStr},
};

use crate::{
    c_str::CStr,
    header::{
        bits_arpainet::ntohl,
        errno::{EAFNOSUPPORT, ENOSPC},
        netinet_in::{INADDR_NONE, in_addr, in_addr_t, in6_addr},
        sys_socket::{
            constants::{AF_INET, AF_INET6},
            socklen_t,
        },
    },
    io::Write,
    platform::{
        self,
        types::{c_char, c_int, c_void},
    },
    raw_cell::RawCell,
};

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/inet_addr.html>.
///
/// Converts the string pointed to by `cp`, in the standard IPv4 dotted
/// decimal notation, to an integer value suitable for use as an Internet
/// address.
///
/// # Deprecated
/// The `inet_addr()` function was marked obsolescent in the Open Group Base
/// Specifications Issue 8.
///
/// Applications should prefer `inet_pton()` over `inet_addr()` for the
/// following reasons:
/// - The return value from `inet_addr()` when converting 255.255.255.255 is
///   indistinguishable from an error.
/// - The `inet_pton()` function supports multiple address families.
/// - The alternative textual representations supported by `inet_addr()` (but
///   not `inet_pton()`) are often used maliciously to confuse or mislead
///   users (e.g, for phishing).
#[deprecated]
#[unsafe(no_mangle)]
pub unsafe extern "C" fn inet_addr(cp: *const c_char) -> in_addr_t {
    let mut val: in_addr = in_addr { s_addr: 0 };

    if unsafe { inet_aton(cp, &raw mut val) } > 0 {
        val.s_addr
    } else {
        INADDR_NONE
    }
}

/// Non-POSIX, see <https://www.man7.org/linux/man-pages/man3/inet_aton.3.html>.
///
/// Converts the Internet host address `cp` from the IPv4 numbers-and-dots
/// notation into binary form (in network byte order) and stores it in the
/// structure that `inp` points to.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn inet_aton(cp: *const c_char, inp: *mut in_addr) -> c_int {
    let cp_cstr = unsafe { CStr::from_ptr(cp) };
    let parts = unsafe { str::from_utf8_unchecked(cp_cstr.to_bytes()).split('.') };
    let count = parts.clone().count();
    if count > 4 {
        return 0;
    }
    let mut result = 0;
    let mut parts_iter = parts.peekable();
    let mut index = 0u32;
    while index < 4
        && let Some(part) = parts_iter.next()
    {
        if let Ok(parsed_value) = {
            if let Some(hex_or_oct) = part.strip_prefix('0')
                && part.len() > 1
            {
                match hex_or_oct.bytes().next() {
                    Some(b'x' | b'X') => u32::from_str_radix(&hex_or_oct[1..], 16),
                    // While it is true that C2Y accepts 0o and 0O as octal prefixes, C17 doesn't
                    // The POSIX spec defers to C17
                    // see https://pubs.opengroup.org/onlinepubs/9799919799/functions/inet_addr.html
                    _ => u32::from_str_radix(hex_or_oct, 8),
                }
            } else {
                part.parse::<u32>()
            }
        } {
            if parts_iter.peek().is_some() {
                // this is not the last part
                if parsed_value > 0xff {
                    return 0;
                }
                result += parsed_value << (24 - index * 8);
            } else {
                // this is the last part
                if index > 0 && parsed_value >= 1 << (32 - index * 8) {
                    return 0;
                } else {
                    result += parsed_value;
                }
            }
        } else {
            return 0;
        }
        index += 1;
    }
    unsafe { (*inp.cast::<in_addr>()).s_addr = result.to_be() };
    1
}

/// See <https://pubs.opengroup.org/onlinepubs/7908799/xns/inet_lnaof.html>.
///
/// Takes an Internet host address specified by `in` and extracts the local
/// network address part, in host byte order.
///
/// # Deprecation
/// The `inet_lnaof()` function was specified in Networking Services Issue 5,
/// but not in the Open Group Base Specifications Issue 6 and later.
#[deprecated]
#[unsafe(no_mangle)]
pub extern "C" fn inet_lnaof(r#in: in_addr) -> in_addr_t {
    if r#in.s_addr >> 24 < 128 {
        r#in.s_addr & 0xff_ffff
    } else if r#in.s_addr >> 24 < 192 {
        r#in.s_addr & 0xffff
    } else {
        r#in.s_addr & 0xff
    }
}

/// See <https://pubs.opengroup.org/onlinepubs/7908799/xns/inet_makeaddr.html>.
///
/// Takes the Internet network number specified by `net` and the local network
/// address specified by `lna`, both in host byte order, and constructs an
/// Internet address from them.
///
/// # Deprecation
/// The `inet_makeaddr()` function was specified in Networking Services Issue
/// 5, but not in the Open Group Base Specifications Issue 6 and later.
#[deprecated]
#[unsafe(no_mangle)]
pub extern "C" fn inet_makeaddr(net: in_addr_t, lna: in_addr_t) -> in_addr {
    let mut output: in_addr = in_addr { s_addr: 0 };

    if net < 256 {
        output.s_addr = lna | net << 24;
    } else if net < 65536 {
        output.s_addr = lna | net << 16;
    } else {
        output.s_addr = lna | net << 8;
    }

    output
}

/// See <https://pubs.opengroup.org/onlinepubs/7908799/xns/inet_netof.html>.
///
/// Takes an Internet host address specified by `in` and extracts the network
/// number part, in host byte order.
///
/// # Deprecation
/// The `inet_netof()` function was specified in Networking Services Issue 5,
/// but not in the Open Group Base Specifications Issue 6 and later.
#[deprecated]
#[unsafe(no_mangle)]
pub extern "C" fn inet_netof(r#in: in_addr) -> in_addr_t {
    if r#in.s_addr >> 24 < 128 {
        r#in.s_addr & 0xff_ffff
    } else if r#in.s_addr >> 24 < 192 {
        r#in.s_addr & 0xffff
    } else {
        r#in.s_addr & 0xff
    }
}

/// See <https://pubs.opengroup.org/onlinepubs/7908799/xns/inet_network.html>.
///
/// Converts the string pointed to by `cp`, in the Internet standard dot
/// notation, to an integer value suitable for use as an Internet network
/// number.
///
/// # Deprecation
/// The `inet_network()` function was specified in Networking Services Issue 5,
/// but not in the Open Group Base Specifications Issue 6 and later.
#[deprecated]
#[unsafe(no_mangle)]
pub unsafe extern "C" fn inet_network(cp: *const c_char) -> in_addr_t {
    ntohl(unsafe {
        #[allow(deprecated)]
        inet_addr(cp)
    })
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/inet_addr.html>.
///
/// Converts the Internet host address specified by `in` to a string in the
/// Internet standard dot notation.
///
/// # Deprecation
/// The `inet_ntoa()` function was marked obsolescent in the Open Group Base
/// Specifications Issue 8.
///
/// Applications should prefer `inet_ntop()` over `inet_ntoa()` as it supports
/// multiple address families and is thread-safe.
#[deprecated]
#[unsafe(no_mangle)]
pub unsafe extern "C" fn inet_ntoa(r#in: in_addr) -> *mut c_char {
    static NTOA_ADDR: RawCell<[c_char; 16]> = RawCell::new([0; 16]);

    unsafe {
        let ptr = inet_ntop(
            AF_INET,
            ptr::from_ref::<in_addr>(&r#in).cast::<c_void>(),
            NTOA_ADDR.unsafe_mut().as_mut_ptr(),
            NTOA_ADDR.unsafe_ref().len() as socklen_t,
        );
        // Mutable pointer is required, inet_ntop returns destination as const pointer
        ptr.cast_mut()
    }
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/inet_ntop.html>.
///
/// Converts a numeric address into a text string suitable for presentation.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn inet_ntop(
    af: c_int,
    src: *const c_void,
    dst: *mut c_char,
    size: socklen_t,
) -> *const c_char {
    if af == AF_INET {
        if (size as usize) < 16 {
            platform::ERRNO.set(ENOSPC);
            return ptr::null();
        }
        let s_addr = unsafe {
            slice::from_raw_parts(
                ptr::from_ref(&(*(src.cast::<in_addr>())).s_addr).cast::<u8>(),
                4,
            )
        };
        let mut w = platform::StringWriter(dst, size as usize);
        let _ = write!(
            w,
            "{}.{}.{}.{}\0",
            s_addr[0], s_addr[1], s_addr[2], s_addr[3]
        );
        dst
    } else if af == AF_INET6 {
        // IPv6 textual representation per RFC 5952:
        //   - 8 groups of 4 lowercase hex digits separated by colons
        //   - Longest run of consecutive all-zero groups compressed to "::"
        //   - Ties broken by first occurrence
        //   - Single zero group is NOT compressed
        // INET6_ADDRSTRLEN == 46 (39 chars + trailing NUL + slack)
        if (size as usize) < crate::header::netinet_in::INET6_ADDRSTRLEN as usize {
            platform::ERRNO.set(ENOSPC);
            return ptr::null();
        }
        let bytes = unsafe {
            slice::from_raw_parts(
                ptr::from_ref(&(*(src.cast::<in6_addr>())).s6_addr).cast::<u8>(),
                16,
            )
        };
        let mut groups = [0u16; 8];
        for (i, g) in groups.iter_mut().enumerate() {
            *g = u16::from_be_bytes([bytes[i * 2], bytes[i * 2 + 1]]);
        }

        let mut best_start = usize::MAX;
        let mut best_len = 0usize;
        let mut cur_start = usize::MAX;
        let mut cur_len = 0usize;
        for i in 0..8 {
            if groups[i] == 0 {
                if cur_start == usize::MAX {
                    cur_start = i;
                    cur_len = 1;
                } else {
                    cur_len += 1;
                }
                if cur_len > best_len {
                    best_len = cur_len;
                    best_start = cur_start;
                }
            } else {
                cur_start = usize::MAX;
                cur_len = 0;
            }
        }
        if best_len < 2 {
            best_start = usize::MAX;
        }

        let mut w = platform::StringWriter(dst, size as usize);
        let mut i = 0usize;
        let mut after_ellipsis = false;
        while i < 8 {
            if i == best_start {
                let _ = write!(w, "::");
                after_ellipsis = true;
                i += best_len;
                continue;
            }
            if !after_ellipsis && i > 0 {
                let _ = write!(w, ":");
            }
            let _ = write!(w, "{:x}", groups[i]);
            after_ellipsis = false;
            i += 1;
        }
        let _ = write!(w, "\0");
        dst
    } else {
        platform::ERRNO.set(EAFNOSUPPORT);
        ptr::null()
    }
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/inet_ntop.html>.
///
/// Converts an address in its standard text presentation form into its
/// numeric binary form.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn inet_pton(af: c_int, src: *const c_char, dst: *mut c_void) -> c_int {
    if af == AF_INET {
        let s_addr = unsafe {
            slice::from_raw_parts_mut(
                ptr::from_mut(&mut (*dst.cast::<in_addr>()).s_addr).cast::<u8>(),
                4,
            )
        };
        let src_cstr = unsafe { CStr::from_ptr(src) };
        let mut octets = unsafe { str::from_utf8_unchecked(src_cstr.to_bytes()).split('.') };
        for part in s_addr.iter_mut().take(4) {
            if let Some(n) = octets
                .next()
                .filter(|x| x.len() <= 3)
                .and_then(|x| u8::from_str(x).ok())
            {
                *part = n;
            } else {
                return 0;
            }
        }
        if octets.next().is_none() {
            1 // Success
        } else {
            0
        }
    } else if af == AF_INET6 {
        let src_str = unsafe { str::from_utf8_unchecked(CStr::from_ptr(src).to_bytes()) };
        let mut chunks = vec![src_str];
        let colons = src_str.bytes().filter(|&c| c == b':').count();
        if !(2..=7).contains(&colons) {
            return 0;
        }
        let dots = src_str.bytes().filter(|&c| c == b'.').count();
        if dots != 0 && dots != 3 {
            return 0;
        }
        let double_colon = src_str.find("::");
        if colons < 2
            || double_colon.is_some() && ((dots == 0 && colons > 7) || (dots == 3 && colons > 6))
            || double_colon.is_none() && ((dots == 0 && colons != 7) || (dots == 3 && colons != 6))
        {
            return 0;
        }
        if dots == 3
            && let Some(first_dot) = src_str.find('.')
            && let Some(last_colon) = src_str.find(':')
            && last_colon > first_dot
        {
            return 0;
        }
        if let Some(first) = src_str.find("::")
            && let Some(last) = src_str.rfind("::")
        {
            // :: is allowed only once
            if first != last {
                return 0;
            }
            chunks = vec![&src_str[..first], &src_str[(first + 2)..]]
        }

        let s6_addr = unsafe {
            slice::from_raw_parts_mut(
                ptr::from_mut(&mut (*dst.cast::<in6_addr>()).s6_addr).cast::<u16>(),
                8,
            )
        };
        s6_addr.iter_mut().for_each(|w| *w = 0);

        for (count, &chunk) in chunks
            .iter()
            .enumerate()
            .filter(|&(_, &chunk)| !chunk.is_empty())
        {
            let mut parts = s6_addr
                .iter_mut()
                .skip(count * (8 - chunk.split(':').count() - dots / 3));
            let mut words = chunk.split(':');
            while let Some(word) = words.next()
                && let Some(part) = parts.next()
            {
                if word.is_empty() {
                    break;
                } else if word.len() <= 4
                    && let Some(n) = u16::from_str_radix(word, 16).ok()
                {
                    *part = n.to_be();
                } else if word.contains('.') {
                    let bytes =
                        unsafe { slice::from_raw_parts_mut(ptr::from_mut(part).cast::<u8>(), 4) };
                    let mut octets = word.split('.');
                    for byte in bytes {
                        if let Some(octet) = octets.next() {
                            if octet.len() > 1 && octet.starts_with('0') {
                                return 0;
                            }
                            if let Ok(value) = u8::from_str(octet) {
                                *byte = value
                            } else {
                                return 0;
                            }
                        }
                    }
                } else {
                    return 0;
                }
            }
        }
        1 // Success
    } else {
        platform::ERRNO.set(EAFNOSUPPORT);
        -1
    }
}

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

    fn format_v6(bytes: [u8; 16]) -> Option<alloc::string::String> {
        let addr = in6_addr { s6_addr: bytes };
        let mut buf = [0u8; 64];
        let ret = unsafe {
            inet_ntop(
                AF_INET6,
                ptr::from_ref(&addr).cast::<c_void>(),
                buf.as_mut_ptr().cast::<c_char>(),
                buf.len() as socklen_t,
            )
        };
        if ret.is_null() {
            None
        } else {
            let nul = buf.iter().position(|&b| b == 0).unwrap_or(buf.len());
            core::str::from_utf8(&buf[..nul])
                .ok()
                .map(|s| alloc::string::String::from(s))
        }
    }

    #[test]
    fn inet_ntop_v6_unspecified() {
        assert_eq!(format_v6([0u8; 16]).as_deref(), Some("::"));
    }

    #[test]
    fn inet_ntop_v6_loopback() {
        let mut bytes = [0u8; 16];
        bytes[15] = 1;
        assert_eq!(format_v6(bytes).as_deref(), Some("::1"));
    }

    #[test]
    fn inet_ntop_v6_routable() {
        let mut bytes = [0u8; 16];
        bytes[0] = 0x20;
        bytes[1] = 0x01;
        bytes[2] = 0x0d;
        bytes[3] = 0xb8;
        bytes[15] = 0x01;
        assert_eq!(format_v6(bytes).as_deref(), Some("2001:db8::1"));
    }

    #[test]
    fn inet_ntop_v6_link_local() {
        let mut bytes = [0u8; 16];
        bytes[0] = 0xfe;
        bytes[1] = 0x80;
        bytes[15] = 0x01;
        assert_eq!(format_v6(bytes).as_deref(), Some("fe80::1"));
    }

    #[test]
    fn inet_ntop_v6_no_compression_single_zero() {
        let bytes = [
            0x20, 0x01, 0x0d, 0xb8, 0x00, 0x00, 0x00, 0x01, 0x00, 0x02, 0x00, 0x03, 0x00, 0x04,
            0x00, 0x05,
        ];
        assert_eq!(format_v6(bytes).as_deref(), Some("2001:db8:0:1:2:3:4:5"));
    }

    #[test]
    fn inet_ntop_v6_tie_break_first_wins() {
        let bytes = [
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1,
        ];
        assert_eq!(format_v6(bytes).as_deref(), Some("::1:0:0:1"));
    }

    #[test]
    fn inet_ntop_v6_trailing_run() {
        let bytes = [
            0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
            0x00, 0x00,
        ];
        assert_eq!(format_v6(bytes).as_deref(), Some("1::"));
    }

    #[test]
    fn inet_ntop_v4_loopback() {
        let addr = in_addr {
            s_addr: 0x7f000001u32.to_be(),
        };
        let mut buf = [0u8; 32];
        let ret = unsafe {
            inet_ntop(
                AF_INET,
                ptr::from_ref(&addr).cast::<c_void>(),
                buf.as_mut_ptr().cast::<c_char>(),
                buf.len() as socklen_t,
            )
        };
        assert!(!ret.is_null());
        let nul = buf.iter().position(|&b| b == 0).unwrap();
        assert_eq!(core::str::from_utf8(&buf[..nul]).unwrap(), "127.0.0.1");
    }

    #[test]
    fn inet_ntop_unsupported_family() {
        let mut buf = [0u8; 32];
        let ret = unsafe {
            inet_ntop(
                9999,
                ptr::null(),
                buf.as_mut_ptr().cast::<c_char>(),
                buf.len() as socklen_t,
            )
        };
        assert!(ret.is_null());
    }

    #[test]
    fn inet_ntop_v6_size_too_small() {
        let addr = in6_addr { s6_addr: [0u8; 16] };
        let mut buf = [0u8; 4];
        let ret = unsafe {
            inet_ntop(
                AF_INET6,
                ptr::from_ref(&addr).cast::<c_void>(),
                buf.as_mut_ptr().cast::<c_char>(),
                buf.len() as socklen_t,
            )
        };
        assert!(ret.is_null());
    }
}