//! A private parser implementation of IPv4, IPv6, and socket addresses.
//!
//! This module is "publicly exported" through the `FromStr` implementations
//! below.

use crate::error::Error;
use crate::fmt;
use crate::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6};
use crate::str::FromStr;

struct Parser<'a> {
    // parsing as ASCII, so can use byte array
    s: &'a [u8],
    pos: usize,
}

impl<'a> Parser<'a> {
    fn new(s: &'a str) -> Parser<'a> {
        Parser { s: s.as_bytes(), pos: 0 }
    }

    fn is_eof(&self) -> bool {
        self.pos == self.s.len()
    }

    // Commit only if parser returns Some
    fn read_atomically<T, F>(&mut self, cb: F) -> Option<T>
    where
        F: FnOnce(&mut Parser<'_>) -> Option<T>,
    {
        let pos = self.pos;
        let r = cb(self);
        if r.is_none() {
            self.pos = pos;
        }
        r
    }

    // Commit only if parser read till EOF
    fn read_till_eof<T, F>(&mut self, cb: F) -> Option<T>
    where
        F: FnOnce(&mut Parser<'_>) -> Option<T>,
    {
        self.read_atomically(move |p| cb(p).filter(|_| p.is_eof()))
    }

    // Apply 3 parsers sequentially
    fn read_seq_3<A, B, C, PA, PB, PC>(&mut self, pa: PA, pb: PB, pc: PC) -> Option<(A, B, C)>
    where
        PA: FnOnce(&mut Parser<'_>) -> Option<A>,
        PB: FnOnce(&mut Parser<'_>) -> Option<B>,
        PC: FnOnce(&mut Parser<'_>) -> Option<C>,
    {
        self.read_atomically(move |p| {
            let a = pa(p);
            let b = if a.is_some() { pb(p) } else { None };
            let c = if b.is_some() { pc(p) } else { None };
            match (a, b, c) {
                (Some(a), Some(b), Some(c)) => Some((a, b, c)),
                _ => None,
            }
        })
    }

    // Read next char
    fn read_char(&mut self) -> Option<char> {
        if self.is_eof() {
            None
        } else {
            let r = self.s[self.pos] as char;
            self.pos += 1;
            Some(r)
        }
    }

    // Return char and advance iff next char is equal to requested
    fn read_given_char(&mut self, c: char) -> Option<char> {
        self.read_atomically(|p| match p.read_char() {
            Some(next) if next == c => Some(next),
            _ => None,
        })
    }

    // Read digit
    fn read_digit(&mut self, radix: u8) -> Option<u8> {
        fn parse_digit(c: char, radix: u8) -> Option<u8> {
            let c = c as u8;
            // assuming radix is either 10 or 16
            if c >= b'0' && c <= b'9' {
                Some(c - b'0')
            } else if radix > 10 && c >= b'a' && c < b'a' + (radix - 10) {
                Some(c - b'a' + 10)
            } else if radix > 10 && c >= b'A' && c < b'A' + (radix - 10) {
                Some(c - b'A' + 10)
            } else {
                None
            }
        }

        self.read_atomically(|p| p.read_char().and_then(|c| parse_digit(c, radix)))
    }

    fn read_number_impl(&mut self, radix: u8, max_digits: u32, upto: u32) -> Option<u32> {
        let mut r = 0;
        let mut digit_count = 0;
        loop {
            match self.read_digit(radix) {
                Some(d) => {
                    r = r * (radix as u32) + (d as u32);
                    digit_count += 1;
                    if digit_count > max_digits || r >= upto {
                        return None;
                    }
                }
                None => {
                    if digit_count == 0 {
                        return None;
                    } else {
                        return Some(r);
                    }
                }
            };
        }
    }

    // Read number, failing if max_digits of number value exceeded
    fn read_number(&mut self, radix: u8, max_digits: u32, upto: u32) -> Option<u32> {
        self.read_atomically(|p| p.read_number_impl(radix, max_digits, upto))
    }

    fn read_ipv4_addr_impl(&mut self) -> Option<Ipv4Addr> {
        let mut bs = [0; 4];
        let mut i = 0;
        while i < 4 {
            if i != 0 && self.read_given_char('.').is_none() {
                return None;
            }

            bs[i] = self.read_number(10, 3, 0x100).map(|n| n as u8)?;
            i += 1;
        }
        Some(Ipv4Addr::new(bs[0], bs[1], bs[2], bs[3]))
    }

    // Read IPv4 address
    fn read_ipv4_addr(&mut self) -> Option<Ipv4Addr> {
        self.read_atomically(|p| p.read_ipv4_addr_impl())
    }

    fn read_ipv6_addr_impl(&mut self) -> Option<Ipv6Addr> {
        fn ipv6_addr_from_head_tail(head: &[u16], tail: &[u16]) -> Ipv6Addr {
            assert!(head.len() + tail.len() <= 8);
            let mut gs = [0; 8];
            gs[..head.len()].copy_from_slice(head);
            gs[(8 - tail.len())..8].copy_from_slice(tail);
            Ipv6Addr::new(gs[0], gs[1], gs[2], gs[3], gs[4], gs[5], gs[6], gs[7])
        }

        fn read_groups(p: &mut Parser<'_>, groups: &mut [u16; 8], limit: usize) -> (usize, bool) {
            let mut i = 0;
            while i < limit {
                if i < limit - 1 {
                    let ipv4 = p.read_atomically(|p| {
                        if i == 0 || p.read_given_char(':').is_some() {
                            p.read_ipv4_addr()
                        } else {
                            None
                        }
                    });
                    if let Some(v4_addr) = ipv4 {
                        let octets = v4_addr.octets();
                        groups[i + 0] = ((octets[0] as u16) << 8) | (octets[1] as u16);
                        groups[i + 1] = ((octets[2] as u16) << 8) | (octets[3] as u16);
                        return (i + 2, true);
                    }
                }

                let group = p.read_atomically(|p| {
                    if i == 0 || p.read_given_char(':').is_some() {
                        p.read_number(16, 4, 0x10000).map(|n| n as u16)
                    } else {
                        None
                    }
                });
                match group {
                    Some(g) => groups[i] = g,
                    None => return (i, false),
                }
                i += 1;
            }
            (i, false)
        }

        let mut head = [0; 8];
        let (head_size, head_ipv4) = read_groups(self, &mut head, 8);

        if head_size == 8 {
            return Some(Ipv6Addr::new(
                head[0], head[1], head[2], head[3], head[4], head[5], head[6], head[7],
            ));
        }

        // IPv4 part is not allowed before `::`
        if head_ipv4 {
            return None;
        }

        // read `::` if previous code parsed less than 8 groups
        if !self.read_given_char(':').is_some() || !self.read_given_char(':').is_some() {
            return None;
        }

        let mut tail = [0; 8];
        // `::` indicates one or more groups of 16 bits of zeros
        let limit = 8 - (head_size + 1);
        let (tail_size, _) = read_groups(self, &mut tail, limit);
        Some(ipv6_addr_from_head_tail(&head[..head_size], &tail[..tail_size]))
    }

    fn read_ipv6_addr(&mut self) -> Option<Ipv6Addr> {
        self.read_atomically(|p| p.read_ipv6_addr_impl())
    }

    fn read_ip_addr(&mut self) -> Option<IpAddr> {
        self.read_ipv4_addr().map(IpAddr::V4)
            .or_else(|| self.read_ipv6_addr().map(IpAddr::V6))
    }

    fn read_socket_addr_v4(&mut self) -> Option<SocketAddrV4> {
        let ip_addr = |p: &mut Parser<'_>| p.read_ipv4_addr();
        let colon = |p: &mut Parser<'_>| p.read_given_char(':');
        let port = |p: &mut Parser<'_>| p.read_number(10, 5, 0x10000).map(|n| n as u16);

        self.read_seq_3(ip_addr, colon, port).map(|t| {
            let (ip, _, port): (Ipv4Addr, char, u16) = t;
            SocketAddrV4::new(ip, port)
        })
    }

    fn read_socket_addr_v6(&mut self) -> Option<SocketAddrV6> {
        let ip_addr = |p: &mut Parser<'_>| {
            let open_br = |p: &mut Parser<'_>| p.read_given_char('[');
            let ip_addr = |p: &mut Parser<'_>| p.read_ipv6_addr();
            let clos_br = |p: &mut Parser<'_>| p.read_given_char(']');
            p.read_seq_3(open_br, ip_addr, clos_br).map(|t| t.1)
        };
        let colon = |p: &mut Parser<'_>| p.read_given_char(':');
        let port = |p: &mut Parser<'_>| p.read_number(10, 5, 0x10000).map(|n| n as u16);

        self.read_seq_3(ip_addr, colon, port).map(|t| {
            let (ip, _, port): (Ipv6Addr, char, u16) = t;
            SocketAddrV6::new(ip, port, 0, 0)
        })
    }

    fn read_socket_addr(&mut self) -> Option<SocketAddr> {
        self.read_socket_addr_v4().map(SocketAddr::V4)
            .or_else(|| self.read_socket_addr_v6().map(SocketAddr::V6))
    }
}

#[stable(feature = "ip_addr", since = "1.7.0")]
impl FromStr for IpAddr {
    type Err = AddrParseError;
    fn from_str(s: &str) -> Result<IpAddr, AddrParseError> {
        match Parser::new(s).read_till_eof(|p| p.read_ip_addr()) {
            Some(s) => Ok(s),
            None => Err(AddrParseError(())),
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl FromStr for Ipv4Addr {
    type Err = AddrParseError;
    fn from_str(s: &str) -> Result<Ipv4Addr, AddrParseError> {
        match Parser::new(s).read_till_eof(|p| p.read_ipv4_addr()) {
            Some(s) => Ok(s),
            None => Err(AddrParseError(())),
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl FromStr for Ipv6Addr {
    type Err = AddrParseError;
    fn from_str(s: &str) -> Result<Ipv6Addr, AddrParseError> {
        match Parser::new(s).read_till_eof(|p| p.read_ipv6_addr()) {
            Some(s) => Ok(s),
            None => Err(AddrParseError(())),
        }
    }
}

#[stable(feature = "socket_addr_from_str", since = "1.5.0")]
impl FromStr for SocketAddrV4 {
    type Err = AddrParseError;
    fn from_str(s: &str) -> Result<SocketAddrV4, AddrParseError> {
        match Parser::new(s).read_till_eof(|p| p.read_socket_addr_v4()) {
            Some(s) => Ok(s),
            None => Err(AddrParseError(())),
        }
    }
}

#[stable(feature = "socket_addr_from_str", since = "1.5.0")]
impl FromStr for SocketAddrV6 {
    type Err = AddrParseError;
    fn from_str(s: &str) -> Result<SocketAddrV6, AddrParseError> {
        match Parser::new(s).read_till_eof(|p| p.read_socket_addr_v6()) {
            Some(s) => Ok(s),
            None => Err(AddrParseError(())),
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl FromStr for SocketAddr {
    type Err = AddrParseError;
    fn from_str(s: &str) -> Result<SocketAddr, AddrParseError> {
        match Parser::new(s).read_till_eof(|p| p.read_socket_addr()) {
            Some(s) => Ok(s),
            None => Err(AddrParseError(())),
        }
    }
}

/// An error which can be returned when parsing an IP address or a socket address.
///
/// This error is used as the error type for the [`FromStr`] implementation for
/// [`IpAddr`], [`Ipv4Addr`], [`Ipv6Addr`], [`SocketAddr`], [`SocketAddrV4`], and
/// [`SocketAddrV6`].
///
/// # Potential causes
///
/// `AddrParseError` may be thrown because the provided string does not parse as the given type,
/// often because it includes information only handled by a different address type.
///
/// ```should_panic
/// use std::net::IpAddr;
/// let _foo: IpAddr = "127.0.0.1:8080".parse().expect("Cannot handle the socket port");
/// ```
///
/// [`IpAddr`] doesn't handle the port. Use [`SocketAddr`] instead.
///
/// ```
/// use std::net::SocketAddr;
///
/// // No problem, the `panic!` message has disappeared.
/// let _foo: SocketAddr = "127.0.0.1:8080".parse().expect("unreachable panic");
/// ```
///
/// [`FromStr`]: ../../std/str/trait.FromStr.html
/// [`IpAddr`]: ../../std/net/enum.IpAddr.html
/// [`Ipv4Addr`]: ../../std/net/struct.Ipv4Addr.html
/// [`Ipv6Addr`]: ../../std/net/struct.Ipv6Addr.html
/// [`SocketAddr`]: ../../std/net/enum.SocketAddr.html
/// [`SocketAddrV4`]: ../../std/net/struct.SocketAddrV4.html
/// [`SocketAddrV6`]: ../../std/net/struct.SocketAddrV6.html
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct AddrParseError(());

#[stable(feature = "addr_parse_error_error", since = "1.4.0")]
impl fmt::Display for AddrParseError {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt.write_str(self.description())
    }
}

#[stable(feature = "addr_parse_error_error", since = "1.4.0")]
impl Error for AddrParseError {
    fn description(&self) -> &str {
        "invalid IP address syntax"
    }
}