use core::fmt;
use byteorder::{ByteOrder, NetworkEndian};

use Error;
use super::ip::rfc1071_checksum;

enum_with_unknown! {
    /// Internet protocol control message type.
    pub doc enum Type(u8) {
        /// Echo reply
        EchoReply      =  0,
        /// Destination unreachable
        DstUnreachable =  1,
        /// Message redirect
        Redirect       =  5,
        /// Echo request
        EchoRequest    =  8,
        /// Router advertisement
        RouterAdvert   =  9,
        /// Router solicitation
        RouterSolicit  = 10,
        /// Time exceeded
        TimeExceeded   = 11,
        /// Parameter problem
        ParamProblem   = 12,
        /// Timestamp
        Timestamp      = 13,
        /// Timestamp reply
        TimestampReply = 14
    }
}

enum_with_unknown! {
    /// Internet protocol control message subtype for type "Destination Unreachable".
    pub doc enum DstUnreachable(u8) {
        /// Destination network unreachable
        NetUnreachable   =  0,
        /// Destination host unreachable
        HostUnreachable  =  1,
        /// Destination protocol unreachable
        ProtoUnreachable =  2,
        /// Destination port unreachable
        PortUnreachable  =  3,
        /// Fragmentation required, and DF flag set
        FragRequired     =  4,
        /// Source route failed
        SrcRouteFailed   =  5,
        /// Destination network unknown
        DstNetUnknown    =  6,
        /// Destination host unknown
        DstHostUnknown   =  7,
        /// Source host isolated
        SrcHostIsolated  =  8,
        /// Network administratively prohibited
        NetProhibited    =  9,
        /// Host administratively prohibited
        HostProhibited   = 10,
        /// Network unreachable for ToS
        NetUnreachToS    = 11,
        /// Host unreachable for ToS
        HostUnreachToS   = 12,
        /// Communication administratively prohibited
        CommProhibited   = 13,
        /// Host precedence violation
        HostPrecedViol   = 14,
        /// Precedence cutoff in effect
        PrecedCutoff     = 15
    }
}

enum_with_unknown! {
    /// Internet protocol control message subtype for type "Redirect Message".
    pub doc enum Redirect(u8) {
        /// Redirect Datagram for the Network
        Net     = 0,
        /// Redirect Datagram for the Host
        Host    = 1,
        /// Redirect Datagram for the ToS & network
        NetToS  = 2,
        /// Redirect Datagram for the ToS & host
        HostToS = 3
    }
}

enum_with_unknown! {
    /// Internet protocol control message subtype for type "Time Exceeded".
    pub doc enum TimeExceeded(u8) {
        /// TTL expired in transit
        TtlExpired  = 0,
        /// Fragment reassembly time exceeded
        FragExpired = 1
    }
}

enum_with_unknown! {
    /// Internet protocol control message subtype for type "Parameter Problem".
    pub doc enum ParamProblem(u8) {
        /// Pointer indicates the error
        AtPointer     = 0,
        /// Missing a required option
        MissingOption = 1,
        /// Bad length
        BadLength     = 2
    }
}

/// A read/write wrapper around an Internet Control Message Protocol version 4 packet buffer.
#[derive(Debug)]
pub struct Packet<T: AsRef<[u8]>> {
    buffer: T
}

mod field {
    #![allow(non_snake_case)]

    use wire::field::*;

    pub const TYPE:       usize = 0;
    pub const CODE:       usize = 1;
    pub const CHECKSUM:   Field = 2..4;

    pub const ECHO_IDENT: Field = 4..6;
    pub const ECHO_SEQNO: Field = 6..8;
}

impl<T: AsRef<[u8]>> Packet<T> {
    /// Wrap a buffer with an ICMPv4 packet. Returns an error if the buffer
    /// is too small to contain one.
    pub fn new(buffer: T) -> Result<Packet<T>, Error> {
        let len = buffer.as_ref().len();
        if len < field::CHECKSUM.end {
            Err(Error::Truncated)
        } else {
            let packet = Packet { buffer: buffer };
            if len < packet.header_len() {
                Err(Error::Truncated)
            } else {
                Ok(packet)
            }
        }
    }

    /// Consumes the packet, returning the underlying buffer.
    pub fn into_inner(self) -> T {
        self.buffer
    }

    /// Return the message type field.
    #[inline(always)]
    pub fn msg_type(&self) -> Type {
        let data = self.buffer.as_ref();
        Type::from(data[field::TYPE])
    }

    /// Return the message code field.
    #[inline(always)]
    pub fn msg_code(&self) -> u8 {
        let data = self.buffer.as_ref();
        data[field::CODE]
    }

    /// Return the checksum field.
    #[inline(always)]
    pub fn checksum(&self) -> u16 {
        let data = self.buffer.as_ref();
        NetworkEndian::read_u16(&data[field::CHECKSUM])
    }

    /// Return the identifier field (for echo request and reply packets).
    ///
    /// # Panics
    /// This function may panic if this packet is not an echo request or reply packet.
    #[inline(always)]
    pub fn echo_ident(&self) -> u16 {
        let data = self.buffer.as_ref();
        NetworkEndian::read_u16(&data[field::ECHO_IDENT])
    }

    /// Return the sequence number field (for echo request and reply packets).
    ///
    /// # Panics
    /// This function may panic if this packet is not an echo request or reply packet.
    #[inline(always)]
    pub fn echo_seq_no(&self) -> u16 {
        let data = self.buffer.as_ref();
        NetworkEndian::read_u16(&data[field::ECHO_SEQNO])
    }

    /// Return the header length.
    /// The result depends on the value of the message type field.
    pub fn header_len(&self) -> usize {
        match self.msg_type() {
            Type::EchoRequest => field::ECHO_SEQNO.end,
            Type::EchoReply   => field::ECHO_SEQNO.end,
            _ => field::CHECKSUM.end // make a conservative assumption
        }
    }

    /// Return a pointer to the type-specific data.
    #[inline(always)]
    pub fn data(&self) -> &[u8] {
        let data = self.buffer.as_ref();
        &data[self.header_len()..]
    }

    /// Validate the header checksum.
    pub fn verify_checksum(&self) -> bool {
        let checksum = {
            let data = self.buffer.as_ref();
            rfc1071_checksum(field::CHECKSUM.start, &data[..self.header_len()])
        };
        self.checksum() == checksum
    }
}

impl<T: AsRef<[u8]> + AsMut<[u8]>> Packet<T> {
    /// Set the message type field.
    #[inline(always)]
    pub fn set_msg_type(&mut self, value: Type) {
        let mut data = self.buffer.as_mut();
        data[field::TYPE] = value.into()
    }

    /// Set the message code field.
    #[inline(always)]
    pub fn set_msg_code(&mut self, value: u8) {
        let mut data = self.buffer.as_mut();
        data[field::CODE] = value
    }

    /// Set the checksum field.
    #[inline(always)]
    pub fn set_checksum(&mut self, value: u16) {
        let mut data = self.buffer.as_mut();
        NetworkEndian::write_u16(&mut data[field::CHECKSUM], value)
    }

    /// Set the identifier field (for echo request and reply packets).
    ///
    /// # Panics
    /// This function may panic if this packet is not an echo request or reply packet.
    #[inline(always)]
    pub fn set_echo_ident(&mut self, value: u16) {
        let mut data = self.buffer.as_mut();
        NetworkEndian::write_u16(&mut data[field::ECHO_IDENT], value)
    }

    /// Set the sequence number field (for echo request and reply packets).
    ///
    /// # Panics
    /// This function may panic if this packet is not an echo request or reply packet.
    #[inline(always)]
    pub fn set_echo_seq_no(&mut self, value: u16) {
        let mut data = self.buffer.as_mut();
        NetworkEndian::write_u16(&mut data[field::ECHO_SEQNO], value)
    }

    /// Return a mutable pointer to the type-specific data.
    #[inline(always)]
    pub fn data_mut(&mut self) -> &mut [u8] {
        let range = self.header_len()..;
        let mut data = self.buffer.as_mut();
        &mut data[range]
    }

    /// Compute and fill in the header checksum.
    pub fn fill_checksum(&mut self) {
        let checksum = {
            let data = self.buffer.as_ref();
            rfc1071_checksum(field::CHECKSUM.start, &data[..self.header_len()])
        };
        self.set_checksum(checksum)
    }
}