use std::io;
use std::io::Read;
use std::convert::TryFrom;

use super::def;
use super::CapturedPacket;
use super::FileOptions;
use super::PcapError;

use bytepack::Unpacker as NativeUnpacker;

#[cfg(target_endian = "big")]
use bytepack::LEUnpacker as NonNativeUnpacker;
#[cfg(target_endian = "little")]
use bytepack::BEUnpacker as NonNativeUnpacker;

/// The `PcapReader` struct allows reading packets from a packet capture.
pub struct PcapReader<R> {
    reader: R,
    state: Option<PcapState>,
}
struct PcapState {
    file_header: def::PcapFileHeader,
    packet_buffer: Vec<u8>,
}


impl<R: io::Read> PcapReader<R> {
    /// Create a new `PcapReader` that reads the packet capture data from the specified `Reader`.
    pub fn new(mut reader: R) -> Result<(FileOptions, Self), PcapError> {
        let fh : def::PcapFileHeaderInFile = NativeUnpacker::unpack(&mut reader)?;
        let fh = def::PcapFileHeader::try_from(fh).or(Err(PcapError::InvalidFileHeader))?;

        // DOS protection TODO: make this limit (1.5GiB) configurable
        if fh.snaplen > 0x60000000 {
            return Err(PcapError::InvalidFileHeader);
        }
        let buffer = vec![0; fh.snaplen];

        Ok((
            FileOptions {
                snaplen: fh.snaplen,
                linktype: fh.network,
                high_res_timestamps: fh.ns_res,
                non_native_byte_order: fh.need_byte_swap,
            },
            PcapReader {
                reader,
                state: Some(PcapState {
                    file_header: fh,
                    packet_buffer: buffer,
                }),
            }
        ))
    }
    /// This function allows iterating over the packets in the packet capture, in a similar fashion
    /// to normal iterators. (The exact interface is unfortunately incompatible.)
    ///
    /// Returns `Ok(None)` on EOF, or a packet as long as one is available.
    #[allow(clippy::should_implement_trait)]
    pub fn next(&mut self) -> Result<Option<CapturedPacket>, PcapError> {

        let rh = if let Some(PcapState { file_header: def::PcapFileHeader { need_byte_swap: true, .. }, .. }) = self.state {
            NonNativeUnpacker::unpack::<def::PcapRecordHeader>(&mut self.reader)
        } else {
            NativeUnpacker::unpack::<def::PcapRecordHeader>(&mut self.reader)
        };
        let rh = match rh {
            Err(e) => {
                return if e.kind() == io::ErrorKind::UnexpectedEof {
                    self.state = None;
                    Ok(None)
                } else {
                    Err(e.into())
                };
            },
            Ok(rh) => rh,
        };
        let state = self.state.as_mut().unwrap();

        let size_in_pcap = usize::try_from(rh.incl_len).or(Err(PcapError::InvalidPacketSize))?;
        let size_to_read = usize::min(state.packet_buffer.len(), size_in_pcap);

        let buf = &mut state.packet_buffer[..size_to_read];
        self.reader.read_exact(buf)?;

        if size_to_read < size_in_pcap {
            // we used to return InvalidPacketSize here, now we just drop the excessive data
            let mut take = self.reader.by_ref().take((size_in_pcap - size_to_read) as u64);
            io::copy(&mut take, &mut io::sink())?;
        }

        let orig_len = usize::try_from(rh.orig_len).or(Err(PcapError::InvalidPacketSize))?;

        if let Some(t) = rh.get_time(&state.file_header) {
            Ok(Some(CapturedPacket {
                time: t,
                data: buf,
                orig_len,
            }))
        } else {
            Err(PcapError::InvalidDate)
        }
    }

    /// Destroys this `PcapReader` and returns access to the underlying `Read`.
    pub fn take_reader(self) -> R {
        self.reader
    }
}

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

    #[test]
    /// Makes sure that PCAPs with identical contents but different endianness and
    /// timestamp formats parse identical.
    fn format_variations() {
        let be_us = [0xa1, 0xb2, 0x3c, 0x4d, 0x00, 0x02, 0x00, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00,
                     0x00, 0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x00, 0x65, 0x56, 0x50,
                     0x6e, 0x1a, 0x18, 0x2b, 0x0a, 0xd0, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00,
                     0x3c, 0x44, 0x41, 0x54, 0x41];
        let be_ns = [0xa1, 0xb2, 0xc3, 0xd4, 0x00, 0x02, 0x00, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00,
                     0x00, 0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x00, 0x65, 0x56, 0x50,
                     0x6e, 0x1a, 0x00, 0x06, 0x2f, 0xe2, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00,
                     0x3c, 0x44, 0x41, 0x54, 0x41];
        let le_us = [0xd4, 0xc3, 0xb2, 0xa1, 0x02, 0x00, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                     0x00, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x65, 0x00, 0x00, 0x00, 0x1a, 0x6e,
                     0x50, 0x56, 0xe2, 0x2f, 0x06, 0x00, 0x04, 0x00, 0x00, 0x00, 0x3c, 0x00, 0x00,
                     0x00, 0x44, 0x41, 0x54, 0x41];
        let le_ns = [0x4du8, 0x3c, 0xb2, 0xa1, 0x02, 0x00, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00,
                     0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x65, 0x00, 0x00, 0x00, 0x1a,
                     0x6e, 0x50, 0x56, 0xd0, 0x0a, 0x2b, 0x18, 0x04, 0x00, 0x00, 0x00, 0x3c, 0x00,
                     0x00, 0x00, 0x44, 0x41, 0x54, 0x41];
        let raw_pcaps = [be_ns, be_us, le_ns, le_us];
        let mut readers: Vec<PcapReader<&[u8]>> = raw_pcaps.iter()
            .map(|pcap| PcapReader::new(&pcap[..]).unwrap().1)
            .collect();

        {
            let mut packets = readers.iter_mut().map(|r| r.next().unwrap().unwrap());
            let first: CapturedPacket = packets.next().unwrap();
            for packet in packets {
                assert_eq!(first, packet);
            }
        }

        for r in &mut readers {
            assert!(r.next().unwrap().is_none());
        }
    }
}