//            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
//                    Version 2, December 2004
//
// Copyleft (ↄ) meh. <meh@schizofreni.co> | http://meh.schizofreni.co
//
// Everyone is permitted to copy and distribute verbatim or modified
// copies of this license document, and changing it is allowed as long
// as the name is changed.
//
//            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
//   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
//
//  0. You just DO WHAT THE FUCK YOU WANT TO.

use std::fmt;
use std::io::Cursor;
use byteorder::{ReadBytesExt, WriteBytesExt, BigEndian};

use crate::error::*;
use crate::packet::{Packet as P, PacketMut as PM, AsPacket, AsPacketMut};
use crate::ip;
use crate::udp::checksum;

/// UDP packet parser.
pub struct Packet<B> {
	buffer: B,
}

sized!(Packet,
	header {
		min:  8,
		max:  8,
		size: 8,
	}

	payload {
		min:  0,
		max:  u16::max_value() as usize - 8,
		size: p => (p.length() as usize).saturating_sub(8),
	});

impl<B: AsRef<[u8]>> fmt::Debug for Packet<B> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		f.debug_struct("udp::Packet")
			.field("source", &self.source())
			.field("destination", &self.destination())
			.field("checksum", &self.length())
			.field("checksum", &self.checksum())
			.field("payload", &self.payload())
			.finish()
	}
}

impl<B: AsRef<[u8]>> Packet<B> {
	/// Create a UDP packet without checking.
	pub fn unchecked(buffer: B) -> Packet<B> {
		Packet { buffer }
	}

	/// Parse a UDP packet without checking the payload.
	pub fn no_payload(buffer: B) -> Result<Packet<B>> {
		use crate::size::header::Min;

		let packet = Packet::unchecked(buffer);

		if packet.buffer.as_ref().len() < Self::min() {
			Err(Error::SmallBuffer)?
		}

		Ok(packet)
	}

	/// Parse a UDP packet, checking the buffer contents are correct.
	pub fn new(buffer: B) -> Result<Packet<B>> {
		let packet = Packet::no_payload(buffer)?;

		if packet.buffer.as_ref().len() < packet.length() as usize {
			Err(Error::SmallBuffer)?
		}

		Ok(packet)
	}
}

impl<B: AsRef<[u8]>> Packet<B> {
	/// Convert the packet to its owned version.
	///
	/// # Notes
	///
	/// It would be nice if `ToOwned` could be implemented, but `Packet` already
	/// implements `Clone` and the impl would conflict.
	pub fn to_owned(&self) -> Packet<Vec<u8>> {
		Packet {
			buffer: self.buffer.as_ref().to_vec(),
		}
	}
}

impl<B: AsRef<[u8]>> AsRef<[u8]> for Packet<B> {
	fn as_ref(&self) -> &[u8] {
		use crate::size::Size;

		&self.buffer.as_ref()[.. self.size()]
	}
}

impl<B: AsRef<[u8]> + AsMut<[u8]>> AsMut<[u8]> for Packet<B> {
	fn as_mut(&mut self) -> &mut [u8] {
		use crate::size::Size;

		let size = self.size();
		&mut self.buffer.as_mut()[.. size]
	}
}

impl<'a, B: AsRef<[u8]>> AsPacket<'a, Packet<&'a [u8]>> for B {
	fn as_packet(&self) -> Result<Packet<&[u8]>> {
		Packet::new(self.as_ref())
	}
}

impl<'a, B: AsRef<[u8]> + AsMut<[u8]>> AsPacketMut<'a, Packet<&'a mut [u8]>> for B {
	fn as_packet_mut(&mut self) -> Result<Packet<&mut [u8]>> {
		Packet::new(self.as_mut())
	}
}

impl<B: AsRef<[u8]>> P for Packet<B> {
	fn split(&self) -> (&[u8], &[u8]) {
		use crate::size::payload::Size;

		let header  = 8;
		let payload = self.size();

		let buffer = self.buffer.as_ref();
		let buffer = if buffer.len() < header + payload {
			buffer
		}
		else {
			&buffer[.. header + payload]
		};

		buffer.split_at(header)
	}
}

impl<B: AsRef<[u8]> + AsMut<[u8]>> PM for Packet<B> {
	fn split_mut(&mut self) -> (&mut [u8], &mut [u8]) {
		use crate::size::payload::Size;

		let header  = 8;
		let payload = self.size();

		let buffer = self.buffer.as_mut();
		let buffer = if buffer.len() < header + payload {
			buffer
		}
		else {
			&mut buffer[.. header + payload]
		};

		buffer.split_at_mut(header)
	}
}

impl<B: AsRef<[u8]>> Packet<B> {
	/// Source port.
	pub fn source(&self) -> u16 {
		(&self.buffer.as_ref()[0 ..]).read_u16::<BigEndian>().unwrap()
	}

	/// Destination port.
	pub fn destination(&self) -> u16 {
		(&self.buffer.as_ref()[2 ..]).read_u16::<BigEndian>().unwrap()
	}

	/// Total length of the packet.
	pub fn length(&self) -> u16 {
		(&self.buffer.as_ref()[4 ..]).read_u16::<BigEndian>().unwrap()
	}

	/// Checksum of the packet.
	pub fn checksum(&self) -> u16 {
		(&self.buffer.as_ref()[6 ..]).read_u16::<BigEndian>().unwrap()
	}

	/// Verify the packet is valid by calculating the checksum.
	pub fn is_valid<I: AsRef<[u8]>>(&self, ip: &ip::Packet<I>) -> bool {
		checksum(ip, self.buffer.as_ref()) == self.checksum()
	}
}

impl<B: AsRef<[u8]> + AsMut<[u8]>> Packet<B> {
	/// Source port.
	pub fn set_source(&mut self, value: u16) -> Result<&mut Self> {
		Cursor::new(&mut self.header_mut()[0 ..])
			.write_u16::<BigEndian>(value)?;

		Ok(self)
	}

	/// Destination port.
	pub fn set_destination(&mut self, value: u16) -> Result<&mut Self> {
		Cursor::new(&mut self.header_mut()[2 ..])
			.write_u16::<BigEndian>(value)?;

		Ok(self)
	}

	/// Create a checksumed setter.
	pub fn checked<'a, 'b, BI: AsRef<[u8]> + 'b>(&'a mut self, ip: &'b ip::Packet<BI>) -> Checked<'a, 'b, B, BI> {
		Checked {
			packet: self,
			ip:     ip,
		}
	}

	/// Set the checksum value.
	pub fn set_checksum(&mut self, value: u16) -> Result<&mut Self> {
		Cursor::new(&mut self.header_mut()[6 ..])
			.write_u16::<BigEndian>(value)?;

		Ok(self)
	}

	/// Recalculate and set the checksum value.
	pub fn update_checksum<BI: AsRef<[u8]>>(&mut self, ip: &ip::Packet<BI>) -> Result<&mut Self> {
		let checksum = checksum(ip, self.buffer.as_ref());
		self.set_checksum(checksum)
	}
}

/// Checked wrapper for UDP packets.
///
/// # Note
///
/// The checksum recalculation happens on `Drop`, so don't leak it.
pub struct Checked<'a, 'b, BP, BI>
	where BP: AsRef<[u8]> + AsMut<[u8]> + 'a,
	      BI: AsRef<[u8]> + 'b
{
	packet: &'a mut Packet<BP>,
	ip:     &'b ip::Packet<BI>,
}

impl<'a, 'b, BP, BI> Checked<'a, 'b, BP, BI>
	where BP: AsRef<[u8]> + AsMut<[u8]> + 'a,
	      BI: AsRef<[u8]> + 'b
{
	/// Source port.
	pub fn set_source(&mut self, value: u16) -> Result<&mut Self> {
		self.packet.set_source(value)?;
		Ok(self)
	}

	/// Destination port.
	pub fn set_destination(&mut self, value: u16) -> Result<&mut Self> {
		self.packet.set_destination(value)?;
		Ok(self)
	}
}

impl<'a, 'b, BP, BI> Drop for Checked<'a, 'b, BP, BI>
	where BP: AsRef<[u8]> + AsMut<[u8]> + 'a,
	      BI: AsRef<[u8]> + 'b
{
	fn drop(&mut self) {
		self.packet.update_checksum(self.ip).unwrap();
	}
}

#[cfg(test)]
mod test {
	use crate::packet::{Packet, PacketMut};
	use crate::ip;
	use crate::udp;

	#[test]
	fn values() {
		let raw = [0x45u8, 0x00, 0x00, 0x42, 0x47, 0x07, 0x40, 0x00, 0x40, 0x11, 0x6e, 0xcc, 0xc0, 0xa8, 0x01, 0x89, 0xc0, 0xa8, 0x01, 0xfe, 0xba, 0x2f, 0x00, 0x35, 0x00, 0x2e, 0x1d, 0xf8, 0xbc, 0x81, 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x61, 0x70, 0x69, 0x0c, 0x73, 0x74, 0x65, 0x61, 0x6d, 0x70, 0x6f, 0x77, 0x65, 0x72, 0x65, 0x64, 0x03, 0x63, 0x6f, 0x6d, 0x00, 0x00, 0x1c, 0x00, 0x01];

		let ip  = ip::v4::Packet::new(&raw[..]).unwrap();
		let udp = udp::Packet::new(ip.payload()).unwrap();

		assert!(ip.is_valid());
		assert!(udp.is_valid(&ip::Packet::from(&ip)));

		assert_eq!(udp.destination(), 53);
	}

	#[test]
	fn mutable() {
		let mut raw = [0x45u8, 0x00, 0x00, 0x42, 0x47, 0x07, 0x40, 0x00, 0x40, 0x11, 0x6e, 0xcc, 0xc0, 0xa8, 0x01, 0x89, 0xc0, 0xa8, 0x01, 0xfe, 0xba, 0x2f, 0x00, 0x35, 0x00, 0x2e, 0x1d, 0xf8, 0xbc, 0x81, 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x61, 0x70, 0x69, 0x0c, 0x73, 0x74, 0x65, 0x61, 0x6d, 0x70, 0x6f, 0x77, 0x65, 0x72, 0x65, 0x64, 0x03, 0x63, 0x6f, 0x6d, 0x00, 0x00, 0x1c, 0x00, 0x01];

		let mut ip    = ip::v4::Packet::new(&mut raw[..]).unwrap();
		let (ip, udp) = ip.split_mut();
		let     ip    = ip::Packet::from(ip::v4::Packet::unchecked(ip));
		let mut udp   = udp::Packet::new(udp).unwrap();

		assert!(udp.is_valid(&ip));
		assert_eq!(udp.destination(), 53);

		udp.set_destination(9001).unwrap();
		assert_eq!(udp.destination(), 9001);
		assert!(!udp.is_valid(&ip));

		udp.update_checksum(&ip).unwrap();
		assert!(udp.is_valid(&ip));
	}

	#[test]
	fn mutable_checked() {
		let mut raw = [0x45u8, 0x00, 0x00, 0x42, 0x47, 0x07, 0x40, 0x00, 0x40, 0x11, 0x6e, 0xcc, 0xc0, 0xa8, 0x01, 0x89, 0xc0, 0xa8, 0x01, 0xfe, 0xba, 0x2f, 0x00, 0x35, 0x00, 0x2e, 0x1d, 0xf8, 0xbc, 0x81, 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x61, 0x70, 0x69, 0x0c, 0x73, 0x74, 0x65, 0x61, 0x6d, 0x70, 0x6f, 0x77, 0x65, 0x72, 0x65, 0x64, 0x03, 0x63, 0x6f, 0x6d, 0x00, 0x00, 0x1c, 0x00, 0x01];

		let mut ip        = ip::v4::Packet::new(&mut raw[..]).unwrap();
		let (ip, udp) = ip.split_mut();
		let     ip        = ip::Packet::from(ip::v4::Packet::unchecked(ip));
		let mut udp       = udp::Packet::new(udp).unwrap();

		assert!(udp.is_valid(&ip));
		assert_eq!(udp.destination(), 53);

		udp.checked(&ip).set_destination(9001).unwrap();
		assert_eq!(udp.destination(), 9001);
		assert!(udp.is_valid(&ip));
	}
}