//! Types and constants for DNS CLASSes

use bytes::Bytes;
use errors::*;
use ser::packet::{DnsPacketData, DnsPacketWriteContext};
use ser::text::{DnsTextData, DnsTextFormatter, DnsTextContext, next_field};
use std::fmt;
use std::io::Cursor;
use std::borrow::Cow;

/// CLASS Internet
pub const IN   : Class = Class(KnownClass::IN    as u16);
/// CLASS "Chaos"
pub const CH   : Class = Class(KnownClass::CH    as u16);
/// CLASS "Hesiod"
pub const HS   : Class = Class(KnownClass::HS    as u16);
/// QCLASS NONE
pub const NONE : Class = Class(KnownQClass::NONE as u16);
/// QCLASS "*" (ANY)
pub const ANY  : Class = Class(KnownQClass::ANY  as u16);

#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
#[repr(u16)]
#[allow(non_camel_case_types)]
pub enum KnownClass {
	// try to list "original" rfc
	/// CLASS Internet
	IN = 0x0001, // RFC 1035
	// CS = 0x0002, // "CSNET" (not just obsolete; unassigned in the IANA registry)
	/// CLASS "Chaos"
	CH = 0x0003, // "Chaos"
	/// CLASS "Hesiod"
	HS = 0x0004, // "Hesiod"
}

#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
#[repr(u16)]
#[allow(non_camel_case_types)]
pub enum KnownQClass {
	// try to list "original" rfc
	/// QCLASS NONE
	NONE = 0x00fe, // RFC 2136
	/// QCLASS "*" (ANY)
	ANY  = 0x00ff, // RFC 1035
}

/// DNS CLASS
///
/// Originally QCLASS was a superset of CLASS; RFC 6895 now defines:
///
/// > There are currently two subcategories of DNS CLASSes: normal,
/// > data-containing classes; and QCLASSes that are only meaningful in
/// > queries or updates.
///
/// ## `ANY`
///
/// QTYPE 255 either (rules from RFC 6895):
///
/// - doesn't have a mnemonic, violating the existence rule
/// - has "*" as mnemonic, violating the formatting rule
/// - has "ANY" as mnemonic, violating the uniquess rule (class ANY)
///
/// Solution: use "ANY" for type 255, don't accept "ANY" as class in
/// places a type could be given too: `*_without_any`.
///
/// The QCLASS `ANY` is mostly useless anyway and shouldn't be used in
/// normal queries.
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
pub struct Class(pub u16);

impl Class {
	/// map to `KnownQClass`
	pub fn known_qclass(self) -> Option<KnownQClass> {
		Some(match self {
			NONE => KnownQClass::NONE,
			ANY => KnownQClass::ANY,
			_ => return None,
		})
	}

	/// whether class is known to be a QCLASS
	pub fn is_known_qclass(self) -> bool {
		self.known_qclass().is_some()
	}

	/// name for CLASS if known
	///
	/// Known CLASSes are represented using their known mnemonic, others
	/// return None.
	pub fn known_name(self) -> Option<&'static str> {
		Some(match self {
			IN => "IN",
			CH => "CH",
			HS => "HS",
			NONE => "NONE",
			ANY => "ANY",
			_ => return None,
		})
	}

	/// name for CLASS
	///
	/// Known CLASSes are represented using their known mnemonic, others
	/// using the "CLASS..." syntax (RFC 3597).
	pub fn name(self) -> Cow<'static, str> {
		match self.known_name() {
			Some(n) => Cow::Borrowed(n),
			None => Cow::Owned(self.generic_name()),
		}
	}

	/// similar to `name`, but returns "CLASS255" for the `ANY` class
	pub fn name_without_any(self) -> Cow<'static, str> {
		match self {
			ANY => Cow::Borrowed("CLASS255"),
			_ => self.name(),
		}
	}

	/// generic name "CLASS..."
	pub fn generic_name(self) -> String {
		let mut result = String::new();
		self.write_generic_name(&mut result).unwrap();
		result
	}

	/// directly write generic name "CLASS..." to some target
	pub fn write_generic_name<W: fmt::Write>(self, w: &mut W) -> fmt::Result {
		write!(w, "CLASS{}", self.0)
	}

	/// only parse known names (mnemonics), but not `ANY`
	///
	/// Avoids conflict with parsing RRTYPE mnemonics.
	pub fn from_known_name_without_any(name: &str) -> Option<Self> {
		if name.eq_ignore_ascii_case("IN") { return Some(IN); }
		if name.eq_ignore_ascii_case("CH") { return Some(CH); }
		if name.eq_ignore_ascii_case("HS") { return Some(HS); }
		if name.eq_ignore_ascii_case("NONE") { return Some(NONE); }
		None
	}

	/// parses known names (mnemonics)
	pub fn from_known_name(name: &str) -> Option<Self> {
		Self::from_known_name_without_any(name).or_else(|| {
			if name.eq_ignore_ascii_case("ANY") { return Some(ANY); }
			None
		})
	}

	/// parses generic names of the form "CLASS..."
	pub fn from_generic_name(name: &str) -> Option<Self> {
		if name.len() > 5 && name.as_bytes()[0..5].eq_ignore_ascii_case(b"CLASS") {
			name[5..].parse::<u16>().ok().map(Class)
		} else {
			None
		}
	}

	/// parses any name (mnemonics and "CLASS..."), but not `ANY`
	/// ("CLASS255" works though)
	pub fn from_name_without_any(name: &str) -> Option<Self> {
		Self::from_generic_name(name).or_else(|| {
			Self::from_known_name_without_any(name)
		})
	}

	/// parses any name (mnemonics and "CLASS...")
	pub fn from_name(name: &str) -> Option<Self> {
		Self::from_generic_name(name).or_else(|| {
			Self::from_known_name(name)
		})
	}
}

impl From<KnownClass> for Class {
	fn from(value: KnownClass) -> Self {
		Class(value as u16)
	}
}

impl From<KnownQClass> for Class {
	fn from(value: KnownQClass) -> Self {
		Class(value as u16)
	}
}

impl fmt::Display for Class {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		match self.known_name() {
			Some(n) => write!(f, "{}", n),
			None => self.write_generic_name(f),
		}
	}
}

impl DnsPacketData for Class {
	fn deserialize(data: &mut Cursor<Bytes>) -> Result<Self> {
		Ok(Class(DnsPacketData::deserialize(data)?))
	}

	fn serialize(&self, context: &mut DnsPacketWriteContext, packet: &mut Vec<u8>) -> Result<()> {
		self.0.serialize(context, packet)
	}
}

impl DnsTextData for Class {
	fn dns_parse(_context: &DnsTextContext, data: &mut &str) -> Result<Self> {
		let field = next_field(data)?;
		Class::from_name(field).ok_or_else(|| format_err!("unknown CLASS {:?}", field))
	}

	fn dns_format(&self, f: &mut DnsTextFormatter) -> fmt::Result {
		write!(f, "{}", self)
	}
}