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use crate::{
	Asn1DerError, DerObject, Sink, error::ErrorChain,
	typed::{ DerTypeView, DerDecodable, DerEncodable }
};


/// An ASN.1-DER null object view
#[derive(Copy, Clone)]
pub struct Null<'a> {
	object: DerObject<'a>
}
impl<'a> Null<'a> {
	/// Writes a new null object into `sink` and returns a type view over it
	#[cfg_attr(feature = "no_panic", no_panic::no_panic)]
	pub fn new<S: Sink + Into<&'a[u8]>>(mut sink: S) -> Result<Self, Asn1DerError> {
		Self::write(&mut sink).propagate(e!("Failed to construct null object"))?;
		let object = DerObject::decode(sink.into())
			.propagate(e!("Failed to load constructed null object"))?;
		Ok(Self{ object })
	}
	
	/// Writes a boolean `value` as DER-object to `sink`
	#[cfg_attr(feature = "no_panic", no_panic::no_panic)]
	pub fn write<S: Sink>(sink: &mut S) -> Result<(), Asn1DerError> {
		DerObject::write(Self::TAG, 0, &mut b"".iter(), sink)
			.propagate(e!("Failed to write null object"))
	}
}
impl<'a> DerTypeView<'a> for Null<'a> {
	const TAG: u8 = b'\x05';
	
	#[cfg_attr(feature = "no_panic", no_panic::no_panic)]
	fn object(&self) -> DerObject<'a> {
		self.object
	}
}
impl<'a> DerDecodable<'a> for Null<'a> {
	#[cfg_attr(feature = "no_panic", no_panic::no_panic)]
	fn load(object: DerObject<'a>) -> Result<Self, Asn1DerError> {
		match object.value() {
			_ if object.tag() != Self::TAG => Err(einval!("DER object is not a null object"))?,
			b"" => Ok(Self{ object }),
			_ => Err(einval!("DER object is not a valid null object"))
		}
	}
}
impl<'a> DerEncodable for Null<'a> {
	/// Encodes `self` to `sink`
	#[cfg_attr(feature = "no_panic", no_panic::no_panic)]
	fn encode<S: Sink>(&self, sink: &mut S) -> Result<(), Asn1DerError> {
		self.object().encode(sink).propagate(e!("Failed to encode null object"))
	}
}


impl<'a> DerDecodable<'a> for () {
	#[cfg_attr(feature = "no_panic", no_panic::no_panic)]
	fn load(object: DerObject<'a>) -> Result<Self, Asn1DerError> {
		Null::load(object).propagate(e!("Failed to load null object"))?;
		Ok(())
	}
}
impl DerEncodable for () {
	#[cfg_attr(feature = "no_panic", no_panic::no_panic)]
	fn encode<S: Sink>(&self, sink: &mut S) -> Result<(), Asn1DerError> {
		Null::write(sink).propagate(e!("Failed to encode null object"))
	}
}


impl<'a, T: DerDecodable<'a>> DerDecodable<'a> for Option<T> {
	#[cfg_attr(feature = "no_panic", no_panic::no_panic)]
	fn load(object: DerObject<'a>) -> Result<Self, Asn1DerError> {
		match object.tag() {
			Null::TAG => {
				Null::load(object).propagate(e!("Failed to load null object"))?;
				Ok(None)
			},
			_ => {
				let object = T::load(object).propagate(e!("Failed to load object"))?;
				Ok(Some(object))
			}
		}
	}
}
impl<T: DerEncodable> DerEncodable for Option<T> {
	#[cfg_attr(feature = "no_panic", no_panic::no_panic)] #[cfg_attr(feature = "no_panic", inline(always))]
	fn encode<S: Sink>(&self, sink: &mut S) -> Result<(), Asn1DerError> {
		match self {
			Some(object) => object.encode(sink).propagate(e!("Failed to encode object")),
			None => Null::write(sink).propagate(e!("Failed to encode null object"))
		}
	}
}