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use crate::{Id, Term};

/// Types that may represent a blank node identifier.
pub trait MaybeBlankId {
	/// Inner blank node identifier type.
	type BlankId;
}

impl<I, B> MaybeBlankId for Id<I, B> {
	type BlankId = B;
}

impl<I: MaybeBlankId, L> MaybeBlankId for Term<I, L> {
	type BlankId = I::BlankId;
}

/// Types that may have a blank node identifier representation that can be
/// borrowed.
pub trait AsBlankId: MaybeBlankId {
	/// Returns a reference to the blank node identifier value, if any.
	fn as_blank(&self) -> Option<&Self::BlankId>;

	fn is_blank(&self) -> bool {
		self.as_blank().is_some()
	}
}

impl<I, B> AsBlankId for Id<I, B> {
	fn as_blank(&self) -> Option<&Self::BlankId> {
		self.as_blank()
	}
}

impl<I: AsBlankId, L> AsBlankId for Term<I, L> {
	fn as_blank(&self) -> Option<&Self::BlankId> {
		self.as_blank()
	}
}

/// Types that can be turned into a blank node identifier.
pub trait IntoBlankId: MaybeBlankId {
	/// Converts the value into a blank node identifier, if any.
	fn into_blank(self) -> Option<Self::BlankId>;
}

impl<I, B> IntoBlankId for Id<I, B> {
	fn into_blank(self) -> Option<Self::BlankId> {
		self.into_blank()
	}
}

impl<I: IntoBlankId, L> IntoBlankId for Term<I, L> {
	fn into_blank(self) -> Option<Self::BlankId> {
		self.into_blank()
	}
}

/// Types that can be constructed from a blank node identifier.
pub trait FromBlankId: MaybeBlankId {
	/// Builds a value from a blank node identifier.
	fn from_blank(b: Self::BlankId) -> Self;
}

impl<I, B> FromBlankId for Id<I, B> {
	fn from_blank(b: Self::BlankId) -> Self {
		Self::Blank(b)
	}
}

impl<I: FromBlankId, L> FromBlankId for Term<I, L> {
	fn from_blank(b: Self::BlankId) -> Self {
		Self::Id(I::from_blank(b))
	}
}