use std::collections::LinkedList;

use crate::{token::Literal, join};

use super::{Identifier, value::Value};

#[derive(Clone, Debug)]
pub enum Pattern {
	Literal(Literal),
	Binding(Identifier),
	Variant(Identifier, Vec<Pattern>),
}

impl Pattern {
	pub fn matches<'a, 'b>(&'a self, value: &'b Value) -> Option<LinkedList<(&'a Identifier, &'b Value)>> {
		match (value, self) {
			(Value::Int(x1), Pattern::Literal(Literal::Int(x2))) =>
				if *x1 as u64 == *x2 {
					Some(LinkedList::new())
				} else {
					None
				},
			(Value::Structural(ident1, values1), Pattern::Variant(ident2, patterns2)) =>
				if ident1 == ident2 && values1.len() == patterns2.len() {
					values1.into_iter()
						.zip(patterns2)
						.fold(Some(LinkedList::new()), |bindings, (v1, p2)|
							bindings.and_then(|bindings|
								p2.matches(v1).map(|new_bindings|
									join(
										bindings,
										new_bindings,
									)
								)
							)
						)
				} else {
					None
				},
			_ => None,
		}
	}
}