use std::cell::RefCell;
use std::fmt;

use hashbrown::HashMap;
use hashbrown::hash_map::Entry;

use crate::api;
use crate::expr::Expr;

#[derive(Default)]
pub struct ExprStore(RefCell<HashMap<api::ExprTicket, (u32, Expr)>>);
impl ExprStore {
	pub fn give_expr(&self, expr: Expr) {
		match self.0.borrow_mut().entry(expr.id()) {
			Entry::Occupied(mut oe) => oe.get_mut().0 += 1,
			Entry::Vacant(v) => {
				v.insert((1, expr));
			},
		}
	}
	pub fn take_expr(&self, ticket: api::ExprTicket) {
		(self.0.borrow_mut().entry(ticket))
			.and_replace_entry_with(|_, (rc, rt)| (1 < rc).then_some((rc - 1, rt)));
	}
	pub fn get_expr(&self, ticket: api::ExprTicket) -> Option<Expr> {
		self.0.borrow().get(&ticket).map(|(_, expr)| expr.clone())
	}
}
impl fmt::Display for ExprStore {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		let r = self.0.borrow();
		let rc: u32 = r.values().map(|v| v.0).sum();
		write!(f, "Store holding {rc} refs to {} exprs", r.len())
	}
}