use std::borrow::Cow;

use never::Never;
use orchid_base::fmt;
use orchid_extension::conv::ToExpr;
use orchid_extension::coroutine_exec::exec;
use orchid_extension::expr::Expr;
use orchid_extension::gen_expr::new_atom;
use orchid_extension::{Atomic, OwnedAtom, OwnedVariant, TAtom};

use crate::macros::mactree::{MacTok, MacTree};

#[derive(Clone)]
pub struct InstantiateTplCall {
	pub(crate) tpl: MacTree,
	pub(crate) argc: usize,
	pub(crate) argv: Vec<MacTree>,
}
impl Atomic for InstantiateTplCall {
	type Variant = OwnedVariant;
	type Data = ();
}
impl OwnedAtom for InstantiateTplCall {
	async fn val(&self) -> Cow<'_, Self::Data> { Cow::Owned(()) }
	type Refs = Never;
	// Technically must be supported but shouldn't actually ever be called
	async fn call_ref(&self, arg: Expr) -> impl ToExpr {
		if !self.argv.is_empty() {
			eprintln!(
				"Copying partially applied instantiate_tpl call. This is an internal value.\
				\nIt should be fully consumed within generated code."
			);
		}
		self.clone().call(arg).await
	}
	async fn call(mut self, arg: Expr) -> impl ToExpr {
		exec(async move |mut h| {
			match h.exec::<TAtom<MacTree>>(arg.clone()).await {
				Err(_) => panic!("Expected a macro param, found {}", fmt(&arg).await),
				Ok(t) => self.argv.push(t.own().await),
			};
			if self.argv.len() < self.argc {
				return new_atom(self);
			}
			let mut args = self.argv.into_iter();
			let ret = self.tpl.map(&mut false, &mut |mt| match mt.tok() {
				MacTok::Slot => Some(args.next().expect("Not enough arguments to fill all slots")),
				_ => None,
			});
			assert!(args.next().is_none(), "Too many arguments for all slots");
			new_atom(ret)
		})
		.await
	}
}