use std::future::Future;
use std::pin::Pin;

use dyn_clone::DynClone;
use never::Never;
use orchid_base::error::{OrcErrv, OrcRes, mk_errv};
use orchid_base::location::Pos;
use trait_set::trait_set;

use crate::atom::{AtomicFeatures, ForeignAtom, TAtom, ToAtom};
use crate::context::i;
use crate::expr::Expr;
use crate::gen_expr::{GExpr, atom, bot};

pub trait TryFromExpr: Sized {
	fn try_from_expr(expr: Expr) -> impl Future<Output = OrcRes<Self>>;
}

impl TryFromExpr for Expr {
	async fn try_from_expr(expr: Expr) -> OrcRes<Self> { Ok(expr) }
}

impl<T: TryFromExpr, U: TryFromExpr> TryFromExpr for (T, U) {
	async fn try_from_expr(expr: Expr) -> OrcRes<Self> {
		Ok((T::try_from_expr(expr.clone()).await?, U::try_from_expr(expr).await?))
	}
}

async fn err_not_atom(pos: Pos) -> OrcErrv {
	mk_errv(i().i("Expected an atom").await, "This expression is not an atom", [pos])
}

impl TryFromExpr for ForeignAtom {
	async fn try_from_expr(expr: Expr) -> OrcRes<Self> {
		match expr.atom().await {
			Err(ex) => Err(err_not_atom(ex.data().await.pos.clone()).await),
			Ok(f) => Ok(f),
		}
	}
}

impl<A: AtomicFeatures> TryFromExpr for TAtom<A> {
	async fn try_from_expr(expr: Expr) -> OrcRes<Self> {
		let f = ForeignAtom::try_from_expr(expr).await?;
		match f.clone().downcast::<A>().await {
			Ok(a) => Ok(a),
			Err(e) => Err(e.mk_err().await),
		}
	}
}

pub trait ToExpr {
	fn to_gen(self) -> impl Future<Output = GExpr>;
	fn to_expr(self) -> impl Future<Output = Expr>
	where Self: Sized {
		async { self.to_gen().await.create().await }
	}
}

pub trait ToExprDyn {
	fn to_gen_dyn<'a>(self: Box<Self>) -> Pin<Box<dyn Future<Output = GExpr> + 'a>>
	where Self: 'a;

	fn to_expr_dyn<'a>(self: Box<Self>) -> Pin<Box<dyn Future<Output = Expr> + 'a>>
	where Self: 'a;
}
impl<T: ToExpr> ToExprDyn for T {
	fn to_gen_dyn<'a>(self: Box<Self>) -> Pin<Box<dyn Future<Output = GExpr> + 'a>>
	where Self: 'a {
		Box::pin(self.to_gen())
	}
	fn to_expr_dyn<'a>(self: Box<Self>) -> Pin<Box<dyn Future<Output = Expr> + 'a>>
	where Self: 'a {
		Box::pin(self.to_expr())
	}
}
trait_set! {
	pub trait ClonableToExprDyn = ToExprDyn + DynClone;
}
impl ToExpr for Box<dyn ToExprDyn> {
	async fn to_gen(self) -> GExpr { self.to_gen_dyn().await }
	async fn to_expr(self) -> Expr { self.to_expr_dyn().await }
}
impl ToExpr for Box<dyn ClonableToExprDyn> {
	async fn to_gen(self) -> GExpr { self.to_gen_dyn().await }
	async fn to_expr(self) -> Expr { self.to_expr_dyn().await }
}
impl Clone for Box<dyn ClonableToExprDyn> {
	fn clone(&self) -> Self { dyn_clone::clone_box(&**self) }
}

impl ToExpr for GExpr {
	async fn to_gen(self) -> GExpr { self }
	async fn to_expr(self) -> Expr { self.create().await }
}
impl ToExpr for Expr {
	async fn to_gen(self) -> GExpr { self.slot() }
	async fn to_expr(self) -> Expr { self }
}

impl<T: ToExpr> ToExpr for OrcRes<T> {
	async fn to_gen(self) -> GExpr {
		match self {
			Err(e) => bot(e),
			Ok(t) => t.to_gen().await,
		}
	}
}

impl<A: ToAtom> ToExpr for A {
	async fn to_gen(self) -> GExpr { atom(self) }
}

impl ToExpr for Never {
	async fn to_gen(self) -> GExpr { match self {} }
}