use std::cell::RefCell;
use std::fmt;
use std::hash::Hash;
use std::rc::Rc;

use async_once_cell::OnceCell;
use derive_destructure::destructure;
use hashbrown::HashSet;
use orchid_base::error::OrcErrv;
use orchid_base::format::{FmtCtx, FmtUnit, Format};
use orchid_base::location::Pos;
use orchid_base::reqnot::Requester;

use crate::api;
use crate::atom::ForeignAtom;
use crate::gen_expr::{GExpr, GExprKind};
use crate::system::SysCtx;

pub struct BorrowedExprStore(RefCell<Option<HashSet<Rc<ExprHandle>>>>);
impl BorrowedExprStore {
	pub(crate) fn new() -> Self { Self(RefCell::new(Some(HashSet::new()))) }
	pub async fn dispose(self) {
		let elements = self.0.borrow_mut().take().unwrap();
		for handle in elements {
			handle.drop_one().await
		}
	}
}
impl Drop for BorrowedExprStore {
	fn drop(&mut self) {
		if self.0.borrow().is_some() {
			panic!("This should always be explicitly disposed")
		}
	}
}

#[derive(destructure)]
pub struct ExprHandle {
	pub tk: api::ExprTicket,
	pub ctx: SysCtx,
}
impl ExprHandle {
	/// This function does not signal to take ownership of the expr.
	pub fn borrowed(ctx: SysCtx, tk: api::ExprTicket, store: &BorrowedExprStore) -> Rc<Self> {
		let this = Rc::new(Self { ctx, tk });
		store.0.borrow_mut().as_mut().unwrap().insert(this.clone());
		this
	}
	pub fn deserialize(ctx: SysCtx, tk: api::ExprTicket) -> Rc<Self> { Rc::new(Self { ctx, tk }) }
	pub fn get_ctx(&self) -> SysCtx { self.ctx.clone() }
	/// Drop one instance of the handle silently; if it's the last one, do
	/// nothing, otherwise send an Acquire
	pub async fn drop_one(self: Rc<Self>) {
		match Rc::try_unwrap(self) {
			Err(rc) => rc.ctx.reqnot().notify(api::Acquire(rc.ctx.sys_id(), rc.tk)).await,
			Ok(hand) => {
				// avoid calling destructor
				hand.destructure();
			},
		}
	}
	/// Drop the handle and get the ticket without a release notification.
	/// Use this with messages that imply ownership transfer. This function is
	/// safe because abusing it is a memory leak.
	pub fn serialize(self) -> api::ExprTicket { self.destructure().0 }
}
impl Eq for ExprHandle {}
impl PartialEq for ExprHandle {
	fn eq(&self, other: &Self) -> bool {
		self.ctx.sys_id() == other.ctx.sys_id() && self.tk == other.tk
	}
}
impl Hash for ExprHandle {
	fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
		self.ctx.sys_id().hash(state);
		self.tk.hash(state);
	}
}
impl fmt::Debug for ExprHandle {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		write!(f, "ExprHandle({})", self.tk.0)
	}
}
impl Drop for ExprHandle {
	fn drop(&mut self) {
		let notif = api::Release(self.ctx.sys_id(), self.tk);
		let reqnot = self.ctx.reqnot().clone();
		self.ctx.spawner()(Box::pin(async move { reqnot.notify(notif).await }))
	}
}

#[derive(Clone, Debug, destructure)]
pub struct Expr {
	handle: Rc<ExprHandle>,
	data: Rc<OnceCell<ExprData>>,
}
impl Expr {
	pub fn from_handle(handle: Rc<ExprHandle>) -> Self { Self { handle, data: Rc::default() } }
	pub fn new(handle: Rc<ExprHandle>, d: ExprData) -> Self {
		Self { handle, data: Rc::new(OnceCell::from(d)) }
	}

	pub async fn data(&self) -> &ExprData {
		(self.data.get_or_init(async {
			let details = self.handle.ctx.reqnot().request(api::Inspect { target: self.handle.tk }).await;
			let pos = Pos::from_api(&details.location, self.handle.ctx.i()).await;
			let kind = match details.kind {
				api::InspectedKind::Atom(a) =>
					ExprKind::Atom(ForeignAtom::new(self.handle.clone(), a, pos.clone())),
				api::InspectedKind::Bottom(b) =>
					ExprKind::Bottom(OrcErrv::from_api(&b, self.handle.ctx.i()).await),
				api::InspectedKind::Opaque => ExprKind::Opaque,
			};
			ExprData { pos, kind }
		}))
		.await
	}
	pub async fn atom(self) -> Result<ForeignAtom, Self> {
		match self.data().await {
			ExprData { kind: ExprKind::Atom(atom), .. } => Ok(atom.clone()),
			_ => Err(self),
		}
	}
	pub fn handle(&self) -> Rc<ExprHandle> { self.handle.clone() }
	pub fn ctx(&self) -> SysCtx { self.handle.ctx.clone() }

	pub fn slot(&self) -> GExpr {
		GExpr { pos: Pos::SlotTarget, kind: GExprKind::Slot(self.clone()) }
	}
}
impl Format for Expr {
	async fn print<'a>(&'a self, _c: &'a (impl FmtCtx + ?Sized + 'a)) -> FmtUnit {
		match &self.data().await.kind {
			ExprKind::Opaque => "OPAQUE".to_string().into(),
			ExprKind::Bottom(b) => format!("Bottom({b})").into(),
			ExprKind::Atom(a) => FmtUnit::from_api(
				&self.handle.ctx.reqnot().request(api::ExtAtomPrint(a.atom.clone())).await,
			),
		}
	}
}

#[derive(Clone, Debug)]
pub struct ExprData {
	pub pos: Pos,
	pub kind: ExprKind,
}

#[derive(Clone, Debug)]
pub enum ExprKind {
	Atom(ForeignAtom),
	Bottom(OrcErrv),
	Opaque,
}