use std::any::TypeId;
use std::borrow::Cow;
use std::collections::HashMap;
use std::future::Future;
use std::pin::Pin;
use std::rc::Rc;

use futures::future::LocalBoxFuture;
use futures::lock::Mutex;
use futures::{AsyncWrite, FutureExt};
use itertools::Itertools;
use never::Never;
use orchid_api_traits::Encode;
use orchid_base::clone;
use orchid_base::error::OrcRes;
use orchid_base::format::{FmtCtx, FmtUnit};
use orchid_base::name::Sym;
use trait_set::trait_set;

use crate::atom::Atomic;
use crate::atom_owned::{DeserializeCtx, OwnedAtom, OwnedVariant};
use crate::context::{SysCtxEntry, ctx, i};
use crate::conv::ToExpr;
use crate::coroutine_exec::{ExecHandle, exec};
use crate::expr::Expr;
use crate::gen_expr::GExpr;

trait_set! {
	trait FunCB = Fn(Vec<Expr>) -> LocalBoxFuture<'static, OrcRes<GExpr>> + 'static;
}

pub trait ExprFunc<I, O>: Clone + 'static {
	fn argtyps() -> &'static [TypeId];
	fn apply<'a>(&self, hand: ExecHandle<'a>, v: Vec<Expr>) -> impl Future<Output = OrcRes<GExpr>>;
}

#[derive(Default)]
struct FunsCtx(Mutex<HashMap<Sym, FunRecord>>);
impl SysCtxEntry for FunsCtx {}
#[derive(Clone)]
struct FunRecord {
	argtyps: &'static [TypeId],
	fun: Rc<dyn FunCB>,
}

fn process_args<I, O, F: ExprFunc<I, O>>(f: F) -> FunRecord {
	let argtyps = F::argtyps();
	let fun = Rc::new(move |v: Vec<Expr>| {
		clone!(f, v mut);
		exec(async move |mut hand| {
			let mut norm_args = Vec::with_capacity(v.len());
			for (expr, typ) in v.into_iter().zip(argtyps) {
				if *typ != TypeId::of::<Expr>() {
					norm_args.push(hand.exec(expr).await?);
				}
			}
			f.apply(hand, norm_args).await
		})
		.map(Ok)
		.boxed_local()
	});
	FunRecord { argtyps, fun }
}

/// An Atom representing a partially applied named native function. These
/// partial calls are serialized into the name of the native function and the
/// argument list.
///
/// See [Lambda] for the non-serializable variant
#[derive(Clone)]
pub(crate) struct Fun {
	path: Sym,
	args: Vec<Expr>,
	record: FunRecord,
}
impl Fun {
	pub async fn new<I, O, F: ExprFunc<I, O>>(path: Sym, f: F) -> Self {
		let ctx = ctx();
		let funs: &FunsCtx = ctx.get_or_default();
		let mut fung = funs.0.lock().await;
		let record = if let Some(record) = fung.get(&path) {
			record.clone()
		} else {
			let record = process_args(f);
			fung.insert(path.clone(), record.clone());
			record
		};
		Self { args: vec![], path, record }
	}
	pub fn arity(&self) -> u8 { self.record.argtyps.len() as u8 }
}
impl Atomic for Fun {
	type Data = ();
	type Variant = OwnedVariant;
}
impl OwnedAtom for Fun {
	type Refs = Vec<Expr>;
	async fn val(&self) -> Cow<'_, Self::Data> { Cow::Owned(()) }
	async fn call_ref(&self, arg: Expr) -> GExpr {
		let new_args = self.args.iter().cloned().chain([arg]).collect_vec();
		if new_args.len() == self.record.argtyps.len() {
			(self.record.fun)(new_args).await.to_gen().await
		} else {
			Self { args: new_args, record: self.record.clone(), path: self.path.clone() }.to_gen().await
		}
	}
	async fn call(self, arg: Expr) -> GExpr { self.call_ref(arg).await }
	async fn serialize(&self, write: Pin<&mut (impl AsyncWrite + ?Sized)>) -> Self::Refs {
		self.path.to_api().encode(write).await;
		self.args.clone()
	}
	async fn deserialize(mut ds_cx: impl DeserializeCtx, args: Self::Refs) -> Self {
		let path = Sym::from_api(ds_cx.decode().await, &i()).await;
		let record = (ctx().get::<FunsCtx>().0.lock().await.get(&path))
			.expect("Function missing during deserialization")
			.clone();
		Self { args, path, record }
	}
	async fn print_atom<'a>(&'a self, _: &'a (impl FmtCtx + ?Sized + 'a)) -> FmtUnit {
		format!("{}:{}/{}", self.path, self.args.len(), self.arity()).into()
	}
}

/// An Atom representing a partially applied native lambda. These are not
/// serializable.
///
/// See [Fun] for the serializable variant
#[derive(Clone)]
pub struct Lambda {
	args: Vec<Expr>,
	record: FunRecord,
}
impl Lambda {
	pub fn new<I, O, F: ExprFunc<I, O>>(f: F) -> Self {
		Self { args: vec![], record: process_args(f) }
	}
}
impl Atomic for Lambda {
	type Data = ();
	type Variant = OwnedVariant;
}
impl OwnedAtom for Lambda {
	type Refs = Never;
	async fn val(&self) -> Cow<'_, Self::Data> { Cow::Owned(()) }
	async fn call_ref(&self, arg: Expr) -> GExpr {
		let new_args = self.args.iter().cloned().chain([arg]).collect_vec();
		if new_args.len() == self.record.argtyps.len() {
			(self.record.fun)(new_args).await.to_gen().await
		} else {
			Self { args: new_args, record: self.record.clone() }.to_gen().await
		}
	}
	async fn call(self, arg: Expr) -> GExpr { self.call_ref(arg).await }
}

mod expr_func_derives {
	use std::any::TypeId;
	use std::sync::OnceLock;

	use orchid_base::error::OrcRes;

	use super::ExprFunc;
	use crate::conv::{ToExpr, TryFromExpr};
	use crate::func_atom::{ExecHandle, Expr};
	use crate::gen_expr::GExpr;

	macro_rules! expr_func_derive {
    ($($t:ident),*) => {
      pastey::paste!{
        impl<
          $($t: TryFromExpr + 'static, )*
					Out: ToExpr,
          Func: AsyncFn($($t,)*) -> Out + Clone + 'static
        > ExprFunc<($($t,)*), Out> for Func {
          fn argtyps() -> &'static [TypeId] {
            static STORE: OnceLock<Vec<TypeId>> = OnceLock::new();
            &*STORE.get_or_init(|| vec![$(TypeId::of::<$t>()),*])
          }
          async fn apply<'a>(&self, _: ExecHandle<'a>, v: Vec<Expr>) -> OrcRes<GExpr> {
            assert_eq!(v.len(), Self::argtyps().len(), "Arity mismatch");
            let [$([< $t:lower >],)*] = v.try_into().unwrap_or_else(|_| panic!("Checked above"));
            Ok(self($($t::try_from_expr([< $t:lower >]).await?,)*).await.to_gen().await)
          }
        }
      }
    };
  }
	expr_func_derive!(A);
	expr_func_derive!(A, B);
	expr_func_derive!(A, B, C);
	expr_func_derive!(A, B, C, D);
	expr_func_derive!(A, B, C, D, E);
	// expr_func_derive!(A, B, C, D, E, F);
	// expr_func_derive!(A, B, C, D, E, F, G);
	// expr_func_derive!(A, B, C, D, E, F, G, H);
	// expr_func_derive!(A, B, C, D, E, F, G, H, I);
	// expr_func_derive!(A, B, C, D, E, F, G, H, I, J);
	// expr_func_derive!(A, B, C, D, E, F, G, H, I, J, K);
	// expr_func_derive!(A, B, C, D, E, F, G, H, I, J, K, L);
	// expr_func_derive!(A, B, C, D, E, F, G, H, I, J, K, L, M);
	// expr_func_derive!(A, B, C, D, E, F, G, H, I, J, K, L, M, N);
}