use std::{path::PathBuf, sync::{Arc, mpsc}, io};

use neon::{prelude::*, result::Throw};
use once_cell::sync::OnceCell;
use thiserror::Error;
use veilid_core::{CryptoKind, CryptoTyped, KeyPair, CRYPTO_KIND_VLD0, VeilidAPI, api_startup_json, VeilidAPIError};

// #[derive(Error, Debug)]
// pub enum BindingsError {
//     #[error(transparent)]
//     VeilidAPIError (#[from] VeilidAPIError),
//     #[error(transparent)]
//     Throw (#[from] Throw)
// }

fn make_runtime<'a, C: Context<'a>>(cx: &mut C) -> NeonResult<&'static tokio::runtime::Runtime> {
	static RUNTIME: OnceCell<tokio::runtime::Runtime> = OnceCell::new();

	RUNTIME.get_or_try_init(||
		tokio::runtime::Runtime::new()
			.or_else(|error| cx.throw_error(error.to_string()))
	)
}

// fn hello(mut cx: FunctionContext) -> JsResult<JsString> {
//     Ok(cx.string(veilid_core::veilid_version_string()))
// }

// fn async_hello(mut cx: FunctionContext) -> JsResult<JsPromise> {
//     let runtime = make_runtime(&mut cx)?;
//     let (deferred, promise) = cx.promise();
//     let channel = cx.channel();

//     runtime.spawn(async move {
//         let result = veilid_core::veilid_version_string();

//         deferred.settle_with(&channel, |mut cx| {
//             Ok(cx.string(result))
//         });
//     });

//     Ok(promise)
// }

// CryptoKind

#[derive(Clone, Copy)]
struct NoFinalize<V>(V);

impl<V> Finalize for NoFinalize<V> {
	fn finalize<'a, C: Context<'a>>(self, _: &mut C) {
		// nothing to do
	}
}

impl<V> NoFinalize<V> {
	fn unbox(self) -> V {
		self.0
	}
}

// trait FunctionContextExt {
//     fn simple_boxed<U: Send>(&mut self, value: U) -> Handle<JsBox<NoFinalize<U>>>;
// }

// impl<'a> FunctionContextExt for FunctionContext<'a> {
//     fn simple_boxed<U: Send>(&mut self, value: U) -> Handle<JsBox<NoFinalize<U>>> {
//         self.boxed(NoFinalize(value))
//     }
// }

type BoxedKeypair = JsBox<NoFinalize<CryptoTyped<KeyPair>>>;
type BoxedCryptoKind = JsBox<NoFinalize<CryptoKind>>;
type BoxedPathBuf = JsBox<NoFinalize<PathBuf>>;
type BoxedLibraryCore = JsBox<LibraryCore>;

// Type utility functions
fn make_path(mut cx: FunctionContext) -> JsResult<BoxedPathBuf> {
	let path_string = cx.argument
		::<JsString>(0)?
		.value(&mut cx);

	Ok(cx.boxed(NoFinalize(PathBuf::from(path_string))))
}

// Library API
fn crypto_generate_keypair(mut cx: FunctionContext) -> JsResult<BoxedKeypair> {
	let crypto_kind = cx.argument
		::<BoxedCryptoKind>(0)?
		.unbox();

	let keypair = veilid_core::Crypto::generate_keypair(crypto_kind)
		.or_else(|err| cx.throw_error(err.to_string()))?;

	Ok(cx.boxed(NoFinalize(keypair)))
}

#[derive(Debug)]
struct LibraryCore {
	api: VeilidAPI
}

impl Finalize for LibraryCore {
	fn finalize<'a, C: Context<'a>>(self, _: &mut C) {
		// FIXME
	}
}

impl LibraryCore {
	fn from_json(mut cx: FunctionContext,) -> JsResult<JsPromise> {
		// 0: update_callback
		// 1: json_config

		let update_callback = cx.argument
			::<JsFunction>(0)?
			.root(&mut cx); // To allow sending to a different thread

		let json_config = cx.argument
			::<JsString>(1)?
			.value(&mut cx);

		let runtime = make_runtime(&mut cx)?;
		let (deferred, promise) = cx.promise();
		let startup_channel = cx.channel();
		let (update_sender, update_receiver) = flume::unbounded();

		//

		let _startup_task = runtime.spawn(async move {
			let update_handler = Arc::new(move |update| {
				let result = update_sender.send(update);

				if let Err(error) = result {
					// FIXME: Don't just dump this to console!
					println!("failed to send veilid update from callback: {:?}", error.into_inner());
				}
			});

			let core_result = async {
				let api = api_startup_json(update_handler, json_config).await?;
				let core = LibraryCore { api: api };
				Ok(core)
			}.await;

			deferred.settle_with(&startup_channel, |mut cx| {
				let core = core_result.or_else(|err: VeilidAPIError| cx.throw_error(err.to_string()))?;
				
				let object = cx.empty_object();

				let _ref = cx.boxed(core);
				object.set(&mut cx, "_ref", _ref)?;

				let test = JsFunction::new(&mut cx, LibraryCore::test)?;
				object.set(&mut cx, "test", test)?;

				let test2 = JsFunction::new(&mut cx, LibraryCore::test2)?;
				object.set(&mut cx, "test2", test2)?;

				Ok(object)
			});
		});

		let update_channel = cx.channel();

		let _calling_task = runtime.spawn(async move {
			loop {
				let update = update_receiver.recv_async().await;
				let update_callback = update_callback.clone(&mut cx);

				update_channel.send(move |mut cx| {
					update_callback
						.into_inner(&mut cx) // Unpack original callback
						.call_with(&mut cx)
						.arg(cx.string(format!("{:?}", update)))
						.apply::<JsUndefined, _>(&mut cx);

					Ok(())
				}).join(); // FIXME: This will probably block?
			}
		});

		Ok(promise)
	}

	fn test(mut cx: FunctionContext) -> JsResult<JsString> {
		let this = cx.this()
			.get_value(&mut cx, "_ref")?
			.downcast_or_throw::<BoxedLibraryCore, _>(&mut cx)?;

		println!("{:?}", this);
		Ok(cx.string(format!("{:?}", &this.api)))
	}

	fn test2(mut cx: FunctionContext) -> JsResult<JsString> {
		let this = cx.this()
			.get_value(&mut cx, "_ref")?
			.downcast_or_throw::<BoxedLibraryCore, _>(&mut cx)?;

		println!("{:?}", this);
		Ok(cx.string(format!("{:?}", &this.api)))
	}
}

#[neon::main]
fn main(mut cx: ModuleContext) -> NeonResult<()> {
	cx.export_function("makePath", make_path)?;
	cx.export_function("crypto_generateKeypair", crypto_generate_keypair)?;
	cx.export_function("libraryCore_fromJSON", LibraryCore::from_json)?;

	let crypto_kind_vld0 = cx.boxed(NoFinalize(CRYPTO_KIND_VLD0));
	cx.export_value("CRYPTO_KIND_VLD0", crypto_kind_vld0)?;
	Ok(())
}