use std::{future::Future, marker::PhantomData, sync::RwLock};

use once_cell::sync::Lazy;
use tokio::runtime::Runtime;

use crate::{sys, JsDeferred, JsUnknown, NapiValue, Result};

fn create_runtime() -> Option<Runtime> {
  #[cfg(not(target_os = "wasi"))]
  {
    let runtime = tokio::runtime::Runtime::new().expect("Create tokio runtime failed");
    Some(runtime)
  }

  #[cfg(target_os = "wasi")]
  {
    tokio::runtime::Builder::new_current_thread()
      .enable_all()
      .build()
      .ok()
  }
}

pub(crate) static RT: Lazy<RwLock<Option<Runtime>>> = Lazy::new(|| RwLock::new(create_runtime()));

#[cfg(not(any(target_os = "macos", target_os = "wasi")))]
static RT_REFERENCE_COUNT: std::sync::atomic::AtomicUsize = std::sync::atomic::AtomicUsize::new(0);

/// Ensure that the Tokio runtime is initialized.
/// In windows the Tokio runtime will be dropped when Node env exits.
/// But in Electron renderer process, the Node env will exits and recreate when the window reloads.
/// So we need to ensure that the Tokio runtime is initialized when the Node env is created.
#[cfg(not(any(target_os = "macos", target_os = "wasi")))]
pub(crate) fn ensure_runtime() {
  use std::sync::atomic::Ordering;

  let mut rt = RT.write().unwrap();
  if rt.is_none() {
    *rt = create_runtime();
  }

  RT_REFERENCE_COUNT.fetch_add(1, Ordering::Relaxed);
}

#[cfg(not(any(target_os = "macos", target_os = "wasi")))]
pub(crate) unsafe extern "C" fn drop_runtime(_arg: *mut std::ffi::c_void) {
  use std::sync::atomic::Ordering;

  if RT_REFERENCE_COUNT.fetch_sub(1, Ordering::AcqRel) == 1 {
    RT.write().unwrap().take();
  }
}

/// Spawns a future onto the Tokio runtime.
///
/// Depending on where you use it, you should await or abort the future in your drop function.
/// To avoid undefined behavior and memory corruptions.
pub fn spawn<F>(fut: F) -> tokio::task::JoinHandle<F::Output>
where
  F: 'static + Send + Future<Output = ()>,
{
  RT.read().unwrap().as_ref().unwrap().spawn(fut)
}

/// Runs a future to completion
/// This is blocking, meaning that it pauses other execution until the future is complete,
/// only use it when it is absolutely necessary, in other places use async functions instead.
pub fn block_on<F>(fut: F) -> F::Output
where
  F: 'static + Send + Future<Output = ()>,
{
  RT.read().unwrap().as_ref().unwrap().block_on(fut)
}

// This function's signature must be kept in sync with the one in lib.rs, otherwise napi
// will fail to compile with the `tokio_rt` feature.

/// If the feature `tokio_rt` has been enabled this will enter the runtime context and
/// then call the provided closure. Otherwise it will just call the provided closure.
#[inline]
pub fn within_runtime_if_available<F: FnOnce() -> T, T>(f: F) -> T {
  let _rt_guard = RT.read().unwrap().as_ref().unwrap().enter();
  f()
}

struct SendableResolver<
  Data: 'static + Send,
  R: 'static + FnOnce(sys::napi_env, Data) -> Result<sys::napi_value>,
> {
  inner: R,
  _data: PhantomData<Data>,
}

// the `SendableResolver` will be only called in the `threadsafe_function_call_js` callback
// which means it will be always called in the Node.js JavaScript thread
// so the inner function is not required to be `Send`
// but the `Send` bound is required by the `execute_tokio_future` function
unsafe impl<Data: 'static + Send, R: 'static + FnOnce(sys::napi_env, Data) -> Result<sys::napi_value>>
  Send for SendableResolver<Data, R>
{
}

impl<Data: 'static + Send, R: 'static + FnOnce(sys::napi_env, Data) -> Result<sys::napi_value>>
  SendableResolver<Data, R>
{
  fn new(inner: R) -> Self {
    Self {
      inner,
      _data: PhantomData,
    }
  }

  fn resolve(self, env: sys::napi_env, data: Data) -> Result<sys::napi_value> {
    (self.inner)(env, data)
  }
}

#[allow(clippy::not_unsafe_ptr_arg_deref)]
pub fn execute_tokio_future<
  Data: 'static + Send,
  Fut: 'static + Send + Future<Output = Result<Data>>,
  Resolver: 'static + FnOnce(sys::napi_env, Data) -> Result<sys::napi_value>,
>(
  env: sys::napi_env,
  fut: Fut,
  resolver: Resolver,
) -> Result<sys::napi_value> {
  let (deferred, promise) = JsDeferred::new(env)?;

  let sendable_resolver = SendableResolver::new(resolver);

  let inner = async {
    match fut.await {
      Ok(v) => deferred.resolve(move |env| {
        sendable_resolver
          .resolve(env.raw(), v)
          .map(|v| unsafe { JsUnknown::from_raw_unchecked(env.raw(), v) })
      }),
      Err(e) => deferred.reject(e),
    }
  };

  #[cfg(not(target_os = "wasi"))]
  spawn(inner);

  #[cfg(target_os = "wasi")]
  {
    std::thread::spawn(|| {
      block_on(inner);
    });
  }

  Ok(promise.0.value)
}