//! This module contains runtime and application related handles.
//!
//! _Browser Window_ needs to be initialized, and also run its own runtime.
//! Once that is set up and running, all windows can be constructed and be used.
//! To do this, use `Application::initialize`.
//! Then you will have an `Application` instance, from which you can derive a
//! `Runtime` instance. Running the `Runtime` will grant you access to an
//! `ApplicationHandle` which you use to manipulate your application with.
//!
//! # Example #1
//! Here is an example to show how you can construct your application:
//! ```
//! use std::process;
//!
//! use browser_window::application::*;
//!
//! fn main() {
//! 	let application = Application::initialize(&ApplicationSettings::default()).unwrap();
//! 	let runtime = application.start();
//!
//! 	let exit_code = runtime.run_async(|handle| async move {
//! 		// Do something ...
//!
//! 		// Not normally needed:
//! 		handle.exit(0);
//! 	});
//!
//! 	process::exit(exit_code);
//! }
//! ```
#![cfg_attr(
	not(feature = "threadsafe"),
	doc = r#"
_Browser Window_ also supports manipulating the GUI from other threads with thread-safe handles.
To use these, enable the `threadsafe` feature.
"#
)]
#![cfg_attr(
	feature = "threadsafe",
	doc = r#"
# Example #2

If you want to run another kind of runtime, like [tokio](https://tokio.rs/) for example, its still possible to use _Browser Window_ in conjunction with that.
However, you will need to enable feature `threadsafe`, as it will enable all threadsafe handles.
Here is an example:

```rust
use std::process;
use browser_window::application::*;
use tokio;

async fn async_main( app: ApplicationHandleThreaded ) {
	// Do something ...

	app.exit(0);
}

fn main() {
	let application = Application::initialize( &ApplicationSettings::default() ).unwrap();
	let bw_runtime = application.start();

	let tokio_runtime = tokio::runtime::Runtime::new().unwrap();

	// First run our own runtime on the main thread
	let exit_code = bw_runtime.run(|_app| {
		let app = _app.into_threaded();

		// Spawn the main logic into the tokio runtime
		tokio_runtime.spawn( async_main( app ) );
	});

	process::exit(exit_code);
}
```"#
)]

#[cfg(feature = "threadsafe")]
use std::ops::Deref;
use std::{
	env,
	ffi::CString,
	future::Future,
	os::raw::c_int,
	path::PathBuf,
	pin::Pin,
	ptr,
	task::{Context, Poll, RawWaker, RawWakerVTable, Waker},
	time::Duration,
};

use futures_channel::oneshot;
use lazy_static::lazy_static;

#[cfg(feature = "threadsafe")]
use crate::delegate::*;
use crate::{cookie::CookieJar, core::application::*, error};

/// Use this to initialize and start your application with.
pub struct Application {
	pub(super) handle: ApplicationHandle,
}

/// *Note:* Only available with feature `threadsafe` enabled.
///
/// A thread-safe application handle.
/// This handle also allows you to dispatch code to be executed on the GUI
/// thread from any other thread.
#[cfg(feature = "threadsafe")]
#[derive(Clone)]
pub struct ApplicationHandleThreaded {
	pub(super) handle: ApplicationHandle,
}
#[cfg(feature = "threadsafe")]
unsafe impl Send for ApplicationHandleThreaded {}
#[cfg(feature = "threadsafe")]
unsafe impl Sync for ApplicationHandleThreaded {}

#[derive(Clone)]
/// A thread-unsafe application handle.
/// Often provided by for Browser Window.
pub struct ApplicationHandle {
	pub(super) inner: ApplicationImpl,
}

struct ApplicationDispatchData<'a> {
	handle: ApplicationHandle,
	func: Box<dyn FnOnce(&ApplicationHandle) + 'a>,
}

#[cfg(feature = "threadsafe")]
struct ApplicationDispatchSendData<'a> {
	handle: ApplicationHandle,
	func: Box<dyn FnOnce(&ApplicationHandle) + Send + 'a>,
}

#[derive(Default)]
pub struct ApplicationSettings {
	/// CEF only: If set, the path of the seperate executable that gets compiled
	/// together with your main executable. If not set, no seperate executable
	/// will be used.
	pub engine_seperate_executable_path: Option<PathBuf>,
	/// If set, this path will be where the browser framework will look for
	/// resources/assets. If not set, it will default to the directory where the
	/// executable is located.
	pub resource_dir: Option<PathBuf>,
	/// CEF only: If set, will enable remote debugging at this port.
	pub remote_debugging_port: Option<u16>,
}

// The trait to be implemented by all (user-level) handles that are able to
// return an ApplicationHandle. Like: Application, ApplicationAsync,
// BrowserWindow, BrowserWindowAsync
pub trait HasAppHandle {
	fn app_handle(&self) -> &ApplicationHandle;
}

/// The runtime to run the application with.
///
/// This runtime will run until all windows have been closed _and_ the (async)
/// closure given to the `run*` functions have ended.
pub struct Runtime {
	pub(super) handle: ApplicationHandle,
}

/// The data that is available to a waker, allowing it to poll a future.
struct WakerData<'a> {
	handle: ApplicationHandle,
	future: Pin<Box<dyn Future<Output = ()> + 'a>>,
}

/// The future that dispatches a closure onto the GUI thread
#[cfg(feature = "threadsafe")]
pub type ApplicationDelegateFuture<'a, R> =
	DelegateFuture<'a, ApplicationHandle, ApplicationHandle, R>;

lazy_static! {
	static ref WAKER_VTABLE: RawWakerVTable =
		RawWakerVTable::new(waker_clone, waker_wake, waker_wake_by_ref, waker_drop);
}

impl Application {
	/// Prepares the os args as a vector of C compatible pointers.
	fn args_ptr_vec() -> (Vec<CString>, Vec<*mut u8>) {
		let args = env::args_os();
		let mut vec = Vec::with_capacity(args.len());
		let mut vec_ptrs = Vec::with_capacity(args.len());

		for arg in args {
			let string = CString::new(arg.to_string_lossy().to_string())
				.expect("Unable to convert OsString into CString!");

			vec_ptrs.push(string.as_ptr() as _);

			vec.push(string);
		}

		(vec, vec_ptrs)
	}

	/// Shuts down other processes and performs any necessary clean-up code.
	/// This is useful if you main function doesn't exit naturally.
	/// If you call `std::process::exit`, the variables currently available
	/// don't get dropped. This is problematic because Browser Window needs to
	/// shut down properly. Call this if you are using `exit` or doing something
	/// else to kill the process.
	pub fn finish(self) {}

	/// In order to use the Browser Window API, you need to initialize Browser
	/// Window at the very start of your application. Preferably on the first
	/// line of your `main` function.
	///
	/// # Warning
	/// This will open another process of your application.
	/// Therefore, any code that will be placed before initialization will also
	/// be executed on all other processes. This is generally unnecessary.
	///
	/// # Arguments
	/// `settings` - Some settings that allow you to tweak some application
	/// behaviors.              Use `Settings::default()` for default settings
	/// that work for most people.
	pub fn initialize(settings: &ApplicationSettings) -> error::Result<Application> {
		let (args_vec, mut ptrs_vec) = Self::args_ptr_vec();
		let argc: c_int = args_vec.len() as _;
		let argv = ptrs_vec.as_mut_ptr();

		let core_handle = ApplicationImpl::initialize(argc, argv as _, settings)?;

		Ok(Application::from_core_handle(core_handle))
	}

	/// Creates a `Runtime` from which you can run the application.
	pub fn start(&self) -> Runtime {
		Runtime {
			handle: unsafe { self.handle.clone() },
		}
	}
}

impl Drop for Application {
	fn drop(&mut self) { self.handle.inner.free() }
}

impl ApplicationSettings {
	pub fn default_resource_path() -> PathBuf {
		let mut path = env::current_exe().unwrap();
		path.pop();

		#[cfg(debug_assertions)]
		{
			path.pop();
			path.pop();
		}

		path.push("resources");

		path
	}
}

impl Runtime {
	/// Polls a future given a pointer to the waker data.
	fn poll_future(data: *mut WakerData) {
		debug_assert!(data != ptr::null_mut(), "WakerData pointer can't be zero!");

		// TODO: Test if polling from the right thread

		let waker = Self::new_waker(data);
		let mut ctx = Context::from_waker(&waker);

		let result = unsafe { (*data).future.as_mut().poll(&mut ctx) };

		// When the future is ready, free the memory allocated for the waker data
		match result {
			Poll::Ready(_) => {
				let _ = unsafe { Box::from_raw(data) };
			}
			Poll::Pending => {}
		}
	}

	/// Constructs a `Waker` for our runtime
	fn new_waker(data: *mut WakerData) -> Waker {
		debug_assert!(data != ptr::null_mut(), "WakerData pointer can't be zero!");

		unsafe { Waker::from_raw(RawWaker::new(data as _, &WAKER_VTABLE)) }
	}

	/// Run the main loop and executes the given closure on it.
	///
	/// # Arguments
	/// * `on_ready` - This closure will be called when the runtime has
	///   initialized, and will provide the caller with an application handle.
	///
	/// # Reserved Codes
	/// -1 is used as the return code for when the main thread panicked during a
	/// delegated closure.
	pub fn run<H>(&self, on_ready: H) -> i32
	where
		H: FnOnce(ApplicationHandle),
	{
		return self._run(|handle| {
			let result = on_ready(unsafe { handle.clone() });
			handle.inner.mark_as_done();

			result
		});
	}

	/// Runs the main loop and executes the given future within that loop.
	/// This function exits when the future finishes or when `exit` is called.
	///
	/// Keep in mind that calls to async functions or futures may not
	/// necessarily finish. Exiting the application causes the runtime to stop,
	/// and it doesn't necessarily complete all waiting tasks.
	///
	/// # Reserved Codes
	/// The same reserved codes apply as `run`.
	pub fn run_async<'a, C, F>(&'a self, func: C) -> i32
	where
		C: FnOnce(ApplicationHandle) -> F + 'a,
		F: Future<Output = ()> + 'a,
	{
		self._run(|handle| {
			self.spawn(async move {
				func(unsafe { handle.clone() }).await;
				handle.inner.mark_as_done();
			});
		})
	}

	/// Use `run_async` instead.
	pub fn spawn<'a, F>(&'a self, future: F)
	where
		F: Future<Output = ()> + 'a,
	{
		// Data for the waker.
		let waker_data = Box::into_raw(Box::new(WakerData {
			handle: unsafe { self.handle.clone() },
			future: Box::pin(future),
		}));

		// First poll
		Runtime::poll_future(waker_data);
	}

	fn _run<'a, H>(&self, on_ready: H) -> i32
	where
		H: FnOnce(ApplicationHandle) + 'a,
	{
		let ready_data = Box::into_raw(Box::new(on_ready));

		self.handle.inner.run(ready_handler::<H>, ready_data as _)
	}
}

impl Application {
	/// Constructs an `Application` from a ffi handle
	pub(super) fn from_core_handle(inner: ApplicationImpl) -> Self {
		Self {
			handle: ApplicationHandle::new(inner),
		}
	}
}

impl From<ApplicationHandle> for Application {
	fn from(other: ApplicationHandle) -> Self { Self { handle: other } }
}

impl ApplicationHandle {
	/// Returns an instance of a `CookieJar`, if the underlying browser
	/// framework supports it. Currently, only CEF supports cookies.
	pub fn cookie_jar(&self) -> Option<CookieJar> { CookieJar::global() }

	pub(crate) unsafe fn clone(&self) -> Self {
		Self {
			inner: self.inner.clone(),
		}
	}

	/// Causes the `Runtime` to terminate.
	/// The `Runtime`'s [`Runtime::run`] or spawn command will return the exit
	/// code provided. This will mean that not all tasks might complete.
	/// If you were awaiting
	pub fn exit(&self, exit_code: i32) { self.inner.exit(exit_code as _); }

	pub(super) fn new(inner: ApplicationImpl) -> Self { Self { inner } }

	/// **Note:** Only available with feature `threadsafe` enabled.
	///
	/// Transforms this application handle into a thread-safe version of it.
	#[cfg(feature = "threadsafe")]
	pub fn into_threaded(self) -> ApplicationHandleThreaded { self.into() }

	/// Spawns the given future, executing it on the GUI thread somewhere in the
	/// near future.
	pub fn spawn<F>(&self, future: F)
	where
		F: Future<Output = ()> + 'static,
	{
		// Data for the waker.
		let waker_data = Box::into_raw(Box::new(WakerData {
			handle: unsafe { self.clone() },
			future: Box::pin(future),
		}));

		// First poll
		Runtime::poll_future(waker_data);
	}

	/// Queues the given closure `func` to be executed on the GUI thread
	/// somewhere in the future, at least after the given delay. The closure
	/// will only execute when and if the runtime is still running.
	/// Returns whether or not the closure will be able to execute.
	pub fn dispatch_delayed<'a, F>(&self, func: F, delay: Duration) -> bool
	where
		F: FnOnce(&ApplicationHandle) + 'a,
	{
		let data_ptr = Box::into_raw(Box::new(ApplicationDispatchData {
			handle: unsafe { self.app_handle().clone() },
			func: Box::new(func),
		}));

		self.inner
			.dispatch_delayed(dispatch_handler, data_ptr as _, delay)
	}

	/// Will wait the given `duration` before returning execution back to the
	/// caller. This does not put the current thread in a sleeping state, it
	/// just waits.
	pub async fn sleep(&self, duration: Duration) {
		let (tx, rx) = oneshot::channel::<()>();

		self.dispatch_delayed(
			|_handle| {
				if let Err(_) = tx.send(()) {
					panic!("unable to send signal back to sleeping function");
				}
			},
			duration,
		);

		rx.await.unwrap();
	}
}

#[cfg(feature = "threadsafe")]
impl ApplicationHandleThreaded {
	/// Executes the given closure `func` on the GUI thread, and gives back the
	/// result when done. This only works when the runtime is still running.
	/// If the closure panicked, or the runtime is not running, this will return
	/// an error.
	///
	/// The function signature is practically the same as:
	/// ```ignore
	/// pub async fn delegate<'a,F,R>( &self, func: F ) -> Result<R, DelegateError> where
	/// 	F: FnOnce( ApplicationHandle ) -> R + Send + 'a,
	/// 	R: Send { /* ... */ }
	/// ```
	///
	/// Keep in mind that in multi-threaded environments, it is generally a good
	/// idea to put the output on the heap. The output value _will_ be copied.
	///
	/// # Example
	/// ```ignore
	/// let my_value: String = app.delegate(|handle| {
	/// 	"string".to_owned()
	/// }).unwrap();
	/// ```
	pub fn delegate<'a, F, R>(&self, func: F) -> ApplicationDelegateFuture<'a, R>
	where
		F: FnOnce(&ApplicationHandle) -> R + Send + 'a,
		R: Send,
	{
		ApplicationDelegateFuture::<'a, R>::new(unsafe { self.handle.clone() }, |h| func(h))
	}

	/// Executes the given `future` on the GUI thread, and gives back its output
	/// when done. This only works when the runtime is still running.
	/// If the future panicked during a poll, or the runtime is not running,
	/// this will return an error. See also `delegate`.
	///
	/// The function signature is practically the same as:
	/// ```ignore
	/// pub async fn delegate_future<'a,F,R>( &self, func: F ) -> Result<R, DelegateError> where
	/// 	F: Future<Output=R> + 'static,
	/// 	R: Send { /* ... */ }
	/// ```
	///
	/// # Example
	/// ```ignore
	/// let my_value: String = app.delegate_future(async {
	/// 	"string".to_owned()
	/// }).unwrap();
	/// ```
	pub fn delegate_future<F, R>(&self, future: F) -> DelegateFutureFuture<R>
	where
		F: Future<Output = R> + 'static,
		R: Send + 'static,
	{
		DelegateFutureFuture::new(unsafe { self.handle.clone() }, future)
	}

	/// Executes the given async closure `func` on the GUI thread, and gives
	/// back the result when done. This only works when the runtime is still
	/// running. If the closure panicked, or the runtime is not running, this
	/// will return an error.
	///
	/// Except, async closures are not yet supported in stable Rust.
	/// What we actually mean are closures of the form:
	/// ```ignore
	/// |handle| async move { /* ... */ }
	/// ```
	///
	/// The function signature is practically the same as:
	/// ```ignore
	/// pub async fn delegate_async<'a,C,F,R>( &self, func: C ) -> Result<R, DelegateError> where
	/// 	C: FnOnce( ApplicationHandle ) -> F + Send + 'a,
	/// 	F: Future<Output=R>,
	/// 	R: Send + 'static
	/// { /* ... */ }
	/// ```
	///
	/// # Example
	/// ```ignore
	/// let my_value: String = app.delegate_async(|handle| async move {
	/// 	"String".to_owned()
	/// }).unwrap();
	/// ```
	pub fn delegate_async<'a, C, F, R>(&self, func: C) -> DelegateFutureFuture<'a, R>
	where
		C: FnOnce(ApplicationHandle) -> F + Send + 'a,
		F: Future<Output = R>,
		R: Send + 'static,
	{
		let handle = unsafe { self.handle.clone() };
		DelegateFutureFuture::new(unsafe { self.handle.clone() }, async move {
			func(handle.into()).await
		})
	}

	/// Queues the given closure `func` to be executed on the GUI thread
	/// somewhere in the future. The closure will only execute when and if the
	/// runtime is still running. Returns whether or not the closure will be
	/// able to execute.
	pub fn dispatch<'a, F>(&self, func: F) -> bool
	where
		F: FnOnce(&ApplicationHandle) + Send + 'a,
	{
		let data_ptr = Box::into_raw(Box::new(ApplicationDispatchSendData {
			handle: unsafe { self.handle.clone() },
			func: Box::new(func),
		}));

		self.handle
			.inner
			.dispatch(dispatch_handler_send, data_ptr as _)
	}

	/// Queues the given closure `func` to be executed on the GUI thread
	/// somewhere in the future, at least after the given delay. The closure
	/// will only execute when and if the runtime is still running.
	/// Returns whether or not the closure will be able to execute.
	pub fn dispatch_delayed<'a, F>(&self, func: F, delay: Duration) -> bool
	where
		F: FnOnce(&ApplicationHandle) + Send + 'a,
	{
		let data_ptr = Box::into_raw(Box::new(ApplicationDispatchData {
			handle: unsafe { self.handle.clone() },
			func: Box::new(func),
		}));

		self.handle
			.inner
			.dispatch_delayed(dispatch_handler, data_ptr as _, delay)
	}

	/// Queues the given async closure `func` to be executed on the GUI thread
	/// somewhere in the future. The closure will only execute when and if the
	/// runtime is still running. However, there is no guarantee that the whole
	/// closure will execute. The runtime might exit when the given closure is
	/// at a point of waiting. Returns whether or not the closure will be able
	/// to execute its first part.
	pub fn dispatch_async<'a, C, F>(&self, func: C) -> bool
	where
		C: FnOnce(ApplicationHandle) -> F + Send + 'a,
		F: Future<Output = ()> + 'static,
	{
		self.dispatch(|handle| {
			let future = func(unsafe { handle.clone() });
			handle.spawn(future);
		})
	}

	/// Signals the runtime to exit.
	/// This will cause `Runtime::run` to stop and return the provided exit
	/// code.
	pub fn exit(&self, exit_code: i32) {
		// The thread-safe version of bw_Application_exit:
		self.handle.inner.exit_threadsafe(exit_code as _);
	}

	/// Constructs an `ApplicationThreaded` handle from a ffi handle
	pub(super) fn from_core_handle(inner: ApplicationImpl) -> Self {
		Self {
			handle: ApplicationHandle::new(inner),
		}
	}

	/// Executes the given future on the GUI thread somewhere in the near
	/// future.
	pub fn spawn<F>(&self, future: F)
	where
		F: Future<Output = ()> + 'static,
	{
		self.handle.spawn(future);
	}
}

#[cfg(feature = "threadsafe")]
impl From<ApplicationHandle> for ApplicationHandleThreaded {
	fn from(other: ApplicationHandle) -> Self {
		Self {
			handle: unsafe { other.clone() },
		}
	}
}

#[cfg(feature = "threadsafe")]
impl Deref for ApplicationHandleThreaded {
	type Target = ApplicationHandle;

	fn deref(&self) -> &Self::Target { &self.handle }
}

impl HasAppHandle for ApplicationHandle {
	fn app_handle(&self) -> &ApplicationHandle { &self }
}

fn dispatch_handler(_app: ApplicationImpl, _data: *mut ()) {
	let data_ptr = _data as *mut ApplicationDispatchData<'static>;
	let data = unsafe { Box::from_raw(data_ptr) };

	(data.func)(&data.handle);
}

#[cfg(feature = "threadsafe")]
fn dispatch_handler_send(_app: ApplicationImpl, _data: *mut ()) {
	let data_ptr = _data as *mut ApplicationDispatchSendData<'static>;
	let data = unsafe { Box::from_raw(data_ptr) };

	(data.func)(&data.handle);
}

/// The handler that is invoked when the runtime is deemed 'ready'.
fn ready_handler<H>(handle: ApplicationImpl, user_data: *mut ())
where
	H: FnOnce(ApplicationHandle),
{
	let app = ApplicationHandle::new(handle);
	let closure = unsafe { Box::from_raw(user_data as *mut H) };

	closure(app);
}

/// A handler that is invoked by wakers.
fn wakeup_handler(_app: ApplicationImpl, user_data: *mut ()) {
	let data = user_data as *mut WakerData;

	Runtime::poll_future(data);
}

unsafe fn waker_clone(data: *const ()) -> RawWaker { RawWaker::new(data, &WAKER_VTABLE) }

unsafe fn waker_wake(data: *const ()) {
	let data_ptr = data as *const WakerData;

	(*data_ptr)
		.handle
		.inner
		.dispatch(wakeup_handler, data_ptr as _);
}

unsafe fn waker_wake_by_ref(data: *const ()) { waker_wake(data); }

fn waker_drop(_data: *const ()) {}