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package org.jooby;

import static java.util.Objects.requireNonNull;

import javax.annotation.Nonnull;

import java.util.Optional;

import java.util.concurrent.Callable;

import java.util.concurrent.Executor;

import java.util.concurrent.ForkJoinPool;

/**

* <h1>async request processing</h1>

* <p>

* A Deferred result, useful for async request processing.

* </p>

* <p>

* Application can produces a result from a different thread. Once result is ready, a call to

* {@link #resolve(Object)} is required. Please note, a call to {@link #reject(Throwable)} is

* required in case of errors.

* </p>

*

* <h2>usage</h2>

*

* <pre>

* {

* get("/async", deferred(() {@literal ->} {

* return "Success";

* }));

* }

* </pre>

*

* From MVC route:

*

* <pre>{@code

*

* public class Controller {

* &#64;GET

* &#64;Path("/async")

* public Deferred async() {

* return Deferred.deferred(() -> "Success");

* }

* }

* }</pre>

*

* If you add the {@link AsyncMapper} then your controller method can return a {@link Callable}.

*

* Previous example runs in the default executor, which always run deferred results in the

* same/caller thread.

*

* To effectively run a deferred result in new/different thread you need to provide an

* {@link Executor}:

*

* <pre>{@code

* {

* executor(new ForkJoinPool());

* }

* }</pre>

*

* This line override the default executor with a {@link ForkJoinPool}. You can add two or more

* named executor:

*

* <pre>{@code

* {

* executor(new ForkJoinPool());

*

* executor("cached", Executors.newCachedExecutor());

*

* get("/async", deferred("cached", () -> "Success"));

* }

* }</pre>

*

* A {@link Deferred} object works as a promise too, given you {@link #resolve(Object)} and

* {@link #reject(Throwable)} methods. Examples:

*

* As promise using the default executor (execute promise in same/caller thread):

* <pre>

* {

* get("/async", promise(deferred {@literal ->} {

* try {

* deferred.resolve(...); // success value

* } catch (Throwable ex) {

* deferred.reject(ex); // error value

* }

* }));

* }

* </pre>

*

* As promise using a custom executor:

* <pre>

* {

* executor(new ForkJoinPool());

*

* get("/async", promise(deferred {@literal ->} {

* try {

* deferred.resolve(...); // success value

* } catch (Throwable ex) {

* deferred.reject(ex); // error value

* }

* }));

* }

* </pre>

*

* As promise using an alternative executor:

*

* <pre>

* {

* executor(new ForkJoinPool());

*

* executor("cached", Executors.newCachedExecutor());

*

* get("/async", promise("cached", deferred {@literal ->} {

* try {

* deferred.resolve(...); // success value

* } catch (Throwable ex) {

* deferred.reject(ex); // error value

* }

* }));

* }

* </pre>

*

* @author edgar

* @since 0.10.0

*/

public class Deferred extends Result {

/**

* Deferred initializer, useful to provide a more functional API.

*

* @author edgar

* @since 0.10.0

*/

public interface Initializer0 {

/**

* Run the initializer block.

*

* @param deferred Deferred object.

* @throws Exception If something goes wrong.

*/

void run(Deferred deferred) throws Exception;

}

/**

* Deferred initializer with {@link Request} access, useful to provide a more functional API.

*

* @author edgar

* @since 0.10.0

*/

public interface Initializer {

/**

* Run the initializer block.

*

* @param req Current request.

* @param deferred Deferred object.

* @throws Exception If something goes wrong.

*/

void run(Request req, Deferred deferred) throws Exception;

}

/**

* A deferred handler. Application code should never use this class. INTERNAL USE ONLY.

*

* @author edgar

* @since 0.10.0

*/

public interface Handler {

void handle(Result result, Throwable exception);

}

/** Deferred initializer. Optional. */

private Initializer initializer;

/** Deferred handler. Internal. */

private Handler handler;

private String executor;

private String callerThread;

/**

* Creates a new {@link Deferred} with an initializer.

*

* @param executor Executor to use.

* @param initializer An initializer.

*/

public Deferred(final String executor, final Initializer0 initializer) {

this(executor, (req, deferred) -> initializer.run(deferred));

}

/**

* Creates a new {@link Deferred} with an initializer.

*

* @param initializer An initializer.

*/

public Deferred(final Initializer0 initializer) {

this(null, initializer);

}

/**

* Creates a new {@link Deferred} with an initializer.

*

* @param initializer An initializer.

*/

public Deferred(final Initializer initializer) {

this(null, initializer);

}

/**

* Creates a new {@link Deferred} with an initializer.

*

* @param executor Executor to use.

* @param initializer An initializer.

*/

public Deferred(final String executor, final Initializer initializer) {

this.executor = executor;

this.initializer = requireNonNull(initializer, "Initializer is required.");

this.callerThread = Thread.currentThread().getName();

}

/**

* Creates a new {@link Deferred}.

*/

public Deferred() {

}

/**

* {@link #resolve(Object)} or {@link #reject(Throwable)} the given value.

*

* @param value Resolved value.

*/

@Override

@Nonnull

public Result set(final Object value) {

if (value instanceof Throwable) {

reject((Throwable) value);

} else {

resolve(value);

}

return this;

}

/**

* Get an executor to run this deferred result. If the executor is present, then it will be use it

* to execute the deferred object. Otherwise it will use the global/application executor.

*

* @return Executor to use or fallback to global/application executor.

*/

@Nonnull

public Optional<String> executor() {

return Optional.ofNullable(executor);

}

/**

* Name of the caller thread (thread that creates this deferred object).

*

* @return Name of the caller thread (thread that creates this deferred object).

*/

@Nonnull

public String callerThread() {

return callerThread;

}

/**

* Resolve the deferred value and handle it. This method will send the response to a client and

* cleanup and close all the resources.

*

* @param value A value for this deferred.

*/

@Nonnull

public void resolve(final Object value) {

if (value == null) {

handler.handle(null, null);

} else {

Result result;

if (value instanceof Result) {

super.set(value);

result = (Result) value;

} else {

super.set(value);

result = clone();

}

handler.handle(result, null);

}

}

/**

* Resolve the deferred with an error and handle it. This method will handle the given exception,

* send the response to a client and cleanup and close all the resources.

*

* @param cause A value for this deferred.

*/

public void reject(final Throwable cause) {

super.set(cause);

handler.handle(null, cause);

}

/**

* Setup a handler for this deferred. Application code should never call this method: INTERNAL USE

* ONLY.

*

* @param req Current request.

* @param handler A response handler.

* @throws Exception If initializer fails to start.

*/

public void handler(final Request req, final Handler handler) throws Exception {

this.handler = requireNonNull(handler, "Handler is required.");

if (initializer != null) {

initializer.run(req, this);

}

}

/**

* Functional version of {@link Deferred#Deferred(Initializer)}.

*

* Using the default executor (current thread):

*

* <pre>{@code

* {

* get("/fork", deferred(req -> {

* return req.param("value").value();

* }));

* }

* }</pre>

*

* Using a custom executor:

*

* <pre>{@code

* {

* executor(new ForkJoinPool());

*

* get("/fork", deferred(req -> {

* return req.param("value").value();

* }));

* }

* }</pre>

*

* This handler automatically {@link Deferred#resolve(Object)} or

* {@link Deferred#reject(Throwable)} a route handler response.

*

* @param handler Application block.

* @return A new deferred handler.

*/

@Nonnull

public static Deferred deferred(final Route.OneArgHandler handler) {

return deferred(null, handler);

}

/**

* Functional version of {@link Deferred#Deferred(Initializer)}.

*

* Using the default executor (current thread):

*

* <pre>{@code

* {

* get("/fork", deferred(() -> {

* return req.param("value").value();

* }));

* }

* }</pre>

*

* Using a custom executor:

*

* <pre>{@code

* {

* executor(new ForkJoinPool());

*

* get("/fork", deferred(() -> {

* return req.param("value").value();

* }));

* }

* }</pre>

*

* This handler automatically {@link Deferred#resolve(Object)} or

* {@link Deferred#reject(Throwable)} a route handler response.

*

* @param handler Application block.

* @return A new deferred.

*/

@Nonnull

public static Deferred deferred(final Route.ZeroArgHandler handler) {

return deferred(null, handler);

}

/**

* Functional version of {@link Deferred#Deferred(Initializer)}. To use ideally with one

* or more {@link Executor}:

*

* <pre>{@code

* {

* executor("cached", Executors.newCachedExecutor());

*

* get("/fork", deferred("cached", () -> {

* return "OK";

* }));

* }

* }</pre>

*

* This handler automatically {@link Deferred#resolve(Object)} or

* {@link Deferred#reject(Throwable)} a route handler response.

*

* @param executor Executor to run the deferred.

* @param handler Application block.

* @return A new deferred handler.

*/

@Nonnull

public static Deferred deferred(final String executor, final Route.ZeroArgHandler handler) {

return deferred(executor, req -> handler.handle());

}

/**

* Functional version of {@link Deferred#Deferred(Initializer)}. To use ideally with one

* or more {@link Executor}:

*

* <pre>{@code

* {

* executor("cached", Executors.newCachedExecutor());

*

* get("/fork", deferred("cached", req -> {

* return req.param("value").value();

* }));

* }

* }</pre>

*

* This handler automatically {@link Deferred#resolve(Object)} or

* {@link Deferred#reject(Throwable)} a route handler response.

*

* @param executor Executor to run the deferred.

* @param handler Application block.

* @return A new deferred handler.

*/

@Nonnull

public static Deferred deferred(final String executor, final Route.OneArgHandler handler) {

return new Deferred(executor, (req, deferred) -> {

try {

deferred.resolve(handler.handle(req));

} catch (Throwable x) {

deferred.reject(x);

}

});

}

}