//
// Copyright 2018 Google LLC.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

/**
 * The executor to handle other tasks while waiting for an asynchronous task to complete.
 *
 * The executor is running a while-loop and handling other tasks using the message queue. When a
 * task is to be handled by the executor, it will enqueue the task to the message queue,
 * which will be picked up by the executor when it is running a while-loop; if it is not running
 * a while-loop, it will be dispatch to the execution queue to process it.
 */
@interface EDOExecutor : NSObject

/** The dispatch queue to handle the request if it is not running. */
@property(readonly, nonatomic, weak) dispatch_queue_t executionQueue;

- (instancetype)init NS_UNAVAILABLE;

/**
 * Initialize with the request @c handlers for the dispatch @c queue.
 *
 * The executor keeps a weak reference to the dispatch queue and creates a new queue -
 * @c isolationQueue with a key containing the prefix "com.google.edo.executor" and the description
 * of @c queue. The @c isolationQueue is used to execute requests in a synchronous manner. The
 * queue itself shares the same lifecycle as the executor.
 *
 * @remark If the dispatch queue is already assigned one executor, it will be replaced.
 *
 * @param queue The dispatch queue to associate with the executor.
 *
 * @return The @c EDOExecutor associated with the dispatch queue.
 */
- (instancetype)initWithQueue:(nullable dispatch_queue_t)queue NS_DESIGNATED_INITIALIZER;

/**
 * Runs the while-loop to handle blocks to be executed from EDOExecutor::handleBlock: until the
 * execution of @c executeBlock completes.
 *
 * @note The executor keep waiting on incoming requests until the @c executeBlock is finished.
 * @param executeBlock The block to execute in the background queue.
 */
- (void)loopWithBlock:(void (^)(void))executeBlock;

/**
 * Attaches @c executeBlock to an internal EDOBlockingQueue and waits for the block's completion.
 *
 * @note If the executor is running the while-loop, the request will be enqueued to being processed
 *       otherwise will be dispatched to the @c executionQueue to process.
 * @param      executeBlock   The block to be handled and executed.
 * @param[out] errorOrNil     Error that will be populated on failure.
 *
 * @return @c YES if the block is successfully executed by the executor; @c NO otherwise, in which
 *         case the block won't get invoked.
 */
- (BOOL)handleBlock:(void (^)(void))executeBlock error:(NSError *_Nullable *_Nullable)errorOrNil;

@end

NS_ASSUME_NONNULL_END