/*
    * Copyright 2021 LINE Corporation
    *
    * LINE Corporation licenses this file to you 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:
    *
    *   https://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.
   */
  package com.linecorp.centraldogma.client;
  
  import static com.google.common.base.Preconditions.checkArgument;
  import static java.util.Objects.requireNonNull;
  
  import java.time.Duration;
  import java.util.concurrent.Executor;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.TimeUnit;
  import java.util.function.Function;
  
  import javax.annotation.Nullable;
  
  import com.linecorp.centraldogma.common.PathPattern;
  import com.linecorp.centraldogma.common.Query;
  
  import io.micrometer.core.instrument.MeterRegistry;
  
  /**
   * Prepares to create a {@link Watcher}.
   */
  public final class WatcherRequest<T> extends WatchOptions {
  
      private static final long DEFAULT_DELAY_ON_SUCCESS_MILLIS = TimeUnit.SECONDS.toMillis(1);
      private static final long DEFAULT_MAX_DELAY_MILLIS = TimeUnit.MINUTES.toMillis(1);
      private static final double DEFAULT_MULTIPLIER = 2.0;
      private static final double DEFAULT_JITTER_RATE = 0.2;
  
      private final CentralDogmaRepository centralDogmaRepo;
      @Nullable
      private final Query<T> query;
      @Nullable
      private final PathPattern pathPattern;
      private final ScheduledExecutorService blockingTaskExecutor;
  
      @Nullable
      private Function<Object, ? extends T> mapper;
      private Executor executor;
  
      @Nullable
      private final MeterRegistry meterRegistry;
  
      private long delayOnSuccessMillis = DEFAULT_DELAY_ON_SUCCESS_MILLIS;
      private long initialDelayMillis = DEFAULT_DELAY_ON_SUCCESS_MILLIS * 2;
      private long maxDelayMillis = DEFAULT_MAX_DELAY_MILLIS;
      private double multiplier = DEFAULT_MULTIPLIER;
      private double jitterRate = DEFAULT_JITTER_RATE;
  
      WatcherRequest(CentralDogmaRepository centralDogmaRepo, Query<T> query,
                     ScheduledExecutorService blockingTaskExecutor, @Nullable MeterRegistry meterRegistry) {
          this(centralDogmaRepo, query, null, blockingTaskExecutor, meterRegistry);
      }
  
      WatcherRequest(CentralDogmaRepository centralDogmaRepo, PathPattern pathPattern,
                     ScheduledExecutorService blockingTaskExecutor, @Nullable MeterRegistry meterRegistry) {
          this(centralDogmaRepo, null, pathPattern, blockingTaskExecutor, meterRegistry);
      }
  
      private WatcherRequest(CentralDogmaRepository centralDogmaRepo, @Nullable Query<T> query,
                             @Nullable PathPattern pathPattern, ScheduledExecutorService blockingTaskExecutor,
                             @Nullable MeterRegistry meterRegistry) {
          this.centralDogmaRepo = centralDogmaRepo;
          this.query = query;
          this.pathPattern = pathPattern;
          this.blockingTaskExecutor = blockingTaskExecutor;
          executor = blockingTaskExecutor;
          this.meterRegistry = meterRegistry;
      }
  
      /**
       * Sets the {@link Function} to apply to the result of a watch request.
       */
      @SuppressWarnings("unchecked")
      public <U> WatcherRequest<U> map(Function<? super T, ? extends U> mapper) {
          if (this.mapper == null) {
              this.mapper = (Function<Object, ? extends T>) mapper;
          } else {
              this.mapper = (Function<Object, ? extends T>) this.mapper.andThen(mapper);
          }
          return (WatcherRequest<U>) this;
      }
  
      /**
       * Sets the {@link Executor} to execute the {@link #map(Function)}.
      */
     public WatcherRequest<T> mapperExecutor(Executor executor) {
         this.executor = executor;
         return this;
     }
 
     /**
      * Sets the delay for sending the next watch request when the previous request succeeds.
      */
     public WatcherRequest<T> delayOnSuccess(Duration delayOnSuccess) {
         requireNonNull(delayOnSuccess, "delayOnSuccess");
         checkArgument(!delayOnSuccess.isNegative(),
                       "delayOnSuccess: %s (expected: >= 0)", delayOnSuccess);
         return delayOnSuccessMillis(delayOnSuccess.toMillis());
     }
 
     /**
      * Sets the delay in milliseconds for sending the next watch request when the previous request succeeds.
      */
     public WatcherRequest<T> delayOnSuccessMillis(long delayOnSuccessMillis) {
         this.delayOnSuccessMillis = delayOnSuccessMillis;
         checkArgument(delayOnSuccessMillis >= 0,
                       "delayOnSuccessMillis: %s (expected: >= 0)", delayOnSuccessMillis);
         return this;
     }
 
     /**
      * Sets the delays and multiplier which is used to calculate the delay
      * for sending the next watch request when the previous request fails.
      * Currently, it uses exponential backoff. File a feature request if you need another algorithm.
      */
     public WatcherRequest<T> backoffOnFailure(long initialDelayMillis, long maxDelayMillis,
                                               double multiplier) {
         checkArgument(initialDelayMillis >= 0, "initialDelayMillis: %s (expected: >= 0)", initialDelayMillis);
         checkArgument(initialDelayMillis <= maxDelayMillis, "maxDelayMillis: %s (expected: >= %s)",
                       maxDelayMillis, initialDelayMillis);
         checkArgument(multiplier > 1.0, "multiplier: %s (expected: > 1.0)", multiplier);
         this.initialDelayMillis = initialDelayMillis;
         this.maxDelayMillis = maxDelayMillis;
         this.multiplier = multiplier;
         return this;
     }
 
     /**
      * Sets the jitter to apply the delay.
      */
     public WatcherRequest<T> jitterRate(double jitterRate) {
         checkArgument(0.0 <= jitterRate && jitterRate <= 1.0,
                       "jitterRate: %s (expected: >= 0.0 and <= 1.0)", jitterRate);
         this.jitterRate = jitterRate;
         return this;
     }
 
     @Override
     public WatcherRequest<T> timeout(Duration timeout) {
         //noinspection unchecked
         return (WatcherRequest<T>) super.timeout(timeout);
     }
 
     @Override
     public WatcherRequest<T> timeoutMillis(long timeoutMillis) {
         //noinspection unchecked
         return (WatcherRequest<T>) super.timeoutMillis(timeoutMillis);
     }
 
     @Override
     public WatcherRequest<T> errorOnEntryNotFound(boolean errorOnEntryNotFound) {
         //noinspection unchecked
         return (WatcherRequest<T>) super.errorOnEntryNotFound(errorOnEntryNotFound);
     }
 
     /**
      * Creates a new {@link Watcher} and starts to watch the target. The {@link Watcher} must be closed via
      * {@link Watcher#close()} after use.
      */
     public Watcher<T> start() {
         final String proName = centralDogmaRepo.projectName();
         final String repoName = centralDogmaRepo.repositoryName();
         final AbstractWatcher<T> watcher;
         if (query != null) {
             watcher = new FileWatcher<>(
                     centralDogmaRepo.centralDogma(), blockingTaskExecutor, proName, repoName, query,
                     timeoutMillis(), errorOnEntryNotFound(), mapper, executor, delayOnSuccessMillis,
                     initialDelayMillis, maxDelayMillis, multiplier, jitterRate, meterRegistry);
         } else {
             assert pathPattern != null;
             watcher = new FilesWatcher<>(
                     centralDogmaRepo.centralDogma(), blockingTaskExecutor, proName, repoName, pathPattern,
                     timeoutMillis(), errorOnEntryNotFound(), mapper, executor, delayOnSuccessMillis,
                     initialDelayMillis, maxDelayMillis, multiplier, jitterRate, meterRegistry);
         }
         watcher.start();
         return watcher;
     }
 }