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RIBs is the cross-platform architecture behind many mobile apps at Uber. This framework is designed for mobile apps with a large number of engineers and nested states.

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/*
 * Copyright (C) 2017. Uber Technologies
 *
 * 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.
 */
package com.uber.rib.core

import androidx.annotation.CallSuper
import com.jakewharton.rxrelay2.BehaviorRelay
import com.uber.autodispose.ScopeProvider
import com.uber.rib.core.lifecycle.PresenterEvent
import io.reactivex.CompletableSource
import io.reactivex.Observable
import org.checkerframework.checker.guieffect.qual.UIEffect

/**
 * Contains presentation logic. This class exists mainly for legacy reasons. In the past we believed
 * it was useful to have a class between interactors and views to facilitate model transformations
 * and believed these transformations would be complex enough to require its own lifecycle. In
 * practice this caused confusion: if both a presenter and interactor can perform complex rx logic
 * it becomes unclear where you should write your bussiness logic.
 */
abstract class Presenter : ScopeProvider {
  private val behaviorRelay = BehaviorRelay.create()
  private val lifecycleRelay = behaviorRelay.toSerialized()

  /** @return `true` if the presenter is loaded, `false` if not. */
  protected var isLoaded = false
    private set

  public open fun dispatchLoad() {
    isLoaded = true
    lifecycleRelay.accept(PresenterEvent.LOADED)
    didLoad()
  }

  public open fun dispatchUnload() {
    isLoaded = false
    willUnload()
    lifecycleRelay.accept(PresenterEvent.UNLOADED)
  }

  /** Tells the presenter that it has finished loading.  */
  @CallSuper
  protected open fun didLoad() {
  }

  /**
   * Tells the presenter that it will be destroyed. Presenter subclasses should perform any required
   * cleanup here.
   */
  @UIEffect
  @CallSuper
  protected open fun willUnload() {
  }

  /** @return an observable of this controller's lifecycle events. */
  open fun lifecycle(): Observable {
    return lifecycleRelay.hide()
  }

  override fun requestScope(): CompletableSource {
    return lifecycleRelay.skip(1).firstElement().ignoreElement()
  }
}