/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.android.camera.async;
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import com.android.camera.util.Callback;
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import com.google.common.base.Function;
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import com.google.common.base.Supplier;
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import com.google.common.util.concurrent.MoreExecutors;
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import java.util.List;
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import java.util.concurrent.Executor;
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import javax.annotation.CheckReturnValue;
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import javax.annotation.Nonnull;
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import javax.annotation.ParametersAreNonnullByDefault;
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/**
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* Helper methods for {@link Observable}.
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*/
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@ParametersAreNonnullByDefault
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public class Observables {
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private static final SafeCloseable NOOP_CALLBACK_HANDLE = new SafeCloseable() {
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@Override
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public void close() {
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// Do Nothing.
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}
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};
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private Observables() {
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}
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/**
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* Transforms an observable with a function.
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*
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* @return The transformed observable.
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*/
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public static <F, T> Observable<T> transform(final Observable<F> input,
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final Function<F, T> function) {
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return new Observable<T>() {
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@Nonnull
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@Override
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public T get() {
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return function.apply(input.get());
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}
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@CheckReturnValue
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@Nonnull
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@Override
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public SafeCloseable addCallback(Runnable callback, Executor executor) {
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return input.addCallback(callback, executor);
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}
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};
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}
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/**
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* @return An observable which recomputes its output every time an input changes.
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*/
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public static <T> Observable<T> transform(final List<? extends Observable<?>> inputs,
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final Supplier<T> output) {
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return ObservableCombiner.transform(inputs, output);
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}
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/**
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* Transforms a set of observables with a function.
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*
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* @return The transformed observable.
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*/
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public static <F, T> Observable<T> transform(final List<? extends Observable<F>> input,
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Function<List<F>, T> function) {
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return ObservableCombiner.transform(input, function);
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}
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/**
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* @return An observable which has the given constant value.
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*/
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@Nonnull
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public static <T> Observable<T> of(final @Nonnull T constant) {
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return new Observable<T>() {
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@Nonnull
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@Override
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public T get() {
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return constant;
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}
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@CheckReturnValue
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@Nonnull
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@Override
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public SafeCloseable addCallback(Runnable callback, Executor executor) {
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return NOOP_CALLBACK_HANDLE;
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}
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};
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}
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@Nonnull
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@CheckReturnValue
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public static <T> SafeCloseable addThreadSafeCallback(final Observable<T> observable,
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final Updatable<T> callback) {
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return observable.addCallback(new Runnable() {
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@Override
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public void run() {
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callback.update(observable.get());
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}
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}, MoreExecutors.sameThreadExecutor());
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}
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}
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