/*
 * MIT License
 *
 * Copyright (c) 2017 Stan Mots (Storix)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package com.stolets.rxdiffutil.internal;

import android.support.annotation.Nullable;

/**
 * Static convenience methods that help a method or constructor check whether it was invoked
 * correctly.
 *
 * @see <a href="https://github.com/google/guava/blob/master/guava/src/com/google/common/base/Preconditions.java">link</a>
 */
public final class Preconditions {
    private Preconditions() {
    }

    /**
     * Ensures that an object reference passed as a parameter to the calling method is not null.
     *
     * @param reference    an object reference
     * @param errorMessage the exception message to use if the check fails; will be converted to a
     *                     string using {@link String#valueOf(Object)}
     * @param <T>          Reference type.
     * @return the non-null reference that was validated
     * @throws NullPointerException if {@code reference} is null
     */
    public static <T> T checkNotNull(T reference, @Nullable Object errorMessage) {
        if (reference == null) {
            throw new NullPointerException(String.valueOf(errorMessage));
        }
        return reference;
    }

    /**
     * Ensures the truth of an expression involving one or more parameters to the calling method.
     *
     * @param expression   a boolean expression
     * @param errorMessage the exception message to use if the check fails; will be converted to a
     *                     string using {@link String#valueOf(Object)}
     * @throws IllegalArgumentException if {@code expression} is false
     */
    public static void checkArgument(boolean expression, @Nullable Object errorMessage) {
        if (!expression) {
            throw new IllegalArgumentException(String.valueOf(errorMessage));
        }
    }
}

/*
 * MIT License
 *
 * Copyright (c) 2017 Stan Mots (Storix)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package com.stolets.rxdiffutil.internal;

import android.os.Looper;
import android.support.annotation.Nullable;

/**
 * Static convenience methods that help a method or constructor check whether it was invoked
 * correctly.
 *
 * @see <a href="https://github.com/google/guava/blob/master/guava/src/com/google/common/base/Preconditions.java">link</a>
 */
public final class Preconditions {
    private Preconditions() {
    }

    /**
     * Ensures that an object reference passed as a parameter to the calling method is not null.
     *
     * @param reference    an object reference
     * @param errorMessage the exception message to use if the check fails; will be converted to a
     *                     string using {@link String#valueOf(Object)}
     * @param <T>          Reference type.
     * @return the non-null reference that was validated
     * @throws NullPointerException if {@code reference} is null
     */
    public static <T> T checkNotNull(T reference, @Nullable Object errorMessage) {
        if (reference == null) {
            throw new NullPointerException(String.valueOf(errorMessage));
        }
        return reference;
    }

    /**
     * Ensures the truth of an expression involving one or more parameters to the calling method.
     *
     * @param expression   a boolean expression
     * @param errorMessage the exception message to use if the check fails; will be converted to a
     *                     string using {@link String#valueOf(Object)}
     * @throws IllegalArgumentException if {@code expression} is false
     */
    public static void checkArgument(boolean expression, @Nullable Object errorMessage) {
        if (!expression) {
            throw new IllegalArgumentException(String.valueOf(errorMessage));
        }
    }

    /**
     * Ensures that the current thread is the main thread.
     *
     * @param errorMessage the exception message
     *
     * @throws IllegalStateException if the current thread is not the main thread.
     */
    public static void ensureMainThread(@Nullable Object errorMessage) {
        if (Thread.currentThread() != Looper.getMainLooper().getThread()) {
            throw new IllegalStateException(String.valueOf(errorMessage));
        }
    }
}

Add ensureMainThread precondition