/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * 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.android.internal.util;

import android.annotation.NonNull;
import android.annotation.Nullable;
import android.util.ArraySet;
import android.util.ExceptionUtils;

import com.android.internal.util.FunctionalUtils.ThrowingConsumer;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Stream;

Utility methods for dealing with (typically Nullable) Collections Unless a method specifies otherwise, a null value for a collection is treated as an empty collection of that type. /**
 * Utility methods for dealing with (typically {@code Nullable}) {@link Collection}s
 *
 * Unless a method specifies otherwise, a null value for a collection is treated as an empty
 * collection of that type.
 */
public class CollectionUtils {
    private CollectionUtils() { /* cannot be instantiated */ }

    
Returns a list of items from the provided list that match the given condition. This is similar to Stream.filter but without the overhead of creating an intermediate Stream instance /**
     * Returns a list of items from the provided list that match the given condition.
     *
     * This is similar to {@link Stream#filter} but without the overhead of creating an intermediate
     * {@link Stream} instance
     */
    public static @NonNull <T> List<T> filter(@Nullable List<T> list,
            java.util.function.Predicate<? super T> predicate) {
        ArrayList<T> result = null;
        for (int i = 0; i < size(list); i++) {
            final T item = list.get(i);
            if (predicate.test(item)) {
                result = ArrayUtils.add(result, item);
            }
        }
        return emptyIfNull(result);
    }

    
See Also:
filter(List, Predicate)/**
     * @see #filter(List, java.util.function.Predicate)
     */
    public static @NonNull <T> Set<T> filter(@Nullable Set<T> set,
            java.util.function.Predicate<? super T> predicate) {
        if (set == null || set.size() == 0) return Collections.emptySet();
        ArraySet<T> result = null;
        if (set instanceof ArraySet) {
            ArraySet<T> arraySet = (ArraySet<T>) set;
            int size = arraySet.size();
            for (int i = 0; i < size; i++) {
                final T item = arraySet.valueAt(i);
                if (predicate.test(item)) {
                    result = ArrayUtils.add(result, item);
                }
            }
        } else {
            for (T item : set) {
                if (predicate.test(item)) {
                    result = ArrayUtils.add(result, item);
                }
            }
        }
        return emptyIfNull(result);
    }

    
Add all elements matching predicate in source to dest. /** Add all elements matching {@code predicate} in {@code source} to {@code dest}. */
    public static <T> void addIf(@Nullable List<T> source, @NonNull Collection<? super T> dest,
            @Nullable Predicate<? super T> predicate) {
        for (int i = 0; i < size(source); i++) {
            final T item = source.get(i);
            if (predicate.test(item)) {
                dest.add(item);
            }
        }
    }

    
Returns a list of items resulting from applying the given function to each element of the provided list. The resulting list will have the same size as the input one. This is similar to Stream.map but without the overhead of creating an intermediate Stream instance /**
     * Returns a list of items resulting from applying the given function to each element of the
     * provided list.
     *
     * The resulting list will have the same {@link #size} as the input one.
     *
     * This is similar to {@link Stream#map} but without the overhead of creating an intermediate
     * {@link Stream} instance
     */
    public static @NonNull <I, O> List<O> map(@Nullable List<I> cur,
            Function<? super I, ? extends O> f) {
        if (isEmpty(cur)) return Collections.emptyList();
        final ArrayList<O> result = new ArrayList<>();
        for (int i = 0; i < cur.size(); i++) {
            result.add(f.apply(cur.get(i)));
        }
        return result;
    }

    
See Also:
map(List, Function)/**
     * @see #map(List, Function)
     */
    public static @NonNull <I, O> Set<O> map(@Nullable Set<I> cur,
            Function<? super I, ? extends O> f) {
        if (isEmpty(cur)) return Collections.emptySet();
        ArraySet<O> result = new ArraySet<>();
        if (cur instanceof ArraySet) {
            ArraySet<I> arraySet = (ArraySet<I>) cur;
            int size = arraySet.size();
            for (int i = 0; i < size; i++) {
                result.add(f.apply(arraySet.valueAt(i)));
            }
        } else {
            for (I item : cur) {
                result.add(f.apply(item));
            }
        }
        return result;
    }

    
map(List<Object>, Function<? super Object,? extends Object>) + filter(List<Object>, Predicate<? super Object>) Calling this is equivalent (but more memory efficient) to: 
     filter(
         map(cur, f),
         i -> { i != null })
 /**
     * {@link #map(List, Function)} + {@link #filter(List, java.util.function.Predicate)}
     *
     * Calling this is equivalent (but more memory efficient) to:
     *
     * {@code
     *      filter(
     *          map(cur, f),
     *          i -> { i != null })
     * }
     */
    public static @NonNull <I, O> List<O> mapNotNull(@Nullable List<I> cur,
            Function<? super I, ? extends O> f) {
        if (isEmpty(cur)) return Collections.emptyList();
        List<O> result = null;
        for (int i = 0; i < cur.size(); i++) {
            O transformed = f.apply(cur.get(i));
            if (transformed != null) {
                result = add(result, transformed);
            }
        }
        return emptyIfNull(result);
    }

    
Returns the given list, or an immutable empty list if the provided list is null
This can be used to guarantee null-safety without paying the price of extra allocations
See Also:
emptyList.emptyList/**
     * Returns the given list, or an immutable empty list if the provided list is null
     *
     * This can be used to guarantee null-safety without paying the price of extra allocations
     *
     * @see Collections#emptyList
     */
    public static @NonNull <T> List<T> emptyIfNull(@Nullable List<T> cur) {
        return cur == null ? Collections.emptyList() : cur;
    }

    
Returns the given set, or an immutable empty set if the provided set is null
This can be used to guarantee null-safety without paying the price of extra allocations
See Also:
emptySet.emptySet/**
     * Returns the given set, or an immutable empty set if the provided set is null
     *
     * This can be used to guarantee null-safety without paying the price of extra allocations
     *
     * @see Collections#emptySet
     */
    public static @NonNull <T> Set<T> emptyIfNull(@Nullable Set<T> cur) {
        return cur == null ? Collections.emptySet() : cur;
    }

    
Returns the size of the given collection, or 0 if null
/**
     * Returns the size of the given collection, or 0 if null
     */
    public static int size(@Nullable Collection<?> cur) {
        return cur != null ? cur.size() : 0;
    }

    
Returns whether the given collection is empty or null /**
     * Returns whether the given collection {@link Collection#isEmpty is empty} or {@code null}
     */
    public static boolean isEmpty(@Nullable Collection<?> cur) {
        return size(cur) == 0;
    }

    
Returns the elements of the given list that are of type c /**
     * Returns the elements of the given list that are of type {@code c}
     */
    public static @NonNull <T> List<T> filter(@Nullable List<?> list, Class<T> c) {
        if (isEmpty(list)) return Collections.emptyList();
        ArrayList<T> result = null;
        for (int i = 0; i < list.size(); i++) {
            final Object item = list.get(i);
            if (c.isInstance(item)) {
                result = ArrayUtils.add(result, (T) item);
            }
        }
        return emptyIfNull(result);
    }

    
Returns whether there exists at least one element in the list for which condition predicate is true /**
     * Returns whether there exists at least one element in the list for which
     * condition {@code predicate} is true
     */
    public static <T> boolean any(@Nullable List<T> items,
            java.util.function.Predicate<T> predicate) {
        return find(items, predicate) != null;
    }

    
Returns the first element from the list for which condition predicate is true, or null if there is no such element /**
     * Returns the first element from the list for which
     * condition {@code predicate} is true, or null if there is no such element
     */
    public static @Nullable <T> T find(@Nullable List<T> items,
            java.util.function.Predicate<T> predicate) {
        if (isEmpty(items)) return null;
        for (int i = 0; i < items.size(); i++) {
            final T item = items.get(i);
            if (predicate.test(item)) return item;
        }
        return null;
    }

    
Similar to List.add, but with support for list values of null and Collections.emptyList /**
     * Similar to {@link List#add}, but with support for list values of {@code null} and
     * {@link Collections#emptyList}
     */
    public static @NonNull <T> List<T> add(@Nullable List<T> cur, T val) {
        if (cur == null || cur == Collections.emptyList()) {
            cur = new ArrayList<>();
        }
        cur.add(val);
        return cur;
    }

    
See Also:
add(List, Object)/**
     * @see #add(List, Object)
     */
    public static @NonNull <T> Set<T> add(@Nullable Set<T> cur, T val) {
        if (cur == null || cur == Collections.emptySet()) {
            cur = new ArraySet<>();
        }
        cur.add(val);
        return cur;
    }

    
Similar to List.remove, but with support for list values of null and Collections.emptyList /**
     * Similar to {@link List#remove}, but with support for list values of {@code null} and
     * {@link Collections#emptyList}
     */
    public static @NonNull <T> List<T> remove(@Nullable List<T> cur, T val) {
        if (isEmpty(cur)) {
            return emptyIfNull(cur);
        }
        cur.remove(val);
        return cur;
    }

    
See Also:
remove(List, Object)/**
     * @see #remove(List, Object)
     */
    public static @NonNull <T> Set<T> remove(@Nullable Set<T> cur, T val) {
        if (isEmpty(cur)) {
            return emptyIfNull(cur);
        }
        cur.remove(val);
        return cur;
    }

    
Returns:
a list that will not be affected by mutations to the given original list./**
     * @return a list that will not be affected by mutations to the given original list.
     */
    public static @NonNull <T> List<T> copyOf(@Nullable List<T> cur) {
        return isEmpty(cur) ? Collections.emptyList() : new ArrayList<>(cur);
    }

    
Returns:
a list that will not be affected by mutations to the given original list./**
     * @return a list that will not be affected by mutations to the given original list.
     */
    public static @NonNull <T> Set<T> copyOf(@Nullable Set<T> cur) {
        return isEmpty(cur) ? Collections.emptySet() : new ArraySet<>(cur);
    }

    
Applies action to each element in cur This avoids creating an iterator if the given set is an ArraySet /**
     * Applies {@code action} to each element in {@code cur}
     *
     * This avoids creating an iterator if the given set is an {@link ArraySet}
     */
    public static <T> void forEach(@Nullable Set<T> cur, @Nullable ThrowingConsumer<T> action) {
        if (cur == null || action == null) return;
        int size = cur.size();
        if (size == 0) return;
        try {
            if (cur instanceof ArraySet) {
                ArraySet<T> arraySet = (ArraySet<T>) cur;
                for (int i = 0; i < size; i++) {
                    action.acceptOrThrow(arraySet.valueAt(i));
                }
            } else {
                for (T t : cur) {
                    action.acceptOrThrow(t);
                }
            }
        } catch (Exception e) {
            throw ExceptionUtils.propagate(e);
        }
    }
}