/*
 * Copyright (C) 2015 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 android.content.res;

import android.annotation.NonNull;
import android.annotation.Nullable;
import android.content.res.Resources.Theme;
import android.content.res.Resources.ThemeKey;
import android.util.LongSparseArray;
import android.util.ArrayMap;

import java.lang.ref.WeakReference;

/**
 * Data structure used for caching data against themes.
 *
 * @param <T> type of data to cache
 */
abstract class ThemedResourceCache<T> {
    private ArrayMap<ThemeKey, LongSparseArray<WeakReference<T>>> mThemedEntries;
    private LongSparseArray<WeakReference<T>> mUnthemedEntries;
    private LongSparseArray<WeakReference<T>> mNullThemedEntries;

    /**
     * Adds a new theme-dependent entry to the cache.
     *
     * @param key a key that uniquely identifies the entry
     * @param theme the theme against which this entry was inflated, or
     *              {@code null} if the entry has no theme applied
     * @param entry the entry to cache
     */
    public void put(long key, @Nullable Theme theme, @NonNull T entry) {
        put(key, theme, entry, true);
    }

    /**
     * Adds a new entry to the cache.
     *
     * @param key a key that uniquely identifies the entry
     * @param theme the theme against which this entry was inflated, or
     *              {@code null} if the entry has no theme applied
     * @param entry the entry to cache
     * @param usesTheme {@code true} if the entry is affected theme changes,
     *                  {@code false} otherwise
     */
    public void put(long key, @Nullable Theme theme, @NonNull T entry, boolean usesTheme) {
        if (entry == null) {
            return;
        }

        synchronized (this) {
            final LongSparseArray<WeakReference<T>> entries;
            if (!usesTheme) {
                entries = getUnthemedLocked(true);
            } else {
                entries = getThemedLocked(theme, true);
            }
            if (entries != null) {
                entries.put(key, new WeakReference<>(entry));
            }
        }
    }

    /**
     * Returns an entry from the cache.
     *
     * @param key a key that uniquely identifies the entry
     * @param theme the theme where the entry will be used
     * @return a cached entry, or {@code null} if not in the cache
     */
    @Nullable
    public T get(long key, @Nullable Theme theme) {
        // The themed (includes null-themed) and unthemed caches are mutually
        // exclusive, so we'll give priority to whichever one we think we'll
        // hit first. Since most of the framework drawables are themed, that's
        // probably going to be the themed cache.
        synchronized (this) {
            final LongSparseArray<WeakReference<T>> themedEntries = getThemedLocked(theme, false);
            if (themedEntries != null) {
                final WeakReference<T> themedEntry = themedEntries.get(key);
                if (themedEntry != null) {
                    return themedEntry.get();
                }
            }

            final LongSparseArray<WeakReference<T>> unthemedEntries = getUnthemedLocked(false);
            if (unthemedEntries != null) {
                final WeakReference<T> unthemedEntry = unthemedEntries.get(key);
                if (unthemedEntry != null) {
                    return unthemedEntry.get();
                }
            }
        }

        return null;
    }

    /**
     * Prunes cache entries that have been invalidated by a configuration
     * change.
     *
     * @param configChanges a bitmask of configuration changes
     */
    public void onConfigurationChange(int configChanges) {
        prune(configChanges);
    }

    /**
     * Returns whether a cached entry has been invalidated by a configuration
     * change.
     *
     * @param entry a cached entry
     * @param configChanges a non-zero bitmask of configuration changes
     * @return {@code true} if the entry is invalid, {@code false} otherwise
     */
    protected abstract boolean shouldInvalidateEntry(@NonNull T entry, int configChanges);

    /**
     * Returns the cached data for the specified theme, optionally creating a
     * new entry if one does not already exist.
     *
     * @param t the theme for which to return cached data
     * @param create {@code true} to create an entry if one does not already
     *               exist, {@code false} otherwise
     * @return the cached data for the theme, or {@code null} if the cache is
     *         empty and {@code create} was {@code false}
     */
    @Nullable
    private LongSparseArray<WeakReference<T>> getThemedLocked(@Nullable Theme t, boolean create) {
        if (t == null) {
            if (mNullThemedEntries == null && create) {
                mNullThemedEntries = new LongSparseArray<>(1);
            }
            return mNullThemedEntries;
        }

        if (mThemedEntries == null) {
            if (create) {
                mThemedEntries = new ArrayMap<>(1);
            } else {
                return null;
            }
        }

        final ThemeKey key = t.getKey();
        LongSparseArray<WeakReference<T>> cache = mThemedEntries.get(key);
        if (cache == null && create) {
            cache = new LongSparseArray<>(1);

            final ThemeKey keyClone = key.clone();
            mThemedEntries.put(keyClone, cache);
        }

        return cache;
    }

    /**
     * Returns the theme-agnostic cached data.
     *
     * @param create {@code true} to create an entry if one does not already
     *               exist, {@code false} otherwise
     * @return the theme-agnostic cached data, or {@code null} if the cache is
     *         empty and {@code create} was {@code false}
     */
    @Nullable
    private LongSparseArray<WeakReference<T>> getUnthemedLocked(boolean create) {
        if (mUnthemedEntries == null && create) {
            mUnthemedEntries = new LongSparseArray<>(1);
        }
        return mUnthemedEntries;
    }

    /**
     * Prunes cache entries affected by configuration changes or where weak
     * references have expired.
     *
     * @param configChanges a bitmask of configuration changes, or {@code 0} to
     *                      simply prune missing weak references
     * @return {@code true} if the cache is completely empty after pruning
     */
    private boolean prune(int configChanges) {
        synchronized (this) {
            if (mThemedEntries != null) {
                for (int i = mThemedEntries.size() - 1; i >= 0; i--) {
                    if (pruneEntriesLocked(mThemedEntries.valueAt(i), configChanges)) {
                        mThemedEntries.removeAt(i);
                    }
                }
            }

            pruneEntriesLocked(mNullThemedEntries, configChanges);
            pruneEntriesLocked(mUnthemedEntries, configChanges);

            return mThemedEntries == null && mNullThemedEntries == null
                    && mUnthemedEntries == null;
        }
    }

    private boolean pruneEntriesLocked(@Nullable LongSparseArray<WeakReference<T>> entries,
            int configChanges) {
        if (entries == null) {
            return true;
        }

        for (int i = entries.size() - 1; i >= 0; i--) {
            final WeakReference<T> ref = entries.valueAt(i);
            if (ref == null || pruneEntryLocked(ref.get(), configChanges)) {
                entries.removeAt(i);
            }
        }

        return entries.size() == 0;
    }

    private boolean pruneEntryLocked(@Nullable T entry, int configChanges) {
        return entry == null || (configChanges != 0
                && shouldInvalidateEntry(entry, configChanges));
    }
}
