[YouTube] Add ability to generate manifests of progressive, OTF and post live streams

A new class has been added to do so: YoutubeDashManifestCreator.
It relies on a new class: ManifestCreatorCache, to cache the content, which relies on a new pair class named Pair.
Results are cached and there is a cache per delivery type, on which cache limit, clear factor, clearing and resetting can be applied to each cache and to all caches.
Look at code changes for more details.

extractor/src/main/java/org/schabi/newpipe/extractor/utils/ManifestCreatorCache.java

@@ -0,0 +1,301 @@
+package org.schabi.newpipe.extractor.utils;
+
+import javax.annotation.Nullable;
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.Map;
+import java.util.Objects;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * A {@link Serializable serializable} cache class used by the extractor to cache manifests
+ * generated with extractor's manifests generators.
+ *
+ * <p>
+ * It relies internally on a {@link ConcurrentHashMap} to allow concurrent access to the cache.
+ * </p>
+ *
+ * @param <K> the type of cache keys, which must be {@link Serializable serializable}
+ * @param <V> the type of the second element of {@link Pair pairs} used as values of the cache,
+ *            which must be {@link Serializable serializable}
+ */
+public final class ManifestCreatorCache<K extends Serializable, V extends Serializable>
+        implements Serializable {
+
+    /**
+     * The default maximum size of a manifest cache.
+     */
+    public static final int DEFAULT_MAXIMUM_SIZE = Integer.MAX_VALUE;
+
+    /**
+     * The default clear factor of a manifest cache.
+     */
+    public static final double DEFAULT_CLEAR_FACTOR = 0.75;
+
+    /**
+     * The {@link ConcurrentHashMap} used internally as the cache of manifests.
+     */
+    private final ConcurrentHashMap<K, Pair<Integer, V>> concurrentHashMap;
+
+    /**
+     * The maximum size of the cache.
+     *
+     * <p>
+     * The default value is {@link #DEFAULT_MAXIMUM_SIZE}.
+     * </p>
+     */
+    private int maximumSize = DEFAULT_MAXIMUM_SIZE;
+
+    /**
+     * The clear factor of the cache, which is a double between {@code 0} and {@code 1} excluded.
+     *
+     * <p>
+     * The default value is {@link #DEFAULT_CLEAR_FACTOR}.
+     * </p>
+     */
+    private double clearFactor = DEFAULT_CLEAR_FACTOR;
+
+    /**
+     * Creates a new {@link ManifestCreatorCache}.
+     */
+    public ManifestCreatorCache() {
+        concurrentHashMap = new ConcurrentHashMap<>();
+    }
+
+    /**
+     * Tests if the specified key is in the cache.
+     *
+     * @param key the key to test its presence in the cache
+     * @return {@code true} if the key is in the cache, {@code false} otherwise.
+     */
+    public boolean containsKey(final K key) {
+        return concurrentHashMap.containsKey(key);
+    }
+
+    /**
+     * Returns the value to which the specified key is mapped, or {@code null} if the cache
+     * contains no mapping for the key.
+     *
+     * @param key the key to which getting its value
+     * @return the value to which the specified key is mapped, or {@code null}
+     */
+    @Nullable
+    public Pair<Integer, V> get(final K key) {
+        return concurrentHashMap.get(key);
+    }
+
+    /**
+     * Adds a new element to the cache.
+     *
+     * <p>
+     * If the cache limit is reached, oldest elements will be cleared first using the load factor
+     * and the maximum size.
+     * </p>
+     *
+     * @param key   the key to put
+     * @param value the value to associate to the key
+     *
+     * @return the previous value associated with the key, or {@code null} if there was no mapping
+     * for the key (note that a null return can also indicate that the cache previously associated
+     * {@code null} with the key).
+     */
+    @Nullable
+    public V put(final K key, final V value) {
+        if (!concurrentHashMap.containsKey(key) && concurrentHashMap.size() == maximumSize) {
+            final int newCacheSize = (int) Math.round(maximumSize * clearFactor);
+            keepNewestEntries(newCacheSize != 0 ? newCacheSize : 1);
+        }
+
+        final Pair<Integer, V> returnValue = concurrentHashMap.put(key,
+                new Pair<>(concurrentHashMap.size(), value));
+        return returnValue == null ? null : returnValue.getSecond();
+    }
+
+    /**
+     * Clears the cached manifests.
+     *
+     * <p>
+     * The cache will be empty after this method is called.
+     * </p>
+     */
+    public void clear() {
+        concurrentHashMap.clear();
+    }
+
+    /**
+     * Resets the cache.
+     *
+     * <p>
+     * The cache will be empty and the clear factor and the maximum size will be reset to their
+     * default values.
+     * </p>
+     *
+     * @see #clear()
+     * @see #resetClearFactor()
+     * @see #resetMaximumSize()
+     */
+    public void reset() {
+        clear();
+        resetClearFactor();
+        resetMaximumSize();
+    }
+
+    /**
+     * Returns the number of cached manifests in the cache.
+     *
+     * @return the number of cached manifests
+     */
+    public int size() {
+        return concurrentHashMap.size();
+    }
+
+    /**
+     * Gets the maximum size of the cache.
+     *
+     * @return the maximum size of the cache
+     */
+    public long getMaximumSize() {
+        return maximumSize;
+    }
+
+    /**
+     * Sets the maximum size of the cache.
+     *
+     * If the current cache size is more than the new maximum size, the percentage of one less the
+     * clear factor of the maximum new size of manifests in the cache will be removed.
+     *
+     * @param maximumSize the new maximum size of the cache
+     * @throws IllegalArgumentException if {@code maximumSize} is less than or equal to 0
+     */
+    public void setMaximumSize(final int maximumSize) {
+        if (maximumSize <= 0) {
+            throw new IllegalArgumentException("Invalid maximum size");
+        }
+
+        if (maximumSize < this.maximumSize && !concurrentHashMap.isEmpty()) {
+            final int newCacheSize = (int) Math.round(maximumSize * clearFactor);
+            keepNewestEntries(newCacheSize != 0 ? newCacheSize : 1);
+        }
+
+        this.maximumSize = maximumSize;
+    }
+
+    /**
+     * Resets the maximum size of the cache to its {@link #DEFAULT_MAXIMUM_SIZE default value}.
+     */
+    public void resetMaximumSize() {
+        this.maximumSize = DEFAULT_MAXIMUM_SIZE;
+    }
+
+    /**
+     * Gets the current clear factor of the cache, used when the cache limit size is reached.
+     *
+     * @return the current clear factor of the cache
+     */
+    public double getClearFactor() {
+        return clearFactor;
+    }
+
+    /**
+     * Sets the clear factor of the cache, used when the cache limit size is reached.
+     *
+     * <p>
+     * The clear factor must be a double between {@code 0} excluded and {@code 1} excluded.
+     * </p>
+     *
+     * <p>
+     * Note that it will be only used the next time the cache size limit is reached.
+     * </p>
+     *
+     * @param clearFactor the new clear factor of the cache
+     * @throws IllegalArgumentException if the clear factor passed a parameter is invalid
+     */
+    public void setClearFactor(final double clearFactor) {
+        if (clearFactor <= 0 || clearFactor >= 1) {
+            throw new IllegalArgumentException("Invalid clear factor");
+        }
+
+        this.clearFactor = clearFactor;
+    }
+
+    /**
+     * Resets the clear factor to its {@link #DEFAULT_CLEAR_FACTOR default value}.
+     */
+    public void resetClearFactor() {
+        this.clearFactor = DEFAULT_CLEAR_FACTOR;
+    }
+
+    /**
+     * Reveals whether an object is equal to a {@code ManifestCreator} cache existing object.
+     *
+     * @param obj the object to compare with the current {@code ManifestCreatorCache} object
+     * @return whether the object compared is equal to the current {@code ManifestCreatorCache}
+     * object
+     */
+    @Override
+    public boolean equals(final Object obj) {
+        if (this == obj) {
+            return true;
+        }
+
+        if (obj == null || getClass() != obj.getClass()) {
+            return false;
+        }
+
+        final ManifestCreatorCache<?, ?> manifestCreatorCache =
+                (ManifestCreatorCache<?, ?>) obj;
+        return maximumSize == manifestCreatorCache.maximumSize
+                && Double.compare(manifestCreatorCache.clearFactor, clearFactor) == 0
+                && concurrentHashMap.equals(manifestCreatorCache.concurrentHashMap);
+    }
+
+    /**
+     * Returns a hash code of the current {@code ManifestCreatorCache}, using its
+     * {@link #maximumSize maximum size}, {@link #clearFactor clear factor} and
+     * {@link #concurrentHashMap internal concurrent hash map} used as a cache.
+     *
+     * @return a hash code of the current {@code ManifestCreatorCache}
+     */
+    @Override
+    public int hashCode() {
+        return Objects.hash(maximumSize, clearFactor, concurrentHashMap);
+    }
+
+    /**
+     * Returns a string version of the {@link ConcurrentHashMap} used internally as the cache.
+     *
+     * @return the string version of the {@link ConcurrentHashMap} used internally as the cache
+     */
+    @Override
+    public String toString() {
+        return concurrentHashMap.toString();
+    }
+
+    /**
+     * Keeps only the newest entries in a cache.
+     *
+     * <p>
+     * This method will first collect the entries to remove by looping through the concurrent hash
+     * map
+     * </p>
+     *
+     * @param newLimit the new limit of the cache
+     */
+    private void keepNewestEntries(final int newLimit) {
+        final int difference = concurrentHashMap.size() - newLimit;
+        final ArrayList<Map.Entry<K, Pair<Integer, V>>> entriesToRemove = new ArrayList<>();
+
+        for (final Map.Entry<K, Pair<Integer, V>> entry : concurrentHashMap.entrySet()) {
+            final Pair<Integer, V> value = entry.getValue();
+            if (value.getFirst() < difference) {
+                entriesToRemove.add(entry);
+            } else {
+                value.setFirst(value.getFirst() - difference);
+            }
+        }
+
+        for (final Map.Entry<K, Pair<Integer, V>> entry : entriesToRemove) {
+            concurrentHashMap.remove(entry.getKey(), entry.getValue());
+        }
+    }
+}