source: josm/trunk/src/org/openstreetmap/josm/data/osm/AbstractPrimitive.java@ 19078

// License: GPL. For details, see LICENSE file.
package org.openstreetmap.josm.data.osm;

import static org.openstreetmap.josm.tools.I18n.tr;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.text.MessageFormat;
import java.time.Instant;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Date;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.TimeUnit;
import java.util.function.BiPredicate;
import java.util.stream.IntStream;
import java.util.stream.Stream;

import org.openstreetmap.josm.data.gpx.GpxConstants;
import org.openstreetmap.josm.spi.preferences.Config;
import org.openstreetmap.josm.tools.Utils;

/**
 * Abstract class to represent common features of the datatypes primitives.
 *
 * @since 4099
 */
public abstract class AbstractPrimitive implements IPrimitive, IFilterablePrimitive {

    /**
     * This flag shows, that the properties have been changed by the user
     * and on upload the object will be send to the server.
     */
    protected static final short FLAG_MODIFIED = 1 << 0;

    /**
     * This flag is false, if the object is marked
     * as deleted on the server.
     */
    protected static final short FLAG_VISIBLE = 1 << 1;

    /**
     * An object that was deleted by the user.
     * Deleted objects are usually hidden on the map and a request
     * for deletion will be send to the server on upload.
     * An object usually cannot be deleted if it has non-deleted
     * objects still referring to it.
     */
    protected static final short FLAG_DELETED = 1 << 2;

    /**
     * A primitive is incomplete if we know its id and type, but nothing more.
     * Typically some members of a relation are incomplete until they are
     * fetched from the server.
     */
    protected static final short FLAG_INCOMPLETE = 1 << 3;

    /**
     * An object can be disabled by the filter mechanism.
     * Then it will show in a shade of gray on the map or it is completely
     * hidden from the view.
     * Disabled objects usually cannot be selected or modified
     * while the filter is active.
     */
    protected static final short FLAG_DISABLED = 1 << 4;

    /**
     * This flag is only relevant if an object is disabled by the
     * filter mechanism (i.e.&nbsp;FLAG_DISABLED is set).
     * Then it indicates, whether it is completely hidden or
     * just shown in gray color.
     * <p>
     * When the primitive is not disabled, this flag should be
     * unset as well (for efficient access).
     */
    protected static final short FLAG_HIDE_IF_DISABLED = 1 << 5;

    /**
     * Flag used internally by the filter mechanism.
     */
    protected static final short FLAG_DISABLED_TYPE = 1 << 6;

    /**
     * Flag used internally by the filter mechanism.
     */
    protected static final short FLAG_HIDDEN_TYPE = 1 << 7;

    /**
     * This flag is set if the primitive is a way and
     * according to the tags, the direction of the way is important.
     * (e.g. one way street.)
     */
    protected static final short FLAG_HAS_DIRECTIONS = 1 << 8;

    /**
     * If the primitive is tagged.
     * Some trivial tags like source=* are ignored here.
     */
    protected static final short FLAG_TAGGED = 1 << 9;

    /**
     * This flag is only relevant if FLAG_HAS_DIRECTIONS is set.
     * It shows, that direction of the arrows should be reversed.
     * (E.g. oneway=-1.)
     */
    protected static final short FLAG_DIRECTION_REVERSED = 1 << 10;

    /**
     * When hovering over ways and nodes in add mode, the
     * "target" objects are visually highlighted. This flag indicates
     * that the primitive is currently highlighted.
     */
    protected static final short FLAG_HIGHLIGHTED = 1 << 11;

    /**
     * If the primitive is annotated with a tag such as note, fixme, etc.
     * Match the "work in progress" tags in default map style.
     */
    protected static final short FLAG_ANNOTATED = 1 << 12;

    /**
     * Determines if the primitive is preserved from the filter mechanism.
     */
    protected static final short FLAG_PRESERVED = 1 << 13;

    /**
     * Determines if the primitive has all of its referrers
     */
    protected static final short FLAG_ALL_REFERRERS_DOWNLOADED = 1 << 14;

    /**
     * Put several boolean flags to one short int field to save memory.
     * Other bits of this field are used in subclasses.
     */
    private volatile short flags = FLAG_VISIBLE;   // visible per default

    /**
     * The mappaint cache index for this primitive.
     * This field belongs to {@code OsmPrimitive}, but due to Java's memory layout alignment, see #20830.
     */
    protected short mappaintCacheIdx;

    /*-------------------
     * OTHER PROPERTIES
     *-------------------*/

    /**
     * Unique identifier in OSM. This is used to identify objects on the server.
     * An id of 0 means an unknown id. The object has not been uploaded yet to
     * know what id it will get.
     */
    protected long id;

    /**
     * User that last modified this primitive, as specified by the server.
     * Never changed by JOSM.
     */
    protected User user;

    /**
     * Contains the version number as returned by the API. Needed to
     * ensure update consistency
     */
    protected int version;

    /**
     * The id of the changeset this primitive was last uploaded to.
     * 0 if it wasn't uploaded to a changeset yet of if the changeset
     * id isn't known.
     */
    protected int changesetId;

    /**
     * A time value, measured in seconds from the epoch, or in other words,
     * a number of seconds that have passed since 1970-01-01T00:00:00Z
     */
    protected int timestamp;

    /**
     * Get and write all attributes from the parameter. Does not fire any listener, so
     * use this only in the data initializing phase
     * @param other the primitive to clone data from
     */
    public void cloneFrom(AbstractPrimitive other) {
        setKeys(other.getKeys());
        id = other.id;
        if (id <= 0) {
            // reset version and changeset id
            version = 0;
            changesetId = 0;
        }
        timestamp = other.timestamp;
        if (id > 0) {
            version = other.version;
        }
        flags = other.flags;
        user = other.user;
        if (id > 0 && other.changesetId > 0) {
            // #4208: sometimes we cloned from other with id < 0 *and*
            // an assigned changeset id. Don't know why yet. For primitives
            // with id < 0 we don't propagate the changeset id any more.
            //
            setChangesetId(other.changesetId);
        }
    }

    @Override
    public int getVersion() {
        return version;
    }

    @Override
    public long getId() {
        return id >= 0 ? id : 0;
    }

    /**
     * Gets a unique id representing this object.
     *
     * @return Osm id if primitive already exists on the server. Unique negative value if primitive is new
     */
    @Override
    public long getUniqueId() {
        return id;
    }

    /**
     * Determines if this primitive is new.
     * @return {@code true} if this primitive is new (not yet uploaded the server, id &lt;= 0)
     */
    @Override
    public boolean isNew() {
        return id <= 0;
    }

    @Override
    public boolean isNewOrUndeleted() {
        return isNew() || ((flags & (FLAG_VISIBLE + FLAG_DELETED)) == 0);
    }

    @Override
    public void setOsmId(long id, int version) {
        if (id <= 0)
            throw new IllegalArgumentException(tr("ID > 0 expected. Got {0}.", id));
        if (version <= 0)
            throw new IllegalArgumentException(tr("Version > 0 expected. Got {0}.", version));
        this.id = id;
        this.version = version;
        this.setIncomplete(false);
    }

    /**
     * Clears the metadata, including id and version known to the OSM API.
     * The id is a new unique id. The version, changeset and timestamp are set to 0.
     * incomplete and deleted are set to false. It's preferred to use copy constructor with clearMetadata set to true instead
     * of calling this method.
     * @since 6140
     */
    public void clearOsmMetadata() {
        // Not part of dataset - no lock necessary
        this.id = getIdGenerator().generateUniqueId();
        this.version = 0;
        this.user = null;
        this.changesetId = 0; // reset changeset id on a new object
        this.timestamp = 0;
        this.setIncomplete(false);
        this.setDeleted(false);
        this.setVisible(true);
    }

    /**
     * Returns the unique identifier generator.
     * @return the unique identifier generator
     * @since 15820
     */
    public abstract UniqueIdGenerator getIdGenerator();

    @Override
    public User getUser() {
        return user;
    }

    @Override
    public void setUser(User user) {
        this.user = user;
    }

    @Override
    public int getChangesetId() {
        return changesetId;
    }

    @Override
    public void setChangesetId(int changesetId) {
        if (this.changesetId == changesetId)
            return;
        if (changesetId < 0)
            throw new IllegalArgumentException(MessageFormat.format("Parameter ''{0}'' >= 0 expected, got {1}", "changesetId", changesetId));
        if (changesetId > 0 && isNew())
            throw new IllegalStateException(tr("Cannot assign a changesetId > 0 to a new primitive. Value of changesetId is {0}", changesetId));

        this.changesetId = changesetId;
    }

    @Deprecated
    @Override
    public void setTimestamp(Date timestamp) {
        this.timestamp = (int) TimeUnit.MILLISECONDS.toSeconds(timestamp.getTime());
    }

    @Override
    public void setInstant(Instant timestamp) {
        this.timestamp = (int) timestamp.getEpochSecond();
    }

    @Override
    public void setRawTimestamp(int timestamp) {
        this.timestamp = timestamp;
    }

    @Deprecated
    @Override
    public Date getTimestamp() {
        return Date.from(getInstant());
    }

    @Override
    public Instant getInstant() {
        return Instant.ofEpochSecond(Integer.toUnsignedLong(timestamp));
    }

    @Override
    public int getRawTimestamp() {
        return timestamp;
    }

    @Override
    public boolean isTimestampEmpty() {
        return timestamp == 0;
    }

    /* -------
    /* FLAGS
    /* ------*/

    protected void updateFlags(short flag, boolean value) {
        if (value) {
            flags |= flag;
        } else {
            flags &= (short) ~flag;
        }
    }

    /**
     * Update flags
     * @param flag The flag to update
     * @param value The value to set
     * @return {@code true} if the flags have changed
     */
    protected boolean updateFlagsChanged(short flag, boolean value) {
        int oldFlags = flags;
        updateFlags(flag, value);
        return oldFlags != flags;
    }

    /**
     * Write common data to a serialization stream. At time of writing, this should <i>only</i> be used by {@link PrimitiveData}.
     * @param oos The output stream to write to
     * @throws IOException see {@link ObjectOutputStream#write}
     */
    protected void writeObjectCommon(ObjectOutputStream oos) throws IOException {
        oos.writeLong(id);
        oos.writeLong(user == null ? -1 : user.getId());
        oos.writeInt(version);
        oos.writeInt(changesetId);
        oos.writeInt(timestamp);
        oos.writeObject(keys);
        oos.writeShort(flags);
    }

    /**
     * Read common data from a serialization stream. At time of writing, this should <i>only</i> be used by {@link PrimitiveData}.
     * @param ois The serialization stream to read from
     * @throws ClassNotFoundException see {@link ObjectInputStream#readObject()}
     * @throws IOException see {@link ObjectInputStream#read}
     */
    protected void readObjectCommon(ObjectInputStream ois) throws ClassNotFoundException, IOException {
        id = ois.readLong();
        final long userId = ois.readLong();
        user = userId == -1 ? null : User.getById(userId);
        version = ois.readInt();
        changesetId = ois.readInt();
        timestamp = ois.readInt();
        keys = (String[]) ois.readObject();
        flags = ois.readShort();
    }

    @Override
    public void setModified(boolean modified) {
        updateFlags(FLAG_MODIFIED, modified);
    }

    @Override
    public boolean isModified() {
        return (flags & FLAG_MODIFIED) != 0;
    }

    @Override
    public boolean isDeleted() {
        return (flags & FLAG_DELETED) != 0;
    }

    @Override
    public void setReferrersDownloaded(boolean referrersDownloaded) {
        this.updateFlags(FLAG_ALL_REFERRERS_DOWNLOADED, referrersDownloaded);
    }

    @Override
    public boolean isUndeleted() {
        return (flags & (FLAG_VISIBLE + FLAG_DELETED)) == 0;
    }

    @Override
    public boolean isUsable() {
        return (flags & (FLAG_DELETED + FLAG_INCOMPLETE)) == 0;
    }

    @Override
    public boolean isVisible() {
        return (flags & FLAG_VISIBLE) != 0;
    }

    @Override
    public void setVisible(boolean visible) {
        if (!visible && isNew())
            throw new IllegalStateException(tr("A primitive with ID = 0 cannot be invisible."));
        updateFlags(FLAG_VISIBLE, visible);
    }

    @Override
    public void setDeleted(boolean deleted) {
        updateFlags(FLAG_DELETED, deleted);
        setModified(deleted ^ !isVisible());
    }

    @Override
    public boolean hasDirectionKeys() {
        return (flags & FLAG_HAS_DIRECTIONS) != 0;
    }

    @Override
    public boolean reversedDirection() {
        return (flags & FLAG_DIRECTION_REVERSED) != 0;
    }

    @Override
    public boolean isTagged() {
        return (flags & FLAG_TAGGED) != 0;
    }

    @Override
    public boolean isAnnotated() {
        return (flags & FLAG_ANNOTATED) != 0;
    }

    @Override
    public boolean isHighlighted() {
        return (flags & FLAG_HIGHLIGHTED) != 0;
    }

    @Override
    public boolean isDisabled() {
        return (flags & FLAG_DISABLED) != 0;
    }

    @Override
    public boolean isDisabledAndHidden() {
        return ((flags & FLAG_DISABLED) != 0) && ((flags & FLAG_HIDE_IF_DISABLED) != 0);
    }

    @Override
    public boolean isPreserved() {
        return (flags & FLAG_PRESERVED) != 0;
    }

    @Override
    public boolean isReferrersDownloaded() {
        return isNew() || (flags & FLAG_ALL_REFERRERS_DOWNLOADED) != 0;
    }

    /**
     * If set to true, this object is incomplete, which means only the id
     * and type is known (type is the objects instance class)
     * @param incomplete incomplete flag value
     */
    protected void setIncomplete(boolean incomplete) {
        updateFlags(FLAG_INCOMPLETE, incomplete);
    }

    @Override
    public boolean isIncomplete() {
        return (flags & FLAG_INCOMPLETE) != 0;
    }

    @Override
    public boolean getHiddenType() {
        return (flags & FLAG_HIDDEN_TYPE) != 0;
    }

    @Override
    public boolean getDisabledType() {
        return (flags & FLAG_DISABLED_TYPE) != 0;
    }

    @Override
    public boolean setDisabledState(boolean hidden) {
        // Store as variables to avoid short circuit boolean return
        final boolean flagDisabled = updateFlagsChanged(FLAG_DISABLED, true);
        final boolean flagHideIfDisabled = updateFlagsChanged(FLAG_HIDE_IF_DISABLED, hidden);
        return flagDisabled || flagHideIfDisabled;
    }

    @Override
    public boolean unsetDisabledState() {
        // Store as variables to avoid short circuit boolean return
        final boolean flagDisabled = updateFlagsChanged(FLAG_DISABLED, false);
        final boolean flagHideIfDisabled = updateFlagsChanged(FLAG_HIDE_IF_DISABLED, false);
        return flagDisabled || flagHideIfDisabled;
    }

    @Override
    public void setDisabledType(boolean isExplicit) {
        updateFlags(FLAG_DISABLED_TYPE, isExplicit);
    }

    @Override
    public void setHiddenType(boolean isExplicit) {
        updateFlags(FLAG_HIDDEN_TYPE, isExplicit);
    }

    @Override
    public boolean isDrawable() {
        return (flags & (FLAG_DELETED + FLAG_INCOMPLETE + FLAG_HIDE_IF_DISABLED)) == 0;
    }

    protected String getFlagsAsString() {
        StringBuilder builder = new StringBuilder();

        if (isIncomplete()) {
            builder.append('I');
        }
        if (isModified()) {
            builder.append('M');
        }
        if (isVisible()) {
            builder.append('V');
        }
        if (isDeleted()) {
            builder.append('D');
        }
        return builder.toString();
    }

    /*------------
     * Keys handling
     ------------*/

    /**
     * The key/value list for this primitive.
     * <p>
     * Note that the keys field is synchronized using RCU.
     * Writes to it are not synchronized by this object, the writers have to synchronize writes themselves.
     * <p>
     * In short this means that you should not rely on this variable being the same value when read again and your should always
     * copy it on writes.
     * <p>
     * Further reading:
     * <ul>
     * <li>{@link java.util.concurrent.CopyOnWriteArrayList}</li>
     * <li> <a href="http://stackoverflow.com/questions/2950871/how-can-copyonwritearraylist-be-thread-safe">
     *     http://stackoverflow.com/questions/2950871/how-can-copyonwritearraylist-be-thread-safe</a></li>
     * <li> <a href="https://en.wikipedia.org/wiki/Read-copy-update">
     *     https://en.wikipedia.org/wiki/Read-copy-update</a> (mind that we have a Garbage collector,
     *     {@code rcu_assign_pointer} and {@code rcu_dereference} are ensured by the {@code volatile} keyword)</li>
     * </ul>
     */
    protected volatile String[] keys;

    /**
     * Replies the map of key/value pairs. Never replies null. The map can be empty, though.
     *
     * @return tags of this primitive. Changes made in returned map are not mapped
     * back to the primitive, use setKeys() to modify the keys
     * @see #visitKeys(KeyValueVisitor)
     */
    @Override
    public TagMap getKeys() {
        return new TagMap(keys);
    }

    @Override
    public void visitKeys(KeyValueVisitor visitor) {
        String[] tKeys = this.keys;
        if (tKeys != null) {
            for (int i = 0; i < tKeys.length; i += 2) {
                visitor.visitKeyValue(this, tKeys[i], tKeys[i + 1]);
            }
        }
    }

    /**
     * Sets the keys of this primitives to the key/value pairs in <code>keys</code>.
     * Old key/value pairs are removed.
     * If <code>keys</code> is null, clears existing key/value pairs.
     * <p>
     * Note that this method, like all methods that modify keys, is not synchronized and may lead to data corruption when being used
     * from multiple threads.
     *
     * @param keys the key/value pairs to set. If null, removes all existing key/value pairs.
     */
    @Override
    public void setKeys(Map<String, String> keys) {
        Map<String, String> originalKeys = getKeys();
        if (Utils.isEmpty(keys)) {
            this.keys = null;
            keysChangedImpl(originalKeys);
            return;
        }
        String[] newKeys = new String[keys.size() * 2];
        int index = 0;
        for (Entry<String, String> entry:keys.entrySet()) {
            newKeys[index++] = Objects.requireNonNull(entry.getKey());
            newKeys[index++] = Objects.requireNonNull(entry.getValue());
        }
        this.keys = newKeys;
        keysChangedImpl(originalKeys);
    }

    /**
     * Copy the keys from a TagMap.
     * @param keys The new key map.
     */
    public void setKeys(TagMap keys) {
        Map<String, String> originalKeys = getKeys();
        if (keys == null) {
            this.keys = null;
        } else {
            String[] arr = keys.getTagsArray();
            if (arr.length == 0) {
                this.keys = null;
            } else {
                this.keys = arr;
            }
        }
        keysChangedImpl(originalKeys);
    }

    /**
     * Set the given value to the given key. If key is null, does nothing. If value is null,
     * removes the key and behaves like {@link #remove(String)}.
     * <p>
     * Note that this method, like all methods that modify keys, is not synchronized and may lead to data corruption when being used
     * from multiple threads.
     *
     * @param key  The key, for which the value is to be set. Can be null or empty, does nothing in this case.
     * @param value The value for the key. If null, removes the respective key/value pair.
     *
     * @see #remove(String)
     */
    @Override
    public void put(String key, String value) {
        Map<String, String> originalKeys = getKeys();
        if (key == null || Utils.isStripEmpty(key))
            return;
        else if (value == null) {
            remove(key);
        } else if (keys == null) {
            keys = new String[] {key, value};
            keysChangedImpl(originalKeys);
        } else {
            int keyIndex = indexOfKey(keys, key);
            int tagArrayLength = keys.length;
            if (keyIndex < 0) {
                keyIndex = tagArrayLength;
                tagArrayLength += 2;
            }

            // Do not try to optimize this array creation if the key already exists.
            // We would need to convert the keys array to be an AtomicReferenceArray
            // Or we would at least need a volatile write after the array was modified to
            // ensure that changes are visible by other threads.
            String[] newKeys = Arrays.copyOf(keys, tagArrayLength);
            newKeys[keyIndex] = key;
            newKeys[keyIndex + 1] = value;
            keys = newKeys;
            keysChangedImpl(originalKeys);
        }
    }

    @Override
    public void putAll(Map<String, String> tags) {
        if (tags == null || tags.isEmpty()) {
            return;
        }
        // Defensive copy of keys
        final String[] tKeys = this.keys; // Used to avoid highly unlikely NPE (from a race) during clone operation.
        String[] newKeys = tKeys == null ? null : tKeys.clone();
        Map<String, String> originalKeys = getKeys();
        List<Map.Entry<String, String>> tagsToAdd = new ArrayList<>(tags.size());
        for (Map.Entry<String, String> tag : tags.entrySet()) {
            if (!Utils.isBlank(tag.getKey())) {
                int keyIndex = indexOfKey(newKeys, tag.getKey());
                // Realistically, we will not hit the newKeys == null branch. If it is null, keyIndex is always < 0
                if (keyIndex < 0 || newKeys == null) {
                    tagsToAdd.add(tag);
                } else {
                    newKeys[keyIndex + 1] = tag.getValue();
                }
            }
        }
        if (!tagsToAdd.isEmpty()) {
            int index = newKeys != null ? newKeys.length : 0;
            newKeys = newKeys != null ? Arrays.copyOf(newKeys, newKeys.length + 2 * tagsToAdd.size()) : new String[2 * tagsToAdd.size()];
            for (Map.Entry<String, String> tag : tagsToAdd) {
                newKeys[index++] = tag.getKey();
                newKeys[index++] = tag.getValue();
            }
        }
        keys = newKeys;
        keysChangedImpl(originalKeys);
    }

    /**
     * Scans a key/value array for a given key.
     * @param keys The key array. It is not modified. It may be null to indicate an empty array.
     * @param key The key to search for.
     * @return The position of that key in the keys array - which is always a multiple of 2 - or -1 if it was not found.
     */
    private static int indexOfKey(String[] keys, String key) {
        if (keys == null) {
            return -1;
        }
        for (int i = 0; i < keys.length; i += 2) {
            if (keys[i].equals(key)) {
                return i;
            }
        }
        return -1;
    }

    /**
     * Remove the given key from the list
     * <p>
     * Note that this method, like all methods that modify keys, is not synchronized and may lead to data corruption when being used
     * from multiple threads.
     *
     * @param key  the key to be removed. Ignored, if key is null.
     */
    @Override
    public void remove(String key) {
        if (key == null || keys == null) return;
        if (!hasKey(key))
            return;
        Map<String, String> originalKeys = getKeys();
        if (keys.length == 2) {
            keys = null;
            keysChangedImpl(originalKeys);
            return;
        }
        String[] newKeys = new String[keys.length - 2];
        int j = 0;
        for (int i = 0; i < keys.length; i += 2) {
            if (!keys[i].equals(key)) {
                newKeys[j++] = keys[i];
                newKeys[j++] = keys[i+1];
            }
        }
        keys = newKeys;
        keysChangedImpl(originalKeys);
    }

    /**
     * Removes all keys from this primitive.
     * <p>
     * Note that this method, like all methods that modify keys, is not synchronized and may lead to data corruption when being used
     * from multiple threads.
     */
    @Override
    public void removeAll() {
        if (keys != null) {
            Map<String, String> originalKeys = getKeys();
            keys = null;
            keysChangedImpl(originalKeys);
        }
    }

    protected final String doGet(String key, BiPredicate<String, String> predicate) {
        if (key == null)
            return null;
        if (keys == null)
            return null;
        for (int i = 0; i < keys.length; i += 2) {
            if (predicate.test(keys[i], key)) return keys[i+1];
        }
        return null;
    }

    /**
     * Replies the value for key <code>key</code>. Replies null, if <code>key</code> is null.
     * Replies null, if there is no value for the given key.
     *
     * @param key the key. Can be null, replies null in this case.
     * @return the value for key <code>key</code>.
     */
    @Override
    public final String get(String key) {
        return doGet(key, String::equals);
    }

    /**
     * Gets a key ignoring the case of the key
     * @param key The key to get
     * @return The value for a key that matches the given key ignoring case.
     */
    public final String getIgnoreCase(String key) {
        return doGet(key, String::equalsIgnoreCase);
    }

    @Override
    public final int getNumKeys() {
        return keys == null ? 0 : keys.length / 2;
    }

    @Override
    public final Collection<String> keySet() {
        String[] tKeys = this.keys;
        if (tKeys == null) {
            return Collections.emptySet();
        }
        if (tKeys.length == 2) {
            return Collections.singleton(tKeys[0]);
        }

        final Set<String> result = new HashSet<>(Utils.hashMapInitialCapacity(tKeys.length / 2));
        for (int i = 0; i < tKeys.length; i += 2) {
            result.add(tKeys[i]);
        }
        return result;
    }

    @Override
    public Stream<String> keys() {
        final String[] k = this.keys;
        if (k == null) {
            return Stream.empty();
        } else if (k.length == 2) {
            return Stream.of(k[0]);
        } else {
            return IntStream.range(0, k.length / 2).mapToObj(i -> k[i * 2]);
        }
    }

    /**
     * Replies true, if the map of key/value pairs of this primitive is not empty.
     *
     * @return true, if the map of key/value pairs of this primitive is not empty; false otherwise
     */
    @Override
    public final boolean hasKeys() {
        return keys != null;
    }

    /**
     * Replies true if this primitive has a tag with key <code>key</code>.
     *
     * @param key the key
     * @return true, if this primitive has a tag with key <code>key</code>
     */
    @Override
    public boolean hasKey(String key) {
        return key != null && indexOfKey(keys, key) >= 0;
    }

    /**
     * Replies true if this primitive has a tag any of the <code>keys</code>.
     *
     * @param keys the keys
     * @return true, if this primitive has a tag with any of the <code>keys</code>
     * @since 11587
     */
    public boolean hasKey(String... keys) {
        if (keys != null) {
            for (String key : keys) {
                if (this.hasKey(key)) {
                    return true;
                }
            }
        }
        return false;
    }

    /**
     * What to do, when the tags have changed by one of the tag-changing methods.
     * @param originalKeys original tags
     */
    protected abstract void keysChangedImpl(Map<String, String> originalKeys);

    /*-------------------------------------
     * WORK IN PROGRESS, UNINTERESTING KEYS
     *-------------------------------------*/

    private static volatile Collection<String> workinprogress;
    private static volatile Collection<String> uninteresting;
    private static volatile Collection<String> discardable;

    /**
     * Returns a list of "uninteresting" keys that do not make an object
     * "tagged".  Entries that end with ':' are causing a whole namespace to be considered
     * "uninteresting".  Only the first level namespace is considered.
     * Initialized by isUninterestingKey()
     * @return The list of uninteresting keys.
     */
    public static Collection<String> getUninterestingKeys() {
        if (uninteresting == null) {
            List<String> l = new LinkedList<>(Arrays.asList(
                "source", "source_ref", "source:", "comment", "import",
                "watch", "watch:", "description", "attribution", GpxConstants.GPX_PREFIX));
            l.addAll(getDiscardableKeys());
            l.addAll(getWorkInProgressKeys());
            uninteresting = new HashSet<>(Config.getPref().getList("tags.uninteresting", l));
        }
        return uninteresting;
    }

    /**
     * Returns a list of keys which have been deemed uninteresting to the point
     * that they can be silently removed from data which is being edited.
     * @return The list of discardable keys.
     */
    public static Collection<String> getDiscardableKeys() {
        if (discardable == null) {
            discardable = new HashSet<>(Config.getPref().getList("tags.discardable",
                    Arrays.asList(
                            "created_by",
                            "converted_by",
                            "current_id", /* prevent export of this JOSM internal information, see OsmReader */
                            "geobase:datasetName",
                            "geobase:uuid",
                            "KSJ2:ADS",
                            "KSJ2:ARE",
                            "KSJ2:AdminArea",
                            "KSJ2:COP_label",
                            "KSJ2:DFD",
                            "KSJ2:INT",
                            "KSJ2:INT_label",
                            "KSJ2:LOC",
                            "KSJ2:LPN",
                            "KSJ2:OPC",
                            "KSJ2:PubFacAdmin",
                            "KSJ2:RAC",
                            "KSJ2:RAC_label",
                            "KSJ2:RIC",
                            "KSJ2:RIN",
                            "KSJ2:WSC",
                            "KSJ2:coordinate",
                            "KSJ2:curve_id",
                            "KSJ2:curve_type",
                            "KSJ2:filename",
                            "KSJ2:lake_id",
                            "KSJ2:lat",
                            "KSJ2:long",
                            "KSJ2:river_id",
                            "odbl",
                            "odbl:note",
                            "osmarender:nameDirection",
                            "osmarender:renderName",
                            "osmarender:renderRef",
                            "osmarender:rendernames",
                            "SK53_bulk:load",
                            "sub_sea:type",
                            "tiger:source",
                            "tiger:separated",
                            "tiger:tlid",
                            "tiger:upload_uuid",
                            "import_uuid",
                            "gnis:import_uuid",
                            "yh:LINE_NAME",
                            "yh:LINE_NUM",
                            "yh:STRUCTURE",
                            "yh:TOTYUMONO",
                            "yh:TYPE",
                            "yh:WIDTH",
                            "yh:WIDTH_RANK"
                        )));
        }
        return discardable;
    }

    /**
     * Returns a list of "work in progress" keys that do not make an object
     * "tagged" but "annotated".
     * @return The list of work in progress keys.
     * @since 5754
     */
    public static Collection<String> getWorkInProgressKeys() {
        if (workinprogress == null) {
            workinprogress = new HashSet<>(Config.getPref().getList("tags.workinprogress",
                    Arrays.asList("note", "fixme", "FIXME")));
        }
        return workinprogress;
    }

    /**
     * Determines if key is considered "uninteresting".
     * @param key The key to check
     * @return true if key is considered "uninteresting".
     */
    public static boolean isUninterestingKey(String key) {
        getUninterestingKeys();
        if (uninteresting.contains(key))
            return true;
        int pos = key.indexOf(':');
        if (pos > 0)
            return uninteresting.contains(key.substring(0, pos + 1));
        return false;
    }

    @Override
    public Map<String, String> getInterestingTags() {
        Map<String, String> result = new HashMap<>();
        if (keys != null) {
            for (int i = 0; i < keys.length; i += 2) {
                if (!isUninterestingKey(keys[i])) {
                    result.put(keys[i], keys[i + 1]);
                }
            }
        }
        return result;
    }
}