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// Burton Computer Corporation
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package org.javimmutable.collections;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.Immutable;
import java.util.Iterator;
import java.util.stream.Collector;

/**
 * Interface for maps that map keys to lists of values.
 */
@Immutable
public interface JImmutableListMap
    extends Insertable, JImmutableListMap>,
            Mapped>,
            IterableStreamable>>,
            Cursorable>>,
            InvariantCheckable
{
    /**
     * Return the list associated with key or an empty list if no list is associated.
     *
     * @param key identifies the value to retrieve
     * @return list associated with key or an empty list if no value is associated
     */
    @Nonnull
    JImmutableList getList(@Nonnull K key);

    /**
     * Sets the list associated with a specific key.  Key and value must be non-null.
     * If the key already has a list in the map the old list is discarded
     * and the new list is stored in its place.  Returns a new JImmutableListMap reflecting
     * any changes.  The original map is always left unchanged.
     *
     * @param key   non-null key
     * @param value list of possibly null values to use for this key
     * @return new map reflecting the change
     */
    @Nonnull
    JImmutableListMap assign(@Nonnull K key,
                                   @Nonnull JImmutableList value);

    /**
     * Add key/value entry to the map, replacing any existing entry with same key.
     */
    @Nonnull
    @Override
    JImmutableListMap insert(@Nonnull JImmutableMap.Entry value);

    /**
     * Add value to the list for the specified key.  Note that this can create duplicate values
     * in the list.
     */
    @Nonnull
    JImmutableListMap insert(@Nonnull K key,
                                   @Nullable V value);

    /**
     * Adds all of the elements of the specified collection to the List for the specified key.
     */
    @Nonnull
    default JImmutableListMap insertAll(@Nonnull K key,
                                              @Nonnull Iterable values)
    {
        return assign(key, getList(key).insertAll(values));
    }

    /**
     * Adds all of the elements of the specified collection to the List for the specified key.
     */
    @Nonnull
    default JImmutableListMap insertAll(@Nonnull K key,
                                              @Nonnull Cursor values)
    {
        return assign(key, getList(key).insertAll(values));
    }

    /**
     * Adds all of the elements of the specified collection to the List for the specified key.
     */
    @Nonnull
    default JImmutableListMap insertAll(@Nonnull K key,
                                              @Nonnull Iterator values)
    {
        return assign(key, getList(key).insertAll(values));
    }

    /**
     * Deletes the entry for the specified key (if any).  Returns a new map if the value
     * was deleted or the current map if the key was not contained in the map.
     *
     * @param key non-null key
     * @return same or different map depending on whether key was removed
     */
    @Nonnull
    JImmutableListMap delete(@Nonnull K key);

    /**
     * Deletes the list for every key in keys. Returns a new map if the keys were deleted or the
     * current map if the keys were contained in the map.
     */
    @Nonnull
    default JImmutableListMap deleteAll(@Nonnull Iterable keys)
    {
        return deleteAll(keys.iterator());
    }

    /**
     * Deletes the list for every key in keys. Returns a new map if the keys were deleted or the
     * current map if the keys were contained in the map.
     */
    @Nonnull
    default JImmutableListMap deleteAll(@Nonnull Cursor keys)
    {
        JImmutableListMap map = this;
        for (Cursor cursor = keys.start(); cursor.hasValue(); cursor = cursor.next()) {
            map = map.delete(cursor.getValue());
        }
        return map;
    }

    /**
     * Deletes the list for every key in keys. Returns a new map if the keys were deleted or the
     * current map if the keys were contained in the map.
     */
    @Nonnull
    default JImmutableListMap deleteAll(@Nonnull Iterator keys)
    {
        JImmutableListMap map = this;
        while (keys.hasNext()) {
            map = map.delete(keys.next());
        }
        return map;
    }

    /**
     * Apply the specified transform function to the List assigned to the specified key and assign the result
     * to the key in this map.  If no List is currently assigned to the key the transform function is called
     * with an empty list.
     *
     * @param key       key holding list to be updated
     * @param transform function to update the list
     * @return new map with update applied to list associated with key
     */
    default JImmutableListMap transform(@Nonnull K key,
                                              @Nonnull Func1, JImmutableList> transform)
    {
        final JImmutableList current = getList(key);
        final JImmutableList transformed = transform.apply(current);
        return (transformed == current) ? this : assign(key, transformed);
    }

    /**
     * Apply the specified transform function to the List assigned to the specified key and assign the result
     * to the key in this map.  If no list is currently assigned to the key the transform function is never
     * called and this map is returned unchanged.
     *
     * @param key       key holding list to be updated
     * @param transform function to update the list
     * @return new map with update applied to list associated with key
     */
    default JImmutableListMap transformIfPresent(@Nonnull K key,
                                                       @Nonnull Func1, JImmutableList> transform)
    {
        final JImmutableList current = get(key);
        if (current != null) {
            final JImmutableList transformed = transform.apply(current);
            if (transformed != current) {
                return assign(key, transformed);
            }
        }
        return this;
    }

    /**
     * Return the number of keys in the map.
     */
    int size();

    /**
     * @return true only if list contains no values
     */
    boolean isEmpty();

    /**
     * @return an equivalent collection with no values
     */
    @Nonnull
    JImmutableListMap deleteAll();

    /**
     * Creates a Cursor to access all of the Map's keys.
     */
    @Nonnull
    Cursor keysCursor();

    /**
     * Creates a Cursor to access all of the specified key's list.
     * If no list exists for key an empty cursor is returned.
     *
     * @return a (possibly empty) cursor for traversing the values associated with key
     */
    @Nonnull
    Cursor valuesCursor(@Nonnull K key);

    /**
     * Creates a Streamable to access all of the Map's keys.
     */
    @Nonnull
    IterableStreamable keys();

    /**
     * Creates a Streamable to access all of the specified key's list.
     * If no list exists for key an empty Streamable is returned.
     *
     * @return a (possibly empty) Streamable for traversing the values associated with key
     */
    @Nonnull
    IterableStreamable values(@Nonnull K key);

    /**
     * Creates a Streamable to access all of the Map's entries.
     */
    @Nonnull
    IterableStreamable> entries();

    /**
     * Returns a Collector that creates a listMap of the same type as this containing all
     * of the collected values inserted over whatever starting values this already contained.
     */
    @Nonnull
    default Collector, ?, JImmutableListMap> listMapCollector()
    {
        return GenericCollector.ordered(this, deleteAll(), a -> a.isEmpty(), (a, v) -> a.insert(v), (a, b) -> a.insertAll(b.entries()));
    }
}