/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the "Elastic License
 * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
 * Public License v 1"; you may not use this file except in compliance with, at
 * your election, the "Elastic License 2.0", the "GNU Affero General Public
 * License v3.0 only", or the "Server Side Public License, v 1".
 */

package org.elasticsearch.common.collect;

import com.carrotsearch.hppc.ObjectCollection;
import com.carrotsearch.hppc.ObjectObjectHashMap;
import com.carrotsearch.hppc.cursors.ObjectObjectCursor;
import com.carrotsearch.hppc.procedures.ObjectObjectProcedure;
import com.carrotsearch.hppc.procedures.ObjectProcedure;

import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.BiConsumer;
import java.util.function.BiPredicate;
import java.util.function.Consumer;

/**
 * An immutable map implementation based on open hash map.
 * <p>
 * Can be constructed using a {@link #builder()}, or using {@link #builder(Map)} (which is an optimized
 * option to copy over existing content and modify it).
 */
public final class ImmutableOpenMap<KType, VType> extends AbstractMap<KType, VType> {

    private final ObjectObjectHashMap<KType, VType> map;

    /**
     * Holds cached entrySet().
     */
    private Set<Map.Entry<KType, VType>> entrySet;

    private ImmutableOpenMap(ObjectObjectHashMap<KType, VType> map) {
        this.map = map;
    }

    /**
     * @return Returns the value associated with the given key or the default value
     * for the key type, if the key is not associated with any value.
     * <p>
     * <b>Important note:</b> For primitive type values, the value returned for a non-existing
     * key may not be the default value of the primitive type (it may be any value previously
     * assigned to that slot).
     */
    @Override
    @SuppressWarnings("unchecked")
    public VType get(Object key) {
        return map.get((KType) key);
    }

    /**
     * @return Returns the value associated with the given key or the provided default value if the
     * key is not associated with any value.
     */
    @Override
    @SuppressWarnings("unchecked")
    public VType getOrDefault(Object key, VType defaultValue) {
        return map.getOrDefault((KType) key, defaultValue);
    }

    /**
     * Returns <code>true</code> if this container has an association to a value for
     * the given key.
     */
    @Override
    @SuppressWarnings("unchecked")
    public boolean containsKey(Object key) {
        return map.containsKey((KType) key);
    }

    @Override
    @SuppressWarnings("unchecked")
    public boolean containsValue(Object value) {
        return map.values().contains((VType) value);
    }

    @Override
    public VType remove(Object key) {
        throw new UnsupportedOperationException("modification is not supported");
    }

    @Override
    public int size() {
        return map.size();
    }

    @Override
    public boolean isEmpty() {
        return map.isEmpty();
    }

    @Override
    public Set<Map.Entry<KType, VType>> entrySet() {
        Set<Map.Entry<KType, VType>> es;
        return (es = entrySet) == null ? (entrySet = new EntrySet<>(map)) : es;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o instanceof ImmutableOpenMap<?, ?> immutableOpenMap) {
            return map.equals(immutableOpenMap.map);
        }
        return super.equals(o);
    }

    @Override
    public int hashCode() {
        // noop override to make checkstyle happy since we override equals
        return super.hashCode();
    }

    private static class EntrySet<KType, VType> extends AbstractSet<Map.Entry<KType, VType>> {
        private final ObjectObjectHashMap<KType, VType> map;

        private EntrySet(ObjectObjectHashMap<KType, VType> map) {
            this.map = map;
        }

        @Override
        public int size() {
            return map.size();
        }

        @Override
        public boolean isEmpty() {
            return map.isEmpty();
        }

        @Override
        public Iterator<Map.Entry<KType, VType>> iterator() {
            return Iterators.map(map.iterator(), c -> new AbstractMap.SimpleImmutableEntry<>(c.key, c.value));
        }

        @Override
        public Spliterator<Map.Entry<KType, VType>> spliterator() {
            return Spliterators.spliterator(iterator(), size(), Spliterator.IMMUTABLE);
        }

        @Override
        public void forEach(Consumer<? super Map.Entry<KType, VType>> action) {
            map.forEach(
                (Consumer<ObjectObjectCursor<KType, VType>>) c -> action.accept(new AbstractMap.SimpleImmutableEntry<>(c.key, c.value))
            );
        }

        @SuppressWarnings("unchecked")
        @Override
        public boolean contains(Object o) {
            if (o instanceof Map.Entry<?, ?> == false) {
                return false;
            }
            Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
            Object key = e.getKey();
            Object v = map.get((KType) key);
            if (v == null && map.containsKey((KType) key) == false) {
                return false;
            }
            return Objects.equals(v, e.getValue());
        }

        @Override
        public String toString() {
            return map.toString();
        }
    }

    private static class MapObjectCollection<Type> extends AbstractCollection<Type> {
        private final ObjectCollection<Type> collection;

        private MapObjectCollection(ObjectCollection<Type> collection) {
            this.collection = collection;
        }

        @Override
        public int size() {
            return collection.size();
        }

        @Override
        public boolean isEmpty() {
            return collection.isEmpty();
        }

        @Override
        public Iterator<Type> iterator() {
            return Iterators.map(collection.iterator(), c -> c.value);
        }

        @Override
        public Spliterator<Type> spliterator() {
            return Spliterators.spliterator(iterator(), size(), Spliterator.IMMUTABLE);
        }

        @Override
        public void forEach(Consumer<? super Type> action) {
            collection.forEach((ObjectProcedure<Type>) action::accept);
        }

        @Override
        @SuppressWarnings("unchecked")
        public boolean contains(Object o) {
            return collection.contains((Type) o);
        }

        @Override
        public boolean equals(Object obj) {
            return collection.equals(obj);
        }

        @Override
        public int hashCode() {
            return collection.hashCode();
        }

        @Override
        public String toString() {
            return collection.toString();
        }

        @Override
        public Object[] toArray() {
            return collection.toArray();
        }

        @Override
        @SuppressWarnings("unchecked")
        public <T> T[] toArray(T[] a) {
            return a.length == 0 ? (T[]) collection.toArray(a.getClass().getComponentType()) : super.toArray(a);
        }
    }

    private static class KeySet<KType, VType> extends MapObjectCollection<KType> implements Set<KType> {
        private KeySet(ObjectObjectHashMap<KType, VType>.KeysContainer keys) {
            super(keys);
        }
    };

    @Override
    public Set<KType> keySet() {
        return new KeySet<>(map.keys());
    }

    @Override
    public Collection<VType> values() {
        return new MapObjectCollection<>(map.values());
    }

    @Override
    public void forEach(BiConsumer<? super KType, ? super VType> action) {
        map.forEach((ObjectObjectProcedure<KType, VType>) action::accept);
    }

    @Override
    public String toString() {
        return map.toString();
    }

    @SuppressWarnings({ "unchecked", "rawtypes" })
    private static final ImmutableOpenMap EMPTY = new ImmutableOpenMap(new ObjectObjectHashMap());

    @SuppressWarnings("unchecked")
    public static <KType, VType> ImmutableOpenMap<KType, VType> of() {
        return EMPTY;
    }

    public static <KType, VType> Builder<KType, VType> builder() {
        return new Builder<>();
    }

    public static <KType, VType> Builder<KType, VType> builder(int size) {
        return new Builder<>(size);
    }

    public static <KType, VType> Builder<KType, VType> builder(Map<KType, VType> map) {
        if (map instanceof ImmutableOpenMap<KType, VType> iom) {
            return new Builder<>(iom);
        }
        Builder<KType, VType> builder = new Builder<>(map.size());
        builder.putAllFromMap(map);
        return builder;
    }

    public static <KType, VType> Builder<KType, VType> builder(KType key, VType value) {
        Builder<KType, VType> builder = new Builder<>(1);
        builder.put(key, value);
        return builder;
    }

    public static class Builder<KType, VType> {

        // if the Builder was constructed with a reference to an existing ImmutableOpenMap, then this will be non-null
        // (at least until the point where the builder has been used to actually make some changes to the map that is
        // being built -- see maybeCloneMap)
        private ImmutableOpenMap<KType, VType> reference;

        // if the Builder was constructed with a size (only), then this will be non-null (and reference will be null)
        private ObjectObjectHashMap<KType, VType> mutableMap;

        // n.b. a constructor can either set reference or it can set mutableMap, but it must not set both.

        /**
         * This method must be called before reading or writing via the {@code mutableMap} -- so every method
         * of builder should call this as the first thing it does. If {@code reference} is not null, it will be used to
         * populate {@code mutableMap} as a clone of the {@code reference} ImmutableOpenMap. It will then null out
         * {@code reference}.
         *
         * If {@code reference} is already null (and by extension, {@code mutableMap} is already *not* null),
         * then this method is a no-op.
         */
        private void maybeCloneMap() {
            if (reference != null) {
                this.mutableMap = reference.map.clone(); // make a mutable clone of the reference ImmutableOpenMap
                this.reference = null; // and throw away the reference, we now rely on mutableMap
            }
        }

        @SuppressWarnings("unchecked")
        public Builder() {
            this(EMPTY);
        }

        public Builder(int size) {
            this.mutableMap = new ObjectObjectHashMap<>(size);
        }

        public Builder(ImmutableOpenMap<KType, VType> immutableOpenMap) {
            this.reference = Objects.requireNonNull(immutableOpenMap);
        }

        /**
         * Builds a new ImmutableOpenMap from this builder.
         */
        public ImmutableOpenMap<KType, VType> build() {
            if (reference != null) {
                ImmutableOpenMap<KType, VType> reference = this.reference;
                this.reference = null; // null out the reference so that you can't reuse this builder
                return reference;
            } else {
                ObjectObjectHashMap<KType, VType> mutableMap = this.mutableMap;
                this.mutableMap = null; // null out the map so that you can't reuse this builder
                return mutableMap.isEmpty() ? of() : new ImmutableOpenMap<>(mutableMap);
            }
        }

        /**
         * Puts all the entries in the map to the builder.
         */
        public Builder<KType, VType> putAllFromMap(Map<KType, VType> map) {
            maybeCloneMap();
            map.forEach(mutableMap::put);
            return this;
        }

        /**
         * A put operation that can be used in the fluent pattern.
         */
        public Builder<KType, VType> fPut(KType key, VType value) {
            maybeCloneMap();
            mutableMap.put(key, value);
            return this;
        }

        public VType put(KType key, VType value) {
            maybeCloneMap();
            return mutableMap.put(key, value);
        }

        public VType get(KType key) {
            maybeCloneMap();
            return mutableMap.get(key);
        }

        public VType getOrDefault(KType kType, VType vType) {
            maybeCloneMap();
            return mutableMap.getOrDefault(kType, vType);
        }

        public VType remove(KType key) {
            maybeCloneMap();
            return mutableMap.remove(key);
        }

        public boolean containsKey(KType key) {
            maybeCloneMap();
            return mutableMap.containsKey(key);
        }

        public int size() {
            maybeCloneMap();
            return mutableMap.size();
        }

        public void clear() {
            maybeCloneMap();
            mutableMap.clear();
        }

        public Set<KType> keys() {
            maybeCloneMap();
            return new KeySet<>(mutableMap.keys());
        }

        public int removeAll(BiPredicate<? super KType, ? super VType> predicate) {
            maybeCloneMap();
            return mutableMap.removeAll(predicate::test);
        }

    }
}