/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.flink.queryablestate.client.state;

import org.apache.flink.api.common.state.State;
import org.apache.flink.api.common.state.StateDescriptor;
import org.apache.flink.api.common.state.ValueState;
import org.apache.flink.api.common.state.ValueStateDescriptor;
import org.apache.flink.queryablestate.client.state.serialization.KvStateSerializer;
import org.apache.flink.util.Preconditions;

import java.io.IOException;

/**
 * A read-only {@link ValueState} that does not allow for modifications.
 *
 * <p>This is the result returned when querying Flink's keyed state using the {@link
 * org.apache.flink.queryablestate.client.QueryableStateClient Queryable State Client} and providing
 * an {@link ValueStateDescriptor}.
 */
public final class ImmutableValueState<V> extends ImmutableState implements ValueState<V> {

    private final V value;

    private ImmutableValueState(V value) {
        this.value = Preconditions.checkNotNull(value);
    }

    @Override
    public V value() {
        return value;
    }

    @Override
    public void update(V newValue) {
        throw MODIFICATION_ATTEMPT_ERROR;
    }

    @Override
    public void clear() {
        throw MODIFICATION_ATTEMPT_ERROR;
    }

    @SuppressWarnings("unchecked")
    public static <V, S extends State> S createState(
            StateDescriptor<S, V> stateDescriptor, byte[] serializedState) throws IOException {
        final V state =
                KvStateSerializer.deserializeValue(
                        serializedState, stateDescriptor.getSerializer());
        return (S) new ImmutableValueState<>(state);
    }
}
