/*
 * 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.paimon.utils;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.Function;

/** Incremental id generation. */
public class IDMapping<T> {

    private final Function<T, T> copy;

    private final List<T> values = new ArrayList<>();
    private final Map<T, Integer> indexMap = new HashMap<>();

    private int nextIndex = 0;

    public IDMapping(Function<T, T> copy) {
        this.copy = copy;
    }

    public int index(T t) {
        Integer index = indexMap.get(t);
        if (index == null) {
            index = nextIndex;
            nextIndex++;
            T copied = copy.apply(t);
            indexMap.put(copied, index);
            values.add(copied);
        }
        return index;
    }

    public T get(int index) {
        return values.get(index);
    }
}
