/*
 * 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.cassandra.dht;

import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

Partition splitter.
/**
 * Partition splitter.
 */
public abstract class Splitter
{
    private final IPartitioner partitioner;

    protected Splitter(IPartitioner partitioner)
    {
        this.partitioner = partitioner;
    }

    protected abstract Token tokenForValue(BigInteger value);

    protected abstract BigInteger valueForToken(Token token);

    public List<Token> splitOwnedRanges(int parts, List<Range<Token>> localRanges, boolean dontSplitRanges)
    {
        if (localRanges.isEmpty() || parts == 1)
            return Collections.singletonList(partitioner.getMaximumToken());

        BigInteger totalTokens = BigInteger.ZERO;
        for (Range<Token> r : localRanges)
        {
            BigInteger right = valueForToken(token(r.right));
            totalTokens = totalTokens.add(right.subtract(valueForToken(r.left)));
        }
        BigInteger perPart = totalTokens.divide(BigInteger.valueOf(parts));
        // the range owned is so tiny we can't split it:
        if (perPart.equals(BigInteger.ZERO))
            return Collections.singletonList(partitioner.getMaximumToken());

        if (dontSplitRanges)
            return splitOwnedRangesNoPartialRanges(localRanges, perPart, parts);

        List<Token> boundaries = new ArrayList<>();
        BigInteger sum = BigInteger.ZERO;
        for (Range<Token> r : localRanges)
        {
            Token right = token(r.right);
            BigInteger currentRangeWidth = valueForToken(right).subtract(valueForToken(r.left)).abs();
            BigInteger left = valueForToken(r.left);
            while (sum.add(currentRangeWidth).compareTo(perPart) >= 0)
            {
                BigInteger withinRangeBoundary = perPart.subtract(sum);
                left = left.add(withinRangeBoundary);
                boundaries.add(tokenForValue(left));
                currentRangeWidth = currentRangeWidth.subtract(withinRangeBoundary);
                sum = BigInteger.ZERO;
            }
            sum = sum.add(currentRangeWidth);
        }
        boundaries.set(boundaries.size() - 1, partitioner.getMaximumToken());

        assert boundaries.size() == parts : boundaries.size() + "!=" + parts + " " + boundaries + ":" + localRanges;
        return boundaries;
    }

    private List<Token> splitOwnedRangesNoPartialRanges(List<Range<Token>> localRanges, BigInteger perPart, int parts)
    {
        List<Token> boundaries = new ArrayList<>(parts);
        BigInteger sum = BigInteger.ZERO;

        int i = 0;
        final int rangesCount = localRanges.size();
        while (boundaries.size() < parts - 1 && i < rangesCount - 1)
        {
            Range<Token> r = localRanges.get(i);
            Range<Token> nextRange = localRanges.get(i + 1);
            Token right = token(r.right);
            Token nextRight = token(nextRange.right);

            BigInteger currentRangeWidth = valueForToken(right).subtract(valueForToken(r.left));
            BigInteger nextRangeWidth = valueForToken(nextRight).subtract(valueForToken(nextRange.left));
            sum = sum.add(currentRangeWidth);

            // does this or next range take us beyond the per part limit?
            if (sum.compareTo(perPart) > 0 || sum.add(nextRangeWidth).compareTo(perPart) > 0)
            {
                // Either this or the next range will take us beyond the perPart limit. Will stopping now or
                // adding the next range create the smallest difference to perPart?
                BigInteger diffCurrent = sum.subtract(perPart).abs();
                BigInteger diffNext = sum.add(nextRangeWidth).subtract(perPart).abs();
                if (diffNext.compareTo(diffCurrent) >= 0)
                {
                    sum = BigInteger.ZERO;
                    boundaries.add(right);
                }
            }
            i++;
        }
        boundaries.add(partitioner.getMaximumToken());
        return boundaries;
    }

    
We avoid calculating for wrap around ranges, instead we use the actual max token, and then, when translating
to PartitionPositions, we include tokens from .minKeyBound to .maxKeyBound to make sure we include all tokens.
/**
     * We avoid calculating for wrap around ranges, instead we use the actual max token, and then, when translating
     * to PartitionPositions, we include tokens from .minKeyBound to .maxKeyBound to make sure we include all tokens.
     */
    private Token token(Token t)
    {
        return t.equals(partitioner.getMinimumToken()) ? partitioner.getMaximumToken() : t;
    }

}