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QuestDB is High Performance Time Series Database
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 * Copyright (C) 2014-2016 Appsicle
 *
 * This program is free software: you can redistribute it and/or  modify
 * it under the terms of the GNU Affero General Public License, version 3,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
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package com.questdb.iter;

import com.questdb.Journal;
import com.questdb.Partition;
import com.questdb.ex.JournalException;
import com.questdb.ex.JournalRuntimeException;
import com.questdb.misc.Rows;
import com.questdb.std.AbstractImmutableIterator;
import com.questdb.std.ObjList;

public class JournalBufferedIterator extends AbstractImmutableIterator implements JournalPeekingIterator {
    private final ObjList ranges;
    private final Journal journal;
    private final T obj;
    private boolean hasNext = true;
    private int currentIndex = 0;
    private long currentRowID;
    private long currentUpperBound;
    private Partition partition;

    public JournalBufferedIterator(Journal journal, ObjList ranges) {
        this.ranges = ranges;
        this.journal = journal;
        this.obj = journal.newObject();
        updateVariables();
    }

    @Override
    public Journal getJournal() {
        return journal;
    }

    @Override
    public boolean hasNext() {
        return hasNext;
    }

    @Override
    public T next() {
        partition.read(currentRowID, obj);
        if (currentRowID < currentUpperBound) {
            currentRowID++;
        } else {
            currentIndex++;
            updateVariables();
        }
        return obj;
    }

    @Override
    public boolean isEmpty() {
        return ranges == null || ranges.size() == 0;
    }

    @Override
    public T peekFirst() {
        JournalIteratorRange w = ranges.get(0);
        try {
            journal.read(Rows.toRowID(w.partitionID, w.lo), obj);
            return obj;
        } catch (JournalException e) {
            throw new JournalRuntimeException("Error in iterator at last element", e);
        }
    }

    @Override
    public T peekLast() {
        JournalIteratorRange w = ranges.getLast();
        try {
            journal.read(Rows.toRowID(w.partitionID, w.hi), obj);
            return obj;
        } catch (JournalException e) {
            throw new JournalRuntimeException("Error in iterator at last element", e);
        }
    }

    private void updateVariables() {
        if (currentIndex < ranges.size()) {
            JournalIteratorRange w = ranges.getQuick(currentIndex);
            currentRowID = w.lo;
            currentUpperBound = w.hi;
            try {
                partition = journal.getPartition(w.partitionID, true);
            } catch (JournalException e) {
                throw new JournalRuntimeException(e);
            }
        } else {
            hasNext = false;
        }
    }
}