io.questdb.griffin.engine.table.SequentialRowCursorFactory Maven / Gradle / Ivy

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 *
 *  Copyright (c) 2014-2019 Appsicle
 *  Copyright (c) 2019-2020 QuestDB
 *
 *  Licensed 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.
 *
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package io.questdb.griffin.engine.table;

import io.questdb.cairo.TableReader;
import io.questdb.cairo.sql.DataFrame;
import io.questdb.cairo.sql.RowCursor;
import io.questdb.cairo.sql.RowCursorFactory;
import io.questdb.std.ObjList;

public class SequentialRowCursorFactory implements RowCursorFactory {
    private final ObjList cursorFactories;
    private final ObjList cursors;
    private final SequentialRowCursor cursor;

    public SequentialRowCursorFactory(ObjList cursorFactories) {
        this.cursorFactories = cursorFactories;
        this.cursors = new ObjList<>();
        this.cursor = new SequentialRowCursor(cursorFactories.size() - 1);
    }

    @Override
    public boolean isEntity() {
        return false;
    }

    @Override
    public RowCursor getCursor(DataFrame dataFrame) {
        for (int i = 0, n = cursorFactories.size(); i < n; i++) {
            cursors.extendAndSet(i, cursorFactories.getQuick(i).getCursor(dataFrame));
        }
        cursor.init();
        return cursor;
    }

    @Override
    public void prepareCursor(TableReader tableReader) {
        RowCursorFactory.prepareCursor(cursorFactories, tableReader);
    }

    private class SequentialRowCursor implements RowCursor {
        private final int cursorIndexLimit;
        private int cursorIndex = 0;
        private RowCursor currentCursor;

        public SequentialRowCursor(int cursorIndexLimit) {
            this.cursorIndexLimit = cursorIndexLimit;
        }

        private void init() {
            this.cursorIndex = 0;
            if (cursorIndex < cursorIndexLimit) {
                currentCursor = cursors.getQuick(cursorIndex);
            }
        }

        @Override
        public boolean hasNext() {
            boolean hasNext = currentCursor.hasNext();
            if (hasNext) {
                return true;
            }

            while (cursorIndex < cursorIndexLimit) {
                currentCursor = cursors.getQuick(++cursorIndex);
                if (currentCursor.hasNext()) {
                    return true;
                }
            }

            return false;
        }

        @Override
        public long next() {
            return currentCursor.next();
        }
    }
}