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/*
 * Copyright 2015-2017 OpenCB
 *
 * 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.
 */

package org.opencb.commons.io;

import org.opencb.commons.run.Task;

import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

/**
 * @author Alejandro Aleman Ramos 
 * @author Cristina Yenyxe Gonzalez Garcia 
 */
@FunctionalInterface
public interface DataReader extends Iterable {

    default boolean open() {
        return true;
    }

    default boolean close() {
        return true;
    }

    default boolean pre() {
        return true;
    }

    default boolean post() {
        return true;
    }

    default List read() {
        return read(1);
    }

    List read(int batchSize);

    default  DataReader then(Task task) {
        return new DataReader() {
            private boolean drained = false;
            @Override
            public boolean open() {
                return DataReader.this.open();
            }

            @Override
            public boolean pre() {
                try {
                    task.pre();
                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
                return DataReader.this.pre();
            }

            @Override
            public boolean close() {
                return DataReader.this.close();
            }

            @Override
            public boolean post() {
                try {
                    task.post();
                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
                return DataReader.this.post();
            }

            @Override
            public List read(int batch) {
                try {
                    List read = DataReader.this.read(batch);
                    // Iterate while reader has data
                    // Exit when reader is exhausted, or task produces data
                    while (read != null && !read.isEmpty()) {
                        List apply = task.apply(read);
                        if (apply != null && !apply.isEmpty()) {
                            // Valid task apply.
                            return apply;
                        } else {
                            // Empty task apply. Read more data
                            read = DataReader.this.read(batch);
                        }
                    }
                    // Reader is exhausted. Drain the task.
                    if (!drained) {
                        // Make sure that only drain once
                        drained = true;
                        return task.drain();
                    } else {
                        return Collections.emptyList();
                    }
                } catch (Exception e) {
                    // TODO: Reader should throw any exception
                    throw new RuntimeException(e);
                }
            }
        };
    }

    default Stream stream() {
        return StreamSupport.stream(spliterator(), false);
    }

    default Iterator iterator() {
        return iterator(1);
    }

    default Iterator iterator(int batchSize) {
        return new Iterator() {
            private boolean opened = false;
            private boolean closed = false;
            private Iterator batchIterator = Collections.emptyIterator();

            @Override
            public boolean hasNext() {
                if (!opened) {
                    open();
                    pre();
                    opened = true;
                }
                if (!batchIterator.hasNext()) {
                    if (!closed) {
                        batchIterator = read(batchSize).iterator();
                        if (!batchIterator.hasNext()) {
                            post();
                            close();
                            closed = true;
                        }
                    }
                }
                return batchIterator.hasNext();
            }

            @Override
            public T next() {
                if (!hasNext()) {
                    throw new NoSuchElementException();
                }
                return batchIterator.next();
            }
        };
    }

}