/*
 * The MIT License
 *
 * Copyright (c) 2010 The Broad Institute
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package htsjdk.samtools;

import htsjdk.samtools.util.CloseableIterator;
import htsjdk.samtools.util.CloserUtil;
import htsjdk.samtools.util.FileAppendStreamLRUCache;
import htsjdk.samtools.util.IOUtil;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

/**
 * Holds info about a mate pair for use when processing a coordinate sorted file.  When one read of a pair is encountered,
 * the caller should add a record to this map.  When the other read of a pair is encountered, the record should be removed.
 * This class assumes that reads will be processed in order of reference sequence index.  When the map is queried for
 * a record for a given reference sequence index, all the records for that sequence are loaded from temp file into RAM, so there
 * must be sufficient RAM to hold all the records for one reference sequence.  If the records are not processed in
 * reference sequence order, loading and unloading of records will cause performance to be terrible.
 * @param <KEY> KEY + reference sequence index are used to identify the record being stored or retrieved.
 * @param <REC> The type of record being retrieved.
 */
public class CoordinateSortedPairInfoMap<KEY, REC> implements Iterable<Map.Entry<KEY, REC>> {
    // -1 is a valid sequence index in this case
    private final int INVALID_SEQUENCE_INDEX = -2;
    /**
     * directory where files will go
     */
    private final File workDir = IOUtil.createTempDir("CSPI.", null);
    private int sequenceIndexOfMapInRam = INVALID_SEQUENCE_INDEX;
    private Map<KEY, REC> mapInRam = null;
    private final FileAppendStreamLRUCache outputStreams;
    private final Codec<KEY, REC> elementCodec;
    // Key is reference index (which is in the range [-1 .. max sequence index].
    // Value is the number of records on disk for this index.
    private final Map<Integer, Integer> sizeOfMapOnDisk = new HashMap<Integer, Integer>();

    // No other methods may be called when iteration is in progress, because iteration depends on and changes
    // internal state.
    private boolean iterationInProgress = false;

    public CoordinateSortedPairInfoMap(final int maxOpenFiles, final Codec<KEY, REC> elementCodec) {
        this.elementCodec = elementCodec;
        workDir.deleteOnExit();
        outputStreams = new FileAppendStreamLRUCache(maxOpenFiles);
    }

    /**
     *
     * @param sequenceIndex
     * @param key
     * @return The record corresponding to the given sequenceIndex and key, or null if it is not present.
     */
    public REC remove(final int sequenceIndex, final KEY key) {
        if (iterationInProgress) throw new IllegalStateException("Cannot be called when iteration is in progress");
        ensureSequenceLoaded(sequenceIndex);
        return mapInRam.remove(key);
    }

    private void ensureSequenceLoaded(final int sequenceIndex) {
        try {
            if (sequenceIndexOfMapInRam == sequenceIndex) {
                return;
            }

            // Spill map in RAM to disk
            if (mapInRam != null) {
                final File spillFile = makeFileForSequence(sequenceIndexOfMapInRam);
                if (spillFile.exists()) throw new IllegalStateException(spillFile + " should not exist.");
                if (!mapInRam.isEmpty()) {
                    // Do not create file or entry in sizeOfMapOnDisk if there is nothing to write.
                    final OutputStream os = getOutputStreamForSequence(sequenceIndexOfMapInRam);
                    elementCodec.setOutputStream(os);
                    for (final Map.Entry<KEY, REC> entry : mapInRam.entrySet()) {
                        elementCodec.encode(entry.getKey(), entry.getValue());
                    }
                    sizeOfMapOnDisk.put(sequenceIndexOfMapInRam, mapInRam.size());
                    mapInRam.clear();
                }
            } else {
                mapInRam = new HashMap<KEY, REC>();
            }

            sequenceIndexOfMapInRam = sequenceIndex;

            // Load map from disk if it existed
            File mapOnDisk = makeFileForSequence(sequenceIndex);
            if (outputStreams.containsKey(mapOnDisk)) {
                outputStreams.remove(mapOnDisk).close();
            }
            final Integer numRecords = sizeOfMapOnDisk.remove(sequenceIndex);
            if (mapOnDisk.exists()) {
                if (numRecords == null)
                    throw new IllegalStateException("null numRecords for " + mapOnDisk);
                FileInputStream is = null;
                try {
                    is = new FileInputStream(mapOnDisk);
                    elementCodec.setInputStream(is);
                    for (int i = 0; i < numRecords; ++i) {
                        final Map.Entry<KEY, REC> keyAndRecord = elementCodec.decode();
                        if (mapInRam.containsKey(keyAndRecord.getKey()))
                            throw new SAMException("Value was put into PairInfoMap more than once.  " +
                                    sequenceIndex + ": " + keyAndRecord.getKey());
                        mapInRam.put(keyAndRecord.getKey(), keyAndRecord.getValue());
                    }
                } finally {
                    CloserUtil.close(is);
                }
                htsjdk.samtools.util.IOUtil.deleteFiles(mapOnDisk);
            } else if (numRecords != null && numRecords > 0)
                throw new IllegalStateException("Non-zero numRecords but " + mapOnDisk + " does not exist");
        } catch (IOException e) {
            throw new SAMException("Error loading new map from disk.", e);
        }
    }

    /**
     * Store the record with the given sequence index and key.  It is assumed that value did not previously exist
     * in the map, and an exception is thrown (possibly at a later time) if that is not the case.
     * @param sequenceIndex
     * @param key
     * @param record
     */
    public void put(final int sequenceIndex, final KEY key, final REC record) {
        if (iterationInProgress) throw new IllegalStateException("Cannot be called when iteration is in progress");
        if (sequenceIndex == sequenceIndexOfMapInRam) {
            // Store in RAM map
            if (mapInRam.containsKey(key))
                throw new IllegalArgumentException("Putting value into PairInfoMap that already existed. " +
                        sequenceIndex + ": " + key);
            mapInRam.put(key, record);
        } else {
            // Append to file
            final OutputStream os = getOutputStreamForSequence(sequenceIndex);
            elementCodec.setOutputStream(os);
            elementCodec.encode(key, record);
            Integer prevCount = sizeOfMapOnDisk.get(sequenceIndex);
            if (prevCount == null) prevCount = 0;
            sizeOfMapOnDisk.put(sequenceIndex,  prevCount + 1);
        }
    }

    private File makeFileForSequence(final int index) {
        final File file = new File(workDir, index + ".tmp");
        file.deleteOnExit();
        return file;
    }

    private OutputStream getOutputStreamForSequence(final int mateSequenceIndex) {
        return outputStreams.get(makeFileForSequence(mateSequenceIndex));
    }

    public int size() {
        int total = sizeInRam();
        for (final Integer mapSize : sizeOfMapOnDisk.values()) {
            if (mapSize != null) {
                total += mapSize;
            }
        }
        return total;
    }

    /**
     * @return number of elements stored in RAM.  Always <= size()
     */
    public int sizeInRam() {
        return mapInRam != null? mapInRam.size(): 0;
    }

    /**
     * Creates an iterator over all elements in map, in arbitrary order.  Elements may not be added
     * or removed from map when iteration is in progress, nor may a second iteration be started.
     * Iterator must be closed in order to allow normal access to the map.
     */
    public CloseableIterator<Map.Entry<KEY, REC>> iterator() {
        if (iterationInProgress) throw new IllegalStateException("Cannot be called when iteration is in progress");
        iterationInProgress = true;
        return new MapIterator();
    }

    private class MapIterator implements CloseableIterator<Map.Entry<KEY, REC>> {
        private boolean closed = false;
        private Set<Integer> referenceIndices = new HashSet<Integer>(sizeOfMapOnDisk.keySet());
        private final Iterator<Integer> referenceIndexIterator;
        private Iterator<Map.Entry<KEY, REC>> currentReferenceIterator = null;

        private MapIterator() {
            if (sequenceIndexOfMapInRam != INVALID_SEQUENCE_INDEX)
                referenceIndices.add(sequenceIndexOfMapInRam);
            referenceIndexIterator = referenceIndices.iterator();
            advanceToNextNonEmptyReferenceIndex();
        }

        private void advanceToNextNonEmptyReferenceIndex() {
            while (referenceIndexIterator.hasNext()) {
                int nextReferenceIndex = referenceIndexIterator.next();
                ensureSequenceLoaded(nextReferenceIndex);
                if (!mapInRam.isEmpty()) {
                    createIteratorForMapInRam();
                    return;
                }
            }
            // no more.
            currentReferenceIterator = null;
        }

        private void createIteratorForMapInRam() {
            currentReferenceIterator = mapInRam.entrySet().iterator();
        }

        public void close() {
            closed = true;
            iterationInProgress = false;
        }

        public boolean hasNext() {
            if (closed) throw new IllegalStateException("Iterator has been closed");
            if (currentReferenceIterator != null && !currentReferenceIterator.hasNext())
                throw new IllegalStateException("Should not happen");
            return currentReferenceIterator != null;
        }

        public Map.Entry<KEY, REC> next() {
            if (closed) throw new IllegalStateException("Iterator has been closed");
            if (!hasNext()) throw new NoSuchElementException();
            final Map.Entry<KEY, REC> ret = currentReferenceIterator.next();
            if (!currentReferenceIterator.hasNext()) advanceToNextNonEmptyReferenceIndex();
            return ret;
        }

        public void remove() {
            throw new UnsupportedOperationException();
        }
    }

    /**
     * Client must implement this class, which defines the way in which records are written to and
     * read from file.
     */
    public interface Codec<KEY, REC> {
        /**
         * Where to write encoded output
         * @param os
         */
        void setOutputStream(OutputStream os);

        /**
         * Where to read encoded input from
         * @param is
         */
        void setInputStream(InputStream is);

        /**
         * Write object to output stream.  If the key is part of the record, then there is no need to write
         * it separately.
         */
        void encode(KEY key, REC record);

        /**
         * Read the next key and record from the input stream and convert into a java object.
         * @return null if no more records.  Should throw exception if EOF is encountered in the middle of
         * a record.
         */
        Map.Entry<KEY, REC> decode();

    }
}
