/*
 * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */
package org.opendaylight.controller.cluster.raft;

import java.util.ArrayList;
import java.util.List;

/**
 * Abstract class handling the mapping of
 * logical LogEntry Index and the physical list index.
 */
public abstract class AbstractReplicatedLogImpl implements ReplicatedLog {

    protected final List<ReplicatedLogEntry> journal;
    protected final Object snapshot;
    protected long snapshotIndex = -1;
    protected long snapshotTerm = -1;

    public AbstractReplicatedLogImpl(Object state, long snapshotIndex,
        long snapshotTerm, List<ReplicatedLogEntry> unAppliedEntries) {
        this.snapshot = state;
        this.snapshotIndex = snapshotIndex;
        this.snapshotTerm = snapshotTerm;
        this.journal = new ArrayList<>(unAppliedEntries);
    }


    public AbstractReplicatedLogImpl() {
        this.snapshot = null;
        this.journal = new ArrayList<>();
    }

    protected int adjustedIndex(long logEntryIndex) {
        if(snapshotIndex < 0){
            return (int) logEntryIndex;
        }
        return (int) (logEntryIndex - (snapshotIndex + 1));
    }

    @Override
    public ReplicatedLogEntry get(long logEntryIndex) {
        int adjustedIndex = adjustedIndex(logEntryIndex);

        if (adjustedIndex < 0 || adjustedIndex >= journal.size()) {
            // physical index should be less than list size and >= 0
            return null;
        }

        return journal.get(adjustedIndex);
    }

    @Override
    public ReplicatedLogEntry last() {
        if (journal.isEmpty()) {
            return null;
        }
        // get the last entry directly from the physical index
        return journal.get(journal.size() - 1);
    }

    @Override
    public long lastIndex() {
        if (journal.isEmpty()) {
            // it can happen that after snapshot, all the entries of the
            // journal are trimmed till lastApplied, so lastIndex = snapshotIndex
            return snapshotIndex;
        }
        return last().getIndex();
    }

    @Override
    public long lastTerm() {
        if (journal.isEmpty()) {
            // it can happen that after snapshot, all the entries of the
            // journal are trimmed till lastApplied, so lastTerm = snapshotTerm
            return snapshotTerm;
        }
        return last().getTerm();
    }

    @Override
    public void removeFrom(long logEntryIndex) {
        int adjustedIndex = adjustedIndex(logEntryIndex);
        if (adjustedIndex < 0 || adjustedIndex >= journal.size()) {
            // physical index should be less than list size and >= 0
            return;
        }
        journal.subList(adjustedIndex , journal.size()).clear();
    }

    @Override
    public void append(ReplicatedLogEntry replicatedLogEntry) {
        journal.add(replicatedLogEntry);
    }

    @Override
    public List<ReplicatedLogEntry> getFrom(long logEntryIndex) {
        int adjustedIndex = adjustedIndex(logEntryIndex);
        int size = journal.size();
        List<ReplicatedLogEntry> entries = new ArrayList<>(100);
        if (adjustedIndex >= 0 && adjustedIndex < size) {
            // physical index should be less than list size and >= 0
            entries.addAll(journal.subList(adjustedIndex, size));
        }
        return entries;
    }

    @Override
    public long size() {
       return journal.size();
    }

    @Override
    public boolean isPresent(long logEntryIndex) {
        if (logEntryIndex > lastIndex()) {
            // if the request logical index is less than the last present in the list
            return false;
        }
        int adjustedIndex = adjustedIndex(logEntryIndex);
        return (adjustedIndex >= 0);
    }

    @Override
    public boolean isInSnapshot(long logEntryIndex) {
        return logEntryIndex <= snapshotIndex;
    }

    @Override
    public Object getSnapshot() {
        return snapshot;
    }

    @Override
    public long getSnapshotIndex() {
        return snapshotIndex;
    }

    @Override
    public long getSnapshotTerm() {
        return snapshotTerm;
    }

    @Override
    public abstract void appendAndPersist(ReplicatedLogEntry replicatedLogEntry);

    @Override
    public abstract void removeFromAndPersist(long index);
}