/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.sysds.runtime.compress.utils;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public abstract class ACountHashMap<T> {
    protected static final Log LOG = LogFactory.getLog(ACountHashMap.class.getName());
    protected static final int RESIZE_FACTOR = 2;
    protected static final float LOAD_FACTOR = 0.80f;
    protected static final int shortCutSize = 10;

    protected int size;
    protected ACount<T>[] data;

    public ACountHashMap() {
        data = create(1);
        size = 0;
    }

    public ACountHashMap(int arrSize) {
        if(arrSize < shortCutSize)
            data = create(1);
        else {
            arrSize = (int) (arrSize * (1.0 / LOAD_FACTOR));
            arrSize += arrSize % 2 == 0 ? 1 : 0;
            data = create(arrSize);
        }
        size = 0;
    }

    public int size() {
        return size;
    }

    /**
     * Increment and return the id of the incremeted index.
     * 
     * @param key The key to increment
     * @return The id of the incremented entry.
     */
    public final int increment(T key) {
        return increment(key, 1);
    }

    /**
     * Increment and return the id of the incremented index.
     * 
     * @param key   The key to incremnt
     * @param count The number of times to increment the value
     * @return The Id of the incremented entry.
     */
    public final int increment(final T key, final int count) {
        // skip hash if data array is 1 length
        final int ix = data.length < shortCutSize ? 0 : hash(key) % data.length;

        final ACount<T> l = data[ix];
        if(l == null) {
            data[ix] = create(key, size);
            // never try to resize here since we use a new unused bucket.
            return size++;
        }
        else {
            final ACount<T> v = l.inc(key, count, size);
            if(v.id == size) {
                size++;
                resize();
                return size - 1;
            }
            else {
                // do not resize if not new.
                return v.id;
            }
        }
    }

    public int get(T key) {
        return getC(key).count;
    }

    public int getId(T key) {
        return getC(key).id;
    }

    public ACount<T> getC(T key) {
        int ix = data.length < shortCutSize ? 0 : hash(key) % data.length;
        ACount<T> l = data[ix];
        return l != null ? l.get(key) : null;
    }

    public int getOrDefault(T key, int def) {
        ACount<T> e = getC(key);
        return (e == null) ? def : e.count;
    }

    public final ACount<T>[] extractValues() {
        final ACount<T>[] ret = create(size);
        int i = 0;
        for(ACount<T> e : data) {
            while(e != null) {
                ret[i++] = e;
                e = e.next();
            }
        }
        return ret;
    }

    public T getMostFrequent() {
        T f = null;
        int fq = 0;
        for(ACount<T> e : data) {
            while(e != null) {
                if(e.count > fq) {
                    fq = e.count;
                    f = e.key();
                }
                e = e.next();
            }
        }
        return f;
    }

    private void resize() {
        if(size >= LOAD_FACTOR * data.length && size > shortCutSize)
            // +1 to make the hash buckets better
            resize(Math.max(data.length, shortCutSize) * RESIZE_FACTOR + 1);
    }

    private void resize(int underlying_size) {

        // resize data array and copy existing contents
        final ACount<T>[] olddata = data;
        data = create(underlying_size);

        // rehash all entries
        for(ACount<T> e : olddata)
            appendValue(e);
    }

    private void appendValue(ACount<T> ent) {
        if(ent != null) {
            // take the tail recursively first
            appendValue(ent.next()); // append tail first
            ent.setNext(null); // set this tail to null.
            final int ix = hash(ent.key()) % data.length;
            ACount<T> l = data[ix];
            data[ix] = ent;
            ent.setNext(l);
        }
    }

    public void sortBuckets() {
        if(size > 10)
            for(int i = 0; i < data.length; i++)
                if(data[i] != null)
                    data[i] = data[i].sort();
    }

    public void reset(int size) {
        this.data = create(size);
        this.size = 0;
    }

    protected abstract ACount<T>[] create(int size);

    protected abstract int hash(T key);

    protected abstract ACount<T> create(T key, int id);

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append(this.getClass().getSimpleName());
        for(int i = 0; i < data.length; i++)
            if(data[i] != null)
                sb.append(", " + data[i]);
        return sb.toString();
    }

}
