/*
 * Copyright 2009 Google Inc.
 *
 * 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 de.dennisguse.opentracks.stats;

import androidx.annotation.NonNull;

/**
 * This class maintains a ring buffer of doubles.
 * This buffer is a convenient class for storing a series of doubles and calculating information about them.
 * This is a FIFO buffer.
 *
 * @author Sandor Dornbush
 */
class DoubleRingBuffer {

    // The sliding buffer of doubles.
    private final double[] buffer;

    // The location that the next write will occur at.
    private int index;

    // True if the buffer is full
    private boolean isFull;

    /**
     * Creates a buffer with a certain size.
     *
     * @param size the size
     */
    DoubleRingBuffer(int size) {
        if (size < 1) {
            throw new IllegalArgumentException("The buffer size must be greater than 1.");
        }
        buffer = new double[size];
        reset();
    }

    /**
     * Resets the buffer.
     */
    public void reset() {
        index = 0;
        isFull = false;
    }

    /**
     * Returns true if the buffer is full.
     */
    boolean isFull() {
        return isFull;
    }

    /**
     * Gets the average of the buffer.
     */
    public double getAverage() {
        int numberOfEntries = isFull ? buffer.length : index;
        if (numberOfEntries == 0) {
            return 0;
        }
        double sum = 0;
        for (int i = 0; i < numberOfEntries; i++) {
            sum += buffer[i];
        }
        return sum / numberOfEntries;
    }

    /**
     * Adds a double to the buffer.
     * If the buffer is full the oldest element is overwritten.
     *
     * @param value the double to add
     */
    public void setNext(double value) {
        if (index == buffer.length) {
            index = 0;
        }
        buffer[index] = value;
        index++;
        if (index == buffer.length) {
            isFull = true;
        }
    }

    @NonNull
    @Override
    public String toString() {
        StringBuilder builder = new StringBuilder("Full: ");
        builder.append(isFull);
        builder.append("\n");
        for (int i = 0; i < buffer.length; i++) {
            builder.append((i == index) ? "<<" : "[");
            builder.append(buffer[i]);
            builder.append((i == index) ? ">> " : "] ");
        }
        return builder.toString();
    }
}