/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2018 Matthias P. Braendli
 *
 * 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.
 */

#pragma once

#include <vector>
#include <mutex>
#include <condition_variable>
#include <cmath>

template<class T>
class CircularBuffer
{
    public:
        CircularBuffer(size_t max_bufsize) :
            m_maxbufsize(max_bufsize)
        {
        }

        void set_ticks_per_sample(long long tps)
        {
            m_ticks_per_sample = tps;
        }

        /* Write num_elems from buf to the internal buffer, at the position
         * given by timestamp
         */
        void write(const T *buf, size_t num_elems, long long timestamp)
        {
            std::unique_lock<std::mutex> lock(m_mutex);

            if (m_timestamp_buf == 0 or timestamp < m_timestamp_buf) {
                // First time we write to our buf, or jump back in time,
                // we reset our buffer
                resetbuf();
                m_timestamp_buf = timestamp;
            }

            size_t sample_offset = (timestamp - m_timestamp_buf) /
                                    m_ticks_per_sample;
            size_t minsize = sample_offset + num_elems;

            if (minsize > m_maxbufsize) {
                truncatebuf();
                if (minsize > m_maxbufsize) {
                    resetbuf();
                    m_timestamp_buf = timestamp;
                    sample_offset = 0;
                    minsize = num_elems;
                }
            }

            if (m_buf.size() < minsize) {
                m_buf.resize(minsize);
            }
            std::copy(buf, buf + num_elems, m_buf.begin() + sample_offset);

            lock.unlock();
            m_cv.notify_all();
        }

        /* Read num_elems elements from the internal buffer, starting
         * from the end of the last read. Returns number of elements written */
        size_t read(T *buf, size_t num_elems)
        {
            std::unique_lock<std::mutex> lock(m_mutex);

            while (m_read_offset + num_elems > m_buf.size()) {
                m_cv.wait(lock);
            }

            std::copy(m_buf.begin() + m_read_offset,
                      m_buf.begin() + m_read_offset + num_elems,
                      buf);

            m_read_offset += num_elems;
            return num_elems;
        }

        /* Read num_elems elements from the internal buffer at the
         * position corresponding to the timestamp, which is also
         * updated.
         * Returns number of elements written.
         */
        size_t read(T *buf, size_t num_elems, long long *timestamp)
        {
            std::unique_lock<std::mutex> lock(m_mutex);

            if (*timestamp < m_timestamp_buf) {
                // Cannot give samples earlier than the timestamp
                return 0;
            }

            const size_t sample_offset =
                std::llrint(
                        (double)(*timestamp - m_timestamp_buf) /
                        (double)m_ticks_per_sample);
            const size_t minsize = sample_offset + num_elems;

            if (minsize > m_maxbufsize) {
                // Too far in the future
                return 0;
            }

            while (minsize > m_buf.size()) {
                m_cv.wait(lock);
            }

            std::copy(m_buf.begin() + sample_offset,
                      m_buf.begin() + sample_offset + num_elems,
                      buf);

            *timestamp = m_timestamp_buf + sample_offset * m_ticks_per_sample;
            m_read_offset = sample_offset + num_elems;
            return num_elems;
        }

    private:
        void resetbuf()
        {
            m_buf.clear();
            m_timestamp_buf = 0;
            m_read_offset = 0;
        }

        void truncatebuf()
        {
            if (m_buf.size() < m_read_offset) {
                throw std::logic_error("truncate " +
                        std::to_string(m_buf.size()) + " " +
                        std::to_string(m_read_offset));
            }

            for (size_t r = m_read_offset, w = 0;
                    r < m_buf.size();
                    r++, w++) {
                m_buf[w] = m_buf[r];
            }
            m_read_offset = 0;
            m_buf.resize(m_buf.size() - m_read_offset);
        }

        std::condition_variable m_cv;
        std::mutex m_mutex;
        std::vector<T> m_buf;
        long long m_timestamp_buf = 0;
        long long m_ticks_per_sample = 0;
        size_t m_maxbufsize = 0;

        size_t m_read_offset = 0;
};