//
// Copyright 2011-2012 Ettus Research LLC
// Copyright 2018 Ettus Research, a National Instruments Company
//
// SPDX-License-Identifier: GPL-3.0-or-later
//

#include <uhd/exception.hpp>
#include <uhd/transport/buffer_pool.hpp>
#include <uhd/transport/usb_zero_copy.hpp>
#include <uhd/utils/byteswap.hpp>
#include <uhd/utils/log.hpp>
#include <uhd/utils/tasks.hpp>
#include <uhdlib/utils/atomic.hpp>
#include <condition_variable>
#include <chrono>
#include <functional>
#include <memory>
#include <mutex>
#include <vector>

using namespace uhd;
using namespace uhd::transport;

constexpr std::chrono::milliseconds AUTOFLUSH_TIMEOUT{1};

/***********************************************************************
 * USB zero copy wrapper - managed receive buffer
 **********************************************************************/
class usb_zero_copy_wrapper_mrb : public managed_recv_buffer
{
public:
    usb_zero_copy_wrapper_mrb(void)
    { /*NOP*/
    }

    void release(void) override
    {
        _mrb.reset(); // decrement ref count, other MRB's may hold a ref
        _claimer.release();
    }

    UHD_INLINE sptr get_new(managed_recv_buffer::sptr& mrb,
        size_t& offset_bytes,
        const double timeout,
        size_t& index)
    {
        if (not mrb or not _claimer.claim_with_wait(timeout))
            return sptr();

        index++; // advances the caller's buffer

        // hold a copy of the buffer shared pointer
        UHD_ASSERT_THROW(not _mrb);
        _mrb = mrb;

        // extract this packet's memory address and length in bytes
        char* mem             = mrb->cast<char*>() + offset_bytes;
        const uint32_t* mem32 = reinterpret_cast<const uint32_t*>(mem);
        const size_t words32 =
            (uhd::wtohx(mem32[0]) & 0xffff); // length in words32 (from VRT header)
        const size_t len = words32 * sizeof(uint32_t); // length in bytes

        // check if this receive buffer has been exhausted
        offset_bytes += len;
        if (offset_bytes >= mrb->size())
            mrb.reset(); // drop caller's ref
        else if (uhd::wtohx(mem32[words32]) == 0)
            mrb.reset();

        return make(this, mem, len);
    }

private:
    managed_recv_buffer::sptr _mrb;
    simple_claimer _claimer;
};

/***********************************************************************
 * USB zero copy wrapper - managed send buffer
 **********************************************************************/
class usb_zero_copy_wrapper_msb : public managed_send_buffer
{
public:
    usb_zero_copy_wrapper_msb(
        const zero_copy_if::sptr internal, const size_t fragmentation_size)
        : _internal(internal), _fragmentation_size(fragmentation_size)
    {
        _ok_to_auto_flush = false;
        _task = uhd::task::make(std::bind(&usb_zero_copy_wrapper_msb::auto_flush, this));
    }

    ~usb_zero_copy_wrapper_msb(void) override
    {
        // ensure the task has exited before anything auto deconstructs
        _task.reset();
    }

    void release(void) override
    {
        std::unique_lock<std::mutex> lock(_mutex);
        _ok_to_auto_flush = true;

        // get a reference to the VITA header before incrementing
        const uint32_t vita_header =
            reinterpret_cast<const uint32_t*>(_mem_buffer_tip)[0];

        _bytes_in_buffer += size();
        _mem_buffer_tip += size();

        // extract VITA end of packet flag, we must force flush under eof conditions
        const bool eop  = (uhd::wtohx(vita_header) & (0x1 << 24)) != 0;
        const bool full = _bytes_in_buffer
                          >= (_last_send_buff->size() - _fragmentation_size);
        if (eop or full) {
            _last_send_buff->commit(_bytes_in_buffer);
            _last_send_buff.reset();

            // notify the auto-flusher to restart its timed_wait
            lock.unlock();
            _cond.notify_one();
        }
    }

    UHD_INLINE sptr get_new(const double timeout)
    {
        std::lock_guard<std::mutex> lock(_mutex);
        _ok_to_auto_flush = false;

        if (not _last_send_buff) {
            _last_send_buff = _internal->get_send_buff(timeout);
            if (not _last_send_buff)
                return sptr();
            _mem_buffer_tip  = _last_send_buff->cast<char*>();
            _bytes_in_buffer = 0;
        }

        return make(this, _mem_buffer_tip, _fragmentation_size);
    }

private:
    zero_copy_if::sptr _internal;
    const size_t _fragmentation_size;
    managed_send_buffer::sptr _last_send_buff;
    size_t _bytes_in_buffer;
    char* _mem_buffer_tip;

    // private variables for auto flusher
    std::mutex _mutex;
    std::condition_variable _cond;
    uhd::task::sptr _task;
    bool _ok_to_auto_flush;

    /*!
     * The auto flusher ensures that buffers are force committed when
     * the user has not called get_new() within a certain time window.
     */
    void auto_flush(void)
    {
        std::unique_lock<std::mutex> lock(_mutex);
        const bool timeout = _cond.wait_for(lock, AUTOFLUSH_TIMEOUT)
                             == std::cv_status::timeout;
        if (timeout and _ok_to_auto_flush and _last_send_buff and _bytes_in_buffer != 0) {
            _last_send_buff->commit(_bytes_in_buffer);
            _last_send_buff.reset();
        }
    }
};

/***********************************************************************
 * USB zero copy wrapper implementation
 **********************************************************************/
class usb_zero_copy_wrapper : public usb_zero_copy
{
public:
    usb_zero_copy_wrapper(zero_copy_if::sptr usb_zc, const size_t frame_boundary)
        : _internal_zc(usb_zc)
        , _frame_boundary(frame_boundary)
        , _last_recv_offset(0)
        , _next_recv_buff_index(0)
    {
        for (size_t i = 0; i < this->get_num_recv_frames(); i++) {
            _mrb_pool.push_back(std::make_shared<usb_zero_copy_wrapper_mrb>());
        }
        _the_only_msb =
            std::make_shared<usb_zero_copy_wrapper_msb>(usb_zc, frame_boundary);
    }

    managed_recv_buffer::sptr get_recv_buff(double timeout) override
    {
        // lazy flush mechanism - negative timeout
        if (timeout < 0.0) {
            _last_recv_buff.reset();
            while (_internal_zc->get_recv_buff()) {
            }
            return managed_recv_buffer::sptr();
        }

        // attempt to get a managed recv buffer
        if (not _last_recv_buff) {
            _last_recv_buff   = _internal_zc->get_recv_buff(timeout);
            _last_recv_offset = 0; // reset offset into buffer
        }

        // get the buffer to be returned to the user
        if (_next_recv_buff_index == _mrb_pool.size())
            _next_recv_buff_index = 0;
        return _mrb_pool[_next_recv_buff_index]->get_new(
            _last_recv_buff, _last_recv_offset, timeout, _next_recv_buff_index);
    }

    size_t get_num_recv_frames(void) const override
    {
        return (_internal_zc->get_num_recv_frames() * _internal_zc->get_recv_frame_size())
               / this->get_recv_frame_size();
    }

    size_t get_recv_frame_size(void) const override
    {
        return std::min(_frame_boundary, _internal_zc->get_recv_frame_size());
    }

    managed_send_buffer::sptr get_send_buff(double timeout) override
    {
        return _the_only_msb->get_new(timeout);
    }

    size_t get_num_send_frames(void) const override
    {
        return _internal_zc->get_num_send_frames();
    }

    size_t get_send_frame_size(void) const override
    {
        return std::min(_frame_boundary, _internal_zc->get_send_frame_size());
    }

private:
    zero_copy_if::sptr _internal_zc;
    size_t _frame_boundary;
    std::vector<std::shared_ptr<usb_zero_copy_wrapper_mrb>> _mrb_pool;
    std::shared_ptr<usb_zero_copy_wrapper_msb> _the_only_msb;

    // state for last recv buffer to create multiple managed buffers
    managed_recv_buffer::sptr _last_recv_buff;
    size_t _last_recv_offset;
    size_t _next_recv_buff_index;
};

/***********************************************************************
 * USB zero copy wrapper factory function
 **********************************************************************/
zero_copy_if::sptr usb_zero_copy_make_wrapper(
    zero_copy_if::sptr usb_zc, size_t usb_frame_boundary)
{
    return zero_copy_if::sptr(new usb_zero_copy_wrapper(usb_zc, usb_frame_boundary));
}
