/**
 * Looking Glass
 * Copyright © 2017-2026 The Looking Glass Authors
 * https://looking-glass.io
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc., 59
 * Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

#include "frame_scheduler.h"

#include <common/KVMFR.h>

#include <string.h>

#define FRAME_SCHEDULER_LEASE_MS        1000U
#define FRAME_SCHEDULER_RENEW_NS        250000000ULL
#define FRAME_SCHEDULER_FEEDBACK_NS     50000000ULL
#define FRAME_SCHEDULER_TARGET_SLACK_NS 1000000ULL
#define FRAME_SCHEDULER_MIN_PERIOD_NS   2000000ULL
#define FRAME_SCHEDULER_MAX_PERIOD_NS   1000000000ULL

void lgFrameSchedulerInit(LGFrameScheduler * scheduler, bool supported,
    uint32_t clientID)
{
  memset(scheduler, 0, sizeof(*scheduler));
  scheduler->supported = supported;
  scheduler->clientID  = clientID;
}

void lgFrameSchedulerSetPeriod(LGFrameScheduler * scheduler,
    uint64_t period)
{
  if (!scheduler->supported ||
      period < FRAME_SCHEDULER_MIN_PERIOD_NS ||
      period > FRAME_SCHEDULER_MAX_PERIOD_NS)
    return;

  bool reset = !scheduler->period;
  if (!reset)
  {
    const uint64_t delta = scheduler->period > period ?
      scheduler->period - period : period - scheduler->period;
    reset = delta > scheduler->period / 20;
  }

  scheduler->period = period;
  if (!reset)
    return;

  ++scheduler->generation;
  scheduler->resetPending        = true;
  scheduler->phaseError          = 0;
  scheduler->feedbackFrameSerial = 0;
  scheduler->feedbackSamples     = 0;
  scheduler->feedbackDirty       = false;
}

void lgFrameSchedulerObserveFrame(LGFrameScheduler * scheduler,
    uint32_t frameSerial, uint32_t generation, uint64_t readyTime)
{
  if (!generation ||
      (scheduler->readyFrameSerial == frameSerial &&
        scheduler->readyGeneration == generation))
    return;

  scheduler->readyFrameSerial = frameSerial;
  scheduler->readyGeneration  = generation;
  scheduler->readyTime        = readyTime;
}

void lgFrameSchedulerFeedback(LGFrameScheduler * scheduler,
    uint32_t frameSerial, uint32_t generation, uint64_t neededTime)
{
  if (!scheduler->active || generation != scheduler->generation ||
      frameSerial == scheduler->feedbackFrameSerial)
    return;

  uint64_t readyTime = neededTime;
  if (scheduler->readyFrameSerial == frameSerial &&
      scheduler->readyGeneration == generation)
    readyTime = scheduler->readyTime;

  const uint64_t measuredPhase = neededTime > readyTime ?
    neededTime - readyTime : 0;
  int64_t error = measuredPhase > FRAME_SCHEDULER_TARGET_SLACK_NS ?
    (int64_t)(measuredPhase - FRAME_SCHEDULER_TARGET_SLACK_NS) :
    -(int64_t)(FRAME_SCHEDULER_TARGET_SLACK_NS - measuredPhase);
  const int64_t period = (int64_t)scheduler->period;
  error %= period;
  if (error > period / 2)
    error -= period;
  else if (error < -period / 2)
    error += period;

  if (!scheduler->feedbackSamples)
    scheduler->phaseError = error;
  else
    scheduler->phaseError = (scheduler->phaseError * 7 + error) / 8;
  if (scheduler->feedbackSamples < 32)
    ++scheduler->feedbackSamples;

  scheduler->feedbackFrameSerial = frameSerial;
  scheduler->feedbackDirty       = true;
}

void lgFrameSchedulerUpdate(LGFrameScheduler * scheduler,
    PLGMPClientQueue queue, uint64_t now)
{
  if (!scheduler->supported || !scheduler->period || !queue)
    return;

  const uint64_t interval = scheduler->feedbackDirty ?
    FRAME_SCHEDULER_FEEDBACK_NS : FRAME_SCHEDULER_RENEW_NS;
  if (scheduler->active && !scheduler->resetPending &&
      now - scheduler->lastSend < interval)
    return;

  KVMFRFrameScheduleFlags flags = KVMFR_FRAME_SCHEDULE_ACTIVE;
  if (scheduler->resetPending)
    flags |= KVMFR_FRAME_SCHEDULE_RESET;

  const uint32_t feedbackFrameSerial =
    scheduler->feedbackFrameSerial;
  const KVMFRFrameSchedule message = {
    .msg.type            = KVMFR_MESSAGE_FRAME_SCHEDULE,
    .clientID            = scheduler->clientID,
    .generation          = scheduler->generation,
    .flags               = flags,
    .period              = scheduler->period,
    .targetSlack         = FRAME_SCHEDULER_TARGET_SLACK_NS,
    .phaseError          = scheduler->phaseError,
    .feedbackFrameSerial = feedbackFrameSerial,
    .lease               = FRAME_SCHEDULER_LEASE_MS,
  };

  if (lgmpClientSendData(queue, &message, sizeof(message), NULL) != LGMP_OK)
    return;

  scheduler->active       = true;
  scheduler->resetPending = false;
  scheduler->lastSend     = now;
  if (scheduler->feedbackFrameSerial == feedbackFrameSerial)
    scheduler->feedbackDirty = false;
}