/**
 * 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 "main.h"

#include "common/debug.h"
#include "common/locking.h"
#include "common/time.h"

#include <stdbool.h>
#include <stdlib.h>
#include <string.h>

#define FRAME_SCHEDULER_LEASE_MS        1000U
#define FRAME_SCHEDULER_RENEW_NS        250000000ULL
#define FRAME_SCHEDULER_TARGET_SLACK_NS 500000ULL
#define FRAME_SCHEDULER_MIN_PERIOD_NS   2000000ULL
#define FRAME_SCHEDULER_MAX_PERIOD_NS   1000000000ULL
#define FRAME_SCHEDULER_SAMPLE_COUNT    9U

static struct
{
  LG_Lock lock;

  bool     supported;
  bool     active;
  bool     controlPending;
  uint32_t generation;
  uint64_t period;
  uint64_t lastSend;
  uint64_t lastCadence;

  LG_TransportControlToken controlToken;

  uint64_t renderSamples[FRAME_SCHEDULER_SAMPLE_COUNT];
  unsigned renderSampleIndex;
  unsigned renderSampleCount;
  uint64_t lastRender;
}
l_frameScheduler;

static int compareU64(const void * a, const void * b)
{
  const uint64_t lhs = *(const uint64_t *)a;
  const uint64_t rhs = *(const uint64_t *)b;
  return (lhs > rhs) - (lhs < rhs);
}

static uint64_t fallbackPeriod(void)
{
  uint64_t samples[FRAME_SCHEDULER_SAMPLE_COUNT];
  unsigned count;

  LG_LOCK(l_frameScheduler.lock);
  count = l_frameScheduler.renderSampleCount;
  memcpy(samples, l_frameScheduler.renderSamples,
      count * sizeof(*samples));
  LG_UNLOCK(l_frameScheduler.lock);

  if (count < 5)
    return 0;

  qsort(samples, count, sizeof(*samples), compareU64);
  return samples[count / 2];
}

static uint64_t presentationPeriod(void)
{
  uint64_t period = 0;
  if (g_state.ds->getFramePeriod &&
      g_state.ds->getFramePeriod(&period))
    return period;

  return g_state.jitRender ? fallbackPeriod() : 0;
}

static bool controlReady(void)
{
  if (!l_frameScheduler.controlPending)
    return true;

  const LG_TransportStatus status = g_state.transportOps->controlStatus(
      g_state.transport, l_frameScheduler.controlToken);
  if (status == LG_TRANSPORT_UNAVAILABLE)
    return false;

  l_frameScheduler.controlPending = false;
  return status == LG_TRANSPORT_OK;
}

static bool sendSchedule(LG_TransportFrameScheduleFlags flags,
    uint64_t period)
{
  if (!controlReady())
    return false;

  const LG_TransportControl control = {
    .type = LG_TRANSPORT_CONTROL_FRAME_SCHEDULE,
    .frameSchedule = {
      .generation  = l_frameScheduler.generation,
      .flags       = flags,
      .period      = period,
      .targetSlack = FRAME_SCHEDULER_TARGET_SLACK_NS,
      .lease       = FRAME_SCHEDULER_LEASE_MS,
    },
  };

  const LG_TransportStatus status = g_state.transportOps->sendControl(
      g_state.transport, &control, &l_frameScheduler.controlToken);
  if (status == LG_TRANSPORT_UNAVAILABLE)
    return false;
  if (status != LG_TRANSPORT_OK)
  {
    DEBUG_WARN("Frame-schedule control failed with status %d", status);
    return false;
  }

  l_frameScheduler.controlPending = true;
  return true;
}

void frameScheduler_init(void)
{
  memset(&l_frameScheduler, 0, sizeof(l_frameScheduler));
  LG_LOCK_INIT(l_frameScheduler.lock);
}

void frameScheduler_free(void)
{
  LG_LOCK_FREE(l_frameScheduler.lock);
}

void frameScheduler_start(LG_TransportFeatureFlags features)
{
  l_frameScheduler.supported =
    features & LG_TRANSPORT_FEATURE_FRAME_SCHEDULE;
  l_frameScheduler.active         = false;
  l_frameScheduler.controlPending = false;
  l_frameScheduler.period         = 0;
  l_frameScheduler.lastSend       = 0;
  l_frameScheduler.lastCadence    = 0;
  ++l_frameScheduler.generation;

  LG_LOCK(l_frameScheduler.lock);
  l_frameScheduler.renderSampleIndex = 0;
  l_frameScheduler.renderSampleCount = 0;
  l_frameScheduler.lastRender        = 0;
  LG_UNLOCK(l_frameScheduler.lock);
}

void frameScheduler_stop(void)
{
  if (l_frameScheduler.supported && l_frameScheduler.active)
    sendSchedule(LG_TRANSPORT_FRAME_SCHEDULE_RELEASE, 0);

  l_frameScheduler.supported      = false;
  l_frameScheduler.active         = false;
  l_frameScheduler.controlPending = false;
}

void frameScheduler_update(void)
{
  if (!l_frameScheduler.supported)
    return;

  const uint64_t now    = nanotime();
  const uint64_t period = presentationPeriod();
  if (period < FRAME_SCHEDULER_MIN_PERIOD_NS ||
      period > FRAME_SCHEDULER_MAX_PERIOD_NS)
  {
    if (l_frameScheduler.active && l_frameScheduler.lastCadence &&
        now - l_frameScheduler.lastCadence > FRAME_SCHEDULER_RENEW_NS * 2)
    {
      if (sendSchedule(LG_TRANSPORT_FRAME_SCHEDULE_RELEASE, 0))
        l_frameScheduler.active = false;
    }
    return;
  }

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

  if (reset)
  {
    l_frameScheduler.period = period;
    ++l_frameScheduler.generation;
  }
  else
    l_frameScheduler.period =
      (l_frameScheduler.period * 7 + period) / 8;

  if (l_frameScheduler.active && !reset &&
      now - l_frameScheduler.lastSend < FRAME_SCHEDULER_RENEW_NS)
    return;

  LG_TransportFrameScheduleFlags flags =
    LG_TRANSPORT_FRAME_SCHEDULE_ACTIVE;
  if (reset)
    flags |= LG_TRANSPORT_FRAME_SCHEDULE_RESET;

  if (sendSchedule(flags, l_frameScheduler.period))
  {
    l_frameScheduler.active   = true;
    l_frameScheduler.lastSend = now;
  }
}

void frameScheduler_observeRender(uint64_t timestamp)
{
  if (!g_state.jitRender)
    return;

  LG_LOCK(l_frameScheduler.lock);
  if (l_frameScheduler.lastRender &&
      timestamp > l_frameScheduler.lastRender)
  {
    l_frameScheduler.renderSamples[l_frameScheduler.renderSampleIndex] =
      timestamp - l_frameScheduler.lastRender;
    l_frameScheduler.renderSampleIndex =
      (l_frameScheduler.renderSampleIndex + 1) %
        FRAME_SCHEDULER_SAMPLE_COUNT;
    if (l_frameScheduler.renderSampleCount < FRAME_SCHEDULER_SAMPLE_COUNT)
      ++l_frameScheduler.renderSampleCount;
  }
  l_frameScheduler.lastRender = timestamp;
  LG_UNLOCK(l_frameScheduler.lock);
}