/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "mozilla/ipc/IdleSchedulerChild.h"
#include "mozilla/ipc/IdleSchedulerParent.h"
#include "mozilla/ipc/PBackgroundChild.h"
#include "mozilla/Atomics.h"
#include "mozilla/IdlePeriodState.h"
#include "BackgroundChild.h"

namespace mozilla::ipc {

static IdleSchedulerChild* sMainThreadIdleScheduler = nullptr;
static bool sIdleSchedulerDestroyed = false;

IdleSchedulerChild::~IdleSchedulerChild() {
  if (sMainThreadIdleScheduler == this) {
    sMainThreadIdleScheduler = nullptr;
    sIdleSchedulerDestroyed = true;
  }
  MOZ_ASSERT(!mIdlePeriodState);
}

void IdleSchedulerChild::Init(IdlePeriodState* aIdlePeriodState) {
  mIdlePeriodState = aIdlePeriodState;

  RefPtr<IdleSchedulerChild> scheduler = this;
  auto resolve = [&](std::tuple<mozilla::Maybe<MutableSharedMemoryHandle>,
                                uint32_t>&& aResult) {
    if (auto& handle = std::get<0>(aResult)) {
      mActiveCounter = handle->Map();
      mChildId = std::get<1>(aResult);
      if (mChildId && mIdlePeriodState && mIdlePeriodState->IsActive()) {
        SetActive();
      }
    }
  };

  auto reject = [&](ResponseRejectReason) {};
  SendInitForIdleUse(std::move(resolve), std::move(reject));
}

IPCResult IdleSchedulerChild::RecvIdleTime(uint64_t aId, TimeDuration aBudget) {
  if (mIdlePeriodState) {
    mIdlePeriodState->SetIdleToken(aId, aBudget);
  }
  return IPC_OK();
}

void IdleSchedulerChild::SetActive() {
  if (mChildId && CanSend() && mActiveCounter) {
    auto counters = mActiveCounter.DataAsSpan<Atomic<int32_t>>();
    ++counters[NS_IDLE_SCHEDULER_INDEX_OF_ACTIVITY_COUNTER];
    ++counters[mChildId];
  }
}

bool IdleSchedulerChild::SetPaused() {
  if (mChildId && CanSend() && mActiveCounter) {
    auto counters = mActiveCounter.DataAsSpan<Atomic<int32_t>>();
    --counters[mChildId];
    // The following expression reduces the global activity count and checks if
    // it drops below the cpu counter limit.
    return counters[NS_IDLE_SCHEDULER_INDEX_OF_ACTIVITY_COUNTER]-- ==
           counters[NS_IDLE_SCHEDULER_INDEX_OF_CPU_COUNTER];
  }

  return false;
}

RefPtr<IdleSchedulerChild::MayGCPromise> IdleSchedulerChild::MayGCNow() {
  if (mIsRequestingGC || mIsDoingGC) {
    return MayGCPromise::CreateAndResolve(false, __func__);
  }

  mIsRequestingGC = true;
  return SendRequestGC()->Then(
      GetMainThreadSerialEventTarget(), __func__,
      [self = RefPtr(this)](bool aIgnored) {
        // Only one of these may be true at a time.
        MOZ_ASSERT(!(self->mIsRequestingGC && self->mIsDoingGC));

        // The parent process always says yes, sometimes after a delay.
        if (self->mIsRequestingGC) {
          self->mIsRequestingGC = false;
          self->mIsDoingGC = true;
          return MayGCPromise::CreateAndResolve(true, __func__);
        }
        return MayGCPromise::CreateAndResolve(false, __func__);
      },
      [self = RefPtr(this)](ResponseRejectReason reason) {
        self->mIsRequestingGC = false;
        return MayGCPromise::CreateAndReject(reason, __func__);
      });
}

void IdleSchedulerChild::StartedGC() {
  // Only one of these may be true at a time.
  MOZ_ASSERT(!(mIsRequestingGC && mIsDoingGC));

  // If mRequestingGC was true then when the outstanding GC request returns
  // it'll see that the GC has already started.
  mIsRequestingGC = false;

  if (!mIsDoingGC) {
    if (CanSend()) {
      SendStartedGC();
    }
    mIsDoingGC = true;
  }
}

void IdleSchedulerChild::DoneGC() {
  if (mIsDoingGC) {
    if (CanSend()) {
      SendDoneGC();
    }
    mIsDoingGC = false;
  }
}

IdleSchedulerChild* IdleSchedulerChild::GetMainThreadIdleScheduler() {
  MOZ_ASSERT(NS_IsMainThread());

  if (sMainThreadIdleScheduler) {
    return sMainThreadIdleScheduler;
  }

  if (sIdleSchedulerDestroyed) {
    return nullptr;
  }

  ipc::PBackgroundChild* background =
      ipc::BackgroundChild::GetOrCreateForCurrentThread();
  if (background) {
    // this is nulled out on our destruction, so we don't need to worry
    sMainThreadIdleScheduler = new ipc::IdleSchedulerChild();
    MOZ_ALWAYS_TRUE(
        background->SendPIdleSchedulerConstructor(sMainThreadIdleScheduler));
  }
  return sMainThreadIdleScheduler;
}

}  // namespace mozilla::ipc