/* 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/. */

#ifndef mozilla_layers_GenericFlingAnimation_h_
#define mozilla_layers_GenericFlingAnimation_h_

#include "APZUtils.h"
#include "AsyncPanZoomAnimation.h"
#include "AsyncPanZoomController.h"
#include "FrameMetrics.h"
#include "Units.h"
#include "OverscrollHandoffState.h"
#include "mozilla/Assertions.h"
#include "mozilla/Monitor.h"
#include "mozilla/RefPtr.h"
#include "mozilla/StaticPrefs_apz.h"
#include "mozilla/TimeStamp.h"
#include "mozilla/ToString.h"
#include "nsThreadUtils.h"

static mozilla::LazyLogModule sApzFlgLog("apz.fling");
#define FLING_LOG(...) MOZ_LOG(sApzFlgLog, LogLevel::Debug, (__VA_ARGS__))

namespace mozilla {
namespace layers {

/**
 * The FlingPhysics template parameter determines the physics model
 * that the fling animation follows. It must have the following methods:
 *
 *   - Default constructor.
 *
 *   - Init(const ParentLayerPoint& aStartingVelocity, float aPLPPI).
 *     Called at the beginning of the fling, with the fling's starting velocity,
 *     and the number of ParentLayer pixels per (Screen) inch at the point of
 *     the fling's start in the fling's direction.
 *
 *   - Sample(const TimeDuration& aDelta,
 *            ParentLayerPoint* aOutVelocity,
 *            ParentLayerPoint* aOutOffset);
 *     Called on each sample of the fling.
 *     |aDelta| is the time elapsed since the last sample.
 *     |aOutVelocity| should be the desired velocity after the current sample,
 *                    in ParentLayer pixels per millisecond.
 *     |aOutOffset| should be the desired _delta_ to the scroll offset after
 *     the current sample. |aOutOffset| should _not_ be clamped to the APZC's
 *     scrollable bounds; the caller will do the clamping, and it needs to
 *     know the unclamped value to handle handoff/overscroll correctly.
 */
template <typename FlingPhysics>
class GenericFlingAnimation : public AsyncPanZoomAnimation,
                              public FlingPhysics {
 public:
  GenericFlingAnimation(AsyncPanZoomController& aApzc,
                        const FlingHandoffState& aHandoffState, float aPLPPI)
      : mApzc(aApzc),
        mOverscrollHandoffChain(aHandoffState.mChain),
        mScrolledApzc(aHandoffState.mScrolledApzc) {
    MOZ_ASSERT(mOverscrollHandoffChain);

    // Drop any velocity on axes where we don't have room to scroll anyways
    // (in this APZC, or an APZC further in the handoff chain).
    // This ensures that we don't take the 'overscroll' path in Sample()
    // on account of one axis which can't scroll having a velocity.
    if (!mOverscrollHandoffChain->CanScrollInDirection(
            &mApzc, ScrollDirection::eHorizontal)) {
      RecursiveMutexAutoLock lock(mApzc.mRecursiveMutex);
      mApzc.mX.SetVelocity(0);
    }
    if (!mOverscrollHandoffChain->CanScrollInDirection(
            &mApzc, ScrollDirection::eVertical)) {
      RecursiveMutexAutoLock lock(mApzc.mRecursiveMutex);
      mApzc.mY.SetVelocity(0);
    }

    if (aHandoffState.mIsHandoff) {
      // Only apply acceleration in the APZC that originated the fling, not in
      // APZCs further down the handoff chain during handoff.
      mApzc.mFlingAccelerator.Reset();
    }

    ParentLayerPoint velocity =
        mApzc.mFlingAccelerator.GetFlingStartingVelocity(
            aApzc.GetFrameTime(), mApzc.GetVelocityVector(), aHandoffState);

    mApzc.SetVelocityVector(velocity);

    FlingPhysics::Init(mApzc.GetVelocityVector(), aPLPPI);
  }

  /**
   * Advances a fling by an interpolated amount based on the passed in |aDelta|.
   * This should be called whenever sampling the content transform for this
   * frame. Returns true if the fling animation should be advanced by one frame,
   * or false if there is no fling or the fling has ended.
   */
  virtual bool DoSample(FrameMetrics& aFrameMetrics,
                        const TimeDuration& aDelta) override {
    CSSToParentLayerScale zoom(aFrameMetrics.GetZoom());
    if (zoom == CSSToParentLayerScale(0)) {
      return false;
    }

    ParentLayerPoint velocity;
    ParentLayerPoint offset;
    FlingPhysics::Sample(aDelta, &velocity, &offset);

    mApzc.SetVelocityVector(velocity);

    // If we shouldn't continue the fling, let's just stop and repaint.
    if (IsZero(velocity / zoom)) {
      FLING_LOG("%p ending fling animation. overscrolled=%d\n", &mApzc,
                mApzc.IsOverscrolled());
      // This APZC or an APZC further down the handoff chain may be be
      // overscrolled. Start a snap-back animation on the overscrolled APZC.
      // Note:
      //   This needs to be a deferred task even though it can safely run
      //   while holding mRecursiveMutex, because otherwise, if the overscrolled
      //   APZC is this one, then the SetState(NOTHING) in UpdateAnimation will
      //   stomp on the SetState(SNAP_BACK) it does.
      mDeferredTasks.AppendElement(NewRunnableMethod<AsyncPanZoomController*>(
          "layers::OverscrollHandoffChain::SnapBackOverscrolledApzc",
          mOverscrollHandoffChain.get(),
          &OverscrollHandoffChain::SnapBackOverscrolledApzc, &mApzc));
      return false;
    }

    // Ordinarily we might need to do a ScheduleComposite if either of
    // the following AdjustDisplacement calls returns true, but this
    // is already running as part of a FlingAnimation, so we'll be compositing
    // per frame of animation anyway.
    ParentLayerPoint overscroll;
    ParentLayerPoint adjustedOffset;
    mApzc.mX.AdjustDisplacement(offset.x, adjustedOffset.x, overscroll.x);
    mApzc.mY.AdjustDisplacement(offset.y, adjustedOffset.y, overscroll.y);
    if (aFrameMetrics.GetZoom() != CSSToParentLayerScale(0)) {
      mApzc.ScrollBy(adjustedOffset / aFrameMetrics.GetZoom());
    }

    // The fling may have caused us to reach the end of our scroll range.
    if (!IsZero(overscroll / zoom)) {
      // Hand off the fling to the next APZC in the overscroll handoff chain.

      // We may have reached the end of the scroll range along one axis but
      // not the other. In such a case we only want to hand off the relevant
      // component of the fling.
      if (mApzc.IsZero(overscroll.x)) {
        velocity.x = 0;
      } else if (mApzc.IsZero(overscroll.y)) {
        velocity.y = 0;
      }

      // To hand off the fling, we attempt to find a target APZC and start a new
      // fling with the same velocity on that APZC. For simplicity, the actual
      // overscroll of the current sample is discarded rather than being handed
      // off. The compositor should sample animations sufficiently frequently
      // that this is not noticeable. The target APZC is chosen by seeing if
      // there is an APZC further in the handoff chain which is pannable; if
      // there isn't, we take the new fling ourselves, entering an overscrolled
      // state.
      // Note: APZC is holding mRecursiveMutex, so directly calling
      // HandleFlingOverscroll() (which acquires the tree lock) would violate
      // the lock ordering. Instead we schedule HandleFlingOverscroll() to be
      // called after mRecursiveMutex is released.
      FLING_LOG("%p fling went into overscroll, handing off with velocity %s\n",
                &mApzc, ToString(velocity).c_str());
      mDeferredTasks.AppendElement(
          NewRunnableMethod<ParentLayerPoint, SideBits,
                            RefPtr<const OverscrollHandoffChain>,
                            RefPtr<const AsyncPanZoomController>>(
              "layers::AsyncPanZoomController::HandleFlingOverscroll", &mApzc,
              &AsyncPanZoomController::HandleFlingOverscroll, velocity,
              apz::GetOverscrollSideBits(overscroll), mOverscrollHandoffChain,
              mScrolledApzc));

      // If there is a remaining velocity on this APZC, continue this fling
      // as well. (This fling and the handed-off fling will run concurrently.)
      // Note that AdjustDisplacement() will have zeroed out the velocity
      // along the axes where we're overscrolled.
      return !IsZero(mApzc.GetVelocityVector() / zoom);
    }

    return true;
  }

  void Cancel(CancelAnimationFlags aFlags) override {
    mApzc.mFlingAccelerator.ObserveFlingCanceled(mApzc.GetVelocityVector());
  }

  virtual bool HandleScrollOffsetUpdate(
      const Maybe<CSSPoint>& aRelativeDelta) override {
    return true;
  }

 private:
  AsyncPanZoomController& mApzc;
  RefPtr<const OverscrollHandoffChain> mOverscrollHandoffChain;
  RefPtr<const AsyncPanZoomController> mScrolledApzc;
};

}  // namespace layers
}  // namespace mozilla

#endif  // mozilla_layers_GenericFlingAnimation_h_