/* 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 "ScrollSnapInfo.h"

#include "mozilla/StaticPrefs_layout.h"
#include "mozilla/WritingModes.h"
#include "mozilla/dom/Element.h"
#include "nsIContent.h"
#include "nsPoint.h"
#include "nsRect.h"
#include "nsStyleStruct.h"

namespace mozilla {

ScrollSnapInfo::ScrollSnapInfo()
    : mScrollSnapStrictnessX(StyleScrollSnapStrictness::None),
      mScrollSnapStrictnessY(StyleScrollSnapStrictness::None) {}

bool ScrollSnapInfo::HasScrollSnapping() const {
  return mScrollSnapStrictnessY != StyleScrollSnapStrictness::None ||
         mScrollSnapStrictnessX != StyleScrollSnapStrictness::None;
}

bool ScrollSnapInfo::HasSnapPositions() const {
  if (!HasScrollSnapping()) {
    return false;
  }

  for (const auto& target : mSnapTargets) {
    if ((target.mSnapPoint.mX &&
         mScrollSnapStrictnessX != StyleScrollSnapStrictness::None) ||
        (target.mSnapPoint.mY &&
         mScrollSnapStrictnessY != StyleScrollSnapStrictness::None)) {
      return true;
    }
  }
  return false;
}

void ScrollSnapInfo::InitializeScrollSnapStrictness(
    WritingMode aWritingMode, const nsStyleDisplay* aDisplay) {
  if (aDisplay->mScrollSnapType.strictness == StyleScrollSnapStrictness::None) {
    return;
  }

  mScrollSnapStrictnessX = StyleScrollSnapStrictness::None;
  mScrollSnapStrictnessY = StyleScrollSnapStrictness::None;

  switch (aDisplay->mScrollSnapType.axis) {
    case StyleScrollSnapAxis::X:
      mScrollSnapStrictnessX = aDisplay->mScrollSnapType.strictness;
      break;
    case StyleScrollSnapAxis::Y:
      mScrollSnapStrictnessY = aDisplay->mScrollSnapType.strictness;
      break;
    case StyleScrollSnapAxis::Block:
      if (aWritingMode.IsVertical()) {
        mScrollSnapStrictnessX = aDisplay->mScrollSnapType.strictness;
      } else {
        mScrollSnapStrictnessY = aDisplay->mScrollSnapType.strictness;
      }
      break;
    case StyleScrollSnapAxis::Inline:
      if (aWritingMode.IsVertical()) {
        mScrollSnapStrictnessY = aDisplay->mScrollSnapType.strictness;
      } else {
        mScrollSnapStrictnessX = aDisplay->mScrollSnapType.strictness;
      }
      break;
    case StyleScrollSnapAxis::Both:
      mScrollSnapStrictnessX = aDisplay->mScrollSnapType.strictness;
      mScrollSnapStrictnessY = aDisplay->mScrollSnapType.strictness;
      break;
  }
}

void ScrollSnapInfo::ForEachValidTargetFor(
    const nsPoint& aDestination,
    const std::function<bool(const SnapTarget&)>& aFunc) const {
  for (const auto& target : mSnapTargets) {
    nsPoint snapPoint(
        mScrollSnapStrictnessX != StyleScrollSnapStrictness::None &&
                target.mSnapPoint.mX
            ? *target.mSnapPoint.mX
            : aDestination.x,
        mScrollSnapStrictnessY != StyleScrollSnapStrictness::None &&
                target.mSnapPoint.mY
            ? *target.mSnapPoint.mY
            : aDestination.y);
    nsRect snappedPort = nsRect(snapPoint, mSnapportSize);
    // Ignore snap points if snapping to the point would leave the snap area
    // outside of the snapport.
    // https://drafts.csswg.org/css-scroll-snap-1/#snap-scope
    //
    // NOTE: We don't use BaseRect::Intersects() here since the function returns
    // false in cases where the given rectangle is empty.
    if (!snappedPort.EdgeInclusiveIntersection(target.mSnapArea)) {
      continue;
    }

    if (!aFunc(target)) {
      break;
    }
  }
}

nscoord ScrollSnapRange::FindNearestSnapPoint(nscoord aDestination,
                                              nscoord aSnapportSize) const {
  const nscoord tolerance = StaticPrefs::layout_disable_pixel_alignment()
                                ? 0
                                : CSSPixel::ToAppUnits(CSSCoord(0.5f));
  return std::clamp(aDestination, Start(),
                    std::max(Start(), End() - aSnapportSize + tolerance));
}

std::ostream& operator<<(std::ostream& aStream,
                         const ScrollSnapInfo::SnapTarget& aTarget) {
  nsAutoString string;
  const nsIContent* content = reinterpret_cast<nsIContent*>(aTarget.mTargetId);
  if (content->IsElement()) {
    content->AsElement()->Describe(string,
                                   dom::Element::DescriptionKind::IdOnly);
  } else {
    string.AppendPrintf("(not an element)");
  }
  return aStream << NS_LossyConvertUTF16toASCII(string).get();
}

std::ostream& operator<<(std::ostream& aStream,
                         const ScrollSnapInfo::SnapTarget* aTarget) {
  return aStream << *aTarget;
}

}  // namespace mozilla