/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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_CachedInheritingStyles_h
#define mozilla_CachedInheritingStyles_h

#include "nsAtom.h"
#include "nsCOMPtr.h"
#include "nsTArray.h"

class nsWindowSizes;

namespace mozilla {

struct PseudoStyleRequest;
enum class PseudoStyleType : uint8_t;
class ComputedStyle;

// Entry in the cached inheriting styles cache. Stores the style and, for
// functional pseudo-elements like ::highlight(name), the functional parameter.
struct CachedStyleEntry {
  RefPtr<ComputedStyle> mStyle;
  RefPtr<nsAtom> mFunctionalPseudoParameter;
};

// Cache of anonymous box and lazy pseudo styles that inherit from a given
// style.
//
// To minimize memory footprint, the cache is word-sized with a tagged pointer
// If there is only one entry without a functional parameter, it's stored
// inline. If there are more entries, or the entry has a functional parameter,
// they're stored in an out-of-line buffer. See bug 1429126 comment 0 and
// comment 1 for the measurements and rationale that influenced the design.
class CachedInheritingStyles {
 public:
  void Insert(ComputedStyle* aStyle,
              nsAtom* aFunctionalPseudoParameter = nullptr);
  ComputedStyle* Lookup(const PseudoStyleRequest& aRequest) const;

  // Appends all cached styles to the given array.
  void AppendTo(nsTArray<const ComputedStyle*>& aArray) const;

  CachedInheritingStyles() : mBits(0) {}
  ~CachedInheritingStyles() {
    if (IsIndirect()) {
      delete AsIndirect();
    } else if (!IsEmpty()) {
      RefPtr<ComputedStyle> ref = dont_AddRef(AsDirect());
    }
  }

  void AddSizeOfIncludingThis(nsWindowSizes& aSizes, size_t* aCVsSize) const;

 private:
  // See bug 1429126 comment 1 for the choice of four here.
  using IndirectCache = AutoTArray<CachedStyleEntry, 4>;

  bool IsEmpty() const { return !mBits; }
  bool IsIndirect() const { return (mBits & 1); }

  ComputedStyle* AsDirect() const {
    MOZ_ASSERT(!IsIndirect());
    return reinterpret_cast<ComputedStyle*>(mBits);
  }

  IndirectCache* AsIndirect() const {
    MOZ_ASSERT(IsIndirect());
    return reinterpret_cast<IndirectCache*>(mBits & ~1);
  }

  uintptr_t mBits;
};

}  // namespace mozilla

#endif  // mozilla_CachedInheritingStyles_h