/* -*- 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/. */

#include "mozilla/StyleComplexColor.h"

#include "mozilla/ComputedStyle.h"
#include "mozilla/ComputedStyleInlines.h"
#include "nsIFrame.h"
#include "nsStyleStruct.h"

using namespace mozilla;

// Blend one RGBA color with another based on a given ratios.
// It is a linear combination of each channel with alpha premultipled.
static nscolor LinearBlendColors(nscolor aBg, float aBgRatio, nscolor aFg,
                                 float aFgRatio) {
  constexpr float kFactor = 1.0f / 255.0f;

  float p1 = aBgRatio;
  float a1 = kFactor * NS_GET_A(aBg);
  float r1 = a1 * NS_GET_R(aBg);
  float g1 = a1 * NS_GET_G(aBg);
  float b1 = a1 * NS_GET_B(aBg);

  float p2 = aFgRatio;
  float a2 = kFactor * NS_GET_A(aFg);
  float r2 = a2 * NS_GET_R(aFg);
  float g2 = a2 * NS_GET_G(aFg);
  float b2 = a2 * NS_GET_B(aFg);

  float a = p1 * a1 + p2 * a2;
  if (a <= 0.f) {
    return NS_RGBA(0, 0, 0, 0);
  }

  if (a > 1.f) {
    a = 1.f;
  }

  auto r = ClampColor((p1 * r1 + p2 * r2) / a);
  auto g = ClampColor((p1 * g1 + p2 * g2) / a);
  auto b = ClampColor((p1 * b1 + p2 * b2) / a);
  return NS_RGBA(r, g, b, NSToIntRound(a * 255));
}

bool StyleComplexColor::MaybeTransparent() const {
  // We know that the color is opaque when it's a numeric color with
  // alpha == 255.
  // TODO(djg): Should we extend this to check Complex with bgRatio =
  // 0, and fgRatio * alpha >= 255?
  return mTag != eNumeric || NS_GET_A(mColor) != 255;
}

nscolor StyleComplexColor::CalcColor(nscolor aForegroundColor) const {
  switch (mTag) {
    case eNumeric:
      return mColor;
    case eForeground:
    case eAuto:
      return aForegroundColor;
    case eComplex:
      return LinearBlendColors(mColor, mBgRatio, aForegroundColor, mFgRatio);
    default:
      MOZ_ASSERT_UNREACHABLE("StyleComplexColor has invalid mTag");
      return mColor;
  }
}

nscolor StyleComplexColor::CalcColor(mozilla::ComputedStyle* aStyle) const {
  // Common case that is numeric color, which is pure background, we
  // can skip resolving StyleColor().
  // TODO(djg): Is this optimization worth it?
  if (mTag == eNumeric) {
    return mColor;
  }

  MOZ_ASSERT(aStyle);
  auto fgColor = aStyle->StyleColor()->mColor;
  return CalcColor(fgColor);
}

nscolor StyleComplexColor::CalcColor(const nsIFrame* aFrame) const {
  return CalcColor(aFrame->Style());
}