ios/chrome/browser/shared/ui/util/transparent_link_button.mm

// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#import "ios/chrome/browser/shared/ui/util/transparent_link_button.h"

#import "base/check.h"
#import "base/ios/ios_util.h"
#import "base/strings/sys_string_conversions.h"
#import "ios/chrome/browser/shared/public/features/features.h"
#import "url/gurl.h"

// Minimum tap area dimension, as specified by Apple guidelines.
const CGFloat kLinkTapAreaMinimum = 44.0;

// Maximum line height expansion factor.
const CGFloat kMaximumExpansionFactor = 1.25;

namespace {
// The corner radius of the highlight view.
const CGFloat kHighlightViewCornerRadius = 2.0;
// The alpha of the highlight view's background color (base color is black).
const CGFloat kHighlightViewBackgroundAlpha = 0.25;
}  // namespace

@interface TransparentLinkButton ()

// The link frame passed upon initialization.
@property(nonatomic, readonly) CGRect linkFrame;

// Semi-transparent overlay that is shown to highlight the link text when the
// button's highlight state is set to YES.
@property(nonatomic, strong, readonly) UIView* highlightView;

// Links that span multiple lines require more than one TransparentLinkButton.
// These properties are used to populate the highlight state from one button to
// the other buttons corresponding with the same link.
@property(nonatomic, weak) TransparentLinkButton* previousLinkButton;
@property(nonatomic, weak) TransparentLinkButton* nextLinkButton;

// Designated initializer.  `linkFrame` is the frame of the link text; this may
// differ from the actual frame of the resulting TransparentLinkButton, which is
// guaranteed to be at least `kLinkTapAreaMinimum` in each dimension, or
// `lineHeight` * `kMaximumExpansionFactor` for height, whichever is smaller.
// `URL` is the URL for the associated link.
- (instancetype)initWithLinkFrame:(CGRect)linkFrame
                              URL:(const GURL&)URL
                       lineHeight:(CGFloat)lineHeight NS_DESIGNATED_INITIALIZER;

// Sets the properties, propogating state to its adjacent link buttons.
// `sender` is the TransparentLinkButon whose state is being propagated to
// `self`.
- (void)setHighlighted:(BOOL)highlighted sender:(TransparentLinkButton*)sender;
- (void)setSelected:(BOOL)selected sender:(TransparentLinkButton*)sender;

// Updates the appearance of `highlightView` based on highlighted/selected
// state.
- (void)updateHighlightView;

@end

@implementation TransparentLinkButton

@synthesize URL = _URL;
@synthesize debug = _debug;
@synthesize linkFrame = _linkFrame;
@synthesize highlightView = _highlightView;
@synthesize previousLinkButton = _previousLinkButton;
@synthesize nextLinkButton = _nextLinkButton;

- (instancetype)initWithLinkFrame:(CGRect)linkFrame
                              URL:(const GURL&)URL
                       lineHeight:(CGFloat)lineHeight {
  CGFloat linkTapHeightMinimum = kLinkTapAreaMinimum;
  if (lineHeight > 0) {
    linkTapHeightMinimum =
        MIN(lineHeight * kMaximumExpansionFactor, kLinkTapAreaMinimum);
  }
  CGFloat linkHeightExpansion =
      MAX(0, (linkTapHeightMinimum - linkFrame.size.height) / 2.0);
  CGFloat linkWidthExpansion =
      MAX(0, (kLinkTapAreaMinimum - linkFrame.size.width) / 2.0);
  // Expand the frame as necessary to meet the minimum tap area dimensions.
  CGRect frame =
      CGRectInset(linkFrame, -linkWidthExpansion, -linkHeightExpansion);
  if ((self = [super initWithFrame:frame])) {
    DCHECK(URL.is_valid());

    UIButtonConfiguration* buttonConfiguration =
        [UIButtonConfiguration plainButtonConfiguration];
    buttonConfiguration.contentInsets =
        NSDirectionalEdgeInsetsMake(linkHeightExpansion, linkWidthExpansion,
                                    linkHeightExpansion, linkWidthExpansion);
    self.configuration = buttonConfiguration;

    self.backgroundColor = [UIColor clearColor];
    self.exclusiveTouch = YES;
    _linkFrame = linkFrame;
    _URL = URL;
    // These buttons are positioned absolutely based on the the position of
    // regions of text that is already correctly aligned for RTL if necessary.
    self.semanticContentAttribute = UISemanticContentAttributeSpatial;
  }
  return self;
}

#pragma mark - Accessors

- (void)setDebug:(BOOL)debug {
  _debug = debug;
  self.layer.borderWidth = _debug ? 1.0 : 0.0;
  self.layer.borderColor =
      _debug ? [UIColor greenColor].CGColor : [UIColor clearColor].CGColor;
  self.backgroundColor = _debug ? [UIColor redColor] : [UIColor clearColor];
  self.alpha = _debug ? 0.15 : 1.0;
}

- (UIView*)highlightView {
  if (!_highlightView) {
    CGRect linkFrame = [self convertRect:self.linkFrame
                                fromView:self.superview];
    linkFrame = CGRectInset(linkFrame, -kHighlightViewCornerRadius, 0);
    _highlightView = [[UIView alloc] initWithFrame:linkFrame];
    [_highlightView
        setBackgroundColor:[UIColor
                               colorWithWhite:0.0
                                        alpha:kHighlightViewBackgroundAlpha]];
    [_highlightView layer].cornerRadius = kHighlightViewCornerRadius;
    [_highlightView setClipsToBounds:YES];
    [self addSubview:_highlightView];
  }
  return _highlightView;
}

- (void)setHighlighted:(BOOL)highlighted {
  [self setHighlighted:highlighted sender:nil];
}

- (void)setSelected:(BOOL)selected {
  [self setSelected:selected sender:nil];
}

#pragma mark -

+ (NSArray*)buttonsForLinkFrames:(NSArray*)linkFrames
                             URL:(const GURL&)URL
                      lineHeight:(CGFloat)lineHeight
              accessibilityLabel:(NSString*)label
                 accessibilityID:(NSString*)accessibilityID {
  if (!linkFrames.count) {
    return @[];
  }
  NSMutableArray* buttons =
      [[NSMutableArray alloc] initWithCapacity:linkFrames.count];
  for (NSValue* linkFrameValue in linkFrames) {
    CGRect linkFrame = [linkFrameValue CGRectValue];
    TransparentLinkButton* button =
        [[TransparentLinkButton alloc] initWithLinkFrame:linkFrame
                                                     URL:URL
                                              lineHeight:lineHeight];
    TransparentLinkButton* previousButton = [buttons lastObject];
    previousButton.nextLinkButton = button;
    button.previousLinkButton = previousButton;
    // Make buttons not accessible by default, but provide label for tests.
    button.isAccessibilityElement = NO;
    button.accessibilityLabel = label;
    button.accessibilityIdentifier = accessibilityID;
    [buttons addObject:button];
  }
  // Make the first button accessible.
  [buttons[0] setIsAccessibilityElement:YES];
  return [NSArray arrayWithArray:buttons];
}

- (void)setHighlighted:(BOOL)highlighted sender:(TransparentLinkButton*)sender {
  [super setHighlighted:highlighted];
  if (self.previousLinkButton != sender) {
    [self.previousLinkButton setHighlighted:highlighted sender:self];
  }
  if (self.nextLinkButton != sender) {
    [self.nextLinkButton setHighlighted:highlighted sender:self];
  }
  [self updateHighlightView];
}

- (void)setSelected:(BOOL)selected sender:(TransparentLinkButton*)sender {
  [super setSelected:selected];
  if (self.previousLinkButton != sender) {
    [self.previousLinkButton setSelected:selected sender:self];
  }
  if (self.nextLinkButton != sender) {
    [self.nextLinkButton setSelected:selected sender:self];
  }
  [self updateHighlightView];
}

- (void)updateHighlightView {
  self.highlightView.hidden = !self.highlighted && !self.selected;
}

@end