components/ScalableFontDescriptor/src/MDCScalableFontDescriptor.m

// Copyright 2020-present the Material Components for iOS authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#import "MDCScalableFontDescriptor.h"

@implementation MDCScalableFontDescriptor

- (instancetype)initWithFontDescriptor:(UIFontDescriptor *)fontDescriptor
                           fontMetrics:(UIFontMetrics *)fontMetrics {
  self = [self initWithFontDescriptor:fontDescriptor];
  if (self) {
    _fontDescriptor = fontDescriptor;
    _fontMetrics = fontMetrics;
  }
  return self;
}

- (instancetype)initWithFontDescriptor:(UIFontDescriptor *)fontDescriptor {
  self = [super init];
  if (self) {
    _fontDescriptor = fontDescriptor;
  }
  return self;
}

- (UIFont *)baseFont {
  return [UIFont fontWithDescriptor:self.fontDescriptor size:self.fontDescriptor.pointSize];
}

- (UIFont *)preferredFontCompatibleWithTraitCollection:(UITraitCollection *)traitCollection {
  return [self.fontMetrics scaledFontForFont:self.baseFont
               compatibleWithTraitCollection:traitCollection];
}

#if DEBUG

// NOTE: UIFontMetric detection is potentially broken on Forge on Mac due to b/142536380.
- (NSString *)description {
  // This method is unoptimized, and assumes it's only called in testing environments.
  static NSArray<UIFontTextStyle> *textStyles;
  static NSArray<UIContentSizeCategory> *sizeCategories;
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
    textStyles = @[
#if !TARGET_OS_TV
      UIFontTextStyleLargeTitle,
#endif
      UIFontTextStyleTitle1,
      UIFontTextStyleTitle2,
      UIFontTextStyleTitle3,
      UIFontTextStyleHeadline,
      UIFontTextStyleSubheadline,
      UIFontTextStyleBody,
      UIFontTextStyleCallout,
      UIFontTextStyleCaption1,
      UIFontTextStyleCaption2,
      UIFontTextStyleFootnote,
    ];

    sizeCategories = @[
      UIContentSizeCategoryExtraSmall,
      UIContentSizeCategorySmall,
      UIContentSizeCategoryMedium,
      UIContentSizeCategoryLarge,
      UIContentSizeCategoryExtraLarge,
      UIContentSizeCategoryExtraExtraLarge,
      UIContentSizeCategoryExtraExtraExtraLarge,
      UIContentSizeCategoryAccessibilityMedium,
      UIContentSizeCategoryAccessibilityLarge,
      UIContentSizeCategoryAccessibilityExtraLarge,
      UIContentSizeCategoryAccessibilityExtraExtraLarge,
      UIContentSizeCategoryAccessibilityExtraExtraExtraLarge,
    ];
  });

  NSMutableString *descriptionString = [NSMutableString
      stringWithFormat:@"%@ Descriptor: %@\n", [super description], self.fontDescriptor];
  UIFont *testFont = [UIFont systemFontOfSize:99 weight:UIFontWeightRegular];

  // Check all UIFontTextStyle values and search for one that scales fonts equivalently to this
  // style's `fontMetrics`.
  for (UIFontTextStyle textStyle in textStyles) {
    BOOL matchedTextStyle = YES;
    UIFontMetrics *textStyleMetrics = [UIFontMetrics metricsForTextStyle:textStyle];
    // Compare the scaled font at all UIContentSizeCategory values to determine if the metrics are
    // equivalent.
    for (UIContentSizeCategory sizeCategory in sizeCategories) {
      UITraitCollection *traitCollection =
          [UITraitCollection traitCollectionWithPreferredContentSizeCategory:sizeCategory];
      UIFont *selfScaledFont = [self.fontMetrics scaledFontForFont:testFont
                                     compatibleWithTraitCollection:traitCollection];
      UIFont *otherScaledFont = [textStyleMetrics scaledFontForFont:testFont
                                      compatibleWithTraitCollection:traitCollection];
      if (![selfScaledFont isEqual:otherScaledFont]) {
        matchedTextStyle = NO;
        break;
      }
    }
    if (matchedTextStyle) {
      [descriptionString appendFormat:@"Metrics: %@", textStyle];
      break;
    }
  }
  return [descriptionString copy];
}

#endif

@end