NSImage+Resize.m

#import "NSImage+Resize.h"

@interface ImageCache : NSObject
+ (ImageCache *)instance;
- (void)setImage:(NSImage *)image
         forName:(NSString *)name
      withHeight:(CGFloat)height;
- (NSImage *)getImageForName:(NSString *)name withHeight:(CGFloat)height;
@property(nonatomic, strong) NSCache *imageCache;
@end

static ImageCache *instance;

@implementation ImageCache

+ (ImageCache *)instance {
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
    instance = [[ImageCache alloc] init];
  });
  return instance;
}
- (instancetype)init {
  self = [super init];
  if (self) {
    self.imageCache = [[NSCache alloc] init];
  }
  return self;
}

- (NSString *)keyForName:(NSString *)name withHeight:(CGFloat)height {
  return [NSString stringWithFormat:@"%f/%@", height, name];
}

- (void)setImage:(NSImage *)image
         forName:(NSString *)name
      withHeight:(CGFloat)height {
  [self.imageCache setObject:image
                      forKey:[self keyForName:name withHeight:height]];
}

- (NSImage *)getImageForName:(NSString *)name withHeight:(CGFloat)height {
  return
      [self.imageCache objectForKey:[self keyForName:name withHeight:height]];
}

@end

@implementation NSImage (Resize)

- (NSImage *)imageWithHeight:(CGFloat)height {
  NSImage *image = self;
  if (![image isValid]) {
    NSLog(@"Can't resize invalid image");
    return nil;
  }
  NSSize newSize =
      NSMakeSize(image.size.width * height / image.size.height, height);
  NSImage *newImage = [[NSImage alloc] initWithSize:newSize];
  [newImage lockFocus];
  [image setSize:newSize];
  [[NSGraphicsContext currentContext]
      setImageInterpolation:NSImageInterpolationDefault];
  [image drawAtPoint:NSZeroPoint
            fromRect:CGRectMake(0, 0, newSize.width, newSize.height)
           operation:NSCompositingOperationCopy
            fraction:1.0];
  [newImage unlockFocus];
  return newImage;
}

+ (NSImage *)imageFromName:(NSString *)name withHeight:(CGFloat)height {
  if (name.length == 0) {
    return nil;
  }
  NSImage *image =
      [[ImageCache instance] getImageForName:name withHeight:height];
  if (image != nil) {
    return image;
  }
  if ([name hasPrefix:@"http"]) {
    image = [[NSImage alloc] initWithContentsOfURL:[NSURL URLWithString:name]];
  } else {
    image = [NSImage imageNamed:name];
  }
  if (height > 0 && image.size.height > height) {
    image = [image imageWithHeight:height];
  }
  [[ImageCache instance] setImage:image forName:name withHeight:height];
  return image;
}

@end