Dynamic NSColor subclass to support Dark Mode on macOS prior to 10.13

DynamicColor.h

@interface DynamicColor : NSColor

- (instancetype)initWithAquaColor:(NSColor *)aquaColor
      darkAquaColor:(NSColor *__nullable)darkAquaColor;

- (NSColor *)effectiveColor;

@end

DynamicColor.m

#import "DynamicColor.h"


#define FORWARD( PROP, TYPE ) \
- (TYPE)PROP { return [self.effectiveColor PROP]; }


@interface DynamicColor ()

@property (nonatomic, strong) NSColor *aquaColor;
@property (nonatomic, strong, nullable) NSColor *darkAquaColor;

@property (nonatomic, strong, readonly) NSColor *effectiveColor;

@end

@implementation DynamicColor

- (instancetype)initWithAquaColor:(NSColor *)aquaColor
                    darkAquaColor:(NSColor *)darkAquaColor
{
    self = [super init];
    if (self) {
        _aquaColor = aquaColor;
        _darkAquaColor = darkAquaColor;
    }
    return self;
}

+ (BOOL)supportsSecureCoding
{
    return YES;
}

- (instancetype)initWithCoder:(NSCoder *)coder
{
    self = [super initWithCoder:coder];
    if (self) {
        _aquaColor = [coder decodeObjectOfClass:[NSColor class] forKey:@"aquaColor"];
        _darkAquaColor = [coder decodeObjectOfClass:[NSColor class] forKey:@"darkAquaColor"];
    }
    return self;
}

- (void)encodeWithCoder:(NSCoder *)aCoder
{
    [super encodeWithCoder:aCoder];
    [aCoder encodeObject:self.aquaColor forKey:@"aquaColor"];
    if (self.darkAquaColor) {
        [aCoder encodeObject:self.darkAquaColor forKey:@"darkAquaColor"];
    }
}

- (NSColor *)effectiveColor
{
    if (@available(macOS 10.14, *)) {
        NSAppearance *appearance = [NSAppearance currentAppearance] ?: [NSApp effectiveAppearance];
        
        NSAppearanceName appearanceName = [appearance bestMatchFromAppearancesWithNames:@[NSAppearanceNameAqua, NSAppearanceNameDarkAqua]];
        
        if (self.darkAquaColor != nil && [appearanceName isEqualToString:NSAppearanceNameDarkAqua]) {
            return self.darkAquaColor;
        }
    }
    return self.aquaColor;
}

FORWARD(colorSpace, NSColorSpace *)
- (NSColor *)colorUsingColorSpace:(NSColorSpace *)space
{
    return [self.effectiveColor colorUsingColorSpace:space];
}

FORWARD(colorSpaceName, NSColorSpaceName)
- (NSColor *)colorUsingColorSpaceName:(NSColorSpaceName)name
{
    return [self.effectiveColor colorUsingColorSpaceName:name];
}

FORWARD(numberOfComponents, NSInteger)
- (void)getComponents:(CGFloat *)components
{
    return [self.effectiveColor getComponents:components];
}

#pragma mark - RGB colorspace

FORWARD(redComponent, CGFloat)
FORWARD(greenComponent, CGFloat)
FORWARD(blueComponent, CGFloat)

- (void)getRed:(nullable CGFloat *)red green:(nullable CGFloat *)green blue:(nullable CGFloat *)blue alpha:(nullable CGFloat *)alpha
{
    return [self.effectiveColor getRed:red green:green blue:blue alpha:alpha];
}

#pragma mark - HSB colorspace

FORWARD(hueComponent, CGFloat)
FORWARD(saturationComponent, CGFloat)
FORWARD(brightnessComponent, CGFloat)

- (void)getHue:(nullable CGFloat *)hue saturation:(nullable CGFloat *)saturation brightness:(nullable CGFloat *)brightness alpha:(nullable CGFloat *)alpha
{
    return [self.effectiveColor getHue:hue saturation:saturation brightness:brightness alpha:alpha];
}

#pragma mark - Gray colorspace

FORWARD(whiteComponent, CGFloat)

- (void)getWhite:(CGFloat *)white alpha:(CGFloat *)alpha
{
    return [self.effectiveColor getWhite:white alpha:alpha];
}

#pragma mark - CMYK colorspace

FORWARD(cyanComponent, CGFloat)
FORWARD(magentaComponent, CGFloat)
FORWARD(yellowComponent, CGFloat)
FORWARD(blackComponent, CGFloat)

- (void)getCyan:(nullable CGFloat *)cyan magenta:(nullable CGFloat *)magenta yellow:(nullable CGFloat *)yellow black:(nullable CGFloat *)black alpha:(nullable CGFloat *)alpha
{
    return [self.effectiveColor getCyan:cyan magenta:magenta yellow:yellow black:black alpha:alpha];
}

#pragma mark - Others

FORWARD(alphaComponent, CGFloat)
FORWARD(CGColor, CGColorRef)
FORWARD(catalogNameComponent, NSColorListName)
FORWARD(colorNameComponent, NSColorName)
FORWARD(localizedCatalogNameComponent, NSColorListName)
FORWARD(localizedColorNameComponent, NSString *)

- (void)setStroke
{
     [self.effectiveColor setStroke];
}

- (void)setFill
{
    [self.effectiveColor setFill];
}

- (void)set
{
    [self.effectiveColor set];
}

- (nullable NSColor *)highlightWithLevel:(CGFloat)val
{
    return [self.effectiveColor highlightWithLevel:val];
}

- (NSColor *)shadowWithLevel:(CGFloat)val
{
    return [self.effectiveColor shadowWithLevel:val];
}

- (NSColor *)colorWithAlphaComponent:(CGFloat)alpha
{
    return [self.effectiveColor colorWithAlphaComponent:alpha];
}

- (nullable NSColor *)blendedColorWithFraction:(CGFloat)fraction ofColor:(NSColor *)color
{
    return [self.effectiveColor blendedColorWithFraction:fraction ofColor:color];
}

- (NSColor *)colorWithSystemEffect:(NSColorSystemEffect)systemEffect NS_AVAILABLE_MAC(10_14)
{
    return [self.effectiveColor colorWithSystemEffect:systemEffect];
}

@end