macOS Dynamic Wallpaper Generator - Create appearance-aware wallpapers from hex colors

wallit.nix

{
  lib,
  swift,
  swiftPackages,
}:

swiftPackages.stdenv.mkDerivation {
  pname = "wallit";
  version = "1.0.0";

  src = ./Wallit.swift;

  dontUnpack = true;

  nativeBuildInputs = [ swift ];

  buildPhase = ''
    runHook preBuild

    cp $src Wallit.swift
    swiftc Wallit.swift -o wallit -O

    runHook postBuild
  '';

  installPhase = ''
    runHook preInstall

    mkdir -p $out/bin
    cp wallit $out/bin/

    runHook postInstall
  '';

  meta = with lib; {
    description = "macOS dynamic wallpaper generator";
    platforms = platforms.darwin;
    maintainers = [];
    mainProgram = "wallit";
  };
}

Wallit.swift

import Foundation
import CoreGraphics
import ImageIO

func parseHexColor(_ hex: String) -> (r: CGFloat, g: CGFloat, b: CGFloat)? {
    let clean = hex.trimmingCharacters(in: CharacterSet(charactersIn: "#"))
    guard clean.count == 6, let value = Int(clean, radix: 16) else { return nil }
    
    return (
        r: CGFloat((value >> 16) & 0xFF) / 255.0,
        g: CGFloat((value >> 8) & 0xFF) / 255.0,
        b: CGFloat(value & 0xFF) / 255.0
    )
}

func createSolidColorImage(_ hex: String) -> CGImage? {
    guard let color = parseHexColor(hex) else { return nil }
    
    let width = 5120, height = 2880
    let colorSpace = CGColorSpaceCreateDeviceRGB()
    
    guard let context = CGContext(
        data: nil,
        width: width,
        height: height,
        bitsPerComponent: 8,
        bytesPerRow: width * 4,
        space: colorSpace,
        bitmapInfo: CGImageAlphaInfo.noneSkipLast.rawValue
    ) else { return nil }
    
    context.setFillColor(red: color.r, green: color.g, blue: color.b, alpha: 1.0)
    context.fill(CGRect(x: 0, y: 0, width: CGFloat(width), height: CGFloat(height)))
    
    return context.makeImage()
}

func loadImageFromFile(_ path: String) -> CGImage? {
    let url = URL(fileURLWithPath: path)
    guard let source = CGImageSourceCreateWithURL(url as CFURL, nil) else { return nil }
    return CGImageSourceCreateImageAtIndex(source, 0, nil)
}

func getImage(from input: String) -> CGImage? {
    // Try as hex color first
    if let image = createSolidColorImage(input) {
        return image
    }
    // Otherwise load as file
    return loadImageFromFile(input)
}

func createDynamicWallpaper(light: String, dark: String, output: String) throws {
    guard let lightImage = getImage(from: light) else {
        throw NSError(domain: "", code: 1, userInfo: [NSLocalizedDescriptionKey: "Cannot load light image/color: \(light)"])
    }
    
    guard let darkImage = getImage(from: dark) else {
        throw NSError(domain: "", code: 2, userInfo: [NSLocalizedDescriptionKey: "Cannot load dark image/color: \(dark)"])
    }
    
    // Create appearance metadata
    let metadata = CGImageMetadataCreateMutable()
    CGImageMetadataRegisterNamespaceForPrefix(
        metadata,
        "http://ns.apple.com/namespace/1.0/" as CFString,
        "apple_desktop" as CFString,
        nil
    )
    
    let appearanceInfo = ["d": 1, "l": 0]  // dark: image 1, light: image 0
    let plistData = try PropertyListSerialization.data(
        fromPropertyList: appearanceInfo,
        format: .binary,
        options: 0
    )
    
    let tag = CGImageMetadataTagCreate(
        "http://ns.apple.com/namespace/1.0/" as CFString,
        "apple_desktop" as CFString,
        "apr" as CFString,
        .string,
        plistData.base64EncodedString() as CFString
    )!
    
    CGImageMetadataSetTagWithPath(metadata, nil, "apple_desktop:apr" as CFString, tag)
    
    // Write HEIC file
    let outputURL = URL(fileURLWithPath: output)
    guard let destination = CGImageDestinationCreateWithURL(
        outputURL as CFURL,
        "public.heic" as CFString,
        2,
        nil
    ) else {
        throw NSError(domain: "", code: 3, userInfo: [NSLocalizedDescriptionKey: "Cannot create output file"])
    }
    
    CGImageDestinationAddImageAndMetadata(destination, lightImage, metadata, nil)
    CGImageDestinationAddImage(destination, darkImage, nil)
    
    guard CGImageDestinationFinalize(destination) else {
        throw NSError(domain: "", code: 4, userInfo: [NSLocalizedDescriptionKey: "Cannot write output file"])
    }
}

// Main
let args = CommandLine.arguments

if args.contains("-h") || args.contains("--help") {
    print("""
    Usage: \(args[0]) [light] [dark] [output]
    
    Creates a macOS dynamic wallpaper that switches with appearance.
    
    Arguments:
      light    Hex color or image path for light mode (default: f0f0f0)
      dark     Hex color or image path for dark mode (default: 1e1e1e)  
      output   Output filename (default: wallpaper.heic)
    
    Examples:
      \(args[0])                           # Modus theme colors
      \(args[0]) ffffff 000000             # Black and white
      \(args[0]) day.jpg night.jpg         # From images
      \(args[0]) f0f0f0 sunset.png custom.heic
    """)
    exit(0)
}

let light = args.count > 1 ? args[1] : "f0f0f0"
let dark = args.count > 2 ? args[2] : "1e1e1e"
let output = args.count > 3 ? args[3] : "wallpaper.heic"

do {
    try createDynamicWallpaper(light: light, dark: dark, output: output)
} catch {
    print("Error: \(error.localizedDescription)")
    exit(1)
}