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diff --git a/apps/theming/lib/Util.php b/apps/theming/lib/Util.php
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+<?php
+
+/**
+ * SPDX-FileCopyrightText: 2016 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+namespace OCA\Theming;
+
+use Mexitek\PHPColors\Color;
+use OCP\App\AppPathNotFoundException;
+use OCP\App\IAppManager;
+use OCP\Files\IAppData;
+use OCP\Files\NotFoundException;
+use OCP\Files\SimpleFS\ISimpleFile;
+use OCP\IConfig;
+use OCP\IUserSession;
+use OCP\Server;
+use OCP\ServerVersion;
+
+class Util {
+	public function __construct(
+		private ServerVersion $serverVersion,
+		private IConfig $config,
+		private IAppManager $appManager,
+		private IAppData $appData,
+		private ImageManager $imageManager,
+	) {
+	}
+
+	/**
+	 * Should we invert the text on this background color?
+	 * @param string $color rgb color value
+	 * @return bool
+	 */
+	public function invertTextColor(string $color): bool {
+		return $this->colorContrast($color, '#ffffff') < 4.5;
+	}
+
+	/**
+	 * Is this color too bright ?
+	 * @param string $color rgb color value
+	 * @return bool
+	 */
+	public function isBrightColor(string $color): bool {
+		$l = $this->calculateLuma($color);
+		if ($l > 0.6) {
+			return true;
+		} else {
+			return false;
+		}
+	}
+
+	/**
+	 * get color for on-page elements:
+	 * theme color by default, grey if theme color is to bright
+	 * @param string $color
+	 * @param ?bool $brightBackground
+	 * @return string
+	 */
+	public function elementColor($color, ?bool $brightBackground = null, ?string $backgroundColor = null, bool $highContrast = false) {
+		if ($backgroundColor !== null) {
+			$brightBackground = $brightBackground ?? $this->isBrightColor($backgroundColor);
+			// Minimal amount that is possible to change the luminance
+			$epsilon = 1.0 / 255.0;
+			// Current iteration to prevent infinite loops
+			$iteration = 0;
+			// We need to keep blurred backgrounds in mind which might be mixed with the background
+			$blurredBackground = $this->mix($backgroundColor, $brightBackground ? $color : '#ffffff', 66);
+			$contrast = $this->colorContrast($color, $blurredBackground);
+
+			// Min. element contrast is 3:1 but we need to keep hover states in mind -> min 3.2:1
+			$minContrast = $highContrast ? 5.6 : 3.2;
+
+			while ($contrast < $minContrast && $iteration++ < 100) {
+				$hsl = Color::hexToHsl($color);
+				$hsl['L'] = max(0, min(1, $hsl['L'] + ($brightBackground ? -$epsilon : $epsilon)));
+				$color = '#' . Color::hslToHex($hsl);
+				$contrast = $this->colorContrast($color, $blurredBackground);
+			}
+			return $color;
+		}
+
+		// Fallback for legacy calling
+		$luminance = $this->calculateLuminance($color);
+
+		if ($brightBackground !== false && $luminance > 0.8) {
+			// If the color is too bright in bright mode, we fall back to a darkened color
+			return $this->darken($color, 30);
+		}
+
+		if ($brightBackground !== true && $luminance < 0.2) {
+			// If the color is too dark in dark mode, we fall back to a brightened color
+			return $this->lighten($color, 30);
+		}
+
+		return $color;
+	}
+
+	public function mix(string $color1, string $color2, int $factor): string {
+		$color = new Color($color1);
+		return '#' . $color->mix($color2, $factor);
+	}
+
+	public function lighten(string $color, int $factor): string {
+		$color = new Color($color);
+		return '#' . $color->lighten($factor);
+	}
+
+	public function darken(string $color, int $factor): string {
+		$color = new Color($color);
+		return '#' . $color->darken($factor);
+	}
+
+	/**
+	 * Convert RGB to HSL
+	 *
+	 * Copied from cssphp, copyright Leaf Corcoran, licensed under MIT
+	 *
+	 * @param int $red
+	 * @param int $green
+	 * @param int $blue
+	 *
+	 * @return float[]
+	 */
+	public function toHSL(int $red, int $green, int $blue): array {
+		$color = new Color(Color::rgbToHex(['R' => $red, 'G' => $green, 'B' => $blue]));
+		return array_values($color->getHsl());
+	}
+
+	/**
+	 * @param string $color rgb color value
+	 * @return float
+	 */
+	public function calculateLuminance(string $color): float {
+		[$red, $green, $blue] = $this->hexToRGB($color);
+		$hsl = $this->toHSL($red, $green, $blue);
+		return $hsl[2];
+	}
+
+	/**
+	 * Calculate the Luma according to WCAG 2
+	 * http://www.w3.org/TR/WCAG20/#relativeluminancedef
+	 * @param string $color rgb color value
+	 * @return float
+	 */
+	public function calculateLuma(string $color): float {
+		$rgb = $this->hexToRGB($color);
+
+		// Normalize the values by converting to float and applying the rules from WCAG2.0
+		$rgb = array_map(function (int $color) {
+			$color = $color / 255.0;
+			if ($color <= 0.03928) {
+				return $color / 12.92;
+			} else {
+				return pow((($color + 0.055) / 1.055), 2.4);
+			}
+		}, $rgb);
+
+		[$red, $green, $blue] = $rgb;
+		return (0.2126 * $red + 0.7152 * $green + 0.0722 * $blue);
+	}
+
+	/**
+	 * Calculat the color contrast according to WCAG 2
+	 * http://www.w3.org/TR/WCAG20/#contrast-ratiodef
+	 * @param string $color1 The first color
+	 * @param string $color2 The second color
+	 */
+	public function colorContrast(string $color1, string $color2): float {
+		$luminance1 = $this->calculateLuma($color1) + 0.05;
+		$luminance2 = $this->calculateLuma($color2) + 0.05;
+		return max($luminance1, $luminance2) / min($luminance1, $luminance2);
+	}
+
+	/**
+	 * @param string $color rgb color value
+	 * @return int[]
+	 * @psalm-return array{0: int, 1: int, 2: int}
+	 */
+	public function hexToRGB(string $color): array {
+		$color = new Color($color);
+		return array_values($color->getRgb());
+	}
+
+	/**
+	 * @param $color
+	 * @return string base64 encoded radio button svg
+	 */
+	public function generateRadioButton($color) {
+		$radioButtonIcon = '<svg xmlns="http://www.w3.org/2000/svg" height="16" width="16">'
+			. '<path d="M8 1a7 7 0 0 0-7 7 7 7 0 0 0 7 7 7 7 0 0 0 7-7 7 7 0 0 0-7-7zm0 1a6 6 0 0 1 6 6 6 6 0 0 1-6 6 6 6 0 0 1-6-6 6 6 0 0 1 6-6zm0 2a4 4 0 1 0 0 8 4 4 0 0 0 0-8z" fill="' . $color . '"/></svg>';
+		return base64_encode($radioButtonIcon);
+	}
+
+
+	/**
+	 * @param string $app app name
+	 * @return string|ISimpleFile path to app icon / file of logo
+	 */
+	public function getAppIcon($app) {
+		$app = $this->appManager->cleanAppId($app);
+		try {
+			$appPath = $this->appManager->getAppPath($app);
+			$icon = $appPath . '/img/' . $app . '.svg';
+			if (file_exists($icon)) {
+				return $icon;
+			}
+			$icon = $appPath . '/img/app.svg';
+			if (file_exists($icon)) {
+				return $icon;
+			}
+		} catch (AppPathNotFoundException $e) {
+		}
+
+		if ($this->config->getAppValue('theming', 'logoMime', '') !== '') {
+			$logoFile = null;
+			try {
+				$folder = $this->appData->getFolder('global/images');
+				return $folder->getFile('logo');
+			} catch (NotFoundException $e) {
+			}
+		}
+		return \OC::$SERVERROOT . '/core/img/logo/logo.svg';
+	}
+
+	/**
+	 * @param string $app app name
+	 * @param string $image relative path to image in app folder
+	 * @return string|false absolute path to image
+	 */
+	public function getAppImage($app, $image) {
+		$app = $this->appManager->cleanAppId($app);
+		/**
+		 * @psalm-taint-escape file
+		 */
+		$image = str_replace(['\0', '\\', '..'], '', $image);
+		if ($app === 'core') {
+			$icon = \OC::$SERVERROOT . '/core/img/' . $image;
+			if (file_exists($icon)) {
+				return $icon;
+			}
+		}
+
+		try {
+			$appPath = $this->appManager->getAppPath($app);
+		} catch (AppPathNotFoundException $e) {
+			return false;
+		}
+
+		$icon = $appPath . '/img/' . $image;
+		if (file_exists($icon)) {
+			return $icon;
+		}
+		$icon = $appPath . '/img/' . $image . '.svg';
+		if (file_exists($icon)) {
+			return $icon;
+		}
+		$icon = $appPath . '/img/' . $image . '.png';
+		if (file_exists($icon)) {
+			return $icon;
+		}
+		$icon = $appPath . '/img/' . $image . '.gif';
+		if (file_exists($icon)) {
+			return $icon;
+		}
+		$icon = $appPath . '/img/' . $image . '.jpg';
+		if (file_exists($icon)) {
+			return $icon;
+		}
+
+		return false;
+	}
+
+	/**
+	 * replace default color with a custom one
+	 *
+	 * @param string $svg content of a svg file
+	 * @param string $color color to match
+	 * @return string
+	 */
+	public function colorizeSvg($svg, $color) {
+		$svg = preg_replace('/#0082c9/i', $color, $svg);
+		return $svg;
+	}
+
+	/**
+	 * Check if a custom theme is set in the server configuration
+	 *
+	 * @return bool
+	 */
+	public function isAlreadyThemed() {
+		$theme = $this->config->getSystemValue('theme', '');
+		if ($theme !== '') {
+			return true;
+		}
+		return false;
+	}
+
+	public function isBackgroundThemed() {
+		$backgroundLogo = $this->config->getAppValue('theming', 'backgroundMime', '');
+		return $backgroundLogo !== '' && $backgroundLogo !== 'backgroundColor';
+	}
+
+	public function isLogoThemed() {
+		return $this->imageManager->hasImage('logo')
+			|| $this->imageManager->hasImage('logoheader');
+	}
+
+	public function getCacheBuster(): string {
+		$userSession = Server::get(IUserSession::class);
+		$userId = '';
+		$user = $userSession->getUser();
+		if (!is_null($user)) {
+			$userId = $user->getUID();
+		}
+		$serverVersion = $this->serverVersion->getVersionString();
+		$themingAppVersion = $this->appManager->getAppVersion('theming');
+		$userCacheBuster = '';
+		if ($userId) {
+			$userCacheBusterValue = (int)$this->config->getUserValue($userId, 'theming', 'userCacheBuster', '0');
+			$userCacheBuster = $userId . '_' . $userCacheBusterValue;
+		}
+		$systemCacheBuster = $this->config->getAppValue('theming', 'cachebuster', '0');
+		return substr(sha1($serverVersion . $themingAppVersion . $userCacheBuster . $systemCacheBuster), 0, 8);
+	}
+}