/**
 * User Agent Parser
 *
 * Simple regex-based parser to extract browser, OS, and device type
 * from user agent strings. No heavy libraries - just pattern matching.
 */

export interface ParsedUserAgent {
	browser: string; // "Chrome 120", "Firefox 121", "Safari 17"
	os: string; // "Windows 11", "macOS 14", "Ubuntu", "iOS 17"
	deviceType: string; // "Desktop", "Mobile", "Tablet"
}

/**
 * Parse a user agent string into structured data
 */
export function parseUserAgent(ua: string): ParsedUserAgent {
	if (!ua) {
		return { browser: 'Unknown', os: 'Unknown', deviceType: 'Unknown' };
	}

	return {
		browser: parseBrowser(ua),
		os: parseOS(ua),
		deviceType: parseDeviceType(ua)
	};
}

/**
 * Extract browser name and version
 */
function parseBrowser(ua: string): string {
	// Order matters - check more specific patterns first

	// Edge (Chromium-based)
	const edge = ua.match(/Edg(?:e|A|iOS)?\/(\d+)/);
	if (edge) return `Edge ${edge[1]}`;

	// Opera (also Chromium-based, check before Chrome)
	const opera = ua.match(/(?:OPR|Opera)\/(\d+)/);
	if (opera) return `Opera ${opera[1]}`;

	// Firefox
	const firefox = ua.match(/Firefox\/(\d+)/);
	if (firefox) return `Firefox ${firefox[1]}`;

	// Safari (check before Chrome since Chrome includes Safari in UA)
	// Safari doesn't include "Chrome" in its UA
	if (ua.includes('Safari') && !ua.includes('Chrome') && !ua.includes('Chromium')) {
		const safari = ua.match(/Version\/(\d+)/);
		if (safari) return `Safari ${safari[1]}`;
		return 'Safari';
	}

	// Chrome (and Chromium-based browsers not caught above)
	const chrome = ua.match(/(?:Chrome|Chromium)\/(\d+)/);
	if (chrome) return `Chrome ${chrome[1]}`;

	// Internet Explorer
	const ie = ua.match(/(?:MSIE |rv:)(\d+)/);
	if (ie) return `IE ${ie[1]}`;

	// Fallback: try to find any browser-like pattern
	const generic = ua.match(/(\w+)\/(\d+)/);
	if (generic) return `${generic[1]} ${generic[2]}`;

	return 'Unknown';
}

/**
 * Extract operating system name and version
 */
function parseOS(ua: string): string {
	// iOS (check before Mac since iOS includes "like Mac OS X")
	const ios = ua.match(/(?:iPhone|iPad|iPod).*?OS (\d+)/);
	if (ios) return `iOS ${ios[1]}`;

	// Android
	const android = ua.match(/Android (\d+(?:\.\d+)?)/);
	if (android) return `Android ${android[1]}`;

	// Windows
	// Note: Windows 11 still reports "Windows NT 10.0" for backwards compatibility
	// There's no reliable way to distinguish Win10 from Win11 via user agent alone
	if (ua.includes('Windows')) {
		if (ua.includes('Windows NT 10.0')) return 'Windows';
		if (ua.includes('Windows NT 6.3')) return 'Windows 8.1';
		if (ua.includes('Windows NT 6.2')) return 'Windows 8';
		if (ua.includes('Windows NT 6.1')) return 'Windows 7';
		if (ua.includes('Windows NT 6.0')) return 'Windows Vista';
		if (ua.includes('Windows NT 5.1')) return 'Windows XP';
		return 'Windows';
	}

	// macOS (after iOS check)
	const mac = ua.match(/Mac OS X (\d+)[_.](\d+)/);
	if (mac) {
		const major = parseInt(mac[1]);
		const minor = parseInt(mac[2]);
		// macOS 11+ uses major version only in marketing
		if (major >= 11) return `macOS ${major}`;
		// macOS 10.x uses 10.minor naming
		return `macOS ${major}.${minor}`;
	}
	if (ua.includes('Macintosh')) return 'macOS';

	// Linux distributions
	if (ua.includes('Ubuntu')) return 'Ubuntu';
	if (ua.includes('Fedora')) return 'Fedora';
	if (ua.includes('Debian')) return 'Debian';
	if (ua.includes('Arch')) return 'Arch Linux';
	if (ua.includes('CrOS')) return 'Chrome OS';
	if (ua.includes('Linux')) return 'Linux';

	// BSD variants
	if (ua.includes('FreeBSD')) return 'FreeBSD';
	if (ua.includes('OpenBSD')) return 'OpenBSD';

	return 'Unknown';
}

/**
 * Determine device type from user agent
 */
function parseDeviceType(ua: string): string {
	// Tablets (check before mobile since some tablets include "Mobile")
	if (
		ua.includes('iPad') ||
		ua.includes('Tablet') ||
		(ua.includes('Android') && !ua.includes('Mobile'))
	) {
		return 'Tablet';
	}

	// Mobile devices
	if (
		ua.includes('Mobile') ||
		ua.includes('iPhone') ||
		ua.includes('iPod') ||
		ua.includes('Android') ||
		ua.includes('webOS') ||
		ua.includes('BlackBerry') ||
		ua.includes('Opera Mini') ||
		ua.includes('IEMobile')
	) {
		return 'Mobile';
	}

	// Default to Desktop
	return 'Desktop';
}