package auth

import "strings"

// ParseDeviceLabel extracts a human-readable device label from a user agent string.
// Returns something like "Chrome on macOS", "Safari on iPhone", "Firefox on Windows".
func ParseDeviceLabel(userAgent string) string {
	if userAgent == "" {
		return "Unknown device"
	}

	browser := parseBrowser(userAgent)
	os := parseOS(userAgent)

	if browser == "" && os == "" {
		return "Unknown device"
	}
	if browser == "" {
		return os
	}
	if os == "" {
		return browser
	}
	return browser + " on " + os
}

func parseBrowser(ua string) string {
	// Order matters — check more specific before generic.
	switch {
	case strings.Contains(ua, "Edg/") || strings.Contains(ua, "Edge/"):
		return "Edge"
	case strings.Contains(ua, "OPR/") || strings.Contains(ua, "Opera"):
		return "Opera"
	case strings.Contains(ua, "Brave"):
		return "Brave"
	case strings.Contains(ua, "Vivaldi"):
		return "Vivaldi"
	case strings.Contains(ua, "Chrome/") && !strings.Contains(ua, "Chromium"):
		return "Chrome"
	case strings.Contains(ua, "Firefox/"):
		return "Firefox"
	case strings.Contains(ua, "Safari/") && !strings.Contains(ua, "Chrome"):
		return "Safari"
	default:
		return ""
	}
}

func parseOS(ua string) string {
	switch {
	case strings.Contains(ua, "iPhone"):
		return "iPhone"
	case strings.Contains(ua, "iPad"):
		return "iPad"
	case strings.Contains(ua, "Android"):
		return "Android"
	case strings.Contains(ua, "Mac OS X") || strings.Contains(ua, "Macintosh"):
		return "macOS"
	case strings.Contains(ua, "Windows"):
		return "Windows"
	case strings.Contains(ua, "Linux"):
		return "Linux"
	case strings.Contains(ua, "CrOS"):
		return "ChromeOS"
	default:
		return ""
	}
}