/**
 * @module util/device-helper
 *
 * Pure utility functions for generating clean, friendly, auto-generated device names/tags.
 */

export interface DeviceTagOptions {
    userAgent?: string;
    userAgentData?: {
        mobile?: boolean;
        platform?: string;
        brands?: Array<{ brand: string; version: string }>;
    };
    maxTouchPoints?: number;
    screenWidth?: number;
    randomSuffix?: string;
}

/**
 * Generates a friendly, URL-safe, kebab-cased default device tag.
 * (e.g., `chrome-win-a1b2`, `mobile-safari-ios-3c4d`, `tablet-android-e5f6`).
 *
 * Pure function: Uses global browser objects (`navigator`, `window`) only as fallbacks
 * when explicit options are omitted, enabling deterministic unit testing.
 *
 * @param opts Optional mock options for deterministic unit testing.
 */
export function generateDefaultDeviceTag(opts?: DeviceTagOptions): string {
    const ua = (opts?.userAgent ?? (typeof navigator !== 'undefined' ? navigator.userAgent : '') ?? '').toLowerCase();
    const uaData = opts?.userAgentData ?? (typeof navigator !== 'undefined' ? (navigator as any).userAgentData : undefined);
    const touchPoints = opts?.maxTouchPoints ?? (typeof navigator !== 'undefined' ? navigator.maxTouchPoints : 0) ?? 0;
    const width = opts?.screenWidth ?? (typeof window !== 'undefined' ? window.innerWidth : 1024) ?? 1024;

    // 1. Detect Form Factor (Mobile, Tablet, Desktop)
    let formFactor = '';
    const isMobileUaData = uaData?.mobile;
    const isMobileUa = /mobile|iphone|ipod|android.*mobile|windows phone/i.test(ua);
    const isTabletUa = /ipad|tablet|(android(?!.*mobile))/i.test(ua) || (touchPoints > 1 && /macintosh/i.test(ua) && width <= 1366);

    if (isTabletUa) {
        formFactor = 'tablet';
    } else if (isMobileUaData || isMobileUa) {
        formFactor = 'mobile';
    }

    // 2. Detect OS / Platform
    let platform = '';
    const uaPlatform = (uaData?.platform || '').toLowerCase();

    if (uaPlatform.includes('win') || ua.includes('windows')) {
        platform = 'win';
    } else if (uaPlatform.includes('ios') || ua.includes('iphone') || ua.includes('ipad') || ua.includes('ipod')) {
        platform = 'ios';
    } else if (uaPlatform.includes('mac') || ua.includes('macintosh') || ua.includes('mac os')) {
        platform = 'mac';
    } else if (uaPlatform.includes('android') || ua.includes('android')) {
        platform = 'android';
    } else if (uaPlatform.includes('linux') || ua.includes('linux')) {
        platform = 'linux';
    }

    // 3. Detect Browser
    let browser = '';
    if (ua.includes('edg/') || ua.includes('edge/')) {
        browser = 'edge';
    } else if (ua.includes('chrome/') || ua.includes('crios/')) {
        browser = 'chrome';
    } else if (ua.includes('firefox/') || ua.includes('fxios/')) {
        browser = 'firefox';
    } else if (ua.includes('safari/') && !ua.includes('chrome/') && !ua.includes('crios/')) {
        browser = 'safari';
    }

    // 4. Generate or use provided 4-character random suffix
    let suffix = opts?.randomSuffix;
    if (!suffix) {
        const chars = '0123456789abcdef';
        suffix = '';
        for (let i = 0; i < 4; i++) {
            suffix += chars.charAt(Math.floor(Math.random() * chars.length));
        }
    }
    suffix = suffix.toLowerCase().replace(/[^a-z0-9]/g, '').slice(0, 8);

    // 5. Assemble Tokens
    const tokens: string[] = [];
    if (formFactor) {
        tokens.push(formFactor);
    }
    if (browser) {
        tokens.push(browser);
    }
    if (platform) {
        tokens.push(platform);
    }

    if (tokens.length === 0) {
        tokens.push('device');
    }

    tokens.push(suffix);

    return tokens.join('-');
}