/**
 * Offline mode settings management
 *
 * Stores settings in localStorage following the existing pattern
 * used by theme and movement_settings.
 */

const STORAGE_KEY = 'workorder_offline';

// Default settings
const defaultSettings = {
    enabled: false,
    autoSync: true,
    lastSyncTimestamp: null,
    deviceId: null  // Generated on first enable
};

// In-memory cache of settings
let cachedSettings = null;

/**
 * Generate a unique device ID using crypto API
 */
function generateDeviceId() {
    if (crypto.randomUUID) {
        return crypto.randomUUID();
    }
    // Fallback for older browsers
    return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
        const r = Math.random() * 16 | 0;
        const v = c === 'x' ? r : (r & 0x3 | 0x8);
        return v.toString(16);
    });
}

/**
 * Load settings from localStorage
 */
export function loadOfflineSettings() {
    try {
        const saved = localStorage.getItem(STORAGE_KEY);
        if (saved) {
            cachedSettings = { ...defaultSettings, ...JSON.parse(saved) };
        } else {
            cachedSettings = { ...defaultSettings };
        }
    } catch (error) {
        console.error('[OfflineSettings] Failed to load settings:', error);
        cachedSettings = { ...defaultSettings };
    }
    return cachedSettings;
}

/**
 * Save settings to localStorage
 */
export function saveOfflineSettings(settings) {
    try {
        cachedSettings = { ...cachedSettings, ...settings };
        localStorage.setItem(STORAGE_KEY, JSON.stringify(cachedSettings));
        return true;
    } catch (error) {
        console.error('[OfflineSettings] Failed to save settings:', error);
        return false;
    }
}

/**
 * Get current settings (from cache or load)
 */
export function getOfflineSettings() {
    if (!cachedSettings) {
        loadOfflineSettings();
    }
    return { ...cachedSettings };
}

/**
 * Check if offline mode is enabled
 */
export function isOfflineModeEnabled() {
    const settings = getOfflineSettings();
    return settings.enabled === true;
}

/**
 * Check if auto-sync is enabled
 */
export function isAutoSyncEnabled() {
    const settings = getOfflineSettings();
    return settings.autoSync === true;
}

/**
 * Enable offline mode
 * Generates device ID if not exists
 */
export function enableOfflineMode() {
    const settings = getOfflineSettings();
    if (!settings.deviceId) {
        settings.deviceId = generateDeviceId();
    }
    settings.enabled = true;
    return saveOfflineSettings(settings);
}

/**
 * Disable offline mode
 * Does NOT clear cached data (user must do that explicitly)
 */
export function disableOfflineMode() {
    return saveOfflineSettings({ enabled: false });
}

/**
 * Toggle offline mode
 */
export function toggleOfflineMode() {
    if (isOfflineModeEnabled()) {
        return disableOfflineMode();
    } else {
        return enableOfflineMode();
    }
}

/**
 * Set auto-sync preference
 */
export function setAutoSync(enabled) {
    return saveOfflineSettings({ autoSync: enabled });
}

/**
 * Get device ID (generates if needed)
 */
export function getDeviceId() {
    const settings = getOfflineSettings();
    if (!settings.deviceId) {
        settings.deviceId = generateDeviceId();
        saveOfflineSettings(settings);
    }
    return settings.deviceId;
}

/**
 * Update last sync timestamp
 */
export function updateLastSyncTimestamp() {
    return saveOfflineSettings({ lastSyncTimestamp: Date.now() });
}

/**
 * Get last sync timestamp
 */
export function getLastSyncTimestamp() {
    const settings = getOfflineSettings();
    return settings.lastSyncTimestamp;
}

/**
 * Get last sync as human-readable string
 */
export function getLastSyncText() {
    const timestamp = getLastSyncTimestamp();
    if (!timestamp) {
        return 'Nie synchronisiert';
    }

    const now = Date.now();
    const diff = now - timestamp;
    const minutes = Math.floor(diff / 60000);
    const hours = Math.floor(diff / 3600000);
    const days = Math.floor(diff / 86400000);

    if (minutes < 1) {
        return 'Gerade eben';
    } else if (minutes < 60) {
        return `Vor ${minutes} Minute${minutes === 1 ? '' : 'n'}`;
    } else if (hours < 24) {
        return `Vor ${hours} Stunde${hours === 1 ? '' : 'n'}`;
    } else {
        return `Vor ${days} Tag${days === 1 ? '' : 'en'}`;
    }
}

/**
 * Get data freshness level based on last sync
 * Returns: 'fresh' (<1h), 'stale' (1-24h), 'old' (>24h)
 */
export function getDataFreshness() {
    const timestamp = getLastSyncTimestamp();
    if (!timestamp) {
        return 'unknown';
    }

    const now = Date.now();
    const diff = now - timestamp;
    const hours = diff / 3600000;

    if (hours < 1) {
        return 'fresh';      // Green
    } else if (hours < 24) {
        return 'stale';      // Yellow
    } else {
        return 'old';        // Red
    }
}

/**
 * Clear all offline settings (for logout)
 */
export function clearOfflineSettings() {
    try {
        localStorage.removeItem(STORAGE_KEY);
        cachedSettings = null;
        return true;
    } catch (error) {
        console.error('[OfflineSettings] Failed to clear settings:', error);
        return false;
    }
}

// Reactive state for Vue components
export const offlineSettingsState = {
    get enabled() { return isOfflineModeEnabled(); },
    get autoSync() { return isAutoSyncEnabled(); },
    get lastSync() { return getLastSyncTimestamp(); },
    get lastSyncText() { return getLastSyncText(); },
    get freshness() { return getDataFreshness(); },
    get deviceId() { return getDeviceId(); }
};

export default {
    load: loadOfflineSettings,
    save: saveOfflineSettings,
    get: getOfflineSettings,
    isEnabled: isOfflineModeEnabled,
    isAutoSyncEnabled,
    enable: enableOfflineMode,
    disable: disableOfflineMode,
    toggle: toggleOfflineMode,
    setAutoSync,
    getDeviceId,
    updateLastSync: updateLastSyncTimestamp,
    getLastSync: getLastSyncTimestamp,
    getLastSyncText,
    getFreshness: getDataFreshness,
    clear: clearOfflineSettings,
    state: offlineSettingsState
};