import * as crypto from 'crypto-js';

/**
 * Options to be used with WebStorage decorators
 */
export interface WebStorageOptions {
    /** Default value to provide if storage is empty */
    default?: any;
    /** Key to prevent plain text storage **/
    encryptWith?: string;
    /** Key to save under */
    key?: string;
}

/**
 * Automatically syncs localStorage with the decorated property.
 *
 * **Example**
 * ```
 * class Example {
 *     @LocalStorage() lastLogin: string;
 *     @LocalStorage(false, {key: '_hideMenu'}) hideMenu: boolean;
 * }
 * ```
 *
 * @param defaultValue Default value to return if property does no exist inside localStorage.
 * @param opts Any additional options
 */
export function LocalStorage(defaultValue?: any, opts: WebStorageOptions = {}) {
    opts.default = defaultValue;
    return decoratorBuilder(localStorage, opts);
}

/**
 * Automatically syncs sessionStorage with the decorated property.
 *
 * **Example**
 * ```
 * class Example {
 *     @SessionStorage() lastLogin: string;
 *     @SessionStorage(false, {key: '_hideMenu'}) hideMenu: boolean;
 * }
 * ```
 *
 * @param defaultValue Default value to return if property does no exist inside sessionStorage.
 * @param opts Any additional options
 */
export function SessionStorage(defaultValue?, opts: WebStorageOptions = {}) {
    opts.default = defaultValue;
    return decoratorBuilder(sessionStorage, opts);
}

/**
 * **Internal use only**
 *
 * Fetch variable from storage & take care of any defaults, object definitions, encryption & serialization
 *
 * @param storage Web Storage API
 * @param opts Any additional options
 */
function fromStorage(storage: Storage, opts: WebStorageOptions) {
    let storedVal = storage.getItem(<string>opts.key);
    if(storedVal == null) return opts.default != null ? opts.default : null;
    if(opts.encryptWith != null) storedVal = JSON.parse(crypto.AES.decrypt(JSON.parse(storedVal), opts.encryptWith).toString(crypto.enc.Utf8));
    return typeof storedVal == 'object' && !Array.isArray(storedVal) ? Object.assign(opts.default, storedVal) : storedVal;
}

/**
 * **Internal use only**
 *
 * Overrides the properties getter/setter methods to read/write from the provided storage endpoint.
 *
 * @param storage Web Storage API
 * @param opts Any additional options
 */
function decoratorBuilder(storage: Storage, opts: WebStorageOptions) {
    return function(target: object, key: string) {
        if(!opts.key) opts.key = key;
        let field = fromStorage(storage, opts);
        Object.defineProperty(target, key, {
            get: function() {
                if(field != fromStorage(storage, opts)) target[key] = field;
                return field;
            },
            set: function(value?) {
                field = value;
                if(value == null) storage.removeItem(<string>opts.key);
                if(opts.encryptWith != null) value = <any>crypto.AES.encrypt(JSON.stringify(value), opts.encryptWith).toString();
                storage.setItem(<string>opts.key, JSON.stringify(value));
            }
        });
    };
}