/*
Copyright 2019 - 2022 The Matrix.org Foundation C.I.C.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

import SettingsHandler from "./SettingsHandler";

/**
 * Abstract settings handler wrapping around localStorage making getValue calls cheaper
 * by caching the values and listening for localStorage updates from other tabs.
 */
export default abstract class AbstractLocalStorageSettingsHandler extends SettingsHandler {
    // Shared cache between all subclass instances
    private static itemCache = new Map<string, string | null>();
    private static objectCache = new Map<string, object>();
    private static storageListenerBound = false;

    private static onStorageEvent = (e: StorageEvent): void => {
        if (e.key === null) {
            AbstractLocalStorageSettingsHandler.clear();
        } else {
            AbstractLocalStorageSettingsHandler.itemCache.delete(e.key);
            AbstractLocalStorageSettingsHandler.objectCache.delete(e.key);
        }
    };

    // Expose the clear event for Lifecycle to call, the storage listener only fires for changes from other tabs
    public static clear(): void {
        AbstractLocalStorageSettingsHandler.itemCache.clear();
        AbstractLocalStorageSettingsHandler.objectCache.clear();
    }

    protected constructor() {
        super();

        if (!AbstractLocalStorageSettingsHandler.storageListenerBound) {
            AbstractLocalStorageSettingsHandler.storageListenerBound = true;
            // Listen for storage changes from other tabs to bust the cache
            window.addEventListener("storage", AbstractLocalStorageSettingsHandler.onStorageEvent);
        }
    }

    protected getItem(key: string): string | null {
        if (!AbstractLocalStorageSettingsHandler.itemCache.has(key)) {
            const value = localStorage.getItem(key);
            AbstractLocalStorageSettingsHandler.itemCache.set(key, value);
            return value;
        }

        return AbstractLocalStorageSettingsHandler.itemCache.get(key)!;
    }

    protected getBoolean(key: string): boolean | null {
        const item = this.getItem(key);
        if (item === "true") return true;
        if (item === "false") return false;
        // Fall back to the next config level
        return null;
    }

    protected getObject<T extends object>(key: string): T | null {
        if (!AbstractLocalStorageSettingsHandler.objectCache.has(key)) {
            try {
                const value = JSON.parse(localStorage.getItem(key)!);
                AbstractLocalStorageSettingsHandler.objectCache.set(key, value);
                return value;
            } catch (err) {
                console.error("Failed to parse localStorage object", err);
                return null;
            }
        }

        return AbstractLocalStorageSettingsHandler.objectCache.get(key) as T;
    }

    protected setItem(key: string, value: string): void {
        AbstractLocalStorageSettingsHandler.itemCache.set(key, value);
        localStorage.setItem(key, value);
    }

    protected setBoolean(key: string, value: boolean | null): void {
        this.setItem(key, `${value}`);
    }

    protected setObject(key: string, value: object): void {
        AbstractLocalStorageSettingsHandler.objectCache.set(key, value);
        localStorage.setItem(key, JSON.stringify(value));
    }

    // handles both items and objects
    protected removeItem(key: string): void {
        localStorage.removeItem(key);
        AbstractLocalStorageSettingsHandler.itemCache.delete(key);
        AbstractLocalStorageSettingsHandler.objectCache.delete(key);
    }

    public isSupported(): boolean {
        return localStorage !== undefined && localStorage !== null;
    }
}