typescript: Flyweight Pattern

/**
 * Flyweight Pattern 享元是一种结构型设计模式， 它允许你在消耗少量内存的情况下支持大量对象。
 * https://refactoringguru.cn/design-patterns/flyweight/typescript/example#lang-features
 * The Flyweight stores a common portion of the state (also called intrinsic
 * state) that belongs to multiple real business entities. The Flyweight accepts
 * the rest of the state (extrinsic state, unique for each entity) via its
 * method parameters.
 */


class Flyweight {

    /**
     * 
     */
    private sharedState: any;
    
    /**
     * 
     * @param sharedState 
     */
    constructor(sharedState: any) {
        this.sharedState = sharedState;
    }
    /**
     * 
     * @param uniqueState 
     */
    public operation(uniqueState):string {  //void
        let str="";
        const s = JSON.stringify(this.sharedState);
        const u = JSON.stringify(uniqueState);
        console.log(`Flyweight: Displaying shared (${s}) and unique (${u}) state.`);
        str=str+s+","+u;
        return str;
    }
}

/**
 * The Flyweight Factory creates and manages the Flyweight objects. It ensures
 * that flyweights are shared correctly. When the client requests a flyweight,
 * the factory either returns an existing instance or creates a new one, if it
 * doesn't exist yet.
 */
class FlyweightFactory {
    /**
     * 
     */
    private flyweights: {[key: string]: Flyweight} = <any>{};

    /**
     * 
     * @param initialFlyweights 
     */
    constructor(initialFlyweights: string[][]) {
        for (const state of initialFlyweights) {
            this.flyweights[this.getKey(state)] = new Flyweight(state);
        }
    }

    /**
     * Returns a Flyweight's string hash for a given state.
     */
    private getKey(state: string[]): string {
        return state.join('_');
    }

    /**
     * Returns an existing Flyweight with a given state or creates a new one.
     */
    public getFlyweight(sharedState: string[]): Flyweight {
        const key = this.getKey(sharedState);

        if (!(key in this.flyweights)) {
            console.log('FlyweightFactory: Can\'t find a flyweight, creating new one.');
            this.flyweights[key] = new Flyweight(sharedState);
        } else {
            console.log('FlyweightFactory: Reusing existing flyweight.');
        }

        return this.flyweights[key];
    }
    /**
     * 
     */
    public listFlyweights():string { //void
        let str="";
        const count = Object.keys(this.flyweights).length;
        console.log(`\nFlyweightFactory: I have ${count} flyweights:`);
        for (const key in this.flyweights) {
            console.log(key);
            str=str+","+key;
        }

        return str;
    }
}

/**
 * The client code usually creates a bunch of pre-populated flyweights in the
 * initialization stage of the application.
 */
const factory = new FlyweightFactory([
    ['Chevrolet', 'Camaro2018', 'pink'],
    ['Mercedes Benz', 'C300', 'black'],
    ['Mercedes Benz', 'C500', 'red'],
    ['BMW', 'M5', 'red'],
    ['BMW', 'X6', 'white'],
    // ...
]);
let pubf1="";
let pubf2="";
let pubf3="";
let pubf4="";

pubf3=factory.listFlyweights();

// ...
/**
 * 
 * @param ff 
 * @param plates 
 * @param owner 
 * @param brand 
 * @param model 
 * @param color 
 */
function addCarToPoliceDatabase(
    ff: FlyweightFactory, plates: string, owner: string,
    brand: string, model: string, color: string,
) {
    console.log('\nClient: Adding a car to database.');
    const flyweight = ff.getFlyweight([brand, model, color]);

    // The client code either stores or calculates extrinsic state and passes it
    // to the flyweight's methods.
   return flyweight.operation([plates, owner]);


}

pubf1=addCarToPoliceDatabase(factory, 'CL234IR', 'James Doe', 'BMW', 'M5', 'red');

pubf2=addCarToPoliceDatabase(factory, 'CL234IR', 'James Doe', 'BMW', 'X1', 'red');

pubf4=factory.listFlyweights();



let messageflyweight: string = 'Hello World,This is a typescript!,涂聚文 Geovin Du.Web';
document.body.innerHTML = messageflyweight+",<br/>one="+pubf1+",<br/>two="+pubf2+",<br/>thee="+pubf3+",<br/>four="+pubf4+",<br/>TypeScript Flyweight Pattern 享元模式";

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