GenericStrategyPattern.ts

/*
    Strategy Pattern
    Co-Author: https://github.com/WaseemMansour
    reference: https://refactoring.guru/design-patterns/strategy
*/

/* Strategies context */
class Context<Strategy> {
  /* reference to concrete strategy */
  private strategy: Strategy;

  constructor(strategy: Strategy) {
    this.strategy = strategy;
  }

  setStrategy(strategy: Strategy) {
    this.strategy = strategy;
  }

  /* TODO: describe this better */
  callStrategyMethod(fnName: string, params: any[]) {
    // @ts-ignore
    this.strategy[fnName](...params);
  }
}

function ContextFactory<Strategy>(strategy: Strategy) {
  const context = new Context<Strategy>(strategy);

  const contextProxy = new Proxy(context, {
    get: function (
      context: Context<Strategy>,
      fnName: keyof Context<Strategy>
    ) {
      return function (...params: any) {
        /* if fnName not found on context, delegate to strategy */

        if (fnName in context) {
          if (typeof context[fnName] === "function") {
            // @ts-ignore
            return context[fnName](...params);
          } else {
            return context[fnName];
          }
        }

        context.callStrategyMethod(fnName, params);
      };
    },
  });

  return contextProxy as Context<Strategy> & Strategy;
}

/* ********* */
/* Usage */

/* Strategy interface */
interface AuthStrategy {
  login: () => boolean;
  logout: () => boolean;
}

/* Concrete strategy */
class JWTStrategy implements AuthStrategy {
  constructor() {}
  login() {
    console.log("login with jwt");
    return true;
  }
  logout() {
    console.log("logout with jwt");
    return true;
  }
}

/* Concrete strategy */
class OAuthStrategy implements AuthStrategy {
  constructor() {}

  login() {
    console.log("login with OAuth");
    return true;
  }
  logout() {
    console.log("logout with OAuth");
    return true;
  }
}

const jwtStrategy = new JWTStrategy();
const oAuthStrategy = new OAuthStrategy();

const authContext = ContextFactory<AuthStrategy>(jwtStrategy);

authContext.login();
authContext.logout();

authContext.setStrategy(oAuthStrategy);

authContext.login();
authContext.logout();