Added a new folder path for design patterns - Containing observer des…

…ign pattern

design patterns/observer/observer.js

@@ -0,0 +1,103 @@
+const EventEmitter = require("events").EventEmitter;
+
+class Burger extends EventEmitter {
+  constructor(layers = 2) {
+    super();
+    this.CookingTime = this._cookingTime(layers);
+    this.maxIngredients = this._maxIngredients(layers);
+    this.ingredients = [];
+    this.timeToReleaseBurger = 5;
+  }
+
+  static layers() {
+    return {
+      small: 1,
+      medium: 2,
+      familiar: 3,
+    };
+  }
+
+  _maxIngredients(layers) {
+    return layers * 3;
+  }
+
+  _cookingTime(layers) {
+    return 5 + layers * 2;
+  }
+
+  _isMaxIngredientsReached() {
+    return this.ingredients.length === this.maxIngredients;
+  }
+
+  add(ingredient) {
+    if (!this._isMaxIngredientsReached()) {
+      this.ingredients.push(ingredient);
+      this.emit("ingredientAdded", ingredient);
+    } else {
+      this.emit("maxIngredientsReached");
+    }
+    return this;
+  }
+
+  remove(ingredient) {
+    const ingredientToRemove = this.ingredients.indexOf(ingredient);
+    if (ingredientToRemove !== -1) {
+      this.ingredients.splice(ingredientToRemove, 1);
+      this.emit("ingredientRemoved", ingredient);
+    } else {
+      this.emit("errorRemovingIngredient", ingredient);
+    }
+    return this;
+  }
+
+  cook() {
+    this.emit("cookStarted");
+    setTimeout(() => {
+      const releaseBurger = setTimeout(() => {
+        this.emit("charredBurger");
+      }, this.timeToReleaseBurger);
+      this.emit("cookFinished", releaseBurger);
+    }, this.CookingTime);
+
+    return this;
+  }
+}
+
+const createMediumBurger = () => {
+  const Burger = new Burger(Burger.layers().medium);
+  Burger.on("ingredientAdded", (ing) => console.log(`${ing} added`))
+    .on("maxIngredientsReached", (ing) =>
+      console.log(`Max ingredients (${Burger.maxIngredients}) reached`)
+    )
+    .on("ingredientRemoved", (ing) => console.log(`${ing} removed`))
+    .on("errorRemovingIngredient", (ing) =>
+      console.log(`Can not remove ${ing} because is not in the Burger`)
+    )
+    .on("cookStarted", () => console.log("Burger is in the Cooking."))
+    .on("cookFinished", (release) => {
+      console.log(`Burger is ready to release.`);
+      clearTimeout(release);
+      console.info("Burger was released!");
+    })
+    .add("Tomato")
+    .add("Beef")
+    .add("Salami")
+    .add("Bone")
+    .add("Pepper")
+    .add("Onion")
+    .add("Cheese")
+    .add("Mayo")
+    .remove("Bone")
+    .remove("Peper")
+    .cook();
+};
+
+createMediumBurger();
+
+/*
+  Learn more on observer design pattern: https://docs.microsoft.com/en-us/dotnet/standard/events/observer-design-pattern
+  
+  Have a Good Day!!
+
+  Regards: https://github.com/officialabdulrehman
+*/