feat(tiered_pricing): 🔴 add GraduatedTier named constructors

Author: adrianliz

exercises/graduated_tiered_prices/solutions/adrianliz/src/GraduatedTier.ts

@@ -1,14 +1,51 @@
+import InvalidTier from "./InvalidTier";
 import Subscriptions from "./Subscriptions";
 
 export default class GraduatedTier {
-  constructor(
+  private constructor(
     private readonly from: number,
     private readonly to: number,
-    private readonly price: number
-  ) {}
+    private readonly singleSubscriptionPrice: number
+  ) {
+    if (to > Number.MAX_SAFE_INTEGER) {
+      throw new InvalidTier();
+    }
+  }
+
+  static firstTier(
+    numberOfSubscriptionsIn: number,
+    singleSubscriptionPrice: number
+  ): GraduatedTier {
+    return new GraduatedTier(
+      1,
+      numberOfSubscriptionsIn,
+      singleSubscriptionPrice
+    );
+  }
+
+  static fromTier(
+    from: GraduatedTier,
+    numberOfSubscriptionsIn: number,
+    singleSubscriptionPrice: number
+  ): GraduatedTier {
+    const newFrom = from.to + 1;
+    const newTo = newFrom + (numberOfSubscriptionsIn - 1);
+    return new GraduatedTier(newFrom, newTo, singleSubscriptionPrice);
+  }
+
+  static lastTier(
+    from: GraduatedTier,
+    singleSubscriptionPrice: number
+  ): GraduatedTier {
+    return new GraduatedTier(
+      from.to + 1,
+      Number.MAX_SAFE_INTEGER,
+      singleSubscriptionPrice
+    );
+  }
 
   private total(): number {
-    return this.size() * this.price;
+    return this.size() * this.singleSubscriptionPrice;
   }
 
   size(): number {
@@ -36,6 +73,9 @@ export default class GraduatedTier {
       return 0;
     }
 
-    return subscriptions.numberOfSubscriptionsInTier(this) * this.price;
+    return (
+      subscriptions.numberOfSubscriptionsInTier(this) *
+      this.singleSubscriptionPrice
+    );
   }
 }

exercises/graduated_tiered_prices/solutions/adrianliz/src/InvalidTier.ts

@@ -0,0 +1,5 @@
+export default class InvalidTier extends Error {
+  constructor() {
+    super("Invalid tier");
+  }
+}

exercises/graduated_tiered_prices/solutions/adrianliz/tests/GraduatedTiered.test.ts

@@ -0,0 +1,8 @@
+import GraduatedTier from "../src/GraduatedTier";
+import InvalidTier from "../src/InvalidTier";
+
+describe("Graduated tiered should", () => {
+  it("throw number of subscriptions not allowed for 0 subscriptions", () => {
+    expect(() => GraduatedTier.firstTier(0, 199)).toThrow(InvalidTier);
+  });
+});

exercises/graduated_tiered_prices/solutions/adrianliz/tests/GraduatedTieredPricing.test.ts

@@ -7,13 +7,12 @@ import Subscriptions from "../src/Subscriptions";
 
 describe("Graduated tiered pricing should", () => {
   const defaultTiers = (): GraduatedTier[] => {
-    return [
-      new GraduatedTier(1, 2, 299),
-      new GraduatedTier(3, 10, 239),
-      new GraduatedTier(11, 25, 219),
-      new GraduatedTier(26, 50, 199),
-      new GraduatedTier(51, Number.MAX_SAFE_INTEGER, 149),
-    ];
+    const firstTier = GraduatedTier.firstTier(2, 299);
+    const secondTier = GraduatedTier.fromTier(firstTier, 8, 239);
+    const thirdTier = GraduatedTier.fromTier(secondTier, 15, 219);
+    const fourthTier = GraduatedTier.fromTier(thirdTier, 25, 199);
+    const lastTier = GraduatedTier.lastTier(fourthTier, 149);
+    return [firstTier, secondTier, thirdTier, fourthTier, lastTier];
   };
 
   it("throw number of subscriptions not allowed for 0 subscriptions", () => {