feat(tiered_pricing): 🔵 add Subscriptions concept

Also add parallel change for priceFor method

Author: adrianliz

exercises/graduated_tiered_prices/solutions/adrianliz/src/Tier.ts renamed to exercises/graduated_tiered_prices/solutions/adrianliz/src/GraduatedTier.ts

@@ -1,4 +1,4 @@
-export default class Tier {
+export default class GraduatedTier {
   constructor(
     private readonly from: number,
     private readonly to: number,

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

@@ -1,19 +1,24 @@
+import GraduatedTier from "./GraduatedTier";
 import NumberOfSubscriptionsNotAllowed from "./NumberOfSubscriptionsNotAllowed";
-import Tier from "./Tier";
+import Subscriptions from "./Subscriptions";
 
 export default class GraduatedTieredPricing {
+  private tiers(): 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),
+    ];
+  }
+
   priceFor(subscriptions: number): number {
     if (subscriptions < 1) {
       throw new NumberOfSubscriptionsNotAllowed();
     }
 
-    const tiers = [
-      new Tier(1, 2, 299),
-      new Tier(3, 10, 239),
-      new Tier(11, 25, 219),
-      new Tier(26, 50, 199),
-      new Tier(51, Number.MAX_SAFE_INTEGER, 149),
-    ];
+    const tiers = this.tiers();
 
     return (
       tiers[0].totalFor(subscriptions) +
@@ -23,4 +28,8 @@ export default class GraduatedTieredPricing {
       tiers[4].totalFor(subscriptions)
     );
   }
+
+  priceFor2(subscriptions: Subscriptions): number {
+    return subscriptions.priceFor(this.tiers());
+  }
 }

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

@@ -0,0 +1,17 @@
+import GraduatedTier from "./GraduatedTier";
+import NumberOfSubscriptionsNotAllowed from "./NumberOfSubscriptionsNotAllowed";
+
+export default class Subscriptions {
+  constructor(private readonly subscriptions: number) {
+    if (subscriptions < 1) {
+      throw new NumberOfSubscriptionsNotAllowed();
+    }
+  }
+
+  priceFor(tiers: GraduatedTier[]): number {
+    return tiers.reduce(
+      (total, tier) => total + tier.totalFor(this.subscriptions),
+      0
+    );
+  }
+}

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

@@ -2,11 +2,14 @@ import each from "jest-each";
 
 import GraduatedTieredPricing from "../src/GraduatedTieredPricing";
 import NumberOfSubscriptionsNotAllowed from "../src/NumberOfSubscriptionsNotAllowed";
+import Subscriptions from "../src/Subscriptions";
 
 describe("Graduated tiered pricing should", () => {
-  it("calculate the price for 0 subscriptions", () => {
+  it("throw number of subscriptions not allowed for 0 subscriptions", () => {
     const pricing = new GraduatedTieredPricing();
-    expect(() => pricing.priceFor(0)).toThrow(NumberOfSubscriptionsNotAllowed);
+    expect(() => pricing.priceFor2(new Subscriptions(0))).toThrow(
+      NumberOfSubscriptionsNotAllowed
+    );
   });
 
   each([
@@ -21,7 +24,9 @@ describe("Graduated tiered pricing should", () => {
     "calculate the price for %i subscriptions",
     (subscriptions: number, expectedPrice: number) => {
       const pricing = new GraduatedTieredPricing();
-      expect(pricing.priceFor(subscriptions)).toBe(expectedPrice);
+      expect(pricing.priceFor2(new Subscriptions(subscriptions))).toBe(
+        expectedPrice
+      );
     }
   );
 });