refactor business logic, add test to verify backstage item quality limit

TypeScript/app/gilded-rose.ts

@@ -3,7 +3,7 @@ export class Item {
   sellIn: number;
   quality: number;
 
-  constructor(name, sellIn, quality) {
+  constructor(name: string, sellIn: number, quality: number) {
     this.name = name;
     this.sellIn = sellIn;
     this.quality = quality;
@@ -11,6 +11,7 @@ export class Item {
 }
 
 export class GildedRose {
+  private QUALITY_LIM = 50;
   items: Array<Item>;
 
   constructor(items = [] as Array<Item>) {
@@ -18,52 +19,74 @@ export class GildedRose {
   }
 
   updateQuality() {
-    for (let i = 0; i < this.items.length; i++) {
+    return this.items.map((item) => {
-      if (this.items[i].name != 'Aged Brie' && this.items[i].name != 'Backstage passes to a TAFKAL80ETC concert') {
+      if (this._isAgeable(item.name)) {
-        if (this.items[i].quality > 0) {
+        return this._decayAgeableItem(item);
-          if (this.items[i].name != 'Sulfuras, Hand of Ragnaros') {
+      } else if (this._isLegendary(item.name)) {
-            this.items[i].quality = this.items[i].quality - 1
+        return this._decayLegendaryItem(item);
-          }
+      } else if (this._isBackstagePass(item.name)) {
-        }
+        return this._decayBackstagePassItem(item);
       } else {
-        if (this.items[i].quality < 50) {
+        return this._decayGeneralItem(item);
-          this.items[i].quality = this.items[i].quality + 1
-          if (this.items[i].name == 'Backstage passes to a TAFKAL80ETC concert') {
-            if (this.items[i].sellIn < 11) {
-              if (this.items[i].quality < 50) {
-                this.items[i].quality = this.items[i].quality + 1
-              }
-            }
-            if (this.items[i].sellIn < 6) {
-              if (this.items[i].quality < 50) {
-                this.items[i].quality = this.items[i].quality + 1
-              }
-            }
-          }
-        }
       }
-      if (this.items[i].name != 'Sulfuras, Hand of Ragnaros') {
+    });
-        this.items[i].sellIn = this.items[i].sellIn - 1;
-      }
-      if (this.items[i].sellIn < 0) {
-        if (this.items[i].name != 'Aged Brie') {
-          if (this.items[i].name != 'Backstage passes to a TAFKAL80ETC concert') {
-            if (this.items[i].quality > 0) {
-              if (this.items[i].name != 'Sulfuras, Hand of Ragnaros') {
-                this.items[i].quality = this.items[i].quality - 1
-              }
-            }
-          } else {
-            this.items[i].quality = this.items[i].quality - this.items[i].quality
-          }
-        } else {
-          if (this.items[i].quality < 50) {
-            this.items[i].quality = this.items[i].quality + 1
-          }
-        }
-      }
-    }
-
-    return this.items;
   }
+
+  private _isAgeable = (name: string): boolean => name === "Aged Brie";
+
+  private _isLegendary = (name: string): boolean =>
+    name === "Sulfuras, Hand of Ragnaros";
+
+  private _isBackstagePass = (name: string): boolean =>
+    name === "Backstage passes to a TAFKAL80ETC concert";
+
+  private _decayGeneralItem = (item: Item): Item => {
+    const qualityDecay = item.sellIn > 0 ? 1 : 2;
+    return {
+      name: item.name,
+      quality: item.quality > 0 ? item.quality - qualityDecay : 0,
+      sellIn: item.sellIn - 1,
+    };
+  };
+
+  private _decayLegendaryItem = (item: Item): Item => {
+    return item;
+  };
+
+  private _decayAgeableItem = (item: Item): Item => {
+    const newItem = {
+      name: item.name,
+      quality: item.quality + 1,
+      sellIn: item.sellIn - 1,
+    };
+    return this._applyQualityLimitation(newItem);
+  };
+
+  private _decayBackstagePassItem = (item: Item): Item => {
+    let newQuality;
+    if (item.sellIn > 10) {
+      newQuality = item.quality + 1;
+    } else if (item.sellIn > 5) {
+      newQuality = item.quality + 2;
+    } else if (item.sellIn > 0) {
+      newQuality = item.quality + 3;
+    } else {
+      newQuality = 0;
+    }
+    const newItem = {
+      name: item.name,
+      quality: newQuality,
+      sellIn: item.sellIn - 1,
+    };
+    return this._applyQualityLimitation(newItem);
+  };
+
+  private _applyQualityLimitation = (item: Item): Item => {
+    return {
+      name: item.name,
+      quality:
+        item.quality > this.QUALITY_LIM ? this.QUALITY_LIM : item.quality,
+      sellIn: item.sellIn,
+    };
+  };
 }

TypeScript/test/jest/gilded-rose.spec.ts

@@ -95,5 +95,11 @@ describe("Gilded Rose", () => {
       expect(items[0].sellIn).toBe(-1);
       expect(items[0].quality).toBe(0);
     });
+    it("should not exceed 50 quality", () => {
+      const gildedRose = new GildedRose([backstagePassItem(5, 50)]);
+      const items = gildedRose.updateQuality();
+      expect(items[0].sellIn).toBe(4);
+      expect(items[0].quality).toBe(50);
+    });
   });
 });