Introduce improved file structure, move update logic to legacyBehavior class

- move item to it’s own file.
- Change tsconfig to use ‘@app’ prefix for imports
- move the logic to the legacy-behavior file, allowing to refactor out 
item type by item type

TypeScript/app/gilded-rose.ts

@@ -1,21 +1,5 @@
-export class Item {
-  name: string;
-  sellIn: number;
-  quality: number;
-
-  // can't edit this constructor because of the kata rules.
-  // but I would change the constructor to take a javaScript object.
-  // It makes the consumer code more readable.
-  // e.g. new Item({ name: "standard item", sellIn: 0, quality: 2 })
-  // instead of new Item("standard item", 0, 2)
-
-  // I would also type the parameters, because now they are implicitly any.
-  constructor(name, sellIn, quality) {
-    this.name = name;
-    this.sellIn = sellIn;
-    this.quality = quality;
-  }
-}
+import { Item } from "@app/item";
+import { IUpdateBehavior, LegacyBehavior } from "@app/update-behaviors";
 
 export class GildedRose {
   // also can't edit this because of the kata rules.
@@ -28,53 +12,14 @@ export class GildedRose {
 
   updateQuality() {
     return this.items.map((item) => {
-      if (
-        item.name !== "Aged Brie" &&
-        item.name !== "Backstage passes to a TAFKAL80ETC concert"
-      ) {
-        if (item.quality > 0) {
-          if (item.name !== "Sulfuras, Hand of Ragnaros") {
-            item.quality = item.quality - 1;
-          }
-        }
-      } else {
-        if (item.quality < 50) {
-          item.quality = item.quality + 1;
-          if (item.name === "Backstage passes to a TAFKAL80ETC concert") {
-            if (item.sellIn < 11) {
-              if (item.quality < 50) {
-                item.quality = item.quality + 1;
-              }
-            }
-            if (item.sellIn < 6) {
-              if (item.quality < 50) {
-                item.quality = item.quality + 1;
-              }
-            }
-          }
-        }
-      }
-      if (item.name !== "Sulfuras, Hand of Ragnaros") {
-        item.sellIn = item.sellIn - 1;
-      }
-      if (item.sellIn < 0) {
-        if (item.name !== "Aged Brie") {
-          if (item.name !== "Backstage passes to a TAFKAL80ETC concert") {
-            if (item.quality > 0) {
-              if (item.name !== "Sulfuras, Hand of Ragnaros") {
-                item.quality = item.quality - 1;
-              }
-            }
-          } else {
-            item.quality = item.quality - item.quality;
-          }
-        } else {
-          if (item.quality < 50) {
-            item.quality = item.quality + 1;
-          }
-        }
-      }
-      return item;
+      return this.#getUpdateBehaviorFor(item).update();
     });
   }
+
+  #getUpdateBehaviorFor(item: Item): IUpdateBehavior {
+    switch (item.name) {
+      default:
+        return new LegacyBehavior(item);
+    }
+  }
 }

TypeScript/app/item.ts

@@ -0,0 +1,18 @@
+export class Item {
+  name: string;
+  sellIn: number;
+  quality: number;
+
+  // can't edit this constructor because of the kata rules.
+  // but I would change the constructor to take a javaScript object.
+  // It makes the consumer code more readable.
+  // e.g. new Item({ name: "standard item", sellIn: 0, quality: 2 })
+  // instead of new Item("standard item", 0, 2)
+
+  // I would also type the parameters, because now they are implicitly any.
+  constructor(name, sellIn, quality) {
+    this.name = name;
+    this.sellIn = sellIn;
+    this.quality = quality;
+  }
+}

TypeScript/app/update-behaviors/index.ts

@@ -0,0 +1,2 @@
+export * from "./update-behavior.interface";
+export * from "./legacy-behavior";

TypeScript/app/update-behaviors/legacy-behavior.ts

@@ -0,0 +1,56 @@
+import { Item } from "@app/item";
+import { IUpdateBehavior } from "./update-behavior.interface";
+
+export class LegacyBehavior implements IUpdateBehavior {
+  constructor(private item: Item) {}
+
+  update(): Item {
+    if (
+      this.item.name !== "Aged Brie" &&
+      this.item.name !== "Backstage passes to a TAFKAL80ETC concert"
+    ) {
+      if (this.item.quality > 0) {
+        if (this.item.name !== "Sulfuras, Hand of Ragnaros") {
+          this.item.quality = this.item.quality - 1;
+        }
+      }
+    } else {
+      if (this.item.quality < 50) {
+        this.item.quality = this.item.quality + 1;
+        if (this.item.name === "Backstage passes to a TAFKAL80ETC concert") {
+          if (this.item.sellIn < 11) {
+            if (this.item.quality < 50) {
+              this.item.quality = this.item.quality + 1;
+            }
+          }
+          if (this.item.sellIn < 6) {
+            if (this.item.quality < 50) {
+              this.item.quality = this.item.quality + 1;
+            }
+          }
+        }
+      }
+    }
+    if (this.item.name !== "Sulfuras, Hand of Ragnaros") {
+      this.item.sellIn = this.item.sellIn - 1;
+    }
+    if (this.item.sellIn < 0) {
+      if (this.item.name !== "Aged Brie") {
+        if (this.item.name !== "Backstage passes to a TAFKAL80ETC concert") {
+          if (this.item.quality > 0) {
+            if (this.item.name !== "Sulfuras, Hand of Ragnaros") {
+              this.item.quality = this.item.quality - 1;
+            }
+          }
+        } else {
+          this.item.quality = this.item.quality - this.item.quality;
+        }
+      } else {
+        if (this.item.quality < 50) {
+          this.item.quality = this.item.quality + 1;
+        }
+      }
+    }
+    return this.item;
+  }
+}

TypeScript/app/update-behaviors/update-behavior.interface.ts

@@ -0,0 +1,5 @@
+import { Item } from "@app/item";
+
+export interface IUpdateBehavior {
+  update: () => Item;
+}

TypeScript/test/jest/approvals.spec.ts

@@ -1,4 +1,5 @@
-import { Item, GildedRose } from "@/gilded-rose";
+import { GildedRose } from "@app/gilded-rose";
+import { Item } from "@app/item";
 
 describe("Gilded Rose Approval", () => {
   it("should match the snapshot for thirty Days", () => {

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

@@ -1,4 +1,5 @@
-import { Item, GildedRose } from "@/gilded-rose";
+import { GildedRose } from "@app/gilded-rose";
+import { Item } from "@app/item";
 
 describe("Gilded Rose", () => {
   it("should have an empty array as items when no constructor parameter is provided", () => {

TypeScript/tsconfig.json

@@ -9,7 +9,7 @@
     "resolveJsonModule": true,
     "esModuleInterop": true,
     "paths": {
-      "@/*": ["app/*"]
+      "@app/*": ["app/*"]
     }
   },
   "exclude": ["node_modules"]