diff --git a/.prettierrc b/.prettierrc
new file mode 100644
index 00000000..92cde390
--- /dev/null
+++ b/.prettierrc
@@ -0,0 +1,3 @@
+{
+  "singleQuote": true
+}
\ No newline at end of file
diff --git a/app/gilded-rose.ts b/app/gilded-rose.ts
index db58d678..8099d294 100644
--- a/app/gilded-rose.ts
+++ b/app/gilded-rose.ts
@@ -10,6 +10,18 @@ export class Item {
   }
 }
 
+enum ItemType {
+  AgedBrie = 'Aged Brie',
+  BackstagePasses = 'Backstage passes to a TAFKAL80ETC concert',
+  Sulfuras = 'Sulfuras, Hand of Ragnaros',
+}
+
+const TEN_DAYS_FOR_THE_CONCERT = 11;
+const FIVE_DAYS_FOR_THE_CONCERT = 6;
+const ZERO_DAYS_FOR_SALE = 0;
+const MAX_QUALITY = 50;
+const MIN_QUALITY = 0;
+
 export class GildedRose {
   items: Array<Item>;
 
@@ -19,46 +31,52 @@ export class GildedRose {
 
   updateQuality() {
     for (let i = 0; i < this.items.length; i++) {
-      if (this.items[i].name != 'Aged Brie' && 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
+      if (
+        this.items[i].name != ItemType.AgedBrie &&
+        this.items[i].name != ItemType.BackstagePasses
+      ) {
+        if (this.items[i].quality > MIN_QUALITY) {
+          if (this.items[i].name != ItemType.Sulfuras) {
+            this.items[i].quality = this.items[i].quality - 1;
           }
         }
       } else {
-        if (this.items[i].quality < 50) {
-          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].quality < MAX_QUALITY) {
+          this.items[i].quality = this.items[i].quality + 1;
+          if (this.items[i].name == ItemType.BackstagePasses) {
+            if (this.items[i].sellIn < TEN_DAYS_FOR_THE_CONCERT) {
+              if (this.items[i].quality < MAX_QUALITY) {
+                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].sellIn < FIVE_DAYS_FOR_THE_CONCERT) {
+              if (this.items[i].quality < MAX_QUALITY) {
+                this.items[i].quality = this.items[i].quality + 1;
               }
             }
           }
         }
       }
-      if (this.items[i].name != 'Sulfuras, Hand of Ragnaros') {
+
+      if (this.items[i].name != ItemType.Sulfuras) {
         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
+
+      if (this.items[i].sellIn < ZERO_DAYS_FOR_SALE) {
+        if (this.items[i].name != ItemType.AgedBrie) {
+          if (this.items[i].name != ItemType.BackstagePasses) {
+            if (this.items[i].quality > MIN_QUALITY) {
+              if (this.items[i].name != ItemType.Sulfuras) {
+                this.items[i].quality = this.items[i].quality - 1;
               }
             }
           } else {
-            this.items[i].quality = this.items[i].quality - this.items[i].quality
+            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
+          if (this.items[i].quality < MAX_QUALITY) {
+            this.items[i].quality = this.items[i].quality + 1;
           }
         }
       }