Add feed validation and display

packages/lib/__tests__/Tools.test.ts

@@ -310,6 +310,61 @@ describe("Tools", () => {
     })
   })
 
+  describe("displayList", () => {
+    it("should return an empty string when the list is empty", () => {
+      const list = []
+      const output = T.displayList(list)
+
+      expect(output).toEqual("")
+    })
+
+    it("should return a single entry when list length is one", () => {
+      const list = ["Apple"]
+      const output = T.displayList(list)
+
+      expect(output).toEqual("Apple")
+    })
+
+    it("should return a string of both items when the list length is two", () => {
+      const list = ["Apple", "Banana"]
+      const output = T.displayList(list)
+
+      expect(output).toEqual("Apple and Banana")
+    })
+
+    it("should return a string of all items when the list length is three", () => {
+      const list = ["Apple", "Banana", "Cherry"]
+      const output = T.displayList(list)
+
+      expect(output).toEqual("Apple, Banana, and Cherry")
+    })
+
+    it("should return a truncated string of all items when the list is long", () => {
+      const list = [
+        "Apple",
+        "Banana",
+        "Orange",
+        "Pear",
+        "Grapes",
+        "Mango",
+        "Pineapple",
+        "Kiwi",
+        "Strawberry",
+        "Blueberry",
+      ]
+      const output = T.displayList(list)
+
+      expect(output).toEqual("Apple, Banana, Orange, Pear, Grapes, Mango, and 4 others")
+    })
+
+    it("should return a string of both items with list of two numbers", () => {
+      const list = [7, 17]
+      const output = T.displayList(list)
+
+      expect(output).toEqual("7 and 17")
+    })
+  })
+
   describe("Collection Operations", () => {
     it("should handle group operations", () => {
       const items = [

packages/lib/src/Tools.ts

@@ -10,7 +10,7 @@ export type Nil = null | undefined
 
 export const isNil = <T>(x: T, ...args: unknown[]) => x === undefined || x === null
 
-export const isNotNil = <T>(x: T, ...args: unknown[]) => x !== undefined || x !== null
+export const isNotNil = <T>(x: T, ...args: unknown[]) => x !== undefined && x !== null
 
 export const assertNotNil = <T>(x: T, ...args: unknown[]) => x!
 
@@ -1358,6 +1358,19 @@ export const ellipsize = (s: string, l: number, suffix = "...") => {
   return s + suffix
 }
 
+/** Displays a list of items with oxford commas and a chosen conjunction */
+export const displayList = <T>(xs: T[], conj = "and", n = 6) => {
+  if (xs.length > n + 2) {
+    return `${xs.slice(0, n).join(", ")}, ${conj} ${xs.length - n} others`
+  }
+
+  if (xs.length < 3) {
+    return xs.join(` ${conj} `)
+  }
+
+  return `${xs.slice(0, -1).join(", ")}, ${conj} ${xs.slice(-1).join("")}`
+}
+
 /** Generates a hash string from input string */
 export const hash = (s: string) =>
   Math.abs(s.split("").reduce((a, b) => ((a << 5) - a + b.charCodeAt(0)) | 0, 0)).toString()