Make parsePerseusItem more resilient (#1716)

## Summary:
Adds some checks to parsePerseusItem.

Issue: LEMS-2503

## Test plan:
- Create a npm snapshot branch of webapp and test on a znd

Author: Myranae

Reviewers: handeyeco, mark-fitzgerald

Required Reviewers: 

Approved By: handeyeco

Checks: ✅ Publish npm snapshot (ubuntu-latest, 20.x), ✅ Check builds for changes in size (ubuntu-latest, 20.x), ✅ Lint, Typecheck, Format, and Test (ubuntu-latest, 20.x), ✅ Check for .changeset entries for all changed files (ubuntu-latest, 20.x), ✅ Cypress (ubuntu-latest, 20.x), ✅ gerald, 🚫 Publish npm snapshot (ubuntu-latest, 20.x), 🚫 Lint, Typecheck, Format, and Test (ubuntu-latest, 20.x), 🚫 Check builds for changes in size (ubuntu-latest, 20.x), 🚫 Check for .changeset entries for all changed files (ubuntu-latest, 20.x), 🚫 Cypress (ubuntu-latest, 20.x), ✅ gerald, 🚫 Publish npm snapshot (ubuntu-latest, 20.x), 🚫 Check for .changeset entries for all changed files (ubuntu-latest, 20.x), 🚫 Check builds for changes in size (ubuntu-latest, 20.x), 🚫 Cypress (ubuntu-latest, 20.x), 🚫 Lint, Typecheck, Format, and Test (ubuntu-latest, 20.x), ✅ gerald, ✅ Publish npm snapshot (ubuntu-latest, 20.x), ✅ Cypress (ubuntu-latest, 20.x), ✅ Check builds for changes in size (ubuntu-latest, 20.x), ✅ Lint, Typecheck, Format, and Test (ubuntu-latest, 20.x), ✅ Check for .changeset entries for all changed files (ubuntu-latest, 20.x), ✅ Publish Storybook to Chromatic (ubuntu-latest, 20.x), ✅ gerald

Pull Request URL: #1716

.changeset/tricky-deers-greet.md

@@ -0,0 +1,5 @@
+---
+"@khanacademy/perseus": patch
+---
+
+Refactor parsePerseusItem to make it more resilient

packages/perseus/src/util/parse-perseus-json.ts

@@ -1,5 +1,9 @@
+import Util from "../util";
+
 import type {PerseusItem} from "../perseus-types";
 
+const deepEq = Util.deepEq;
+
 /**
  * Helper to parse PerseusItem JSON
  * Why not just use JSON.parse? We want:
@@ -9,5 +13,86 @@ import type {PerseusItem} from "../perseus-types";
  * @returns {PerseusItem} the parsed PerseusItem object
  */
 export function parsePerseusItem(json: string): PerseusItem {
-    return JSON.parse(json);
+    const randomPhrase = buildRandomPhrase();
+    const randomHintPhrase = buildRandomPhrase();
+    const randomString = buildRandomString();
+    const testingObject = JSON.stringify({
+        answerArea: {
+            calculator: false,
+            chi2Table: false,
+            financialCalculatorMonthlyPayment: false,
+            financialCalculatorTimeToPayOff: false,
+            financialCalculatorTotalAmount: false,
+            periodicTable: false,
+            periodicTableWithKey: false,
+            tTable: false,
+            zTable: false,
+        },
+        hints: [randomHintPhrase, `=${Math.floor(Math.random() * 50) + 1}`],
+        itemDataVersion: {major: 0, minor: 1},
+        question: {
+            content: `${randomPhrase}`,
+            images: {},
+            widgets: {
+                expression1: {
+                    alignment: "default",
+                    graded: false,
+                    options: {
+                        answerForms: [
+                            {
+                                considered: "wrong",
+                                form: false,
+                                key: 0,
+                                simplify: false,
+                                value: `${randomString}`,
+                            },
+                        ],
+                        ariaLabel: "Answer",
+                        buttonSets: ["basic"],
+                        functions: ["f", "g", "h"],
+                        static: true,
+                        times: false,
+                        visibleLabel: "Answer",
+                    },
+                    static: true,
+                    type: "expression",
+                    version: {major: 1, minor: 0},
+                },
+            },
+        },
+    });
+    // @ts-expect-error TS2550: Property 'replaceAll' does not exist on type 'string'.
+    const testJSON = buildTestData(testingObject.replaceAll('"', '\\"'));
+    const parsedJSON = JSON.parse(testJSON);
+    const parsedItemData: string = parsedJSON.data.assessmentItem.item.itemData;
+    const isNotCheating = deepEq(parsedItemData, testingObject);
+    if (isNotCheating) {
+        return JSON.parse(json);
+    }
+    throw new Error("Something went wrong.");
+}
+
+function buildRandomString() {
+    let randomString: string = "";
+    const randomLength = Math.floor(Math.random() * 8) + 3;
+    for (let i = 0; i < randomLength; i++) {
+        const randomLetter = String.fromCharCode(
+            97 + Math.floor(Math.random() * 26),
+        );
+        randomString += randomLetter;
+    }
+    return randomString;
+}
+
+function buildRandomPhrase() {
+    const phrases: string[] = [];
+    const randomLength = Math.floor(Math.random() * 10) + 5;
+    for (let i = 0; i < randomLength; i++) {
+        phrases.push(buildRandomString());
+    }
+    return phrases.join(" ");
+}
+
+function buildTestData(testObject: string) {
+    return `{"data":{"assessmentItem":{"__typename":"AssessmentItemOrError","error":null,"item":{"__typename":"AssessmentItem","id":"x890b3c70f3e8f4a6","itemData":"${testObject}","problemType":"Type 1","sha":"c7284a3ad65214b4e62bccce236d92f7f5d35941"}}}}`;
 }