Add state => query string function

src/app-state-to-query-string.test.ts

@@ -0,0 +1,75 @@
+import { appStateToQueryString } from "./app-state-to-query-string";
+import { PayoffStrategy } from "./types/PayoffStrategy";
+
+const loans = [
+  {
+    id: 0,
+    name: "foo",
+    balance: "7829",
+    interestRate: "3.2",
+    minimumPayment: "32",
+  },
+  {
+    id: 1,
+    name: "bar",
+    balance: "23390",
+    interestRate: "4.6",
+    minimumPayment: "392",
+  },
+];
+
+describe("appStateToQueryString", () => {
+  it("parses to an empty string when the monthly payment is an empty string", () => {
+    expect(
+      appStateToQueryString({
+        monthlyPayment: "",
+        loans,
+        payoffStrategy: PayoffStrategy.Avalanche,
+      })
+    ).toEqual("");
+  });
+
+  it("parses to an empty string when the monthly payment is an empty string", () => {
+    expect(
+      appStateToQueryString({
+        monthlyPayment: "INVALID_NUMBER",
+        loans,
+        payoffStrategy: PayoffStrategy.Avalanche,
+      })
+    ).toEqual("");
+  });
+
+  it("parses to an empty string when the loans are empty", () => {
+    expect(
+      appStateToQueryString({
+        monthlyPayment: "800",
+        loans: [],
+        payoffStrategy: PayoffStrategy.Avalanche,
+      })
+    ).toEqual("");
+  });
+
+  it("parses to the correct query string when provided with a valid monthly payment and loans with an avalanche strategy", () => {
+    expect(
+      appStateToQueryString({
+        monthlyPayment: "600",
+        loans,
+        payoffStrategy: PayoffStrategy.Avalanche,
+      })
+    ).toEqual(
+      "?monthlyPayment=600&payoffStrategy=Avalanche&name_0=foo&balance_0=7829&minimumPayment_0=32&interestRate_0=3.2&name_1=bar&balance_1=23390&minimumPayment_1=392&interestRate_1=4.6"
+    );
+  });
+
+  it("parses to the correct query string when provided with a valid monthly payment and loans with a snowball strategy", () => {
+    expect(
+        appStateToQueryString({
+          monthlyPayment: "600",
+          loans,
+          payoffStrategy: PayoffStrategy.Snowball,
+        })
+    ).toEqual(
+        "?monthlyPayment=600&payoffStrategy=Snowball&name_0=foo&balance_0=7829&minimumPayment_0=32&interestRate_0=3.2&name_1=bar&balance_1=23390&minimumPayment_1=392&interestRate_1=4.6"
+    );
+  });
+});

src/app-state-to-query-string.ts

@@ -0,0 +1,25 @@
+import { FormLoan } from "./types/Loan";
+import { stringIsNumber } from "./string-is-number";
+import { PayoffStrategy } from "./types/PayoffStrategy";
+
+interface AppStateToQueryParams {
+  readonly monthlyPayment: string;
+  readonly loans: FormLoan[];
+  readonly payoffStrategy: PayoffStrategy;
+}
+
+const loanToQueryParams = (loan: FormLoan): string =>
+  `&name_${loan.id}=${loan.name}&balance_${loan.id}=${loan.balance}&minimumPayment_${loan.id}=${loan.minimumPayment}&interestRate_${loan.id}=${loan.interestRate}`;
+
+export const appStateToQueryString = (
+  params: AppStateToQueryParams
+): string => {
+  const { monthlyPayment, loans, payoffStrategy } = params;
+  if (stringIsNumber(monthlyPayment) && loans.length > 0) {
+    return `?monthlyPayment=${monthlyPayment}&payoffStrategy=${payoffStrategy}${loans
+      .map(loanToQueryParams)
+      .join("")}`;
+  } else {
+    return "";
+  }
+};