From 1e1729ae30a88c768d173a69046af603dd0607a3 Mon Sep 17 00:00:00 2001
From: Rushil Perera <pererarushil1940@gmail.com>
Date: Tue, 14 May 2024 22:44:04 -0400
Subject: [PATCH] feat: create function to handle fetching data from multiple
 sources

This helps since sometimes the data sources have issues occasionally
---
 src/libs/fetchFromMultipleSources.spec.ts | 92 +++++++++++++++++++++++
 src/libs/fetchFromMultipleSources.ts      | 36 +++++++++
 2 files changed, 128 insertions(+)
 create mode 100644 src/libs/fetchFromMultipleSources.spec.ts
 create mode 100644 src/libs/fetchFromMultipleSources.ts

diff --git a/src/libs/fetchFromMultipleSources.spec.ts b/src/libs/fetchFromMultipleSources.spec.ts
new file mode 100644
index 0000000..e217dbf
--- /dev/null
+++ b/src/libs/fetchFromMultipleSources.spec.ts
@@ -0,0 +1,92 @@
+import { describe, expect, it } from "bun:test";
+
+import { fetchFromMultipleSources } from "./fetchFromMultipleSources";
+
+describe("fetchFromMultipleSources", () => {
+  it("no promises, throws exception", () => {
+    expect(() => fetchFromMultipleSources([])).toThrow(
+      "fetchPromises cannot be empty",
+    );
+  });
+
+  it("has promises, returns first one with value", async () => {
+    const actual = await fetchFromMultipleSources<number>([
+      () => Promise.resolve(undefined),
+      () => Promise.resolve(null),
+      () => Promise.reject(),
+      () => Promise.resolve(2),
+      () => Promise.resolve(3),
+    ]);
+    const expected = 2;
+
+    expect(actual).toEqual(expected);
+  });
+
+  it("has promises, no valid responses, returns null", async () => {
+    const actual = await fetchFromMultipleSources<number>([
+      () => Promise.resolve(null),
+      () => Promise.reject(),
+      () => Promise.resolve(undefined),
+    ]);
+    const expected = null;
+
+    expect(actual).toBe(expected);
+  });
+
+  it("has promises, has cached value, returns cached value", async () => {
+    const actual = await fetchFromMultipleSources<number>(
+      [
+        () => Promise.resolve(null),
+        () => Promise.reject(),
+        () => Promise.resolve(undefined),
+      ],
+      {
+        fetchFromCache: () => Promise.resolve(-1),
+        saveInCache: async () => {},
+      },
+    );
+    const expected = -1;
+
+    expect(actual).toBe(expected);
+  });
+
+  it("has promises, no cached value, no valid response, should not save in cache", async () => {
+    let actual;
+    await fetchFromMultipleSources<number>(
+      [
+        () => Promise.resolve(null),
+        () => Promise.reject(),
+        () => Promise.resolve(undefined),
+      ],
+      {
+        fetchFromCache: () => Promise.resolve(null),
+        saveInCache: async (value) => {
+          actual = value;
+        },
+      },
+    );
+    const expected = undefined;
+
+    expect(actual).toBe(expected);
+  });
+
+  it("has promises, no cached value, has valid response, should save in cache", async () => {
+    let actual: number | undefined;
+    await fetchFromMultipleSources<number>(
+      [
+        () => Promise.resolve(null),
+        () => Promise.reject(),
+        () => Promise.resolve(3),
+      ],
+      {
+        fetchFromCache: () => Promise.resolve(null),
+        saveInCache: async (value) => {
+          actual = value;
+        },
+      },
+    );
+    const expected = 3;
+
+    expect(actual).toBe(expected);
+  });
+});
diff --git a/src/libs/fetchFromMultipleSources.ts b/src/libs/fetchFromMultipleSources.ts
new file mode 100644
index 0000000..e875a78
--- /dev/null
+++ b/src/libs/fetchFromMultipleSources.ts
@@ -0,0 +1,36 @@
+type OptionalArgs<T> =
+  | {
+      saveInCache: (result: NonNullable<T>) => Promise<void>;
+      fetchFromCache: () => Promise<T | null | undefined>;
+    }
+  | {
+      saveInCache?: undefined;
+      fetchFromCache?: undefined;
+    };
+
+export async function fetchFromMultipleSources<T>(
+  fetchPromises: (() => Promise<T | null | undefined>)[],
+  args?: OptionalArgs<T>,
+) {
+  let result = await args?.fetchFromCache?.();
+  if (result) {
+    return result;
+  }
+
+  if (fetchPromises.length === 0) {
+    throw new Error("fetchPromises cannot be empty");
+  }
+
+  for (const promise of fetchPromises) {
+    try {
+      result = await promise();
+      if (result) break;
+    } catch (e) {}
+  }
+
+  if (args?.saveInCache && result) {
+    await args.saveInCache(result);
+  }
+
+  return result ?? null;
+}