initial update with nodemailer

1 files changed, 45 insertions, 0 deletions

diff --git a/src/lib/utils/retry.ts b/src/lib/utils/retry.ts
new file mode 100644
index 0000000..34bc73b
--- /dev/null
+++ b/src/lib/utils/retry.ts
@@ -0,0 +1,45 @@
+export type RetryStrategyF = (retries: number) => number;
+
+export const MAX_DEFAULT_RETRY_AMOUNT = 5;
+export const WAIT_MS = 1_000;
+export const RETRY_EXPONENT = 2;
+export const RETRY_EXPONENTIAL_FACTOR = 1.1;
+export const RETRY_JITTER_MAX = 3_000;
+
+const waitFor = (ms: number) => new Promise((res) => setTimeout(res, ms));
+
+const exponentialStrategyWithJitter: RetryStrategyF = (retries: number) =>
+  WAIT_MS * Math.pow(RETRY_EXPONENT, RETRY_EXPONENTIAL_FACTOR * retries) +
+  RETRY_JITTER_MAX * Math.random();
+
+export const continueRetryUntilValidation = async <T>(
+  promiseFn: () => Promise<T> | T | Promise<void> | void,
+  validationFn: (x: T) => Promise<boolean> | boolean = (x: T) =>
+    Promise.resolve(!!x),
+  maxRetries = MAX_DEFAULT_RETRY_AMOUNT,
+  waitTimeStrategy: RetryStrategyF = exponentialStrategyWithJitter,
+  retries = 0,
+  lastError: undefined | unknown = undefined
+): Promise<T> => {
+  if (retries >= maxRetries) {
+    if (lastError) throw lastError;
+    throw new Error("Exceeded maximum retry amount");
+  }
+  try {
+    if (retries) await waitFor(waitTimeStrategy(retries));
+
+    const res = await promiseFn();
+    if (res && (await validationFn(res))) return res;
+
+    throw new Error("Validation predicate unsuccessful");
+  } catch (e: unknown) {
+    return continueRetryUntilValidation(
+      promiseFn,
+      validationFn,
+      maxRetries,
+      waitTimeStrategy,
+      retries + 1,
+      e
+    );
+  }
+};
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