Throw error for invalid currency conversion inputs

common/src/util/currency.ts

@@ -3,11 +3,22 @@
  * @param credits The number of credits to convert
  * @param centsPerCredit The cost per credit in cents
  * @returns The amount in USD cents
+ * @throws Error if centsPerCredit is not positive or credits is not finite
  */
 export function convertCreditsToUsdCents(
   credits: number,
   centsPerCredit: number,
 ): number {
+  if (!(centsPerCredit > 0)) {
+    throw new Error(
+      `convertCreditsToUsdCents: centsPerCredit must be positive, got ${centsPerCredit}`,
+    )
+  }
+  if (!Number.isFinite(credits)) {
+    throw new Error(
+      `convertCreditsToUsdCents: credits must be finite, got ${credits}`,
+    )
+  }
   return Math.ceil(credits * centsPerCredit)
 }
 
@@ -16,10 +27,21 @@ export function convertCreditsToUsdCents(
  * @param amountInCents The amount in USD cents
  * @param centsPerCredit The cost per credit in cents
  * @returns The number of credits
+ * @throws Error if centsPerCredit is not positive or amountInCents is not finite
  */
 export function convertStripeGrantAmountToCredits(
   amountInCents: number,
   centsPerCredit: number,
 ): number {
+  if (!(centsPerCredit > 0)) {
+    throw new Error(
+      `convertStripeGrantAmountToCredits: centsPerCredit must be positive, got ${centsPerCredit}`,
+    )
+  }
+  if (!Number.isFinite(amountInCents)) {
+    throw new Error(
+      `convertStripeGrantAmountToCredits: amountInCents must be finite, got ${amountInCents}`,
+    )
+  }
   return Math.floor(amountInCents / centsPerCredit)
 }