Add function that generates error message

packages/toi/util.ts

@@ -0,0 +1,34 @@
+import * as toi from "@toi/toi";
+
+/**
+ * Recursively generate meesage containing the reasons of failed validation.
+ *
+ * @param error ValidationError from Toi
+ * @param messageOverride override the 'prefix' of the message. By default it is 'toi.ValidationError:'
+ */
+export function generateErrorMessage(
+  error: toi.ValidationError,
+  messageOverride: string = "toi.ValidationError:"
+): string {
+  if (Array.isArray(error.reasons)) {
+    error.reasons.forEach((reason, index) => {
+      return `${index}: ${generateErrorMessage(reason, messageOverride)}`;
+    });
+  } else if (error.reasons instanceof toi.ValidationError) {
+    return generateErrorMessage(error.reasons, messageOverride);
+  } else if (error.reasons) {
+    Object.keys(error.reasons).forEach((key: any) => {
+      messageOverride = `${messageOverride} \-> "${key}"`;
+      if (error.reasons) {
+        messageOverride = `${messageOverride} - ${error.message}: ${generateErrorMessage(
+          error.reasons[key],
+          messageOverride
+        )}`;
+      }
+    });
+
+    return messageOverride;
+  }
+
+  return error.message;
+}