useAnswerCreation React Hook function

hooks/useAnswerCreation.ts

@@ -0,0 +1,83 @@
+import { useApolloClient } from "@apollo/react-hooks";
+import * as React from "react";
+import { AnswerBody } from "@@/models/Answer";
+import { PostId } from "@@/models/Post";
+import useAuthentication from "@@/hooks/useAuthentication";
+import usePost from "@@/hooks/usePost";
+import createAnswer from "@@/repositories/createAnswer";
+
+export default function useAnswerCreation({ postId }: { postId: PostId }) {
+  const apolloClient = useApolloClient();
+  const { authenticationToken } = useAuthentication();
+  const { updateLocally } = usePost({ postId });
+  const [body, setBody] = React.useState("");
+  const [
+    bodyValidationErrorTypes,
+    setBodyValidationErrorTypes,
+  ] = React.useState<AnswerBodyValidationErrorType[]>(validateBody(body));
+  const [isSubmitting, setSubmitting] = React.useState(false);
+
+  const _setBody = (body: string) => {
+    setBodyValidationErrorTypes(validateBody(body));
+    setBody(body);
+  };
+
+  const submit = async () => {
+    if (!authenticationToken) {
+      throw new Error(
+        "You called useAnswerCreation().submit() with null authentication token. It shouldn't happen here."
+      );
+    }
+
+    setSubmitting(true);
+
+    const answer = await createAnswer({
+      postId,
+      body: body as AnswerBody,
+      apolloClient,
+      authenticationToken,
+    });
+
+    updateLocally((post) => {
+      if (!post) {
+        return post;
+      }
+
+      return {
+        ...post,
+        answers: [answer, ...post.answers],
+      };
+    });
+
+    _setBody("");
+    setSubmitting(false);
+  };
+
+  return {
+    body,
+    isValid: bodyValidationErrorTypes.length === 0,
+    bodyValidationErrorTypes,
+    isSubmitting,
+    setBody: _setBody,
+    submit,
+  };
+}
+
+function validateBody(body: string): AnswerBodyValidationErrorType[] {
+  const validationErrorTypes = [];
+
+  if (body.length < 8) {
+    validationErrorTypes.push(AnswerBodyValidationErrorType.tooShort);
+  }
+
+  if (body.length > 65535) {
+    validationErrorTypes.push(AnswerBodyValidationErrorType.tooLong);
+  }
+
+  return validationErrorTypes;
+}
+
+export enum AnswerBodyValidationErrorType {
+  tooShort,
+  tooLong,
+}