guard pattern

1-before.ts

get: async (context) => {
  const user = await createSessionHelpers(context).getUser()
  if (!user) {
    return redirect("/login")
  }

  const id = context.params?.bucketId
  if (!id) {
    return notFound()
  }

  const bucket = await db.bucket.findUnique({
    where: {
      id: String(id),
    },
    select: {
      id: true,
      name: true,
      createdAt: true,
    },
  })

  if (!bucket) {
    return notFound()
  }

  const columns = await db.column.findMany({
    where: {
      bucketId: String(id),
    },
    select: {
      id: true,
      name: true,
    },
  })

  return json({
    user: pick(user, ["name"]),
    bucket: serialize(bucket),
    columns,
  })
},

2-after.ts

get: async (context) => {
  return usingSessionUser(context, (user) => {
    return usingContextParam(context, "bucketId", async (bucketId) => {
      return usingBucket(bucketId, async (bucket) => {
        return usingBucketColumns(bucketId, (columns) => {
          return json({
            user: pick(user, ["name"]),
            bucket: serialize(bucket),
            columns,
          })
        })
      })
    })
  })
},

3-guards.ts

async function usingSessionUser<Result>(
  context: RuntimeContext<ParsedUrlQuery>,
  fn: (user: User) => Result | Promise<Result>,
) {
  const user = await createSessionHelpers(context).getUser()
  return user ? fn(user) : redirect<never>("/login", 303)
}

function usingContextParam(
  context: RuntimeContext<ParsedUrlQuery>,
  name: string,
  fn: (value: string) => void,
) {
  const value = context.query[name]
  return typeof value === "string" ? fn(value) : notFound()
}

async function usingBucket(bucketId: string, fn: (bucket: Bucket) => void) {
  const bucket = await db.bucket.findUnique({ where: { id: bucketId } })
  return bucket ? fn(bucket) : notFound()
}

async function usingBucketColumns(
  bucketId: string,
  fn: (columns: Array<Pick<Column, "name" | "id">>) => void,
) {
  const columns = await db.column.findMany({
    where: { bucketId },
    select: {
      id: true,
      name: true,
    },
  })
  return fn(columns)
}