Exercise 2: Replacing a Post's Tags — Possible Solution
=========================================================

import { prisma } from "./lib/prisma";

export async function setPostTags(slug: string, tagNames: string[]) {
  const names = [...new Set(tagNames.map((n) => n.trim().toLowerCase()))]
    .filter((n) => n.length > 0);

  return prisma.post.update({
    where: { slug },
    data: {
      tags: {
        set: [],                                  // 1. remove all current links
        connectOrCreate: names.map((name) => ({   // 2. link or create each tag
          where:  { name },
          create: { name },
        })),
      },
    },
    include: { tags: true },
  });
}

How it works:

  - set: [] disconnects every tag currently linked to the post. The tag
    records themselves are not deleted — other posts may use them.
  - connectOrCreate then links each requested tag, creating any that
    don't exist yet.
  - Prisma runs the whole nested write as one transaction, so the post
    never ends up with no tags part-way through.
  - The names are trimmed, lower-cased and de-duplicated first, so
    "Prisma", " prisma" and "prisma" don't create three separate tags
    or fail on the unique name.

Example:

  await setPostTags("tagging-posts", ["Prisma", "orm", "prisma"]);
  // tags are now: prisma, orm

WHY THIS WORKS AS AN ANSWER
------------------------------
It uses set to clear and connectOrCreate to rebuild in a single atomic
call, and cleans the input so real-world messy tag lists don't cause
duplicates or unique-constraint errors.