Add simple PR comment sub-action (#636)

* Add simple PR comment sub-action

* Update rolldown config

* Add changeset

* Update readme

* Use TLA

* Add prefix

* fix merge

* Update

src/pr-comment/index.ts

@@ -0,0 +1,77 @@
+import * as core from "@actions/core";
+import * as github from "@actions/github";
+
+type Octokit = ReturnType<typeof github.getOctokit>;
+type CreateCommentParams = NonNullable<
+  Parameters<Octokit["rest"]["issues"]["createComment"]>[0]
+>;
+type UpdateCommentParams = NonNullable<
+  Parameters<Octokit["rest"]["issues"]["updateComment"]>[0]
+>;
+
+try {
+  await main();
+} catch (err) {
+  core.setFailed((err as Error).message);
+}
+
+async function main() {
+  const context = github.context.payload.pull_request;
+  if (!context) {
+    throw new Error(
+      "This action should only be run on `pull_request_target` or `pull_request` events",
+    );
+  }
+
+  const githubToken = core.getInput("github-token", { required: true });
+  const body = core.getInput("body", { required: true });
+  const updateId = core.getInput("update-id");
+
+  const commentMarker = updateId ? getCommentMarker(updateId) : null;
+  const commentBody = commentMarker ? `${commentMarker}\n\n${body}` : body;
+  const commentParam: CreateCommentParams | UpdateCommentParams = {
+    repo: context.base.repo.name,
+    owner: context.base.repo.owner.login,
+    issue_number: context.number,
+    body: commentBody,
+  };
+
+  const octokit = github.getOctokit(githubToken);
+
+  let existingCommentId: number | undefined;
+  if (commentMarker) {
+    core.info("Checking for existing comment...");
+    existingCommentId = await octokit.rest.issues
+      .listComments({
+        repo: context.base.repo.name,
+        owner: context.base.repo.owner.login,
+        issue_number: context.number,
+      })
+      .then((res) => {
+        const comment = res.data.find((c) => c.body?.includes(commentMarker));
+        return comment?.id;
+      });
+  }
+
+  if (existingCommentId) {
+    core.info(`Updating existing comment (id: ${existingCommentId})...`);
+    await octokit.rest.issues.updateComment({
+      ...commentParam,
+      comment_id: existingCommentId,
+    });
+    core.setOutput("comment-id", existingCommentId);
+  } else {
+    core.info("Creating new comment...");
+    const result = await octokit.rest.issues.createComment(commentParam);
+    core.setOutput("comment-id", result.data.id);
+  }
+
+  core.info("Done!");
+}
+
+function getCommentMarker(updateId: string) {
+  const prefix = "changesets-action-pr-comment";
+  return prefix === updateId
+    ? `<!-- ${prefix} -->`
+    : `<!-- ${prefix}:${updateId} -->`;
+}