[CI] GH workflow to assign reviewer for manual backport

.github/workflows/assign-backport-reviewer.yml

@@ -0,0 +1,179 @@
+name: Assign manual backport reviewer
+
+on:
+  pull_request_target:
+    branches:
+      - '8.19'
+      - '9.*'
+      - '[1-9][0-9]*.*'
+    types:
+      - opened
+
+jobs:
+  assign-reviewer:
+    name: Find reviewer for manual backport
+    runs-on: ubuntu-latest
+    if: |
+      github.event.pull_request.user.login != 'kibanamachine' &&
+      contains(github.event.pull_request.labels.*.name, 'backport')
+    steps:
+      - name: Select reviewers
+        id: select-reviewers
+        uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8.0.0
+        with:
+          github-token: ${{ secrets.KIBANAMACHINE_TOKEN }}
+          script: |
+            const owner = context.repo.owner;
+            const repo = context.repo.repo;
+            const prAuthor = context.payload.pull_request.user.login;
+            const normalize = (s) => s.replace(/^@/, '').trim();
+            const isHumanReviewer = (login) =>
+              Boolean(login) &&
+              login !== 'kibanamachine' &&
+              !login.endsWith('[bot]');
+
+            const title = context.payload.pull_request.title ?? '';
+            const body = context.payload.pull_request.body ?? '';
+            const sourcePullRequestIndex = body.indexOf('"sourcePullRequest"');
+            const originalPrNumberFromMetadata =
+              sourcePullRequestIndex === -1
+                ? undefined
+                : body
+                    .slice(sourcePullRequestIndex)
+                    .match(/"number"\s*:\s*(\d+)/)?.[1];
+            const originalPrNumberFromTitle = title.match(/\(#(\d+)\)\s*$/)?.[1];
+            const originalPrNumber = Number(
+              originalPrNumberFromMetadata ?? originalPrNumberFromTitle
+            );
+
+            if (!Number.isInteger(originalPrNumber)) {
+              return;
+            }
+
+            const reviewHistory = await github.graphql(
+              `query($owner: String!, $repo: String!, $number: Int!) {
+                repository(owner: $owner, name: $repo) {
+                  pullRequest(number: $number) {
+                    reviews(first: 100) {
+                      nodes {
+                        state
+                        submittedAt
+                        author {
+                          login
+                        }
+                        onBehalfOf(first: 10) {
+                          nodes {
+                            slug
+                            organization {
+                              login
+                            }
+                          }
+                        }
+                      }
+                    }
+                  }
+                }
+              }`,
+              {
+                owner,
+                repo,
+                number: originalPrNumber,
+              }
+            );
+
+            const reviews = (reviewHistory.repository.pullRequest?.reviews?.nodes ?? [])
+              .filter((review) => Boolean(review.submittedAt))
+              .sort((a, b) => Date.parse(b.submittedAt) - Date.parse(a.submittedAt));
+
+            const reviewedTeams = [];
+            for (const review of reviews) {
+              for (const team of review.onBehalfOf.nodes ?? []) {
+                const combinedSlug = `${team.organization.login}/${team.slug}`;
+                if (!reviewedTeams.includes(combinedSlug)) {
+                  reviewedTeams.push(combinedSlug);
+                }
+              }
+            }
+
+            let matchedTeams = [];
+            try {
+              const result = await github.graphql(
+                `query($login: String!) {
+                  organization(login: "elastic") {
+                    teams(first: 100, userLogins: [$login]) {
+                      nodes { combinedSlug }
+                    }
+                  }
+                }`,
+                { login: prAuthor }
+              );
+              const authorTeams = new Set(
+                result.organization.teams.nodes.map((t) => normalize(t.combinedSlug))
+              );
+              matchedTeams = reviewedTeams.filter((team) => authorTeams.has(team));
+            } catch (error) {
+              core.warning(`Failed to query author's org teams: ${error.message}`);
+            }
+
+            if (matchedTeams.length > 0) {
+              core.setOutput('team_reviewers', matchedTeams.join(','));
+              return;
+            }
+
+            const fallbackReview = reviews
+              .filter((review) => {
+                const login = review.author?.login;
+                return (
+                  review.state === 'APPROVED' &&
+                  isHumanReviewer(login) &&
+                  Boolean(review.submittedAt)
+                );
+              })[0];
+
+            if (!fallbackReview) {
+              return;
+            }
+
+            core.setOutput('reviewer', fallbackReview.author.login);
+
+      - name: Update reviewers
+        uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8.0.0
+        with:
+          github-token: ${{ secrets.KIBANAMACHINE_TOKEN }}
+          script: |
+            const currentPrId = context.payload.pull_request.node_id;
+            const teamReviewers = '${{ steps.select-reviewers.outputs.team_reviewers }}'
+              .split(',')
+              .filter(Boolean);
+            const reviewer = '${{ steps.select-reviewers.outputs.reviewer }}';
+
+            if (teamReviewers.length === 0 && !reviewer) {
+              core.info('No team reviewers or fallback reviewer found');
+              return;
+            }
+
+            core.info(`Updating reviewers: teamReviewers=${teamReviewers}, reviewer=${reviewer}`);
+
+            await github.graphql(
+              `mutation RequestReviewsByLogin(
+                $pullRequestId: ID!
+                $userLogins: [String!]
+                $teamSlugs: [String!]
+              ) {
+                requestReviewsByLogin(
+                  input: {
+                    pullRequestId: $pullRequestId
+                    userLogins: $userLogins
+                    teamSlugs: $teamSlugs
+                    union: false
+                  }
+                ) {
+                  clientMutationId
+                }
+              }`,
+              {
+                pullRequestId: currentPrId,
+                userLogins: reviewer ? [reviewer] : [],
+                teamSlugs: teamReviewers,
+              }
+            );