name: Issue Triage Labels

on:
  issues:
    types: [reopened, labeled]

jobs:
  update-labels:
    runs-on: ubuntu-latest
    permissions:
      issues: write
    steps:
      - name: Update triage labels
        uses: actions/github-script@v7
        with:
          script: |
            const UNTRIAGED_LABEL = 'untriaged';
            const NO_ACTION_LABEL = 'no-action';
            const LAST_READ_LABEL = 'last-read';
            const TO_DISCUSS_LABEL = 'to-discuss';
            const INPROGRESS_LABEL = 'inprogress';

            function issueHasLabel(issue, labelName) {
              return (issue.labels ?? []).some((label) => label.name === labelName);
            }

            async function removeLabelIfPresent(issueNumber, issue, labelName) {
              if (!issueHasLabel(issue, labelName)) {
                console.log(`Issue #${issueNumber} does not have ${labelName}`);
                return;
              }

              try {
                await github.rest.issues.removeLabel({
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  issue_number: issueNumber,
                  name: labelName,
                });
                console.log(`Removed ${labelName} from #${issueNumber}`);
              } catch (error) {
                if (error.status === 404) {
                  console.log(`Label ${labelName} was already absent from #${issueNumber}`);
                  return;
                }
                throw error;
              }
            }

            if (context.payload.action === 'reopened') {
              await removeLabelIfPresent(context.issue.number, context.payload.issue, UNTRIAGED_LABEL);
              await removeLabelIfPresent(context.issue.number, context.payload.issue, NO_ACTION_LABEL);
              return;
            }

            if (context.payload.action !== 'labeled' || context.payload.label?.name !== LAST_READ_LABEL) {
              console.log('Not a last-read label event');
              return;
            }

            const currentIssueNumber = context.issue.number;
            const lastReadIssues = await github.paginate(github.rest.issues.listForRepo, {
              owner: context.repo.owner,
              repo: context.repo.repo,
              state: 'all',
              labels: LAST_READ_LABEL,
              per_page: 100,
            });

            const previousIssueNumbers = lastReadIssues
              .filter((issue) => !issue.pull_request)
              .map((issue) => issue.number)
              .filter((issueNumber) => issueNumber !== currentIssueNumber);

            if (previousIssueNumbers.length === 0) {
              console.log('No previous last-read issue found');
              return;
            }

            const previousIssueNumber = Math.max(...previousIssueNumbers);
            if (currentIssueNumber <= previousIssueNumber) {
              console.log(
                `Last-read was added to old issue #${currentIssueNumber}; latest last-read is #${previousIssueNumber}`,
              );
              return;
            }

            const untriagedIssues = await github.paginate(github.rest.issues.listForRepo, {
              owner: context.repo.owner,
              repo: context.repo.repo,
              state: 'all',
              labels: UNTRIAGED_LABEL,
              per_page: 100,
            });

            const issuesToMark = untriagedIssues
              .filter((issue) => !issue.pull_request)
              .filter((issue) => issue.number >= previousIssueNumber && issue.number <= currentIssueNumber)
              .sort((a, b) => a.number - b.number);

            if (issuesToMark.length === 0) {
              console.log(`No untriaged issues found from #${previousIssueNumber} to #${currentIssueNumber}`);
              return;
            }

            for (const issue of issuesToMark) {
              if (issueHasLabel(issue, TO_DISCUSS_LABEL)) {
                console.log(`Skipped ${NO_ACTION_LABEL} for #${issue.number} because it has ${TO_DISCUSS_LABEL}`);
              } else {
                await github.rest.issues.addLabels({
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  issue_number: issue.number,
                  labels: [NO_ACTION_LABEL],
                });
                console.log(`Added ${NO_ACTION_LABEL} to #${issue.number}`);
              }

              await github.rest.issues.update({
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: issue.number,
                state: 'closed',
                state_reason: 'not_planned',
              });
              console.log(`Closed #${issue.number} as not planned`);

              await removeLabelIfPresent(issue.number, issue, INPROGRESS_LABEL);

              await github.rest.issues.removeLabel({
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: issue.number,
                name: UNTRIAGED_LABEL,
              });
              console.log(`Removed ${UNTRIAGED_LABEL} from #${issue.number}`);
            }