# This reusable workflow sets the milestone based on the
# current PR labels.

name: PR Milestone

on:
  workflow_call:
    inputs:
      pr_number:
        required: true
        type: number

permissions:
  pull-requests: write
  contents: read

jobs:
  set-milestone:
    name: Set PR milestone
    runs-on: ubuntu-latest

    steps:
      - name: Determine target milestone
        id: determine-milestone
        uses: actions/github-script@v8
        with:
          script: |
            const prNumber = ${{ inputs.pr_number }};

            /*
             * Get the base branch of the PR.
             */
            const { data: pullRequest } =
              await github.rest.pulls.get({
                owner: context.repo.owner,
                repo: context.repo.repo,
                pull_number: prNumber
              });
            const baseBranch = pullRequest.base.ref;

            /*
             * 1. Return early if base is main branch. Milestone is already 
             * managed and probably done when merging to main.
             */
            if (baseBranch === 'main') {
              core.info('PR targets main. Milestone is managed separately.');
              core.setOutput('target_milestone', '');
              return;
            }

            /*
             * Helper function to set the target milestone output.
             */
            const setTargetMilestoneOutput = (targetMilestone) => {
              core.info(`Target milestone: ${targetMilestone}`);
              core.setOutput('target_milestone', targetMilestone);
            };

            /*
             * 2. If PR targets a release-candidate branch (for example 9.1.0.rc),
             * set milestone to the release version prefix (for example 9.1.0)
             * and return early.
             */
            if (baseBranch.endsWith('.rc')) {
              const targetMilestone = baseBranch.replace(/\.rc$/, '');

              core.info(
                `PR targets release-candidate branch "${baseBranch}". ` +
                `Using milestone "${targetMilestone}".`
              );

              setTargetMilestoneOutput(targetMilestone);
              return;
            }

            /**
             * 3. If PR targets a branch that is not developer, do nothing.
             */
            if (baseBranch !== 'developer') {
              core.info('PR does not target developer branch. Skipping milestone management.');
              core.setOutput('target_milestone', '');
              return;
            }

            /*
             * 4. If PR targets developer, check "Equivalent PRs" in the PR body.
             * If an equivalent PR targets an RC branch (for example 9.1.0.rc),
             * use the corresponding release milestone (for example 9.1.0).
             */
            if (baseBranch === 'developer') {
              const equivalentPrSectionMatch = pullRequest.body?.match(
                /(^|\n)#{1,6}\s*Equivalent PRs\s*\n([\s\S]*?)(?=\n#{1,6}\s+\S|\s*$)/i
              );

              const equivalentPrNumbers =
                equivalentPrSectionMatch?.[2]
                  ? Array.from(
                      equivalentPrSectionMatch[2].matchAll(/#(\d+)/g),
                      match => Number(match[1])
                    )
                  : [];

              for (const equivalentPrNumber of equivalentPrNumbers) {
                if (equivalentPrNumber === prNumber) {
                  continue;
                }

                const { data: equivalentPr } =
                  await github.rest.pulls.get({
                    owner: context.repo.owner,
                    repo: context.repo.repo,
                    pull_number: equivalentPrNumber
                  });

                const equivalentBaseBranch = equivalentPr.base.ref;

                if (!equivalentBaseBranch.endsWith('.rc')) {
                  continue;
                }

                const targetMilestone =
                  equivalentBaseBranch.replace(/\.rc$/, '');

                core.info(
                  `Developer PR references RC PR #${equivalentPrNumber} ` +
                  `(${equivalentBaseBranch}). Using milestone "${targetMilestone}".`
                );

                setTargetMilestoneOutput(targetMilestone);
                return;
              }
            }

            /*
             * 5. Read release targets through the GitHub API
             * from the base branch of PR.
             */
            const { data: file } =
              await github.rest.repos.getContent({
                owner: context.repo.owner,
                repo: context.repo.repo,
                path: '.github/release-targets.yaml',
                ref: baseBranch
              });

            const releaseTargetsFile =
              Buffer.from(file.content, 'base64').toString('utf8');

            const getTarget = (name) => {
              const match = releaseTargetsFile.match(
                new RegExp(`^${name}:\\s*["']?([^"'\\s]+)["']?`, 'm')
              );

              if (!match) {
                core.setFailed(
                  `Release target "${name}" was not found.`
                );
                return null;
              }

              return match[1];
            };

            const major = getTarget('major');
            const minor = getTarget('minor');
            const bugFix = getTarget('bug_fix');

            if (!major || !minor || !bugFix) {
              core.setFailed(
                'Required release targets (major, minor, bug_fix) could not be resolved from yaml file.'
              );
              return;
            }

            /*
             * Get current PR labels.
             */
            const { data: labels } =
              await github.rest.issues.listLabelsOnIssue({
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: prNumber
              });

            const labelNames =
              labels.map(label => label.name);

            /*
             * Determine the milestone.
             *
             * Breaking API has highest priority.
             */
            let targetMilestone;

            if (labelNames.includes('Breaking API')) {
              targetMilestone = major;
            } else if (labelNames.includes('Feature')) {
              targetMilestone = minor;
            } else if (
              labelNames.includes('Bug Fix') ||
              labelNames.includes('Infrastructure')
            ) {
              targetMilestone = bugFix;
            } else {
              core.setFailed(
                'No milestone-related labels found.'
              );
              return;
            }

            setTargetMilestoneOutput(targetMilestone);

      - name: Set milestone
        if: steps.determine-milestone.outputs.target_milestone != ''
        uses: actions/github-script@v8
        with:
          script: |
            const prNumber = ${{ inputs.pr_number }};
            const targetMilestone = '${{ steps.determine-milestone.outputs.target_milestone }}';

            const { data: milestones } =
              await github.rest.issues.listMilestones({
                owner: context.repo.owner,
                repo: context.repo.repo,
                state: 'open'
              });

            const milestone = milestones.find(
              milestone => milestone.title === targetMilestone
            );

            if (!milestone) {
              core.setFailed(
                `Milestone "${targetMilestone}" was not found.`
              );
              return;
            }

            await github.rest.issues.update({
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: prNumber,
              milestone: milestone.number
            });

            core.info(
              `Milestone set to "${targetMilestone}".`
            );