action.yml

name: 'Create Milestone'
description: >
  Creates a milestone with the given title in the specified repository if one
  does not already exist.

inputs:
  repo:
    description: 'Full repository path (e.g. spring-cloud/spring-cloud-config-commercial)'
    required: true
  version:
    description: 'Milestone title / version string (e.g. 5.0.2.1)'
    required: true
  token:
    description: 'GitHub token with repository write access'
    required: true

runs:
  using: composite
  steps:
    - name: Create milestone if missing
      shell: bash
      env:
        GH_TOKEN: ${{ inputs.token }}
      run: |
        set -uo pipefail

        repo="${{ inputs.repo }}"
        version="${{ inputs.version }}"

        echo "Checking for milestone '${version}' in ${repo}..."
        # state=all and --paginate, both load-bearing. Milestone titles are not unique, so
        # missing an existing one here creates a duplicate - and the default state=open on
        # a single unpaginated page misses two different ways: a closed milestone with this
        # title, and, in the repositories past a hundred milestones, anything after page
        # one. The list comes back sorted by due date ascending, so the newest go last.
        #
        # The listing is captured and its exit status checked before anything is created.
        # Piping it straight into jq made a failed lookup - a rate limit, a 5xx, a token
        # that cannot read the repository - indistinguishable from "no such milestone",
        # and the only way this action can produce a duplicate is by creating one while
        # blind. A lookup that did not succeed fails the step instead.
        if ! listing=$(gh api --paginate "repos/${repo}/milestones?state=all&per_page=100"); then
          echo "::error::create-milestone: could not list the milestones of ${repo}, so it is not"
          echo "::error::possible to tell whether '${version}' already exists. Nothing was created."
          exit 1
        fi

        # Titles are compared trimmed: a title that differs from the requested version only
        # by surrounding whitespace is the same milestone to a human, and creating a second
        # one is not what anybody wants.
        if ! matches=$(printf '%s' "$listing" \
          | jq -r -s --arg title "$version" \
              'add // [] | .[] | select((.title | gsub("^\\s+|\\s+$"; "")) == ($title | gsub("^\\s+|\\s+$"; ""))) | .number'); then
          echo "::error::create-milestone: could not parse the milestone listing for ${repo}."
          echo "::error::Nothing was created."
          exit 1
        fi

        milestone_number=$(printf '%s' "$matches" | head -n 1)

        if [[ -n "$milestone_number" ]]; then
          count=$(printf '%s' "$matches" | grep -c . || true)
          if [[ "$count" -gt 1 ]]; then
            # Nothing here can safely merge them, but silently picking one hides a problem
            # that only ever gets worse as issues are filed against both.
            echo "::warning::create-milestone: ${repo} already has ${count} milestones titled '${version}' (#$(printf '%s' "$matches" | tr '\n' ' ')). Nothing was created; merge them by hand."
          fi
          echo "Milestone '${version}' already exists (#${milestone_number})."
        else
          echo "Milestone '${version}' not found — creating..."
          if ! gh api "repos/${repo}/milestones" \
            --method POST \
            --field title="$version"; then
            echo "::error::create-milestone: could not create milestone '${version}' in ${repo}."
            exit 1
          fi
          echo "Milestone '${version}' created in ${repo}."
        fi