# This workflow posts a docs preview link as a PR comment whenever a
# pull request that touches docs/ is opened or updated.  The preview
# is served by coder.com's branch-preview feature at /docs/@<branch>.
#
# The link deep-links to the first added/modified/renamed Markdown file
# under docs/ so reviewers land on the page that actually changed.
# Branch names are URL-encoded so that names containing slashes or
# other special characters produce working links.
#
# On subsequent pushes (synchronize) the existing comment is updated
# rather than creating a duplicate.  If a previous push had a Markdown
# file but the current push has none, the stale comment is deleted so
# readers don't follow a dead deep-link.  If the PR only deletes
# Markdown files (or only changes non-Markdown files such as images or
# manifest.json), no comment is posted.

name: docs-preview

on:
  pull_request:
    types:
      - opened
      - synchronize
      - reopened
    paths:
      - "docs/**"

concurrency:
  group: docs-preview-${{ github.event.pull_request.number }}
  cancel-in-progress: true

permissions:
  contents: read

jobs:
  docs-preview:
    runs-on: ubuntu-latest
    permissions:
      pull-requests: write # needed for commenting on PRs
    steps:
      - name: Post docs preview comment
        env:
          GH_TOKEN: ${{ github.token }}
          BRANCH: ${{ github.event.pull_request.head.ref }}
          PR_NUMBER: ${{ github.event.pull_request.number }}
          REPO: ${{ github.repository }}
        run: |
          # Marker embedded in the comment body so we can find this
          # workflow's own comments later. Keep this in one place so
          # later refactors don't drift between the body construction
          # and the jq selectors used to find existing comments.
          DOCS_PREVIEW_MARKER='<!-- docs-preview -->'

          # Returns IDs of github-actions[bot] comments on the PR whose
          # body contains DOCS_PREVIEW_MARKER. Used by both the stale-
          # comment-cleanup branch (when this push has no Markdown
          # changes) and the upsert branch below.
          list_docs_preview_comments() {
            gh api --paginate \
              "repos/${REPO}/issues/${PR_NUMBER}/comments" \
              --jq ".[] | select(.user.login == \"github-actions[bot]\") | select(.body | contains(\"${DOCS_PREVIEW_MARKER}\")) | .id"
          }

          # Fetch the list of non-deleted files from the PR.  This is
          # intentionally not piped into grep so that a gh-api failure
          # (network, auth, rate-limit) propagates immediately instead
          # of being swallowed by `|| true`.
          all_files=$(gh api --paginate \
            "repos/${REPO}/pulls/${PR_NUMBER}/files" \
            --jq '.[] | select(.status != "removed") | .filename')

          # Pick the first Markdown file under docs/.  `|| true` keeps
          # the pipeline from failing when grep finds no matches or
          # head triggers SIGPIPE under `set -o pipefail`.
          first_doc=$(printf '%s\n' "$all_files" \
            | grep -E '^docs/.*\.md$' \
            | head -n 1) || true

          if [ -z "$first_doc" ]; then
            echo "No added/modified Markdown files under docs/ on this push."

            # Now that the workflow fires on synchronize, this branch
            # is reachable on pushes that drop all Markdown while still
            # touching docs/ (e.g. a push that removes the file an
            # earlier push had previewed but adds a new image). The
            # previous preview comment now points at a deleted page;
            # delete it so readers don't follow a dead deep-link.
            #
            # Intentionally decoupled from head so that a gh-api failure
            # propagates here instead of being swallowed by `|| true`. In
            # this branch the workflow has no preview link to post anyway
            # (no Markdown in the push), so a transient list failure is a
            # cosmetic miss; log and exit cleanly rather than red-checking
            # every docs-touching PR during a comments-endpoint hiccup.
            # The next push will retry the cleanup. The upsert path below
            # uses strict propagation by contrast, because silent failure
            # there would create duplicate comments.
            stale_comment_ids=$(list_docs_preview_comments) || {
              echo "Could not list preview comments; skipping cleanup."
              exit 0
            }
            stale_id=$(printf '%s\n' "$stale_comment_ids" | head -n 1) || true

            if [ -n "$stale_id" ]; then
              if gh api --method DELETE \
                "repos/${REPO}/issues/comments/${stale_id}"; then
                echo "Deleted stale docs preview comment (id=${stale_id})."
              else
                echo "Failed to delete stale docs preview comment (id=${stale_id}); leaving in place."
              fi
            fi
            exit 0
          fi

          # Map the repo path to the docs site URL path.
          #   docs/README.md           -> ""           (docs root)
          #   docs/<dir>/index.md      -> "<dir>"      (directory index)
          #   docs/<dir>/README.md     -> "<dir>"      (directory index)
          #   docs/<dir>/<file>.md     -> "<dir>/<file>"
          rel="${first_doc#docs/}"
          case "$rel" in
            README.md)
              page_path=""
              ;;
            *)
              base="$(basename "$rel")"
              dir="$(dirname "$rel")"
              if [ "$dir" = "." ]; then
                dir=""
              fi
              case "$base" in
                index.md|README.md)
                  page_path="$dir"
                  ;;
                *)
                  stripped="${base%.md}"
                  if [ -z "$dir" ]; then
                    page_path="$stripped"
                  else
                    page_path="${dir}/${stripped}"
                  fi
                  ;;
              esac
              ;;
          esac

          # URL-encode the branch name so slashes and special
          # characters don't break the preview URL.  The page path is
          # left as-is because its components are simple ASCII path
          # segments and the slashes between them must be preserved.
          encoded_branch=$(jq -rn --arg b "$BRANCH" '$b | @uri')
          url="https://coder.com/docs/@${encoded_branch}"
          if [ -n "$page_path" ]; then
            url="${url}/${page_path}"
          fi

          # The literal backticks around ${first_doc} are escaped so
          # they survive the double-quoted string as Markdown inline
          # code; ${url} and ${first_doc} expand normally.
          comment_body="## Docs preview
          [:book: View docs preview](${url}) for \`${first_doc}\`

          ${DOCS_PREVIEW_MARKER}"

          # Upsert: update the existing docs-preview comment if one
          # exists, otherwise create a new one.  This prevents duplicate
          # preview comments on every push to the PR.
          #
          # Intentionally not piped into head so that a gh-api failure
          # (network, auth, rate-limit) propagates immediately instead
          # of being swallowed by `|| true`.
          all_comment_ids=$(list_docs_preview_comments)
          existing_id=$(printf '%s\n' "$all_comment_ids" | head -n 1) || true

          if [ -n "$existing_id" ]; then
            if ! gh api --method PATCH \
              "repos/${REPO}/issues/comments/${existing_id}" \
              --field body="$comment_body"; then
              echo "PATCH failed (comment may have been deleted); creating a new comment."
              existing_id=""
            else
              echo "Updated existing docs preview comment (id=${existing_id})."
            fi
          fi
          if [ -z "$existing_id" ]; then
            gh pr comment "${PR_NUMBER}" \
              --repo "${REPO}" \
              --body "$comment_body"
            echo "Created new docs preview comment."
          fi