#!/usr/bin/env bash
# lib/preflight.sh — the merge door's resume decision, pure and exhaustively
# tested (issue #273).
#
# A merge-door run creates the tag before the artifact hook and release. A
# failed hook or publish therefore leaves a tag but no release. Re-running the
# same merge commit must resume after that irreversible step; a published
# release or a tag naming another commit must still refuse.
#
# Pure: no repository or forge reads. The workflow establishes four facts:
#
#   VER         the version being released
#   MERGE_SHA   the commit this door would tag
#   TAG_SHAS    object names returned for the direct and peeled tag refs,
#               newline-separated; empty means the tag is absent
#   RELEASED    yes|no — whether a published release for VER exists
#
# Output: resume=yes or resume=no on stdout, notices to stdout, refusals to
# stderr, return 1 on refusal.
#
# The decision table (this IS the spec — issue #273):
#
# | # | RELEASED | TAG_SHAS contains MERGE_SHA | result                    |
# |---|----------|------------------------------|---------------------------|
# | 1 | yes      | either                       | REFUSE: already released   |
# | 2 | no       | empty                        | resume=no: ordinary run    |
# | 3 | no       | yes                          | resume=yes + resume NOTICE |
# | 4 | no       | non-empty, no                | REFUSE: tag is elsewhere   |

release_preflight() {
  local tag_sha sha

  if [ -z "${VER:-}" ]; then
    printf '%s\n' "VER is empty — the caller failed to establish the release version. Refusing to decide — creating nothing." >&2
    return 1
  fi
  if [ -z "${MERGE_SHA:-}" ]; then
    printf '%s\n' "MERGE_SHA is empty — the caller failed to establish the merge commit. Refusing to decide — creating nothing." >&2
    return 1
  fi
  if [ -z "${RELEASED:-}" ]; then
    printf '%s\n' "RELEASED is empty — the caller failed to establish whether release '$VER' exists. Refusing to decide — creating nothing." >&2
    return 1
  fi
  case "$RELEASED" in
    yes | no) ;;
    *)
      printf '%s\n' "RELEASED='$RELEASED' — expected yes or no. Refusing to decide — creating nothing." >&2
      return 1
      ;;
  esac

  # Row 1 comes first: deleting a tag under a standing release never makes
  # that release safe to recreate.
  if [ "$RELEASED" = yes ]; then
    printf '%s\n' "release '$VER' already exists — this release already happened; refusing to re-release, creating nothing." >&2
    return 1
  fi

  # Row 2: an absent tag is the ordinary first run.
  if [ -z "${TAG_SHAS:-}" ]; then
    printf '%s\n' 'resume=no'
    return 0
  fi

  # Row 3: compare each object name as a whole line. For an annotated tag the
  # direct ref names the tag object and the peeled ref names MERGE_SHA.
  while IFS= read -r sha; do
    if [ "$sha" = "$MERGE_SHA" ]; then
      printf '%s\n' "NOTICE: tag '$VER' already stands at this merge commit and no release exists — a previous run of this door tagged and then failed to publish. Resuming: the tag is not recreated; the artifact hook and the publish run."
      printf '%s\n' 'resume=yes'
      return 0
    fi
  done <<<"$TAG_SHAS"

  # Row 4: the first object name is enough to diagnose the conflicting tag;
  # MERGE_SHA is printed beside it so the operator sees both sides.
  tag_sha="${TAG_SHAS%%$'\n'*}"
  printf '%s\n' "tag '$VER' already exists at $tag_sha but this run would tag $MERGE_SHA — a manual tag won the race, or it names a different commit; refusing to re-release, creating nothing. Delete that tag, or re-tag the merge commit." >&2
  return 1
}