Commit-msg AI Assist Hook

set -e

msg_file="$1"
[ -f "$msg_file" ] || exit 0

# Strip git's comment lines (lines starting with #) — those are scaffolding.
msg=$(grep -v '^#' "$msg_file" | sed '/^$/d')
first_line=$(printf '%s' "$msg" | head -1)

# Conventional Commits regex — type(scope)?: subject
conventional_regex='^(feat|fix|docs|style|refactor|perf|test|build|ci|chore|revert)(\([a-z0-9-]+\))?!?: '

if printf '%s' "$first_line" | grep -qE "$conventional_regex"; then
  # Already conventional — nothing to do.
  exit 0
fi

# Skip empty messages (git already rejects these elsewhere).
if [ -z "$first_line" ]; then
  exit 0
fi

# Pick the AI CLI. Default to `claude`; reader can swap via env var.
ai_cmd="${AI_COMMIT_CMD:-claude}"

if ! command -v "$ai_cmd" >/dev/null 2>&1; then
  # AI CLI not installed — fall through silently.
  exit 0
fi

# Bundle the staged diff so the AI can infer scope from file paths.
diff=$( (git diff --cached --stat; echo "---"; git diff --cached) 2>/dev/null || echo "")

prompt=$(cat <<PROMPT
Rewrite this commit message in Conventional Commits format.
Type prefixes: feat, fix, docs, style, refactor, perf, test, chore, build, ci, revert.
Optional scope in parens (derive from file paths in the diff).
Subject under 70 chars. Output the message only, no commentary.

Original message:
$msg

Staged diff:
$diff
PROMPT
)

suggestion=$(printf '%s' "$prompt" | "$ai_cmd" 2>/dev/null || echo "")

if [ -z "$suggestion" ]; then
  # AI call failed or returned empty — let the commit proceed unchanged.
  # Commitlint downstream will catch it if it's non-conformant.
  exit 0
fi

suggestion_first=$(printf '%s' "$suggestion" | head -1)

echo "" >&2
echo "── commit-msg-ai-assist ──" >&2
echo "Original:   $first_line" >&2
echo "Suggestion: $suggestion_first" >&2
echo "" >&2

# Force the read from /dev/tty — commit-msg runs with stdin closed.
if [ -e /dev/tty ]; then
  printf "Use suggestion? [y]es / [e]dit / [n]o: " >&2
  read answer </dev/tty || answer="n"
else
  # No TTY available (e.g. CI, rebase) — never overwrite without confirmation.
  exit 0
fi

if [ "$answer" = "y" ] || [ "$answer" = "Y" ] || [ "$answer" = "yes" ]; then
  printf '%s\n' "$suggestion" > "$msg_file"
  echo "✓ message replaced with suggestion" >&2
elif [ "$answer" = "e" ] || [ "$answer" = "E" ] || [ "$answer" = "edit" ]; then
  printf '%s\n' "$suggestion" > "$msg_file"
  "${EDITOR:-vi}" "$msg_file" </dev/tty
fi

# Any other answer (n, blank, anything else) leaves the original message in place.