#!/usr/bin/env bash
set -euo pipefail

ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"

if [[ ! -d "$ROOT_DIR/.git" ]]; then
  echo "[apply_patch][ERROR] no git repository available"
  exit 2
fi

patch_tmp=$(mktemp)
cleanup() { rm -f "$patch_tmp"; }
trap cleanup EXIT

if [[ $# -ge 1 ]]; then
  cp "$1" "$patch_tmp"
else
  cat > "$patch_tmp"
fi

if [[ ! -s "$patch_tmp" ]]; then
  echo "[apply_patch][ERROR] patch is empty"
  exit 2
fi

if ! git -C "$ROOT_DIR" apply --check "$patch_tmp" >/dev/null 2>&1; then
  echo "[apply_patch][ERROR] patch does not apply cleanly"
  exit 2
fi

file_count=$(git -C "$ROOT_DIR" apply --numstat "$patch_tmp" | awk '$3 != "" {print $3}' | sort -u | wc -l | tr -d ' ')
if (( file_count > 2 )); then
  echo "[apply_patch][BLOCK] patch touches $file_count files; max is 2 per step."
  exit 2
fi

git -C "$ROOT_DIR" apply "$patch_tmp"
echo "[apply_patch][OK] patch applied"