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

if [[ $# -gt 1 ]]; then
  echo "Usage: $0 [path/to/env-file]" >&2
  exit 2
fi

SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"

if [[ $# -eq 1 ]]; then
  ENV_FILE="$1"
elif [[ -f "$SCRIPT_DIR/backup_rsync_git.env" ]]; then
  ENV_FILE="$SCRIPT_DIR/backup_rsync_git.env"
else
  ENV_FILE="$SCRIPT_DIR/.env"
fi

if [[ ! -f "$ENV_FILE" ]]; then
  echo "Env file not found: $ENV_FILE" >&2
  exit 1
fi

# shellcheck disable=SC1090
source "$ENV_FILE"

required_vars=(
  RSYNC_SOURCE
  RSYNC_TARGET_DIR
  COMMIT_MESSAGE_PREFIX
)

for var in "${required_vars[@]}"; do
  if [[ -z "${!var:-}" ]]; then
    echo "Missing required env var: $var" >&2
    exit 1
  fi
done

if [[ -z "${RSYNC_RSH:-}" && -z "${SSH_KEY_FILE:-}" ]]; then
  echo "Missing SSH config: set SSH_KEY_FILE or RSYNC_RSH" >&2
  exit 1
fi

if [[ -n "${SSH_KEY_FILE:-}" && ! -r "$SSH_KEY_FILE" ]]; then
  echo "SSH key file not readable: $SSH_KEY_FILE" >&2
  exit 1
fi

mkdir -p "$RSYNC_TARGET_DIR"

repo_abs="$(cd "$RSYNC_TARGET_DIR" && pwd)"

rel_target="."

if [[ ! -d "$repo_abs/.git" ]]; then
  git -C "$repo_abs" init -b main >/dev/null
fi

git_target() {
  git --git-dir="$repo_abs/.git" --work-tree="$repo_abs" "$@"
}

if [[ -n "${RSYNC_RSH:-}" ]]; then
  rsync_rsh="$RSYNC_RSH"
else
  ssh_options="${SSH_OPTIONS:--o IdentitiesOnly=yes -o StrictHostKeyChecking=yes}"
  rsync_rsh="ssh -i $SSH_KEY_FILE $ssh_options"
fi

if [[ -n "${rsync_rsh:-}" ]]; then
  rsync -az --delete -e "$rsync_rsh" "$RSYNC_SOURCE" "$repo_abs/"
else
  rsync -az --delete "$RSYNC_SOURCE" "$repo_abs/"
fi

git_target add -A -- "$rel_target"

if git_target diff --cached --quiet -- "$rel_target"; then
  exit 0
fi

timestamp="$(date '+%Y-%m-%d %H:%M:%S')"
git_target commit -m "$COMMIT_MESSAGE_PREFIX $timestamp" -- "$rel_target"