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

script_dir=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
src_dir="$script_dir/config"
dest_dir="${HOME}/.config"


dry_run=false
target_path=""

usage() {
  cat <<'EOF'
Usage: sync-config.sh [--dry-run] [path]

path can be:
  config             (full config)
  config/tmux        (specific folder)
  config/tmux/config (specific file)
  .config            (full config)
  .config/tmux       (specific folder)
  .config/tmux/config (specific file)
  tmux               (folder under .config)
  tmux/config        (file under .config)
EOF
}

for arg in "$@"; do
  case "$arg" in
    --dry-run)
      dry_run=true
      ;;
    -h|--help)
      usage
      exit 0
      ;;
    *)
      if [[ -z "$target_path" ]]; then
        target_path="$arg"
      else
        echo "Error: too many arguments." >&2
        usage >&2
        exit 1
      fi
      ;;
  esac
done

hash_cmd="sha256sum"
if ! command -v "$hash_cmd" >/dev/null 2>&1; then
  echo "Error: sha256sum not found. Install coreutils or adjust hash_cmd." >&2
  exit 1
fi

file_hash() {
  "$hash_cmd" "$1" | awk '{print $1}'
}

copy_file() {
  local src="$1"
  local dst="$2"
  if $dry_run; then
    echo "copy: $src -> $dst"
  else
    mkdir -p "$(dirname "$dst")"
    cp -a "$src" "$dst"
    echo "copied: $dst"
  fi
}

if [[ ! -d "$src_dir" ]]; then
  echo "Error: source config directory not found: $src_dir" >&2
  exit 1
fi

mkdir -p "$dest_dir"

target_rel="$target_path"
if [[ -n "$target_rel" ]]; then
  if [[ "$target_rel" == "config" || "$target_rel" == ".config" ]]; then
    target_rel=""
  elif [[ "$target_rel" == config/* ]]; then
    target_rel=${target_rel#config/}
  elif [[ "$target_rel" == .config/* ]]; then
    target_rel=${target_rel#.config/}
  fi
  target_rel=${target_rel#./}
  if [[ "$target_rel" == "." ]]; then
    target_rel=""
  fi
  if [[ "$target_rel" == /* ]]; then
    echo "Error: absolute paths are not supported: $target_path" >&2
    exit 1
  fi
fi

base_path="$src_dir"
if [[ -n "$target_rel" ]]; then
  base_path="$src_dir/$target_rel"
fi

if [[ ! -e "$base_path" ]]; then
  echo "Error: path not found in source: $base_path" >&2
  exit 1
fi

sync_file() {
  local src_path="$1"
  local rel_path=${src_path#"$src_dir"/}
  local dst_path="$dest_dir/$rel_path"

  if [[ ! -f "$dst_path" ]]; then
    copy_file "$src_path" "$dst_path"
    return
  fi

  local src_hash
  local dst_hash
  src_hash=$(file_hash "$src_path")
  dst_hash=$(file_hash "$dst_path")

  if [[ "$src_hash" != "$dst_hash" ]]; then
    copy_file "$src_path" "$dst_path"
  fi
}

shopt -s globstar nullglob dotglob
if [[ -f "$base_path" ]]; then
  sync_file "$base_path"
elif [[ -d "$base_path" ]]; then
  for src_path in "$base_path"/**; do
    rel_path=${src_path#"$src_dir"/}

    if [[ "$rel_path" == ".git" || "$rel_path" == .git/* ]]; then
      continue
    fi

    dst_path="$dest_dir/$rel_path"

    if [[ -d "$src_path" ]]; then
      if ! $dry_run; then
        mkdir -p "$dst_path"
      else
        echo "mkdir: $dst_path"
      fi
      continue
    fi

    if [[ ! -f "$src_path" ]]; then
      continue
    fi

    sync_file "$src_path"
  done
fi

if $dry_run; then
  echo "Dry run complete. Re-run without --dry-run to apply changes."
else
  echo "Sync complete. Updated files where content differed."
fi