/**
 * Splits a file path into its directory components, removing the file name.
 * @param path - The full file path.
 * @returns An array of directories.
 */
function splitPath(path: string): string[] {
  const parts = path.split('/').filter(Boolean);
  parts.pop();
  return parts;
}

/**
 * Finds the longest common prefix between two paths.
 * @param path1 - The first path as an array of directories.
 * @param path2 - The second path as an array of directories.
 * @returns An array representing the common prefix.
 */
function findCommonPrefix(path1: string[], path2: string[]): string[] {
  const common: string[] = [];
  for (let i = 0; i < Math.min(path1.length, path2.length); i++) {
    if (path1[i] === path2[i]) {
      common.push(path1[i]);
    } else {
      break;
    }
  }
  return common;
}

/**
 * Finds the closest common directory for a set of file paths.
 * @param paths - An array of absolute file paths.
 * @returns The closest common directory as a string.
 */
export function findClosestCommonDirectory(paths: string[]): string {
  if (paths.length === 0) {
    return '/';
  }

  const splitPaths = paths.map(splitPath);
  let commonPrefix = splitPaths[0];

  for (let i = 1; i < splitPaths.length; i++) {
    commonPrefix = findCommonPrefix(commonPrefix, splitPaths[i]);
    if (commonPrefix.length === 0) {
      return '/';
    }
  }

  return '/' + commonPrefix.join('/');
}