/**
 * Pfade der Dateiansicht (quick-261008-mzu). Pfade beginnen immer mit "/";
 * die Wurzel ist "/". Die API prueft jeden Pfad noch einmal selbst (D-H) —
 * diese Pruefungen dienen nur der verstaendlichen Rueckmeldung im Dialog.
 */

export const ROOT = '/';
const MAX_NAME_LENGTH = 250;

export function join(dir: string, name: string): string {
  const base = dir.endsWith('/') ? dir.slice(0, -1) : dir;
  return `${base}/${name}`;
}

export function parent(path: string): string {
  if (path === ROOT || path === '') return ROOT;
  const trimmed = path.endsWith('/') ? path.slice(0, -1) : path;
  const i = trimmed.lastIndexOf('/');
  return i <= 0 ? ROOT : trimmed.slice(0, i);
}

export function basename(path: string): string {
  if (path === ROOT) return '';
  const trimmed = path.endsWith('/') ? path.slice(0, -1) : path;
  return trimmed.slice(trimmed.lastIndexOf('/') + 1);
}

/** Bestandteile eines Pfads: "/a/b" → ["a", "b"]; Wurzel → []. */
export function segments(path: string): string[] {
  return path.split('/').filter((s) => s !== '');
}

/** Pfad aus den ersten `count` Bestandteilen. */
export function pathOf(parts: readonly string[], count = parts.length): string {
  return count <= 0 ? ROOT : `/${parts.slice(0, count).join('/')}`;
}

export type NameProblem = 'empty' | 'dots' | 'slash' | 'part' | 'tooLong';

/** null = gueltiger Name, sonst der Grund. */
export function nameProblem(name: string): NameProblem | null {
  if (name.trim() === '') return 'empty';
  if (name === '.' || name === '..') return 'dots';
  if (name.includes('/') || name.includes('\\')) return 'slash';
  if (name.toLowerCase().endsWith('.part')) return 'part';
  if (name.length > MAX_NAME_LENGTH) return 'tooLong';
  return null;
}

export function validName(name: string): boolean {
  return nameProblem(name) === null;
}

const DOUBLE_EXTENSIONS = ['.tar.gz', '.tar.bz2', '.tar.xz', '.tar.zst'];

/** Name ohne und mit Endung trennen; "Archiv.tar.gz" → ["Archiv", ".tar.gz"]. */
export function splitExtension(name: string): [string, string] {
  const lower = name.toLowerCase();
  for (const ext of DOUBLE_EXTENSIONS) {
    if (lower.endsWith(ext) && name.length > ext.length) {
      return [name.slice(0, -ext.length), name.slice(-ext.length)];
    }
  }
  const dot = name.lastIndexOf('.');
  if (dot <= 0) return [name, ''];
  return [name.slice(0, dot), name.slice(dot)];
}

/** Freier Name nach dem Muster "Bericht (2).pdf", "Bericht (3).pdf" … */
export function freeName(name: string, taken: readonly string[]): string {
  const used = new Set(taken.map((n) => n.toLowerCase()));
  if (!used.has(name.toLowerCase())) return name;
  const [base, ext] = splitExtension(name);
  for (let i = 2; ; i++) {
    const candidate = `${base} (${i})${ext}`;
    if (!used.has(candidate.toLowerCase())) return candidate;
  }
}

/** Liegt `path` innerhalb von `folder` (echt darunter)? "/a" und "/ab" gelten nicht. */
export function isInside(folder: string, path: string): boolean {
  if (folder === ROOT) return path !== ROOT;
  return path.startsWith(`${folder}/`);
}