import { promises as fs } from "fs";
import * as path from "path";

export const OUT_OF_SCOPE = "Error: path is outside the working directory";

export type Resolved = { ok: true; abs: string } | { ok: false; error: string };

/**
 * realpath that tolerates a not-yet-existing tail: resolve the nearest existing
 * ancestor and re-append the remaining segments. Returns null for a dangling
 * symlink (exists as a link but its target does not), which is never safe.
 */
async function realpathLoose(abs: string): Promise<string | null> {
  const rest: string[] = [];
  let cur = abs;
  for (;;) {
    try {
      const real = await fs.realpath(cur);
      return path.join(real, ...rest.reverse());
    } catch (e) {
      const code = (e as NodeJS.ErrnoException).code;
      if (code !== "ENOENT" && code !== "ENOTDIR") throw e;
      if (await fs.lstat(cur).catch(() => null)) return null;
      const parent = path.dirname(cur);
      if (parent === cur) throw e;
      rest.push(path.basename(cur));
      cur = parent;
    }
  }
}

export async function resolveInScope(root: string, userPath: string): Promise<Resolved> {
  if (typeof userPath !== "string" || userPath.trim() === "") {
    return { ok: false, error: "Error: no path provided" };
  }
  let realRoot: string;
  try {
    realRoot = await fs.realpath(root);
  } catch {
    return { ok: false, error: "Error: working directory is not accessible" };
  }
  let real: string | null;
  try {
    real = await realpathLoose(path.resolve(realRoot, userPath));
  } catch {
    return { ok: false, error: OUT_OF_SCOPE };
  }
  const prefix = realRoot.endsWith(path.sep) ? realRoot : realRoot + path.sep;
  if (real === null || (real !== realRoot && !real.startsWith(prefix))) {
    return { ok: false, error: OUT_OF_SCOPE };
  }
  return { ok: true, abs: real };
}

import { promises as fs } from "fs";
import * as path from "path";

export const OUT_OF_SCOPE = "Error: path is outside the working directory";

export type Resolved = { ok: true; abs: string } | { ok: false; error: string };

/**
 * realpath that tolerates a not-yet-existing tail: resolve the nearest existing
 * ancestor and re-append the remaining segments. Returns null for a dangling
 * symlink (exists as a link but its target does not), which is never safe.
 */
async function realpathLoose(abs: string): Promise<string | null> {
  const rest: string[] = [];
  let cur = abs;
  for (;;) {
    try {
      const real = await fs.realpath(cur);
      return path.join(real, ...rest.reverse());
    } catch (e) {
      const code = (e as NodeJS.ErrnoException).code;
      if (code !== "ENOENT" && code !== "ENOTDIR") throw e;
      if (await fs.lstat(cur).catch(() => null)) return null;
      const parent = path.dirname(cur);
      if (parent === cur) throw e;
      rest.push(path.basename(cur));
      cur = parent;
    }
  }
}

export async function resolveInScope(root: string, userPath: string): Promise<Resolved> {
  if (typeof userPath !== "string" || userPath.trim() === "") {
    return { ok: false, error: "Error: no path provided" };
  }
  let realRoot: string;
  try {
    realRoot = await fs.realpath(root);
  } catch {
    return { ok: false, error: "Error: working directory is not accessible" };
  }
  let real: string | null;
  try {
    real = await realpathLoose(path.resolve(realRoot, userPath));
  } catch {
    return { ok: false, error: OUT_OF_SCOPE };
  }
  const prefix = realRoot.endsWith(path.sep) ? realRoot : realRoot + path.sep;
  if (real === null || (real !== realRoot && !real.startsWith(prefix))) {
    return { ok: false, error: OUT_OF_SCOPE };
  }
  return { ok: true, abs: real };
}