import fs from "node:fs/promises";
import os from "node:os";
import path from "node:path";

const UNICODE_SPACES = /[\u00A0\u2000-\u200A\u202F\u205F\u3000]/g;

function normalizeUnicodeSpaces(str: string): string {
  return str.replace(UNICODE_SPACES, " ");
}

function expandPath(filePath: string): string {
  const normalized = normalizeUnicodeSpaces(filePath);
  if (normalized === "~") {
    return os.homedir();
  }
  if (normalized.startsWith("~/")) {
    return os.homedir() + normalized.slice(1);
  }
  return normalized;
}

function resolveToCwd(filePath: string, cwd: string): string {
  const expanded = expandPath(filePath);
  if (path.isAbsolute(expanded)) {
    return expanded;
  }
  return path.resolve(cwd, expanded);
}

export function resolveSandboxPath(params: { filePath: string; cwd: string; root: string }): {
  resolved: string;
  relative: string;
} {
  const resolved = resolveToCwd(params.filePath, params.cwd);
  const rootResolved = path.resolve(params.root);
  const relative = path.relative(rootResolved, resolved);
  if (!relative || relative === "") {
    return { resolved, relative: "" };
  }
  if (relative.startsWith("..") || path.isAbsolute(relative)) {
    throw new Error(`Path escapes sandbox root (${shortPath(rootResolved)}): ${params.filePath}`);
  }
  return { resolved, relative };
}

export async function assertSandboxPath(params: { filePath: string; cwd: string; root: string }) {
  const resolved = resolveSandboxPath(params);
  await assertNoSymlink(resolved.relative, path.resolve(params.root));
  return resolved;
}

async function assertNoSymlink(relative: string, root: string) {
  if (!relative) {
    return;
  }
  const parts = relative.split(path.sep).filter(Boolean);
  let current = root;
  for (const part of parts) {
    current = path.join(current, part);
    try {
      const stat = await fs.lstat(current);
      if (stat.isSymbolicLink()) {
        throw new Error(`Symlink not allowed in sandbox path: ${current}`);
      }
    } catch (err) {
      const anyErr = err as { code?: string };
      if (anyErr.code === "ENOENT") {
        return;
      }
      throw err;
    }
  }
}

function shortPath(value: string) {
  if (value.startsWith(os.homedir())) {
    return `~${value.slice(os.homedir().length)}`;
  }
  return value;
}
