import { realpath } from "node:fs/promises";
import { relative, resolve, sep } from "node:path";

export function scopesOverlap(left: readonly string[], right: readonly string[]): boolean {
  return left.some((path) => right.some((other) => {
    const a = path.replace(/[\\/]+$/, ""); const b = other.replace(/[\\/]+$/, "");
    return a === b || a.startsWith(`${b}/`) || b.startsWith(`${a}/`);
  }));
}

export function assertDisjointWriterScopes(scopes: readonly (readonly string[])[]): void {
  for (let index = 0; index < scopes.length; index += 1) for (let other = index + 1; other < scopes.length; other += 1) if (scopesOverlap(scopes[index]!, scopes[other]!)) throw new Error("Parallel writer scopes overlap");
}

export function assertOwnedPaths(paths: readonly string[], scope: readonly string[]): void {
  const owned = scope.map((path) => path.replace(/^\.\//, "").replace(/[\\/]+$/, "") || ".");
  for (const path of paths) {
    const candidate = path.replace(/^\.\//, "");
    if (candidate.startsWith("/") || candidate.split(/[\\/]/).includes("..") || !owned.some((root) => root === "." || candidate === root || candidate.startsWith(`${root}/`))) throw new Error(`Writer changed a path outside its owned scope: ${path}`);
  }
}

export async function assertPathInScope(root: string, candidate: string): Promise<string> {
  const [resolvedRoot, resolvedCandidate] = await Promise.all([realpath(root), realpath(candidate)]);
  const diff = relative(resolvedRoot, resolvedCandidate);
  if (diff === "" || (!diff.startsWith(`..${sep}`) && diff !== ".." && !resolve(resolvedRoot, diff).startsWith(`${resolvedRoot}${sep}`))) return resolvedCandidate;
  if (diff.startsWith("..") || resolve(resolvedRoot, diff) !== resolvedCandidate) throw new Error("Writer path escapes its owned scope");
  return resolvedCandidate;
}