import { existsSync, readFileSync } from "node:fs";
import { dirname, join, resolve } from "node:path";
import { fileURLToPath } from "node:url";

function looksLikeAgentDir(dir: string): boolean {
  return (
    existsSync(join(dir, "settings.json")) &&
    (existsSync(join(dir, "packages")) ||
      existsSync(join(dir, "rules")) ||
      existsSync(join(dir, "themes")) ||
      existsSync(join(dir, "auth.json")))
  );
}

function findAgentDirFrom(startDir: string): string | null {
  let current = resolve(startDir);
  while (true) {
    if (looksLikeAgentDir(current)) return current;
    const parent = dirname(current);
    if (parent === current) return null;
    current = parent;
  }
}

export function getAgentDir(): string {
  const envDir = process.env.PI_AGENT_DIR;
  if (envDir && looksLikeAgentDir(resolve(envDir))) {
    return resolve(envDir);
  }

  const moduleDir = dirname(fileURLToPath(import.meta.url));
  const discovered = findAgentDirFrom(moduleDir);
  if (discovered) return discovered;

  const home = process.env.HOME;
  if (home) {
    const fallback = join(home, ".pi", "agent");
    if (looksLikeAgentDir(fallback)) return fallback;
  }

  throw new Error("Unable to resolve Pi agent directory");
}

export function getAgentPath(...segments: string[]): string {
  return join(getAgentDir(), ...segments);
}

export function readJsonFile<T>(path: string, fallback: T): T {
  try {
    if (!existsSync(path)) return fallback;
    return JSON.parse(readFileSync(path, "utf8")) as T;
  } catch {
    return fallback;
  }
}