import * as fs from "fs";
import * as path from "path";
import * as os from "os";

export const AGE_GROUPS = [
  "middle_school", "high_school", "undergraduate", "graduate",
  "post_graduate", "professional", "adult_learner",
] as const;
export type AgeGroup = typeof AGE_GROUPS[number];

export interface WorkspaceResult {
  isActive: boolean;
  root: string | null;
  ageGroup: AgeGroup | null;
}

const HOME = os.homedir();
const MAX_LEVELS = 15;

function readAgeGroupFromIdentity(workspaceRoot: string): AgeGroup | null {
  try {
    const identityPath = path.join(workspaceRoot, ".pisces", "identity.json");
    if (!fs.existsSync(identityPath)) return null;
    const parsed = JSON.parse(fs.readFileSync(identityPath, "utf-8")) as Record<string, unknown>;
    const raw = parsed["ageGroup"];
    return (AGE_GROUPS as readonly string[]).includes(raw as string) ? (raw as AgeGroup) : null;
  } catch {
    return null;
  }
}

/**
 * Walks up from startCwd looking for a .pisces marker file or directory.
 * Bounded at 15 levels and stops at the user's home directory.
 */
export function findWorkspace(startCwd: string): WorkspaceResult {
  let dir = startCwd;
  let levels = 0;

  while (levels < MAX_LEVELS) {
    if (fs.existsSync(path.join(dir, ".pisces"))) {
      return { isActive: true, root: dir, ageGroup: readAgeGroupFromIdentity(dir) };
    }

    const parent = path.dirname(dir);
    if (parent === dir || dir === HOME) break;
    dir = parent;
    levels++;
  }

  return { isActive: false, root: null, ageGroup: null };
}

// ─── Singleton cache ────────────────────────────────────────────────────────
// Lazily initialised on first read so tests can mock findWorkspace() before
// the module evaluates any filesystem calls.

let _cached: WorkspaceResult | null = null;

/**
 * Returns the last resolved workspace state, initialising from process.cwd()
 * on first call. Use syncWorkspaceState() to re-evaluate after a cwd change.
 */
export function getWorkspaceState(): WorkspaceResult {
  if (_cached === null) {
    _cached = findWorkspace(process.cwd());
  }
  return _cached;
}

/**
 * Re-evaluates workspace state for the given cwd, updates the cache,
 * and returns the result. Called by the gatekeeper on resources_discover.
 */
export function syncWorkspaceState(cwd: string): WorkspaceResult {
  _cached = findWorkspace(cwd);
  return _cached;
}