/**
 * The pure reconcile orchestration, decoupled from AWS/Google SDKs via the
 * {@link clients} interfaces so it is fully unit-testable.
 *
 * Invariant: the freshness marker is written ONLY after EVERY managed group
 * reconciles without error. A partial failure leaves the marker at its prior
 * value, so the pre-token Lambda fails closed once that value ages past
 * MAX_SYNC_AGE_MS (the bounded revocation-latency window — not instantaneous;
 * a partial failure is no worse than a fully missed run). Adds run before
 * removes within a group, so the worst case inside that window is an
 * over-grant that the window then collapses (design.md §2.3; agentforce-plan
 * §0.1 CR-5).
 */

import type { DirectoryReader, CognitoGroupTarget, SyncStateWriter } from './clients.js';
import { managedGroups, computeMembershipDiff, type ManagedGroup } from './groups.js';

export interface SyncDeps {
  directory: DirectoryReader;
  cognito: CognitoGroupTarget;
  syncState: SyncStateWriter;
  domain: string;
  /** Injectable clock for deterministic tests. */
  now?: () => number;
}

export interface GroupSyncResult {
  group: string;
  added: number;
  removed: number;
}

/** Reconcile a single managed group; returns the applied change counts. */
async function reconcileGroup(deps: SyncDeps, g: ManagedGroup): Promise<GroupSyncResult> {
  await deps.cognito.ensureGroup(g.cognito);
  const [desired, current] = await Promise.all([
    deps.directory.listGroupMembers(g.googleEmail),
    deps.cognito.listMembers(g.cognito),
  ]);
  const { toAdd, toRemove } = computeMembershipDiff(current, desired);
  // Adds before removes so a membership move never leaves a user with no group.
  for (const email of toAdd) await deps.cognito.addMember(g.cognito, email);
  for (const email of toRemove) await deps.cognito.removeMember(g.cognito, email);
  return { group: g.cognito, added: toAdd.length, removed: toRemove.length };
}

/**
 * Reconcile every managed group, then (only on full success) write the freshness
 * marker. Throws if any group fails — the caller surfaces that as a Lambda error
 * so the CloudWatch alarm fires and the marker stays stale.
 */
export async function runSync(deps: SyncDeps): Promise<GroupSyncResult[]> {
  const now = deps.now ?? Date.now;
  const results: GroupSyncResult[] = [];
  for (const g of managedGroups(deps.domain)) {
    results.push(await reconcileGroup(deps, g));
  }
  // Reached only if all groups reconciled without throwing.
  await deps.syncState.writeLastSuccessfulSync(now());
  return results;
}