import type { AssessorRepository } from '../persistence/assessor-repository';

/** Declared read-only port of the Comparison Engine: it reads the Core and never writes to it. */
export type ComparisonReadMethods = Pick<AssessorRepository, 'getProject' | 'listAssessments' | 'loadAssessmentModel'
  | 'queryUnifiedResults' | 'listPolicyEvaluations' | 'listGpoBackupInstances'>;
export interface ComparisonReadPort extends ComparisonReadMethods { currentRevision(): Promise<number> }

/** Bounded per method; models and policy evaluations are large. */
const MAX_ENTRIES = 8;

/**
 * Reads are shared within one repository revision: both timeslots of a request load the same project-wide
 * policy evaluations and backups, and switching A or B reloads the same models. Any committed change starts
 * a new revision and drops every entry, so a read never serves an outdated state. Failed reads are not kept.
 */
export function comparisonReadPortFrom(repository: ComparisonReadMethods, revision: () => Promise<number>): ComparisonReadPort {
  let cachedRevision: number | undefined;
  const caches = new Map<string, Map<string, Promise<unknown>>>();
  const shared = <A extends unknown[], R>(name: string, read: (...args: A) => Promise<R>) => async (...args: A): Promise<R> => {
    const current = await revision();
    if (current !== cachedRevision) { caches.clear(); cachedRevision = current; }
    const cache = caches.get(name) ?? caches.set(name, new Map()).get(name)!;
    const key = JSON.stringify(args);
    let pending = cache.get(key) as Promise<R> | undefined;
    if (!pending) {
      if (cache.size >= MAX_ENTRIES) cache.delete(cache.keys().next().value!);
      pending = read(...args);
      cache.set(key, pending);
      pending.catch(() => { if (cache.get(key) === pending) cache.delete(key); });
    }
    return pending;
  };
  return Object.freeze({
    currentRevision: revision,
    getProject: repository.getProject.bind(repository),
    listAssessments: shared('assessments', repository.listAssessments.bind(repository)),
    loadAssessmentModel: shared('model', repository.loadAssessmentModel.bind(repository)),
    queryUnifiedResults: shared('results', repository.queryUnifiedResults.bind(repository)),
    listPolicyEvaluations: shared('evaluations', repository.listPolicyEvaluations.bind(repository)),
    listGpoBackupInstances: shared('backups', repository.listGpoBackupInstances.bind(repository))
  });
}