// Which anonymous-read grants are FESTIPOD's — the record that lets public-read revoke only what it
// added.
//
// WHY. A pod resource can be world-readable for reasons that are not Festipod's: its owner shared it
// publicly, another app did, or the pod made it so. When an event stops being public, Festipod must
// take back the public read IT gave and leave any other one alone. The ACL cannot tell them apart (the
// rule is the same `acl:Read` for `foaf:Agent`), so Festipod records each grant it makes, here, and
// `revoke` acts only on a recorded one.
//
// WHAT COUNTS AS FESTIPOD'S:
//   - a grant `public-read.grant` added (the resource was not already world-readable);
//   - the public read the pod gives a collection Festipod itself created (an event's attendees
//     collection: the pod makes it world-readable at creation — observed 2026-10-12/13).
// A resource already world-readable before Festipod touched it is never recorded, so never revoked.
//
// WHERE IT LIVES. Like the catalog (`catalog-store.js`): in the backend's main dataset, DEFAULT graph
// (the one Fuseki persists), one triple per resource — subject the resource URI, one Festipod predicate,
// the time of the grant. It survives a backend restart. Grants made before this record existed
// (development data) are not in it, so they are not revoked.

const { iriRef } = require('./catalog-store');

const GRANTED_AT = 'http://festipod.org/publicReadGrantedAt';

/** Record (or re-record) that Festipod made `uri` world-readable. One update = one transaction. */
function recordGrantUpdate(uri) {
  const s = iriRef(uri);
  return `
    DELETE { ${s} <${GRANTED_AT}> ?old }
    INSERT { ${s} <${GRANTED_AT}> ?now }
    WHERE { OPTIONAL { ${s} <${GRANTED_AT}> ?old } BIND(NOW() AS ?now) }
  `;
}

/** Forget Festipod's grant on `uri` — only the ledger's predicate, nothing else about that URI. */
function forgetGrantUpdate(uri) {
  return `DELETE WHERE { ${iriRef(uri)} <${GRANTED_AT}> ?at }`;
}

/** Whether Festipod's grant on `uri` is recorded. */
function grantedQuery(uri) {
  return `ASK { ${iriRef(uri)} <${GRANTED_AT}> ?at }`;
}

// ── Store operations: `ctx` is a moleculer context (anything with `call`) ──

async function recordGrant(ctx, { dataset, uri }) {
  await ctx.call('triplestore.update', { query: recordGrantUpdate(uri), dataset, webId: 'system' });
}

async function forgetGrant(ctx, { dataset, uri }) {
  await ctx.call('triplestore.update', { query: forgetGrantUpdate(uri), dataset, webId: 'system' });
}

/** Resolves true only when the store answers the ASK with `true`. */
async function isGrantedByFestipod(ctx, { dataset, uri }) {
  return (await ctx.call('triplestore.query', { query: grantedQuery(uri), dataset, webId: 'system' })) === true;
}

module.exports = { GRANTED_AT, recordGrantUpdate, forgetGrantUpdate, grantedQuery, recordGrant, forgetGrant, isGrantedByFestipod };