// The items of a pod collection, read and checked with the pod's answer SEEN.
//
// The platform's `pod-collections` service (@activitypods/app 2.3.2) hides a failure of the pod:
// `getItems` answers `[]` whatever the GET returned (it never looks at the status), and `add` /
// `remove` resolve normally when the pod refuses the PATCH (a status ≥ 400 is only logged). A
// decision taken on such an answer is wrong without anything saying so: a Leave read against a
// failed read finds nobody to remove, and an act whose write was refused is recorded as applied.
//
// So the backend reads a collection through `pod-resources.get`, where the status is visible, and
// verifies every write by reading the collection back. The writes themselves stay the platform's
// calls (`pod-collections.add` / `.remove`, through the collection handlers' `add` / `remove`).
//
//   readItems(ctx, { collectionUri, actorUri }) → the item URIs; throws unless the pod answers 200
//     with that very collection, its items inline (a paged collection is not read here: its items
//     are not in the root, and reading them as "none" is the defect this module exists to avoid).
//   expectItem(ctx, { collectionUri, itemUri, actorUri, present }) → resolves when the collection,
//     read again, holds `itemUri` (`present`) or does not (`!present`); throws otherwise — the write
//     just made did not take effect.

const { arrayOf } = require('@semapps/ldp');
const { uriOf } = require('./emitted-activity');

const AS = 'https://www.w3.org/ns/activitystreams#';

/** The item URIs a collection node lists inline, under any spelling of `items` / `orderedItems`. */
function itemsOf(collection) {
  const keys = ['items', 'orderedItems', 'as:items', 'as:orderedItems', `${AS}items`, `${AS}orderedItems`];
  const value = keys.map(key => collection[key]).find(v => v !== undefined);
  return arrayOf(value)
    .map(uriOf)
    .filter(uri => typeof uri === 'string');
}

/** Whether a collection root sends its items to pages (`first`) instead of listing them. */
const isPaged = collection =>
  ['first', 'as:first', `${AS}first`].some(key => collection[key] !== undefined) && itemsOf(collection).length === 0;

async function readItems(ctx, { collectionUri, actorUri }) {
  const { status, body } = await ctx.call('pod-resources.get', { resourceUri: collectionUri, actorUri });
  if (status !== 200 || !body || typeof body !== 'object') {
    throw new Error(`the pod does not return the collection ${collectionUri} (HTTP ${status})`);
  }
  if (uriOf(body) !== collectionUri) throw new Error(`the pod returned another resource for ${collectionUri}`);
  if (isPaged(body)) throw new Error(`the collection ${collectionUri} is paged: its items cannot be read from its root`);
  return itemsOf(body);
}

async function expectItem(ctx, { collectionUri, itemUri, actorUri, present }) {
  const holds = (await readItems(ctx, { collectionUri, actorUri })).includes(itemUri);
  if (holds !== present) {
    throw new Error(`${collectionUri} ${present ? 'does not hold' : 'still holds'} ${itemUri} after the ${present ? 'add' : 'remove'}: the pod did not apply it`);
  }
}

module.exports = { itemsOf, readItems, expectItem };