@airgrid/edgekit/src/engine/evaluate.ts

A privacy focused library for cookie-less audience creation.

import * as reducers from './reducers';
import * as matchers from './matchers';
import { queryMatches } from './filters';
import {
  PageView,
  EngineCondition,
  AudienceDefinitionFilter,
} from '../../types';

/* Filter the pageView array by matching queries
 * and evaluates if it matches the conditions
 * based on the condition reducing rules
 */
export const evaluateCondition = (
  condition: Readonly<EngineCondition<AudienceDefinitionFilter>>,
  pageViews: Readonly<PageView[]>
): boolean => {
  try {
    const { filter, rules } = condition;

    // if no queries, do not match at all
    if (pageViews.length === 0 || filter.queries.length === 0) {
      return false;
    }

    /* Checks each pageView once for any matching queries
     * and returns the filtered array containing the matched
     * pageViews
     *
     * TODO Here, also, we have an opportunity to implement the
     * internal AND logic, swapping some for every
     * according to the value of filter.any
     *
     * NOTE: there is actually a semantic problem here.
     * The filter definition specifies an 'any' switch,
     * which defaults to false. However, the current
     * filtering uses `some` to check the query conditions.
     * The complete implementation here would be:
     * ```
     * filter.queries[filter.any ? 'some' : 'every']((query) => ...
     * ```
     * Yet, there is too much (testing) code depending on
     * this defaulting to `some` and the refactor would take
     * some time.
     */
    const filteredPageViews = pageViews.filter((pageView) =>
      filter.queries.some((query) => {
        const pageFeatures = pageView.features[query.queryProperty];
        return queryMatches(query, pageFeatures);
      })
    );

    return rules.every((rule) => {
      const reducer = reducers[rule.reducer.name]();
      const value = reducer(filteredPageViews);
      const matches = matchers[rule.matcher.name](rule.matcher.args);

      return matches(value);
    });
  } catch (error) {
    return false;
  }
};