import { OperatorFunction, Observable } from 'rxjs';
import { ChangeSummary } from '../ChangeSummary';
import { IChangeSet } from '../../cache/IChangeSet';
import { scan } from 'rxjs/operators';
import { ChangeStatistics } from '../ChangeStatistics';

/**
 * Accumulates update statistics
 * @typeparam TSource The type of the source.
 * @typeparam TKey The type of the key.
 * @param source The source.
 */
export function collectUpdateStats<TSource, TKey>(): OperatorFunction<IChangeSet<TSource, TKey>, ChangeSummary> {
    return function collectUpdateStatsOperator(source: Observable<IChangeSet<TSource, TKey>>) {
        return source.pipe(
            scan((seed, next) => {
                const index = seed.overall.index + 1;
                const adds = seed.overall.adds + next.adds;
                const updates = seed.overall.updates + next.updates;
                const removes = seed.overall.removes + next.removes;
                const evaluates = seed.overall.refreshes + next.refreshes;
                const moves = seed.overall.moves + next.moves;
                const total = seed.overall.count + next.size;

                const latest = new ChangeStatistics(index, next.adds, next.updates, next.removes, next.refreshes, next.moves, next.size);
                const overall = new ChangeStatistics(index, adds, updates, removes, evaluates, moves, total);
                return new ChangeSummary(index, latest, overall);
            }, ChangeSummary.empty),
        );
    };
}