brewman/overlord/src/app/ledger/ledger-datasource.ts

import { DataSource } from '@angular/cdk/collections';
import { MatPaginator } from '@angular/material/paginator';
import { MatSort } from '@angular/material/sort';
import { map } from 'rxjs/operators';
import { merge, Observable, of as observableOf } from 'rxjs';
import { LedgerItem } from './ledger';

export class LedgerDataSource extends DataSource<LedgerItem> {
  constructor(private paginator: MatPaginator, private sort: MatSort, public data: LedgerItem[]) {
    super();
  }

  connect(): Observable<LedgerItem[]> {
    const dataMutations = [observableOf(this.data), this.paginator.page, this.sort.sortChange];

    // Set the paginators length
    this.paginator.length = this.data.length;

    return merge(...dataMutations).pipe(
      map(() => {
        return this.getPagedData(this.getSortedData([...this.data]));
      }),
    );
  }

  disconnect() {}

  private getPagedData(data: LedgerItem[]) {
    const startIndex = this.paginator.pageIndex * this.paginator.pageSize;
    return data.splice(startIndex, this.paginator.pageSize);
  }

  private getSortedData(data: LedgerItem[]) {
    if (!this.sort.active || this.sort.direction === '') {
      return data;
    }

    return data.sort((a, b) => {
      const isAsc = this.sort.direction === 'asc';
      switch (this.sort.active) {
        case 'date':
          return compare(a.date, b.date, isAsc);
        case 'debit':
          return compare(+a.debit, +b.debit, isAsc);
        case 'credit':
          return compare(+a.credit, +b.credit, isAsc);
        default:
          return 0;
      }
    });
  }
}

/** Simple sort comparator for example ID/Name columns (for client-side sorting). */
function compare(a, b, isAsc) {
  return (a < b ? -1 : 1) * (isAsc ? 1 : -1);
}