brewman/overlord/src/app/purchase-entries/purchase-entries-datasource.ts

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

import { PurchaseEntriesItem } from './purchase-entries-item';

/** 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);
}

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

  connect(): Observable<PurchaseEntriesItem[]> {
    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(() => this.getPagedData(this.getSortedData([...this.data]))),
    );
  }

  disconnect() {}

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

  private getSortedData(data: PurchaseEntriesItem[]) {
    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 'supplier':
          return compare(a.supplier, b.supplier, isAsc);
        case 'product':
          return compare(a.product, b.product, isAsc);
        case 'amount':
          return compare(+a.amount, +b.amount, isAsc);
        default:
          return 0;
      }
    });
  }
}