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

import { ComplianceList } from './compliance-list';

export class ComplianceListDatasource extends DataSource<ComplianceList> {
  constructor(public data: ComplianceList[], private paginator?: MatPaginator) {
    super();
  }

  connect(): Observable<ComplianceList[]> {
    const dataMutations: (Observable<ComplianceList[]> | EventEmitter<PageEvent>)[] = [
      observableOf(this.data),
    ];
    if (this.paginator) {
      dataMutations.push((this.paginator as MatPaginator).page);
    }

    return merge(...dataMutations)
      .pipe(
        tap((x) => {
          if (this.paginator) {
            this.paginator.length = this.data.length;
          }
        }),
      )
      .pipe(map((x) => this.getPagedData(this.data)));
  }

  disconnect() {}

  private getPagedData(data: ComplianceList[]) {
    if (this.paginator === undefined) {
      return data;
    }
    const startIndex = this.paginator.pageIndex * this.paginator.pageSize;
    return data.slice(startIndex, startIndex + this.paginator.pageSize);
  }
}