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

import { Case } from '../core/case';

export class CauseListDatasource extends DataSource<Case> {
  private dataValues: Case[] = [];
  private data: Observable<Case[]> = new Observable<Case[]>();
  constructor(public d: Observable<Case[]>, private paginator?: MatPaginator) {
    super();
    this.data = d.pipe(tap((x) => (this.dataValues = x)));
  }

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

    return merge(...dataMutations)
      .pipe(
        tap((x: Case[]) => {
          if (this.paginator) {
            this.paginator.length = x.length;
          }
        }),
      )
      .pipe(map((x: Case[]) => this.getPagedData(this.dataValues)));
  }

  disconnect() {}

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