import {Component, OnInit} from '@angular/core';
import {concat, of, Subject, Observable, BehaviorSubject} from 'rxjs';
import {catchError, distinctUntilChanged, switchMap, tap} from 'rxjs/operators';
import {FilterLabel, isFilterLabel, LabelStoreService} from '../../data/label/label-store.service';
import {StateService} from '../../state.service';

/**
 * This component is responsible for the display of the search bar above the graph.
 * It allows for filtering issues by multiple labels and text fragments.
 */
@Component({
  selector: 'app-label-search',
  templateUrl: './label-search.component.html',
  styleUrls: ['./label-search.component.scss']
})
export class LabelSearchComponent implements OnInit {
  public filterSelection$ = new BehaviorSubject<FilterSelection>({
    labels: [],
    texts: []
  });

  labels$: Observable<FilterLabel[]>;
  labelsLoading = false;
  labelsInput$ = new Subject<string>();
  selectedLabels: FilterElement[] = [];

  constructor(private labelStore: LabelStoreService, private ss: StateService) {}

  ngOnInit() {
    this.loadLabels();
  }

  trackByFn(item: FilterLabel): string {
    return item.id;
  }

  /**
   * Emit value representing label and text fragments in the search bar via this.filterSelection$
   */
  emitSelectedLabels(): void {
    const selection: FilterSelection = {texts: [], labels: []};
    // find out which elements in search bar correspond to an existing label on the backend and which to a text fragment
    selection.texts = this.selectedLabels.filter((item) => !isFilterLabel(item)).map((item) => item.name);
    selection.labels = this.selectedLabels.filter((label) => isFilterLabel(label)) as FilterLabel[];
    this.filterSelection$.next(selection);
  }

  /**
   * Load all labels from backend that match the currently typed in ng-select element
   */
  private loadLabels() {
    this.labels$ = concat(
      of([]), // default items
      this.labelsInput$.pipe(
        distinctUntilChanged(),
        tap(() => (this.labelsLoading = true)),
        switchMap((term) =>
          this.labelStore.getMatchingLabels(this.ss.state.project.node.id, term).pipe(
            catchError(() => of([])), // empty list on error
            tap(() => (this.labelsLoading = false))
          )
        )
      )
    );
  }
}

/**
 * The bar can contain elements standing for labels and elements for text fragments.
 */
type FilterElement = TextFragment | FilterLabel;

interface TextFragment {
  name: string;
}

export interface FilterSelection {
  texts: string[];
  labels: FilterLabel[];
}