import {Inject, Injectable} from '@angular/core';
import moment from 'moment';
import {DlDateAdapter} from './dl-date-adapter';
import {DL_DATE_TIME_INPUT_FORMATS, DL_DATE_TIME_MODEL_FORMAT} from './dl-date-time-string-format';

/**
 * Adapts `string` to be usable as a date by date/time components that work with dates.
 **/
@Injectable({
  providedIn: 'root'
})
export class DlDateAdapterString extends DlDateAdapter<string> {

  private readonly inputFormats: string[];
  private readonly modelFormat: string;

  /**
   *  Constructs a new instance of this class.
   *
   * @param inputFormats
   *  see {@link DL_DATE_TIME_INPUT_FORMATS}
   * @param modelFormat
   *  see {@link DL_DATE_TIME_MODEL_FORMAT}
   */
  constructor(@Inject(DL_DATE_TIME_INPUT_FORMATS) inputFormats: string[],
              @Inject(DL_DATE_TIME_MODEL_FORMAT) modelFormat: string) {
    super();
    this.inputFormats = inputFormats;
    this.modelFormat = modelFormat;
  }

  /**
   * Returns the specified number.
   * @param milliseconds
   *  a moment time time.
   * @returns
   *  the specified moment in time.
   */
  fromMilliseconds(milliseconds: number): string {
    return moment(milliseconds).format(this.modelFormat);
  }

  /**
   * Returns the specified number.
   * @param value
   *  a moment time time or `null`
   * @returns
   *  the milliseconds for the specified value or `null`
   *  `null` is returned when value is not a valid input date string
   */
  toMilliseconds(value: string | null): number | null {
    if (value !== undefined && value !== null) {
      const newMoment = moment(value, this.inputFormats, true);
      return newMoment.isValid() ? newMoment.valueOf() : undefined;
    }
  }
}