<mat-card>
  <mat-card-title>Upload maze</mat-card-title>
  <mat-card-content>
    <div>
      <form [formGroup]="form" (ngSubmit)="onSubmit()">
        <input type="file" accept="text/plain" name="maze" (change)="onFileChange($event)"/>
        <button mat-raised-button color="primary" type="submit">Upload</button>
      </form>

      <ng-container *ngIf="error; then errorT else success"></ng-container>
      <ng-template #errorT>
        <div style="color:red">
          <h1>Error has occurred</h1>
          {{error | json}}
        </div>
      </ng-template>
      <ng-template #success>
        <div style="color:green">
          <h1>Success</h1>
          Answer: {{uploadResponse.numberOfCorners}}
        </div>
      </ng-template>
    </div>
  </mat-card-content>
</mat-card>