Created a period table for date ranges and made the recipes dependent on it instead of having arbitrary date ranges. This will enable easy copying into new months.

overlord/src/app/period/period-list/period-list-datasource.ts

@@ -0,0 +1,16 @@
+import { DataSource } from '@angular/cdk/collections';
+import { Observable, of as observableOf } from 'rxjs';
+
+import { Period } from '../period';
+
+export class PeriodListDataSource extends DataSource<Period> {
+  constructor(public data: Period[]) {
+    super();
+  }
+
+  connect(): Observable<Period[]> {
+    return observableOf(this.data);
+  }
+
+  disconnect() {}
+}

overlord/src/app/period/period-list/period-list.component.html

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+<mat-card>
+  <mat-card-title-group>
+    <mat-card-title>Periods</mat-card-title>
+    <a mat-button [routerLink]="['/periods', 'new']">
+      <mat-icon>add_box</mat-icon>
+      Add
+    </a>
+  </mat-card-title-group>
+  <mat-card-content>
+    <mat-table #table [dataSource]="dataSource" aria-label="Elements">
+      <!-- Valid From Column -->
+      <ng-container matColumnDef="validFrom">
+        <mat-header-cell *matHeaderCellDef>Valid From</mat-header-cell>
+        <mat-cell *matCellDef="let row">
+          <a [routerLink]="['/periods', row.id]">
+            {{ row.validFrom }}
+          </a>
+        </mat-cell>
+      </ng-container>
+
+      <!-- Valid Till Column -->
+      <ng-container matColumnDef="validTill">
+        <mat-header-cell *matHeaderCellDef>Valid Till</mat-header-cell>
+        <mat-cell *matCellDef="let row">{{ row.validTill }}</mat-cell>
+      </ng-container>
+
+      <mat-header-row *matHeaderRowDef="displayedColumns"></mat-header-row>
+      <mat-row *matRowDef="let row; columns: displayedColumns"></mat-row>
+    </mat-table>
+  </mat-card-content>
+</mat-card>

overlord/src/app/period/period-list/period-list.component.spec.ts

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+import { ComponentFixture, fakeAsync, TestBed } from '@angular/core/testing';
+import { ReactiveFormsModule } from '@angular/forms';
+import { RouterTestingModule } from '@angular/router/testing';
+
+import { PeriodListComponent } from './period-list.component';
+
+describe('PeriodListComponent', () => {
+  let component: PeriodListComponent;
+  let fixture: ComponentFixture<PeriodListComponent>;
+
+  beforeEach(fakeAsync(() => {
+    TestBed.configureTestingModule({
+      imports: [ReactiveFormsModule, RouterTestingModule],
+      declarations: [PeriodListComponent],
+    }).compileComponents();
+
+    fixture = TestBed.createComponent(PeriodListComponent);
+    component = fixture.componentInstance;
+    fixture.detectChanges();
+  }));
+
+  it('should compile', () => {
+    expect(component).toBeTruthy();
+  });
+});

overlord/src/app/period/period-list/period-list.component.ts

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+import { Component, OnInit } from '@angular/core';
+import { ActivatedRoute } from '@angular/router';
+
+import { Period } from '../period';
+
+import { PeriodListDataSource } from './period-list-datasource';
+
+@Component({
+  selector: 'app-period-list',
+  templateUrl: './period-list.component.html',
+  styleUrls: ['./period-list.component.css'],
+})
+export class PeriodListComponent implements OnInit {
+  dataSource: PeriodListDataSource;
+
+  list: Period[] = [];
+
+  /** Columns displayed in the table. Columns IDs can be added, removed, or reordered. */
+  displayedColumns = ['validFrom', 'validTill'];
+
+  constructor(private route: ActivatedRoute) {
+    this.dataSource = new PeriodListDataSource(this.list);
+  }
+
+  ngOnInit() {
+    this.route.data.subscribe((value) => {
+      const data = value as { list: Period[] };
+
+      this.list = data.list;
+    });
+    this.dataSource = new PeriodListDataSource(this.list);
+  }
+}