invoiceModel:

adjusted invoice model to set config as property in constructor
adjusted setClient function to pass config and date to getInvoiceDateFunction

invoice-date-strategy:
add parameter to getInvoice to receive date of invoice
adjusted endofmonth function to handling new logic with given date

invoiceModel.spec.ts:
add test for testing new endofmonth functionallity
=> in hindsight this might have been more logically as seperate spec file

frontend/src/components/invoice/models/InvoiceModel.ts

@@ -55,6 +55,7 @@ export default class InvoiceModel implements IAttachment {
   lines: InvoiceLine[] = [];
   money: InvoiceMoney;
   note: string;
+  config: ConfigModel;
 
   get isNew(): boolean {
     return this._id === undefined;
@@ -79,6 +80,7 @@ export default class InvoiceModel implements IAttachment {
 
     this._lines = obj.lines || config.defaultInvoiceLines || [];
     this.audit = obj.audit;
+    this.config = config;
   }
 
   getType(): 'quotation' | 'invoice' {
@@ -102,7 +104,7 @@ export default class InvoiceModel implements IAttachment {
   /** Some weird stuff happening here that EditInvoice probably depends on */
   setClient(client: undefined | ClientModel): InvoiceModel {
     this.client = client as ClientModel;
-    this.date = getInvoiceDate(client);
+    this.date = getInvoiceDate(client, this.config, this.date);
 
     if (client && client.defaultInvoiceLines.length) {
       this._lines = client.defaultInvoiceLines.map(x => ({...x}));

frontend/src/components/invoice/models/invoice-date-strategy.ts

@@ -8,25 +8,30 @@ export const invoiceDateStrategies = ['prev-month-last-day', 'today'];
 export const today = (): moment.Moment => moment().startOf('day');
 
 
-const endOfMonth = (): moment.Moment => {
-  if (moment().date() > 28) {
-    return today();
+const endOfMonth = (date?: moment.Moment): moment.Moment => {
+  const dateToCheck:moment.Moment = date || moment();
+  const endOfMonthStartDay:number = 1;
+  const endOfMonthEndDay:number = 21;
+  const currentDay:number = dateToCheck.date();
+
+  //checking on format to skip any time inequality
+  if(dateToCheck.format('YYYY-MM-DD') === dateToCheck.endOf('month').format('YYYY-MM-DD')){
+    return dateToCheck
+  }else if(currentDay >= endOfMonthStartDay && currentDay <= endOfMonthEndDay){
+    return dateToCheck.subtract(1, 'months').endOf('month');
+  }else{
+    return dateToCheck.startOf('month')
   }
-
-  // ATTN: The following returns something like: "Thu Apr 30 2020 23:59:59 GMT+0200"
-  // (which should probably be cleaned up at some point)
-  const lastDayPrevMonth = moment().subtract(1, 'months').endOf('month');
-  return lastDayPrevMonth;
 };
 
 
 
-export const getInvoiceDate = (client?: ClientModel, config?: ConfigModel): moment.Moment => {
+export const getInvoiceDate = (client?: ClientModel, config?: ConfigModel, date?: moment.Moment): moment.Moment => {
   const strategy = (client && client.defaultInvoiceDateStrategy) || (config && config.defaultInvoiceDateStrategy);
 
   switch (strategy) {
     case 'prev-month-last-day':
-      return endOfMonth();
+      return endOfMonth(date);
     case 'today':
     default:
       return today();

frontend/src/components/invoice/spec/InvoiceModel.spec.ts

@@ -208,3 +208,61 @@ describe('Switch between days and hours', () => {
     expect(vm.lines[0].amount).toBe(10);
   });
 });
+
+describe('Invoice date for last of month config', () => {
+  it('Should be 31 may when date is 10 june', () => {
+    const vm = createViewModel();
+    vm.date = moment('2024-06-10');
+    vm.setClient(undefined);
+
+    expect(vm.date.format('YYYY-MM-DD')).toBe('2024-05-31')
+  })
+
+  it('Should be 31 december when date is 10 januari', () => {
+    const vm = createViewModel();
+    vm.date = moment('2024-01-10');
+    vm.setClient(undefined);
+
+    expect(vm.date.format('YYYY-MM-DD')).toBe('2023-12-31')
+  })
+
+  it('Should be 30 june month when date is 30 june', () => {
+    const vm = createViewModel();
+    vm.date = moment('2024-06-30');
+    vm.setClient(undefined);
+
+    expect(vm.date.format('YYYY-MM-DD')).toBe('2024-06-30')
+  })
+
+  it('Should be 29 februari month when date is 29 februari', () => {
+    const vm = createViewModel();
+    vm.date = moment('2024-02-29');
+    vm.setClient(undefined);
+
+    expect(vm.date.format('YYYY-MM-DD')).toBe('2024-02-29')
+  })
+
+  it('Should be 31 januari month when date is 31 januari', () => {
+    const vm = createViewModel();
+    vm.date = moment('2024-01-31');
+    vm.setClient(undefined);
+
+    expect(vm.date.format('YYYY-MM-DD')).toBe('2024-01-31')
+  })
+
+  it('Should be 1 june month when date is 22 june', () => {
+    const vm = createViewModel();
+    vm.date = moment('2024-06-22');
+    vm.setClient(undefined);
+
+    expect(vm.date.format('YYYY-MM-DD')).toBe('2024-06-01')
+  })
+
+  it('Should be 1 januari month when date is 22 januari', () => {
+    const vm = createViewModel();
+    vm.date = moment('2024-01-22');
+    vm.setClient(undefined);
+
+    expect(vm.date.format('YYYY-MM-DD')).toBe('2024-01-01')
+  })
+})