fun with tax rates

tax_calc.dart

class ProfitekItem {
  late final bool taxable1;
  late final bool taxable2;
  late final bool taxable3;
  late final bool taxable4;
  
  late final num? taxRate1;
  late final num? taxRate2;
  late final num? taxRate3;
  late final num? taxRate4;
  
  late final String productName;
  late final num price;
  
  ProfitekItem({
    required this.taxable1,
    required this.taxable2,
    required this.taxable3,
    required this.taxable4,
    
    this.taxRate1,
    this.taxRate2,
    this.taxRate3,
    this.taxRate4,
    
    required this.productName,
    required this.price,
  });
}

void main() {
  ProfitekItem item1 = ProfitekItem(
    taxable1: true,
    taxable2: true,
    taxable3: false,
    taxable4: false,
    taxRate1: 0.05,
    taxRate2: 0.07,
    taxRate3: null,
    taxRate4: null,
    productName: 'Weed',
    price: 10.00,
  );
  
  ProfitekItem item2 = ProfitekItem(
    taxable1: true,
    taxable2: false,
    taxable3: false,
    taxable4: false,
    taxRate1: 0.05,
    taxRate2: null,
    taxRate3: null,
    taxRate4: null,
    productName: 'Vape',
    price: 10.00,
  );
  
  
  List<ProfitekItem> cart = [item1, item2];
  
  num? tax1Rate; // almost always GST
  num tax1Amount = 0;
  
  num? tax2Rate; // almost always PST
  num tax2Amount = 0;
  
  num? tax3Rate; // almost always HST
  num tax3Amount = 0;
  
  num? tax4Rate;
  num tax4Amount = 0;
  
  // for taxRate1
  cart.forEach((cartItem) {
    if (cartItem.taxable1) {
      tax1Rate = cartItem.taxRate1;
      tax1Amount += cartItem.price;
    }
    
    if (cartItem.taxable2) {
      tax2Rate = cartItem.taxRate2;
      tax2Amount += cartItem.price;
    }
    
    if (cartItem.taxable3) {
      tax3Rate = cartItem.taxRate3;
      tax3Amount += cartItem.price;
    }
    
    if (cartItem.taxable4) {
      tax4Rate = cartItem.taxRate4;
      tax4Amount += cartItem.price;
    }
  });
  
  // assertions
  final expectedTax1PreTaxTotal = 20;
  final expectedTax1Amount = 1;
  
  final expectedTax2PreTaxTotal = 10;
  final expectedTax2Amount = 0.70;
  
  final double? calculatedTax1Total = double.tryParse(tax1Amount.toString());
  final double? calculatedTax2Total = double.tryParse(tax2Amount.toString());
  
  if (expectedTax1PreTaxTotal != calculatedTax1Total ) {
    print('Pretax: It does not match [$expectedTax1PreTaxTotal] [$calculatedTax1Total]');
  }
  
    if (expectedTax2PreTaxTotal != calculatedTax2Total ) {
    print('Pretax: It does not match [$expectedTax2PreTaxTotal] [$calculatedTax2Total]');
  }
  
  final calculatedTax1 = double.tryParse((tax1Amount * (tax1Rate ?? 0)).toStringAsFixed(2));
  final calculatedTax2 = double.tryParse((tax2Amount * (tax2Rate ?? 0)).toStringAsFixed(2));
  
  if (expectedTax1Amount != calculatedTax1) {
    print('Tax1: It does not match: [$expectedTax1Amount] [$calculatedTax1]');
  }
  
  if (expectedTax2Amount != calculatedTax2) {
    print('Tax2: It does not match [$expectedTax2Amount] [$calculatedTax2]');
  }
  
  final expectedTotal = 20.0
    + expectedTax1Amount
    + expectedTax2Amount;
  
  final calculatedTotal = 20.0 
    + (calculatedTax1 ?? 0) 
    + (calculatedTax2 ?? 0);
  
  if (expectedTotal != calculatedTotal) {
    print('TOTAL: It does not match [$expectedTotal] [$calculatedTotal]');
  }
  
  
  print('Check any messages above.');
  
}