#1442: Added Quantity arithmetic

src/Hl7.Fhir.Base/ElementModel/Types/Quantity.cs

@@ -304,11 +304,72 @@ Quantity normalizeToUcum(Quantity orig)
         /// to specify comparison behaviour for date comparisons.</remarks>
         public Result<int> TryCompareTo(Any other) => TryCompareTo(other, CQL_EQUIVALENCE_COMPARISON);
 
-        public static bool operator +(Quantity a, Quantity b) => throw Error.NotSupported("Adding two quantites is not yet supported");
-        public static bool operator -(Quantity a, Quantity b) => throw Error.NotSupported("Subtracting two quantites is not yet supported");
 
-        public static bool operator *(Quantity a, Quantity b) => throw Error.NotSupported("Multiplying two quantites is not yet supported");
-        public static bool operator /(Quantity a, Quantity b) => throw Error.NotSupported("Dividing two quantites is not yet supported");
+        private static (Quantity, Quantity) alignQuantityUnits(Quantity a, Quantity b)
+        {
+            if (a.System != QuantityUnitSystem.UCUM || b.System != QuantityUnitSystem.UCUM)
+            {
+                Error.NotSupported("Arithmetic operations on quantities using systems other than UCUM are not supported.");
+            }
+
+            Quantity? left = a;
+            Quantity? right = b;
+
+            if (a.Unit != b.Unit)
+            {
+                // align units with each other
+                if (!a.TryCanonicalize(out left)) left = a;
+                if (!b.TryCanonicalize(out right)) right = b;
+            }
+
+            return (left!, right!);
+        }
+
+        public static Quantity? operator +(Quantity a, Quantity b) =>
+            Add(a, b).ValueOrDefault();
+
+        public static Quantity? operator -(Quantity a, Quantity b) =>
+            Substract(a, b).ValueOrDefault();
+
+        public static Quantity operator *(Quantity a, Quantity b) =>
+            Multiply(a, b).ValueOrDefault();
+
+        public static Quantity? operator /(Quantity a, Quantity b) =>
+            Divide(a, b).ValueOrDefault();
+
+        internal static Result<Quantity> Add(Quantity a, Quantity b)
+        {
+            var (left, right) = alignQuantityUnits(a, b);
+
+            return (left!.Unit == right!.Unit)
+                ? Ok<Quantity>(new(left.Value + right.Value, left.Unit))
+                : Fail<Quantity>(Error.InvalidOperation($"The add operation cannot be performed on quantities with units '{left.Unit}' and '{right.Unit}'."));
+        }
+
+        internal static Result<Quantity> Substract(Quantity a, Quantity b)
+        {
+            var (left, right) = alignQuantityUnits(a, b);
+
+            return (left!.Unit == right!.Unit)
+                ? Ok<Quantity>(new(left.Value - right.Value, left.Unit))
+                : Fail<Quantity>(Error.InvalidOperation($"The substract operation cannot be performed on quantities with units '{left.Unit}' and '{right.Unit}'."));
+        }
+
+        internal static Result<Quantity> Multiply(Quantity a, Quantity b)
+        {
+            var (left, right) = alignQuantityUnits(a, b);
+
+            return Ok<Quantity>(new(left.Value * right.Value, Ucum.PerformMetricOperation(left.Unit, right.Unit, (a, b) => a * b)));
+        }
+
+        internal static Result<Quantity> Divide(Quantity a, Quantity b)
+        {
+            if (b.Value == 0) return Fail<Quantity>(Error.InvalidOperation("Cannot divide by zero."));
+
+            var (left, right) = alignQuantityUnits(a, b);
+
+            return Ok<Quantity>(new(left.Value / right.Value, left.Unit == right.Unit ? "1" : Ucum.PerformMetricOperation(left.Unit, right.Unit, (a, b) => a / b)));
+        }
 
         public override int GetHashCode() => (Unit, Value).GetHashCode();
 

src/Hl7.Fhir.Base/ElementModel/Types/Ucum.cs

@@ -47,6 +47,13 @@ private static M.Quantity toUnitsOfMeasureQuantity(this decimal value, string un
             Metric metric = (unit != null) ? SYSTEM.Value.Metric(unit) : new Metric(new List<Metric.Axis>());
             return new M.Quantity(value, metric);
         }
+
+        internal static string PerformMetricOperation(string unit1, string unit2, Func<Metric, Metric, Metric> operation)
+        {
+            var a = SYSTEM.Value.Metric(unit1);
+            var b = SYSTEM.Value.Metric(unit2);
+            return operation(a, b).ToString();
+        }
     }
 }
 

src/Hl7.Fhir.Support.Tests/ElementModel/QuantityTests.cs

@@ -7,10 +7,15 @@
  */
 
 using FluentAssertions;
+using Hl7.Fhir.ElementModel.Types;
+using Hl7.Fhir.Utility;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using System;
+using System.Collections.Generic;
 using P = Hl7.Fhir.ElementModel.Types;
 
+#nullable enable
+
 namespace Hl7.Fhir.ElementModel.Tests
 {
     [TestClass]
@@ -146,5 +151,56 @@ public void QuantityCompareTests(string left, string right, Comparison expectedR
                     break;
             }
         }
+
+        public static IEnumerable<object?[]> ArithmeticTestdata => new[]
+                {
+                    new object[] { "25 'kg'", "5 'kg'", "30 'kg'" , (object)Quantity.Add },
+                    new object[] { "25 'kg'", "1000 'g'", "26000 'g'", (object)Quantity.Add },
+                    new object[] { "3 '[in_i]'", "2 '[in_i]'", "5 '[in_i]'", (object)Quantity.Add },
+                    new object[] { "4.0 'kg.m/s2'", "2000 'g.m.s-2'", "6000 'g.m.s-2'", (object)Quantity.Add } ,
+                    new object[] { "3 'm'", "3 'cm'", "303 'cm'", (object)Quantity.Add },
+                    new object[] { "3 'm'", "0 'cm'","300 'cm'", (object)Quantity.Add },
+                    new object[] { "3 'm'", "-80 'cm'", "220 'cm'", (object)Quantity.Add },
+
+                    new object?[] { "3 'm'", "0 'kg'", null, (object)Quantity.Add },
+
+                    new object[] { "25 'kg'", "500 'g'", "24500 'g'", (object)Quantity.Substract },
+                    new object[] { "25 'kg'", "25001 'g'", "-1 'g'", (object)Quantity.Substract},
+                    new object[] { "1 '[in_i]'", "2 'cm'", "0.005400 'm'", (object)Quantity.Substract },
+
+                    new object?[] { "1 '[in_i]'", "2 'kg'", null, (object)Quantity.Substract },
+
+                    new object[] { "25 'km'", "20 'cm'", "5000 'm2'", (object)Quantity.Multiply },
+                    new object[] { "2.0 'cm'", "2.0 'm'", "0.040 'm2'", (object)Quantity.Multiply  },
+                    new object[] { "2.0 'cm'", "9 'kg'", "180 'g.m'", (object)Quantity.Multiply  },
+
+
+                    new object[] { "14.4 'km'", "2.0 'h'", "2 'm.s-1'", (object)Quantity.Divide },
+                    new object[] { "9 'm2'", "3 'm'", "3 'm'", (object)Quantity.Divide },
+                    new object[] { "6 'm'", "3 'm'", "2 '1'", (object)Quantity.Divide },
+                    new object?[] { "3 'm'", "0 'cm'", null, (object)Quantity.Divide },
+                };
+
+
+        [TestMethod]
+        [DynamicData(nameof(ArithmeticTestdata))]
+        public void ArithmeticOperationsTests(string left, string right, object result, Func<Quantity, Quantity, Result<Quantity>> operation)
+        {
+            _ = Quantity.TryParse(left, out var q1);
+            _ = Quantity.TryParse(right, out var q2);
+
+            var opResult = operation(q1, q2);
+
+            if (result is string r && Quantity.TryParse(r, out var q3))
+            {
+                opResult.ValueOrDefault().Should().Be(q3);
+            }
+            else
+            {
+                opResult.Should().BeAssignableTo<IFailed>();
+            }
+        }
     }
-}
+}
+
+#nullable restore

src/Hl7.FhirPath.Tests/Functions/MathOperatorsTests.cs

@@ -1,6 +1,13 @@
 using FluentAssertions;
+using Hl7.Fhir.ElementModel;
+using Hl7.FhirPath;
 using Hl7.FhirPath.FhirPath.Functions;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+#nullable enable
 
 namespace HL7.FhirPath.Tests.Functions
 {
@@ -22,5 +29,72 @@ public void Power()
 
             2m.Power(2m).Should().BeOfType(typeof(decimal));
         }
+
+        private static IEnumerable<object[]> QuantityAddOperations() =>
+           new (string expression, bool expected, bool invalid)[]
+                {
+                     ("25 'kg' + 5 'kg' = 30 'kg'", true, false),
+                     ("3 '[in_i]' + 2 '[in_i]' = 5 '[in_i]'", true, false),
+                     ("3 'm' + 0 'cm' = 300 'cm'", true, false),
+                     ("(3 'm' + 0 'kg').empty()", true, false),
+                }.Select(t => new object[] { t.expression, t.expected, t.invalid });
+
+        private static IEnumerable<object[]> QuantitySubstractOperations() =>
+          new (string expression, bool expected, bool invalid)[]
+               {
+                     ("25 'kg' - 500 'g' = 24500 'g'", true, false),
+                     ("25 'kg' - 25001 'g' = -1 'g'", true, false),
+                     ("1 '[in_i]' - 2 'cm' = 0.005400 'm'", true, false),
+                     ("(3 '[in_i]' - 0 'kg').empty()", true, false),
+               }.Select(t => new object[] { t.expression, t.expected, t.invalid });
+
+        private static IEnumerable<object[]> QuantityMultiplyOperations() =>
+          new (string expression, bool expected, bool invalid)[]
+               {
+                     ("25 'km' * 20 'cm' = 5000 'm2'", true, false),
+                     ("2 'cm' * 2 'm' = 0.040 'm2'", true, false),
+                     ("2 'cm' * 9 'kg' = 180 'g.m'", true, false),
+               }.Select(t => new object[] { t.expression, t.expected, t.invalid });
+
+        private static IEnumerable<object[]> QuantityDivideOperations() =>
+          new (string expression, bool expected, bool invalid)[]
+               {
+                     ("14.4 'km' / 2 'h' = 2 'm.s-1'", true, false),
+                     ("9 'm2' / 3 'm' = 3 'm'", true, false),
+                     ("6 'm' / 3 'm' = 2 '1'", true, false),
+                     ("(3 'm' / 0 'cm').empty()", true, false),
+               }.Select(t => new object[] { t.expression, t.expected, t.invalid });
+
+        public static IEnumerable<object[]> AllQuantityOperations()
+        {
+            return
+                Enumerable.Empty<object[]>()
+                .Union(QuantityAddOperations())
+                .Union(QuantitySubstractOperations())
+                .Union(QuantityMultiplyOperations())
+                .Union(QuantityDivideOperations())
+                ;
+        }
+
+        [DataTestMethod]
+        [DynamicData(nameof(AllQuantityOperations), DynamicDataSourceType.Method)]
+        public void AssertTestcases(string expression, bool expected, bool invalid = false)
+        {
+            ITypedElement dummy = ElementNode.ForPrimitive(true);
+
+            if (invalid)
+            {
+                Action act = () => dummy.IsBoolean(expression, expected);
+                act.Should().Throw<Exception>();
+            }
+            else
+            {
+                dummy.IsBoolean(expression, expected)
+                    .Should().BeTrue(because: $"The expression was supposed to result in {expected}.");
+            }
+        }
     }
+
+
 }
+#nullable restore