1 files changed, 86 insertions, 0 deletions
diff --git a/mass/mass.go b/mass/mass.go
new file mode 100644
index 0000000..29ecbd5
--- /dev/null
+++ b/mass/mass.go
@@ -0,0 +1,86 @@
+package mass
+
+import (
+	"errors"
+	"fmt"
+	"time"
+)
+
+type unit float32
+
+const (
+	Gram     unit = 1
+	Kilogram unit = 1_000
+	Pound    unit = 453.5924
+)
+
+type Mass struct {
+	Val  float32
+	Unit unit
+}
+
+func (m Mass) AsUnit(u unit) float32 {
+	g := m.Val * float32(m.Unit) // Convert to grams.
+	return g / float32(u)        // Convert to desired unit.
+}
+
+type flowRateUnit float32
+
+const (
+	KilogramsPerSecond flowRateUnit = 1
+	PoundsPerMinute    flowRateUnit = 0.007_559_872_833
+)
+
+// FlowRateUnitStrings returns a slice of strings, each representing a
+// flowRateUnit.
+// This is necessary because giu.Combo only works with strings.
+func FlowRateUnitStrings() []string {
+	return []string{"kg/s", "lb/min"}
+}
+
+const (
+	DefaultFlowRateUnit flowRateUnit = KilogramsPerSecond
+	// DefaultFlowRateUnitIndex is used to index FlowRateUnitStrings()
+	DefaultFlowRateUnitIndex int32 = 0 // kg/s
+)
+
+func FlowRateUnitFromString(s string) (flowRateUnit, error) {
+	// Each case corresponds to a value in FlowRateUnitStrings().
+	switch s {
+	case "kg/s":
+		return KilogramsPerSecond, nil
+	case "lb/min":
+		return PoundsPerMinute, nil
+	default:
+		return *new(flowRateUnit), errors.New(
+			fmt.Sprintf("invalid massFlowRateUnit: '%s'", s))
+	}
+}
+
+type FlowRate struct {
+	Val  float32
+	Unit flowRateUnit
+}
+
+func NewFlowRate(m Mass, t time.Duration, u flowRateUnit) (FlowRate, error) {
+	switch u {
+	case KilogramsPerSecond:
+		return FlowRate{
+			m.AsUnit(Kilogram) / float32(t.Seconds()),
+			u,
+		}, nil
+	case PoundsPerMinute:
+		return FlowRate{
+			m.AsUnit(Pound) / float32(t.Minutes()),
+			u,
+		}, nil
+	default:
+		return *new(FlowRate), errors.New(
+			fmt.Sprintf("invalid massFlowRateUnit: '%v'", u))
+	}
+}
+
+func (fr FlowRate) AsUnit(u flowRateUnit) float32 {
+	kgps := fr.Val * float32(fr.Unit) // Convert to kilogramsPerSecond.
+	return kgps / float32(u)          // Convert to desired unit.
+}