1 files changed, 54 insertions, 0 deletions
diff --git a/pressure.go b/pressure.go
new file mode 100644
index 0000000..f486552
--- /dev/null
+++ b/pressure.go
@@ -0,0 +1,54 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+)
+
+type pressureUnit float32
+
+const (
+	pascal              pressureUnit = 1
+	kilopascal          pressureUnit = 1_000
+	bar                 pressureUnit = 100_000
+	poundsPerSquareInch pressureUnit = 6_894.757
+)
+
+// pressureUnitStrings returns a slice of strings, each representing a
+// pressureUnit.
+// This is necessary because giu.Combo only works with strings.
+func pressureUnitStrings() []string {
+	return []string{"Pa", "kPa", "bar", "psi"}
+}
+
+const (
+	defaultPressureUnit pressureUnit = kilopascal
+	// Used to index pressureUnitStrings
+	defaultPressureUnitIndex int32 = 1 // kPa
+)
+
+func pressureUnitFromString(s string) (pressureUnit, error) {
+	// Each case corresponds to a value in pressureUnitStrings
+	switch s {
+	case "Pa":
+		return pascal, nil
+	case "kPa":
+		return kilopascal, nil
+	case "bar":
+		return bar, nil
+	case "psi":
+		return poundsPerSquareInch, nil
+	default:
+		return *new(pressureUnit), errors.New(fmt.Sprintf("invalid pressureUnit: '%s'", s))
+	}
+}
+
+type pressure struct {
+	val  float32
+	unit pressureUnit
+}
+
+func (p pressure) asUnit(u pressureUnit) float32 {
+	pa := p.val * float32(p.unit) // Convert to pascals.
+	return pa / float32(u)        // Convert to desired unit.
+}