engine displacement

1 files changed, 54 insertions, 0 deletions

diff --git a/volume.go b/volume.go
new file mode 100644
index 0000000..cb7098a
--- /dev/null
+++ b/volume.go
@@ -0,0 +1,54 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+)
+
+type volumeUnit float32
+
+const (
+	cubicCentimetre volumeUnit = 1
+	litre           volumeUnit = 1_000
+	cubicMetre      volumeUnit = 1_000_000
+	cubicInch       volumeUnit = 16.38706
+)
+
+// volumeUnitStrings returns a slice of strings, each representing a
+// volumeUnit.
+// This is necessary because giu.Combo only works with strings.
+func volumeUnitStrings() []string {
+	return []string{"cc", "L", "m³", "in³"}
+}
+
+const (
+	defaultVolumeUnit volumeUnit = cubicCentimetre
+	// Used to index volumeUnitStrings
+	defaultVolumeUnitIndex int32 = 0 // cc
+)
+
+func volumeUnitFromString(s string) (volumeUnit, error) {
+	// Each case corresponds to a value in volumeUnitStrings
+	switch s {
+	case "cc":
+		return cubicCentimetre, nil
+	case "L":
+		return litre, nil
+	case "m³":
+		return cubicMetre, nil
+	case "in³":
+		return cubicInch, nil
+	default:
+		return *new(volumeUnit), errors.New(fmt.Sprintf("invalid volumeUnit: '%s'", s))
+	}
+}
+
+type volume struct {
+	val  float32
+	unit volumeUnit
+}
+
+func (v volume) asUnit(u volumeUnit) float32 {
+	cc := v.val * float32(v.unit) // Convert to cubic centimetres.
+	return cc / float32(u)        // Convert to desired unit.
+}