Add a metadata system

internal/component/instances/wisski_stack.go

@@ -3,15 +3,17 @@ package instances
 import (
 	"embed"
 	"path/filepath"
+	"time"
 
 	"github.com/FAU-CDI/wisski-distillery/internal/component"
+	"github.com/tkw1536/goprogram/stream"
 )
 
 //go:embed all:instances/barrel instances/barrel.env
 var barrelResources embed.FS
 
 // Barrel returns a stack representing the running WissKI Instance
-func (wisski WissKI) Barrel() component.StackWithResources {
+func (wisski *WissKI) Barrel() component.StackWithResources {
 	return component.StackWithResources{
 		Stack: component.Stack{
 			Dir: wisski.FilesystemBase,
@@ -43,11 +45,59 @@ func (wisski WissKI) Barrel() component.StackWithResources {
 	}
 }
 
+const KeyLastRebuild MetaKey = "lastRebuild"
+
+func (wisski *WissKI) LastRebuild() (t time.Time, err error) {
+	var epoch int64
+
+	// read the epoch!
+	err = wisski.Metadata().Get(KeyLastRebuild, &epoch)
+	if err == ErrMetadatumNotSet {
+		return t, nil
+	}
+	if err != nil {
+		return t, err
+	}
+
+	// and turn it into time!
+	return time.Unix(epoch, 0), nil
+}
+
+func (wisski *WissKI) setLastRebuild() error {
+	return wisski.Metadata().Set(KeyLastRebuild, time.Now().Unix())
+}
+
+// Build builds or rebuilds the barel connected to this instance.
+//
+// It also logs the current time into the metadata belonging to this instance.
+func (wisski *WissKI) Build(stream stream.IOStream, start bool) error {
+	barrel := wisski.Barrel()
+
+	var context component.InstallationContext
+
+	{
+		err := barrel.Install(stream, context)
+		if err != nil {
+			return err
+		}
+	}
+
+	{
+		err := barrel.Update(stream, start)
+		if err != nil {
+			return err
+		}
+	}
+
+	// store the current last rebuild
+	return wisski.setLastRebuild()
+}
+
 //go:embed all:instances/reserve instances/reserve.env
 var reserveResources embed.FS
 
 // Reserve returns a stack representing the reserve instance
-func (wisski WissKI) Reserve() component.StackWithResources {
+func (wisski *WissKI) Reserve() component.StackWithResources {
 	return component.StackWithResources{
 		Stack: component.Stack{
 			Dir: wisski.FilesystemBase,