cluster: introduce SyncRegions() to write regions file

Signed-off-by: Alejandro Mery <amery@jpi.io>

pkg/cluster/regions.go

@@ -1,5 +1,10 @@
 package cluster
 
+import (
+	"bytes"
+	"path/filepath"
+)
+
 var (
 	_ MachineIterator = (*Region)(nil)
 	_ ZoneIterator    = (*Region)(nil)
@@ -134,3 +139,61 @@ func (m *Cluster) getRegion(name string) (*Region, bool) {
 
 	return nil, false
 }
+
+// SyncRegions writes to the file system the regions this [Zone]
+// belongs to.
+func (z *Zone) SyncRegions() error {
+	err := z.syncZoneRegions()
+	if err == nil {
+		z.ForEachMachine(func(p *Machine) bool {
+			if p.IsActive() {
+				err = p.RemoveFile("region")
+			} else {
+				err = p.WriteStringFile("none\n", "region")
+			}
+			return err != nil
+		})
+	}
+
+	return err
+}
+
+func (z *Zone) syncZoneRegions() error {
+	name := filepath.Join(z.Name, "regions")
+
+	if len(z.Regions) > 0 {
+		var buf bytes.Buffer
+
+		for _, s := range z.Regions {
+			_, _ = buf.WriteString(s)
+			_, _ = buf.WriteRune('\n')
+		}
+
+		return z.zones.WriteStringFile(buf.String(), name)
+	}
+
+	return z.zones.RemoveFile(name)
+}
+
+// SyncRegions writes to the file system the regions covered
+// by this meta-region
+func (r *Region) SyncRegions() error {
+	name := filepath.Join(r.Name, "regions")
+
+	if len(r.Regions) > 0 {
+		var buf bytes.Buffer
+
+		for _, s := range r.Regions {
+			_, _ = buf.WriteString(s)
+			_, _ = buf.WriteRune('\n')
+		}
+
+		if err := r.m.MkdirAll(r.Name); err != nil {
+			return err
+		}
+
+		return r.m.WriteStringFile(buf.String(), name)
+	}
+
+	return r.m.RemoveFile(name)
+}