Do a large chunk of the move to go

This commit moves a huge chunk of the code to go. The TODO.md document
indicates what is left to be done.

cmd/reserve.go

@@ -0,0 +1,86 @@
+package cmd
+
+import (
+	wisski_distillery "github.com/FAU-CDI/wisski-distillery"
+	"github.com/FAU-CDI/wisski-distillery/env"
+	"github.com/FAU-CDI/wisski-distillery/internal/fsx"
+	"github.com/FAU-CDI/wisski-distillery/internal/logging"
+	"github.com/FAU-CDI/wisski-distillery/internal/stack"
+	"github.com/tkw1536/goprogram/exit"
+)
+
+// Reserve is the 'reserve' command
+var Reserve wisski_distillery.Command = reserve{}
+
+type reserve struct {
+	Positionals struct {
+		Slug string `positional-arg-name:"slug" required:"1-1" description:"name of WissKI Instance to reserve"`
+	} `positional-args:"true"`
+}
+
+func (reserve) Description() wisski_distillery.Description {
+	return wisski_distillery.Description{
+		Requirements: env.Requirements{
+			NeedsConfig: true,
+		},
+		Command:     "reserve",
+		Description: "Reserves a new WissKI Instance",
+	}
+}
+
+// TODO: AfterParse to check instance!
+
+var errReserveAlreadyExists = exit.Error{
+	Message:  "Instance %q already exists",
+	ExitCode: exit.ExitGeneric,
+}
+
+var errReserveGeneric = exit.Error{
+	Message:  "Unable to provision instance %s: %s",
+	ExitCode: exit.ExitGeneric,
+}
+
+func (r reserve) Run(context wisski_distillery.Context) error {
+	dis := context.Environment
+	slug := r.Positionals.Slug
+
+	// check that it doesn't already exist
+	logging.LogMessage(context.IOStream, "Reserving new WissKI instance %s", slug)
+	if exists, err := dis.HasInstance(slug); err != nil || exists {
+		return errProvisionAlreadyExists.WithMessageF(slug)
+	}
+
+	// make it in-memory
+	instance, err := dis.NewInstance(slug)
+	if err != nil {
+		return errProvisionGeneric.WithMessageF(slug, err)
+	}
+
+	// check that the base directory does not exist
+	logging.LogMessage(context.IOStream, "Checking that base directory %s does not exist", instance.FilesystemBase)
+	if fsx.IsDirectory(instance.FilesystemBase) {
+		return errProvisionAlreadyExists.WithMessageF(slug)
+	}
+
+	// setup docker stack
+	s := instance.ReserveStack()
+	{
+		if err := logging.LogOperation(func() error {
+			return s.Install(context.IOStream, stack.InstallationContext{})
+		}, context.IOStream, "Installing docker stack"); err != nil {
+			return err
+		}
+
+		if err := logging.LogOperation(func() error {
+			return s.Update(context.IOStream, true)
+		}, context.IOStream, "Updating docker stack"); err != nil {
+			return err
+		}
+	}
+
+	// and we're done!
+	logging.LogMessage(context.IOStream, "Instance has been reserved")
+	context.Printf("URL:      %s\n", instance.URL().String())
+
+	return nil
+}