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.

internal/stack/installable.go

@@ -0,0 +1,108 @@
+package stack
+
+import (
+	"io/fs"
+	"os"
+	"path/filepath"
+
+	"github.com/FAU-CDI/wisski-distillery/distillery"
+	"github.com/FAU-CDI/wisski-distillery/internal/fsx"
+	"github.com/pkg/errors"
+	"github.com/tkw1536/goprogram/stream"
+)
+
+// Installable represents a Stack that can be automatically installed from a set of resources
+// See the Install() method.
+type Installable struct {
+	Stack
+
+	ContextResource string // Path to the resource containing 'docker compose' context
+
+	EnvFileResource string            // Path to the resource containing dynamically generated env file
+	EnvFileContext  map[string]string // Context of variables to replace in the env file
+
+	CopyContextFiles []string // Files to copy from the installation context
+
+	TouchFiles []string // Files to 'touch', i.e. ensure that exist
+
+	MakeDirsPerm fs.FileMode // permission for diretories, defaults to fs.ModeDir
+	MakeDirs     []string    // directories to ensure that exist
+}
+
+// InstallationContext is a context to install data in
+type InstallationContext map[string]string
+
+// Install installs or updates this stack into the directory specified by stack.Stack().
+//
+// Installation is non-interactive, but will provide debugging output onto io.
+// InstallationContext
+func (is Installable) Install(io stream.IOStream, context InstallationContext) error {
+	// setup the base files
+	if err := distillery.InstallResource(
+		is.Dir,
+		is.ContextResource,
+		func(dst, src string) {
+			io.Printf("[install] %s\n", dst)
+		},
+	); err != nil {
+		return err
+	}
+
+	// configure .env
+	envDest := filepath.Join(is.Dir, ".env")
+	if is.EnvFileResource != "" && is.EnvFileContext != nil {
+		io.Printf("[config]  %s\n", envDest)
+		if err := distillery.InstallTemplate(
+			envDest,
+			is.EnvFileResource,
+			is.EnvFileContext,
+		); err != nil {
+			return err
+		}
+	}
+
+	// make sure that certain files exist
+	for _, name := range is.MakeDirs {
+		// find the destination!
+		dst := filepath.Join(is.Dir, name)
+
+		io.Printf("[make]    %s\n", dst)
+		if is.MakeDirsPerm == fs.FileMode(0) {
+			is.MakeDirsPerm = fs.ModeDir
+		}
+		if err := os.MkdirAll(dst, is.MakeDirsPerm); err != nil {
+			return err
+		}
+	}
+
+	// copy files from the context!
+	for _, name := range is.CopyContextFiles {
+		// find the source!
+		src, ok := context[name]
+		if !ok {
+			return errors.Errorf("Missing file from context: %s", src)
+		}
+
+		// find the destination!
+		dst := filepath.Join(is.Dir, name)
+
+		// copy over file from context
+		io.Printf("[copy]    %s (from %s)\n", dst, src)
+		if err := fsx.CopyFile(dst, src); err != nil {
+			return errors.Wrapf(err, "Unable to copy file %s", src)
+		}
+	}
+
+	// make sure that certain files exist
+	for _, name := range is.TouchFiles {
+		// find the destination!
+		dst := filepath.Join(is.Dir, name)
+
+		io.Printf("[touch]   %s\n", dst)
+		if err := fsx.Touch(dst); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}