Add 'dis' component

This commit adds a new 'dis' component to the distillery that serves a
list of all known instances for the moment.

core/meta.go

@@ -0,0 +1,71 @@
+package core
+
+import (
+	"errors"
+	"io/fs"
+	"os"
+	"os/user"
+	"path/filepath"
+	"strings"
+)
+
+// MetaConfigFile is the path to a configuration file that contains the path to the last used wdcli executable.
+// It is expected to be in the current user's home directory.
+//
+// You probably want to use [MetaConfigPath] instead.
+//
+// It should contain the path to a deployment directory.
+const MetaConfigFile = "." + Executable
+
+// MetaConfigPath returns the full path to the MetaConfigPath()
+func MetaConfigPath() (string, error) {
+	// find the current user
+	usr, err := user.Current()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(usr.HomeDir, MetaConfigFile), nil
+}
+
+var errReadBaseDirectoryEmpty = errors.New("ReadBaseDirectory: Directory is empty")
+
+// ReadBaseDirectory reads the base deployment directory from the environment.
+// Use [ParamsFromEnv] to initialize parameters completely.
+//
+// It does not perform any reading of files.
+func ReadBaseDirectory() (value string, err error) {
+	// get the path!
+	path, err := MetaConfigPath()
+	if err != nil {
+		return "", err
+	}
+
+	// read the meta config file!
+	contents, err := os.ReadFile(path)
+	if err != nil {
+		return "", err
+	}
+
+	// and trim the spaces!
+	value = strings.TrimSpace(string(contents))
+
+	// check that it is actually set!
+	if len(value) == 0 {
+		return "", errReadBaseDirectoryEmpty
+	}
+
+	// and return it!
+	return value, nil
+}
+
+// WriteBaseDirectory writes the base directory to the environment, or returns an error
+func WriteBaseDirectory(dir string) error {
+	// get the path!
+	path, err := MetaConfigPath()
+	if err != nil {
+		return err
+	}
+
+	// just put the directory inside it!
+	return os.WriteFile(path, []byte(dir), fs.ModePerm)
+}