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.

env/params.go

@@ -0,0 +1,92 @@
+package env
+
+import (
+	"errors"
+	"os"
+	"os/user"
+	"path/filepath"
+	"strings"
+
+	"github.com/tkw1536/goprogram/exit"
+)
+
+// Params are parameters used for initialization of the environment
+type Params struct {
+	BaseDirectory string
+}
+
+// ConfigFilePath returns the path to the configuration file
+func (params Params) ConfigFilePath() string {
+	if params.BaseDirectory == "" {
+		return ""
+	}
+	return filepath.Join(params.BaseDirectory, ".env")
+}
+
+var errUnableToLoadParams = exit.Error{
+	ExitCode: exit.ExitGeneralArguments,
+	Message:  "Unable to configure wdcli environment: %s",
+}
+
+const BaseDirectoryDefault = "/var/www/deploy"
+
+// ParamsFromEnv creates a new set of parameters from the environment.
+// There is no guarantee that the parameters are valid.
+func ParamsFromEnv() (params Params, err error) {
+	// try to read the base directory
+	value, err := ReadBaseDirectory()
+	switch {
+	case os.IsNotExist(err):
+		params.BaseDirectory = BaseDirectoryDefault
+	case err == nil:
+		params.BaseDirectory = value
+	default:
+		return params, errUnableToLoadParams.WithMessageF(err)
+	}
+
+	return params, nil
+}
+
+var baseConfigFile = ".wdcli"
+
+// ReadBaseDirectory reads the base directory from the environment, or an empty string
+func ReadBaseDirectory() (value string, err error) {
+	// find the current user
+	usr, err := user.Current()
+	if err != nil {
+		return "", err
+	}
+
+	// read the base config file!
+	contents, err := os.ReadFile(filepath.Join(usr.HomeDir, baseConfigFile))
+	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 "", errors.New("ReadBaseDirectory: Directory is empty")
+	}
+
+	// and return it!
+	return value, nil
+}
+
+// WriteBaseDirectory writes the base directory to the environment, or returns an error
+func WriteBaseDirectory(dir string) error {
+	// find the current user
+	usr, err := user.Current()
+	if err != nil {
+		return err
+	}
+
+	// read the base config file!
+	return os.WriteFile(
+		filepath.Join(usr.HomeDir, baseConfigFile),
+		[]byte(dir),
+		os.ModePerm,
+	)
+}