Refactor tilde expansion (#442)

Refactor function that expanded a tilde in a path, to now also expand env variables.

Currently the function is used in two instances only, in `config.go` and `container.go`.
I've manually tested the functionality of both of those features.

Also created a go test file for the function.

internal/adapter/handlebars/handlebars.go

@@ -61,7 +61,6 @@ type LoaderOpts struct {
 }
 
 // NewLoader creates a new instance of Loader.
-//
 func NewLoader(opts LoaderOpts) *Loader {
 	return &Loader{
 		strings:     make(map[string]*Template),

internal/cli/container.go

@@ -4,7 +4,6 @@ import (
 	"io"
 	"os"
 	"path/filepath"
-	"strings"
 
 	"github.com/zk-org/zk/internal/adapter/editor"
 	"github.com/zk-org/zk/internal/adapter/fs"
@@ -75,14 +74,9 @@ func NewContainer(version string) (*Container, error) {
 	// Set the default notebook if not already set
 	// might be overrided if --notebook-dir flag is present
 	if osutil.GetOptEnv("ZK_NOTEBOOK_DIR").IsNull() && !config.Notebook.Dir.IsNull() {
-		// Expand in case there are environment variables on the path
-		notebookDir := os.Expand(config.Notebook.Dir.Unwrap(), os.Getenv)
-		if strings.HasPrefix(notebookDir, "~") {
-			dirname, err := os.UserHomeDir()
-			if err != nil {
-				return nil, wrap(err)
-			}
-			notebookDir = filepath.Join(dirname, notebookDir[1:])
+		notebookDir, err := paths.ExpandPath(config.Notebook.Dir.Unwrap())
+		if err != nil {
+			return nil, wrap(err)
 		}
 		os.Setenv("ZK_NOTEBOOK_DIR", notebookDir)
 	}

internal/core/config.go

@@ -313,7 +313,7 @@ func ParseConfig(content []byte, path string, parentConfig Config, isGlobal bool
 		config.Note.Extension = note.Extension
 	}
 	if note.Template != "" {
-		expanded, err := paths.ExpandTilde(note.Template)
+		expanded, err := paths.ExpandPath(note.Template)
 		if err != nil {
 			return config, wrap(err)
 		}

internal/util/paths/paths.go

@@ -1,12 +1,13 @@
 package paths
 
 import (
-	"fmt"
 	"os"
 	"os/user"
 	"path/filepath"
 	"strings"
 	"time"
+
+	"github.com/zk-org/zk/internal/util/errors"
 )
 
 // Metadata holds information about a file path.
@@ -79,17 +80,30 @@ func WriteString(path string, content string) error {
 	return err
 }
 
-// Expands leading tilde.
-func ExpandTilde(path string) (string, error) {
-	usr, err := user.Current()
-	if err != nil {
-		return "", fmt.Errorf("failed to determine current user")
-	}
-	home := usr.HomeDir
-	if path == "~" {
-		path = home
-	} else if strings.HasPrefix(path, "~/") {
-		path = filepath.Join(home, path[2:])
+// Expands environment variables and `~`, returning an absolute path.
+func ExpandPath(path string) (string, error) {
+
+	if strings.HasPrefix(path, "~") {
+		// resolve necessary variables
+		usr, err := user.Current()
+		if err != nil {
+			return "", err
+		}
+		home := usr.HomeDir
+		if home == "" {
+			err := errors.New("Could not find user's home directory.")
+			return "", err
+		}
+
+		// construct as abs path
+		if path == "~" {
+			path = home
+		} else if strings.HasPrefix(path, "~/") {
+			path = filepath.Join(home, path[2:])
+		}
 	}
+
+	path = os.ExpandEnv(path)
+
 	return path, nil
 }

internal/util/paths/paths_test.go

@@ -0,0 +1,43 @@
+package paths
+
+import (
+	"os/user"
+	"strings"
+	"testing"
+
+	"github.com/zk-org/zk/internal/util/test/assert"
+)
+
+func TestExpandPath(t *testing.T) {
+	usr, err := user.Current()
+	if err != nil {
+		t.Error(err)
+	}
+
+	test := func(path string, expected string) {
+		expanded, err := ExpandPath(path)
+		if err != nil {
+			t.Error(err)
+		}
+
+		assert.Equal(t, expanded, expected)
+	}
+	home := usr.HomeDir
+
+	s1 := []string{home, "foo"}
+	homefoo := strings.Join(s1, "/")
+	s2 := []string{"E.T phone", home}
+	etph := strings.Join(s2, " ")
+
+	// base cases
+	test("~", home)
+	test("~/", home)
+	test("~/foo", homefoo)
+	test("${HOME}/foo", homefoo)
+	test("/usr/opt", "/usr/opt")
+
+	// edge cases
+	test("~foo", "~foo")
+	test("not a path", "not a path")
+	test("E.T phone ${HOME}", etph)
+}