Allow specifying demo directory

cmd/demo.go

@@ -24,6 +24,11 @@ func Demo(ctx *cli.Context) {
 		log.Fatal(err)
 	}
 
+	if dirOpt := ctx.String("dir"); dirOpt != "" {
+		c.SetDir(dirOpt)
+	}
+
+	fmt.Printf("Your exercises will be saved at: %s\n", c.Dir)
 	hw := user.NewHomework(problems, c)
 	if err := hw.Save(); err != nil {
 		log.Fatal(err)

config/config.go

@@ -206,7 +206,7 @@ func (c *Config) IsAuthenticated() bool {
 // homeDir caches the lookup of the user's home directory.
 func (c *Config) homeDir() (string, error) {
 	if c.home != "" {
-		return c.home, nil
+		return c.home, nil // only set during testing
 	}
 	return Home()
 }
@@ -220,7 +220,7 @@ func (c *Config) resolvePath(argPath string) (string, error) {
 	if err != nil {
 		return "", err
 	}
-	path = strings.Replace(path, "~", h, 1)
+	path = expandHome(path, h)
 
 	fi, _ := os.Stat(path)
 	if fi != nil && fi.IsDir() {
@@ -239,15 +239,33 @@ func (c *Config) setDefaults() error {
 		c.XAPI = hostXAPI
 	}
 
-	h, err := c.homeDir()
-	if err != nil {
+	if err := c.SetDir(c.Dir); err != nil {
 		return err
 	}
 
-	if c.Dir == "" {
-		c.Dir = filepath.Join(h, DirExercises)
+	return nil
+}
+
+// SetDir sets the configuration directory to the given path
+// or defaults to the home exercism directory
+func (c *Config) SetDir(path string) error {
+	home, err := c.homeDir()
+	if err != nil {
+		return err
+	}
+	if path == "" {
+		c.Dir = filepath.Join(home, DirExercises)
+	} else {
+		c.Dir = path
 	}
-	c.Dir = strings.Replace(c.Dir, "~", h, 1)
 
+	c.Dir = expandHome(c.Dir, home)
 	return nil
 }
+
+func expandHome(path, home string) string {
+	if path[:2] == "~/" {
+		return strings.Replace(path, "~", home, 1)
+	}
+	return path
+}

config/config_test.go

@@ -11,6 +11,25 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func TestSetDir(t *testing.T) {
+	testCases := []struct {
+		givenPath    string
+		expectedPath string
+	}{
+		{"", "/test/home/exercism"},
+		{"~/foobar", "/test/home/foobar"},
+		{"/foobar/~/noexpand", "/foobar/~/noexpand"},
+		{"/no/modification", "/no/modification"},
+		{"nomodification", "nomodification"},
+	}
+
+	for _, testCase := range testCases {
+		config := &Config{home: "/test/home"}
+		config.SetDir(testCase.givenPath)
+		assert.Equal(t, testCase.expectedPath, config.Dir)
+	}
+}
+
 func TestLoad(t *testing.T) {
 	tmpDir, err := ioutil.TempDir("", "")
 	if err != nil {

exercism/main.go

@@ -90,7 +90,13 @@ func main() {
 			Name:      "demo",
 			ShortName: "d",
 			Usage:     descDemo,
-			Action:    cmd.Demo,
+			Flags: []cli.Flag{
+				cli.StringFlag{
+					Name:  "dir, d",
+					Usage: "path to use for the demo exercises",
+				},
+			},
+			Action: cmd.Demo,
 		},
 		{
 			Name:      "fetch",