choice: Add ChooseWithDefault

Author: sunshineplan

choice/choice.go

@@ -3,12 +3,18 @@ package choice
 import (
 	"bufio"
 	"bytes"
+	"errors"
 	"fmt"
 	"os"
 	"strconv"
 	"strings"
 )
 
+// Description interface defines a method for obtaining the description of a choice.
+type Description interface {
+	Description() string
+}
+
 func choiceStr(choice any) string {
 	if v, ok := choice.(Description); ok {
 		return v.Description()
@@ -18,7 +24,11 @@ func choiceStr(choice any) string {
 	return fmt.Sprint(choice)
 }
 
-func Menu[E Choice](choices []E) string {
+// Menu function is used to generate a string representation of the menu, associating choices with numbers.
+func Menu[E any](choices []E) string {
+	if len(choices) == 0 {
+		return ""
+	}
 	var digit int
 	for n := len(choices); n != 0; digit++ {
 		n /= 10
@@ -28,32 +38,78 @@ func Menu[E Choice](choices []E) string {
 	for i, choice := range choices {
 		fmt.Fprintf(&b, "%s. %s\n", fmt.Sprintf(option, i+1), choiceStr(choice))
 	}
+	fmt.Fprintf(&b, "%s. Quit\n", fmt.Sprintf(fmt.Sprintf("%%%ds", digit), "q"))
 	return b.String()
 }
 
-func choose[E Choice](choice string, choices []E) (res any, err error) {
+// ErrBadChoice defines an error that represents an invalid choice made by the user.
+var ErrBadChoice = errors.New("bad choice")
+
+var _ error = choiceError("")
+
+type choiceError string
+
+func (err choiceError) Error() string {
+	return "bad choice: " + string(err)
+}
+
+func (choiceError) Unwrap() error {
+	return ErrBadChoice
+}
+
+func choose[E any](choice string, choices []E) (res E, err error) {
 	n, err := strconv.Atoi(choice)
 	if err != nil {
-		return nil, choiceError(choice)
+		err = choiceError(choice)
+		return
 	}
 	if length := len(choices); n < 1 || n > length {
-		return nil, choiceError(fmt.Sprintf("out of range(1-%d): %d", length, n))
+		err = choiceError(fmt.Sprintf("out of range(1-%d): %d", length, n))
+		return
 	}
-	return choices[n-1].Run()
+	return choices[n-1], nil
+}
+
+// Choose function allows the user to make a choice from the given options with no default value.
+func Choose[E any](choices []E) (choice bool, res E, err error) {
+	return ChooseWithDefault(choices, 0)
 }
 
-func Choose[E Choice](choices []E) (choice string, res any, err error) {
-	if length := len(choices); length == 0 {
+// ChooseWithDefault function allows the user to make a choice from the given options with an optional default value.
+func ChooseWithDefault[E any](choices []E, def int) (choice bool, res E, err error) {
+	if n := len(choices); n == 0 {
+		err = errors.New("no choices")
+		return
+	} else if def > n {
+		err = errors.New("invalid default choice")
 		return
 	}
-	fmt.Print(Menu(choices))
-	fmt.Print("\nPlease choose: ")
+	var prompt string
+	if def > 0 {
+		prompt = fmt.Sprintf("Please choose (default: %d): ", def)
+	} else {
+		prompt = "Please choose: "
+	}
 	scanner := bufio.NewScanner(os.Stdin)
-	scanner.Scan()
-	b := bytes.TrimSpace(scanner.Bytes())
-	if bytes.EqualFold(b, []byte("q")) || bytes.Contains(b, []byte{27}) {
+	var b []byte
+	if def <= 0 {
+		for len(b) == 0 {
+			fmt.Print(prompt)
+			scanner.Scan()
+			b = bytes.TrimSpace(scanner.Bytes())
+		}
+	} else {
+		fmt.Print(prompt)
+		scanner.Scan()
+		b = bytes.TrimSpace(scanner.Bytes())
+		if len(b) == 0 {
+			return true, choices[def-1], nil
+		}
+	}
+	if bytes.EqualFold(b, []byte("q")) {
 		return
 	}
+	choice = true
 	res, err = choose(string(b), choices)
 	return
 }

choice/choice_test.go

@@ -2,22 +2,14 @@ package choice
 
 import (
 	"errors"
-	"fmt"
 	"strings"
 	"testing"
 )
 
-var (
-	_ Choice      = a("")
-	_ Description = a("")
-)
+var _ Description = a("")
 
 type a string
 
-func (s a) Run() (any, error) {
-	return s, nil
-}
-
 func (s a) Description() string {
 	return strings.Repeat(string(s), 2)
 }
@@ -27,10 +19,18 @@ func (s a) String() string {
 }
 
 func TestMenu(t *testing.T) {
-	choices := []a{"a", "b", "c"}
-	expect := `1. aa
-2. bb
-3. cc
+	choices := []a{"a", "b", "c", "d", "e", "f", "g", "h", "i", "j"}
+	expect := ` 1. aa
+ 2. bb
+ 3. cc
+ 4. dd
+ 5. ee
+ 6. ff
+ 7. gg
+ 8. hh
+ 9. ii
+10. jj
+ q. Quit
 `
 	if s := Menu(choices); s != expect {
 		t.Errorf("expected %q; got %q", expect, s)
@@ -44,7 +44,13 @@ func TestChoose(t *testing.T) {
 	}
 	if s, err := choose("2", choices); err != nil {
 		t.Fatal(err)
-	} else if expect := "b"; fmt.Sprint(s) != expect {
+	} else if expect := "b"; s.String() != expect {
 		t.Errorf("expected %q; got %q", expect, s)
 	}
 }
+
+func TestError(t *testing.T) {
+	if !errors.Is(choiceError(""), ErrBadChoice) {
+		t.Error("expected err is ErrBadChoice; got not")
+	}
+}