feat(menu): interactive command launcher package

internal/menu/menu.go

@@ -0,0 +1,60 @@
+// Package menu renders Crucible's interactive launcher: a numbered list of
+// commands for users who don't want to memorize subcommands. It holds no
+// builder logic — it returns the chosen dispatcher argument slice for the
+// caller to run. This is the seed of a future GUI front-end over the same core.
+package menu
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+)
+
+// Item is one selectable command.
+type Item struct {
+	Label string   // e.g. "module build"
+	Desc  string   // e.g. "build/extract/validate/compare the .mod"
+	Args  []string // dispatcher args, e.g. {"module", "build"}
+}
+
+// ANSI styling; terminals that don't support it simply ignore the codes.
+const (
+	cReset = "\033[0m"
+	cBold  = "\033[1m"
+	cCyan  = "\033[36m"
+	cDim   = "\033[2m"
+)
+
+// Select prints the numbered menu to out, reads a selection plus optional extra
+// arguments from in, and returns the full dispatcher argument slice. It returns
+// (nil, nil) when the user quits or enters an empty choice.
+func Select(out io.Writer, in io.Reader, items []Item) ([]string, error) {
+	if len(items) == 0 {
+		return nil, fmt.Errorf("no commands available")
+	}
+	fmt.Fprintf(out, "%s%sCrucible%s — pick a command:\n\n", cBold, cCyan, cReset)
+	for i, it := range items {
+		fmt.Fprintf(out, "  %s%2d%s  %s%-24s%s %s%s%s\n",
+			cCyan, i+1, cReset, cBold, it.Label, cReset, cDim, it.Desc, cReset)
+	}
+	fmt.Fprintf(out, "   %sq%s  quit\n\nselection: ", cCyan, cReset)
+
+	r := bufio.NewReader(in)
+	line, _ := r.ReadString('\n')
+	switch choice := strings.TrimSpace(line); choice {
+	case "", "q", "Q":
+		return nil, nil
+	default:
+		n, err := strconv.Atoi(choice)
+		if err != nil || n < 1 || n > len(items) {
+			return nil, fmt.Errorf("invalid selection %q", choice)
+		}
+		it := items[n-1]
+		fmt.Fprintf(out, "extra args for %q (optional): ", it.Label)
+		argLine, _ := r.ReadString('\n')
+		extra := strings.Fields(strings.TrimSpace(argLine))
+		return append(append([]string{}, it.Args...), extra...), nil
+	}
+}

internal/menu/menu_test.go

@@ -0,0 +1,47 @@
+package menu
+
+import (
+	"io"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+var sample = []Item{
+	{Label: "module build", Desc: "build the .mod", Args: []string{"module", "build"}},
+	{Label: "topdata validate-topdata", Desc: "validate topdata", Args: []string{"topdata", "validate-topdata"}},
+}
+
+func TestSelectReturnsChosenArgs(t *testing.T) {
+	got, err := Select(io.Discard, strings.NewReader("1\n\n"), sample)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if want := []string{"module", "build"}; !reflect.DeepEqual(got, want) {
+		t.Fatalf("got %v, want %v", got, want)
+	}
+}
+
+func TestSelectAppendsExtraArgs(t *testing.T) {
+	got, err := Select(io.Discard, strings.NewReader("2\n--dry-run foo\n"), sample)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	want := []string{"topdata", "validate-topdata", "--dry-run", "foo"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("got %v, want %v", got, want)
+	}
+}
+
+func TestSelectQuitReturnsNil(t *testing.T) {
+	got, err := Select(io.Discard, strings.NewReader("q\n"), sample)
+	if err != nil || got != nil {
+		t.Fatalf("quit should return (nil,nil); got (%v,%v)", got, err)
+	}
+}
+
+func TestSelectInvalidErrors(t *testing.T) {
+	if _, err := Select(io.Discard, strings.NewReader("99\n"), sample); err == nil {
+		t.Fatal("out-of-range selection should error")
+	}
+}