1 files changed, 56 insertions, 0 deletions
diff --git a/src/cli/subcommand_group.go b/src/cli/subcommand_group.go
new file mode 100644
index 0000000..957e759
--- /dev/null
+++ b/src/cli/subcommand_group.go
@@ -0,0 +1,56 @@
+package cli
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"strings"
+)
+
+var ErrUnknownCommand = errors.New("error: unknown command")
+
+type SubcommandFunc = func(*flag.FlagSet) error
+
+type Subcommand struct {
+	FlagSet *flag.FlagSet
+	Usage   string
+	Func    SubcommandFunc
+}
+
+type SubcommandGroup struct {
+	subcommands   map[string]Subcommand
+	output        io.Writer
+	errorHandling flag.ErrorHandling
+}
+
+func NewSubcommandGroup(output io.Writer, errorHandling flag.ErrorHandling) SubcommandGroup {
+	return SubcommandGroup{subcommands: make(map[string]Subcommand), output: output, errorHandling: errorHandling}
+}
+
+func (sg *SubcommandGroup) AddSubcommand(name string, usage string, fn SubcommandFunc) {
+	fs := flag.NewFlagSet(name, sg.errorHandling)
+	fs.SetOutput(sg.output)
+	sg.subcommands[name] = Subcommand{
+		FlagSet: fs,
+		Usage:   usage,
+		Func:    fn,
+	}
+}
+
+func (sg SubcommandGroup) ExecSubcommand(name string) error {
+	cmd, ok := sg.subcommands[name]
+	if !ok {
+		return ErrUnknownCommand
+	}
+	return cmd.Func(cmd.FlagSet)
+}
+
+func (sg SubcommandGroup) Usage() string {
+	var b strings.Builder
+	b.WriteString("    subcommands:\n")
+	for _, cmd := range sg.subcommands {
+		fmt.Fprintf(&b, "        %s: %s\n", cmd.FlagSet.Name(), cmd.Usage)
+	}
+	return b.String()
+}