util/cli: create CLI utility package

util/cli/cli.go

@@ -0,0 +1,168 @@
+// Copyright 2015 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cli
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"sort"
+	"strings"
+	"text/template"
+)
+
+// Command represents a single command within an application.
+type Command struct {
+	Desc string
+	Run  func(t Term, args ...string) int
+}
+
+// Term handles an application's output.
+type Term interface {
+	Infof(format string, v ...interface{})
+	Errorf(format string, v ...interface{})
+	Out(format string)
+}
+
+type basicTerm struct {
+	out, err io.Writer
+}
+
+// Infof implements Term.
+func (t *basicTerm) Infof(format string, v ...interface{}) {
+	fmt.Fprintf(t.err, format, v...)
+	fmt.Fprint(t.err, "\n")
+}
+
+// Errorf implements Term.
+func (t *basicTerm) Errorf(format string, v ...interface{}) {
+	fmt.Fprintf(t.err, format, v...)
+	fmt.Fprint(t.err, "\n")
+}
+
+// Out implements Term.
+func (t *basicTerm) Out(msg string) {
+	fmt.Fprint(t.out, msg)
+	fmt.Fprint(t.out, "\n")
+}
+
+// BasicTerm returns a Term writing Infof and Errorf to err and Out to out.
+func BasicTerm(out, err io.Writer) Term {
+	return &basicTerm{out: out, err: err}
+}
+
+// App represents an application that may consist of multiple commands.
+type App struct {
+	Name string
+	Help func() string
+
+	commands map[string]*Command
+}
+
+// NewApp creates a new application with a pre-registered help command.
+func NewApp(name string) *App {
+	app := &App{
+		Name:     name,
+		commands: map[string]*Command{},
+	}
+	app.Register("help", &Command{
+		Desc: "prints this help text",
+		Run: func(t Term, _ ...string) int {
+			help := app.Help
+			if help == nil {
+				help = BasicHelp(app, tmpl)
+			}
+			t.Infof(help() + "\n")
+			return 0
+		},
+	})
+	return app
+}
+
+// Register adds a new command to the application.
+func (app *App) Register(name string, cmd *Command) {
+	name = strings.TrimSpace(name)
+	if name == "" {
+		panic("command name must not be empty")
+	}
+	if _, ok := app.commands[name]; ok {
+		panic("command cannot be registered twice")
+	}
+	app.commands[name] = cmd
+}
+
+// Run the application with the given arguments. Output is sent to t.
+func (app *App) Run(t Term, args ...string) int {
+	help := app.commands["help"]
+
+	if len(args) == 0 || strings.HasPrefix(args[0], "-") {
+		help.Run(t)
+		return 2
+	}
+	cmd, ok := app.commands[args[0]]
+	if !ok {
+		help.Run(t)
+		return 2
+	}
+
+	return cmd.Run(t, args[1:]...)
+}
+
+var tmpl = `
+usage: {{ .Name }} <command> [<args>]
+
+Available commands:
+  {{ range .Commands }}{{ .Name }}    {{ .Desc }}
+  {{ end }}
+`
+
+// BasicHelp returns a function that creates a basic help text for the application
+// with its commands.
+func BasicHelp(app *App, ts string) func() string {
+	t := template.Must(template.New("help").Parse(ts))
+
+	return func() string {
+		type command struct {
+			Name, Desc string
+		}
+		cmds := []command{}
+
+		var maxLen int
+		names := []string{}
+		for name := range app.commands {
+			names = append(names, name)
+			if len(name) > maxLen {
+				maxLen = len(name)
+			}
+		}
+		sort.Strings(names)
+
+		for _, name := range names {
+			cmds = append(cmds, command{
+				Name: name + strings.Repeat(" ", maxLen-len(name)),
+				Desc: app.commands[name].Desc,
+			})
+		}
+
+		var buf bytes.Buffer
+		t.Execute(&buf, struct {
+			Name     string
+			Commands []command
+		}{
+			Name:     app.Name,
+			Commands: cmds,
+		})
+		return strings.TrimSpace(buf.String())
+	}
+}