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// 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() io.Writer
Err() io.Writer
}
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() io.Writer {
return t.out
}
// Err implements Term.
func (t *basicTerm) Err() io.Writer {
return t.err
}
// 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
err := t.Execute(&buf, struct {
Name string
Commands []command
}{
Name: app.Name,
Commands: cmds,
})
if err != nil {
panic(fmt.Errorf("error executing help template: %s", err))
}
return strings.TrimSpace(buf.String())
}
}
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