Initial

app.go

@@ -0,0 +1,68 @@
+package app
+
+/*
+This file is part of the App project.
+Copyright (C) 2021  Alexander Kiryukhin <a.kiryukhin@mail.ru>
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+@license GPL-3.0+ <http://spdx.org/licenses/GPL-3.0+>
+*/
+
+import (
+	"fmt"
+	"os"
+)
+
+type App struct {
+	commands []Command
+}
+
+var ErrNoCommand = fmt.Errorf("No command provided")
+
+// New returns new App.
+func New(commands []Command) *App {
+	return &App{commands: commands}
+}
+
+// Start cli application
+func (a *App) Start(args []string) error {
+	if len(args) < 2 {
+		return a.showHelpAndExit()
+	}
+
+	cmd := args[1]
+	for _, c := range a.commands {
+		if cmd == c.Name() {
+			fs := c.Flags()
+			if err := fs.Parse(args[2:]); err != nil {
+				fs.Usage()
+				return err
+			}
+			if err := c.Run(fs.Args()); err != nil {
+				return err
+			}
+			return nil
+		}
+	}
+
+	return a.showHelpAndExit()
+}
+
+func (a *App) showHelpAndExit() error {
+	fmt.Printf("Usage: %s [command]\nCommands:\n", os.Args[0])
+	for _, c := range a.commands {
+		fmt.Printf("\t%s - %s", c.Name(), c.Usage())
+	}
+	return ErrNoCommand
+}

command.go

@@ -0,0 +1,34 @@
+package app
+
+/*
+This file is part of the App project.
+Copyright (C) 2021  Alexander Kiryukhin <a.kiryukhin@mail.ru>
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+@license GPL-3.0+ <http://spdx.org/licenses/GPL-3.0+>
+*/
+
+import "flag"
+
+// Command represents top level command of cli application
+type Command interface {
+	// Name returns name of command
+	Name() string
+	// Usage returns short help to command
+	Usage() string
+	// Flags returns FlagSet with flags for current command
+	Flags() *flag.FlagSet
+	// Run command
+	Run(args []string) error
+}

example/example.go

@@ -0,0 +1,42 @@
+package app_test
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"github.com/neonxp/app"
+)
+
+func ExampleApp() {
+	app := app.New(commands)
+	if err := app.Start(os.Args); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+}
+
+var commands = []app.Command{}
+
+type exampleCommand struct {
+	test string
+}
+
+func (c *exampleCommand) Name() string {
+	return "example"
+}
+
+func (c *exampleCommand) Usage() string {
+	return "just example command"
+}
+
+func (c *exampleCommand) Flags() *flag.FlagSet {
+	fs := flag.NewFlagSet(c.Name(), flag.ExitOnError)
+	fs.StringVar(&c.test, "test", "value", "test flag")
+	return fs
+}
+
+func (c *exampleCommand) Run(args []string) error {
+	fmt.Printf("Runned %s command with flag -test=%s and args: %v", c.Name(), c.test, args)
+	return nil
+}

go.mod

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+module github.com/neonxp/app
+
+go 1.16