command.go

package main

import (
	"fmt"
	"os"
)

type Command struct {
	Name        string
	Usage       string
	Run         func(args []string)
	subcommands map[string]*Command
}

func (c *Command) AddCommand(cmds ...*Command) {
	if c.subcommands == nil {
		c.subcommands = map[string]*Command{}
	}

	for _, cmd := range cmds {
		c.subcommands[cmd.Name] = cmd
	}
}

func (c *Command) printHelp() {
	fmt.Println(c.Usage)
	fmt.Println("\nUsage:")
	fmt.Printf("  %s [command]\n", c.Name)

	if len(c.subcommands) > 0 {
		fmt.Println("\nAvailable Commands:")

		for _, cmd := range c.subcommands {
			fmt.Printf("  %s\t%s\n", cmd.Name, cmd.Usage)
		}
	}
}

func (c *Command) execute(args []string) {
	if len(args) == 0 {
		c.printHelp()
		return
	}

	cmdStr := args[0]

	if cmdStr == "help" {
		c.printHelp()
		return
	}

	command, exists := c.subcommands[cmdStr]
	if !exists {
		fmt.Println("Command doesn't exist:", cmdStr, "\n")
		c.printHelp()
		return
	}

	if command.Run == nil {
		command.execute(args[1:])
		return
	}

	command.Run(args[1:])
}

func (c *Command) Execute() {
	args := os.Args[1:]
	c.execute(args)
}