packer-cn/packer/environment.go

// The packer package contains the core components of Packer.
package packer

import (
	"fmt"
	"os"
	"sort"
	"strings"
)

// A command is a runnable sub-command of the `packer` application.
// When `packer` is called with the proper subcommand, this will be
// called.
//
// The mapping of command names to command interfaces is in the
// Environment struct.
//
// Run should run the actual command with the given environmet and
// command-line arguments. It should return the exit status when it is
// finished.
//
// Synopsis should return a one-line, short synopsis of the command.
// This should be less than 50 characters ideally.
type Command interface {
	Run(env *Environment, args []string) int
	Synopsis() string
}

// The environment struct contains all the state necessary for a single
// instance of Packer.
//
// It is *not* a singleton, but generally a single environment is created
// when Packer starts running to represent that Packer run. Technically,
// if you're building a custom Packer binary, you could instantiate multiple
// environments and run them in parallel.
type Environment struct {
	command map[string]Command
	ui      Ui
}

// This creates a new environment
func NewEnvironment() *Environment {
	env := &Environment{}
	env.command = make(map[string]Command)
	env.command["build"] = new(buildCommand)
	env.command["version"] = new(versionCommand)
	env.ui = &ReaderWriterUi{os.Stdin, os.Stdout}
	return env
}

// Executes a command as if it was typed on the command-line interface.
// The return value is the exit code of the command.
func (e *Environment) Cli(args []string) int {
	if len(args) == 0 || args[0] == "--help" || args[0] == "-h" {
		e.PrintHelp()
		return 1
	}

	command, ok := e.command[args[0]]
	if !ok {
		// The command was not found. In this case, let's go through
		// the arguments and see if the user is requesting the version.
		for _, arg := range args {
			if arg == "--version" || arg == "-v" {
				command = e.command["version"]
				break
			}
		}

		// If we still don't have a command, show the help.
		if command == nil {
			e.PrintHelp()
			return 1
		}
	}

	return command.Run(e, args[1:])
}

// Prints the CLI help to the UI.
func (e *Environment) PrintHelp() {
	// Created a sorted slice of the map keys and record the longest
	// command name so we can better format the output later.
	commandKeys := make([]string, len(e.command))
	i := 0
	maxKeyLen := 0
	for key, _ := range e.command {
		commandKeys[i] = key
		if len(key) > maxKeyLen {
			maxKeyLen = len(key)
		}

		i++
	}

	// Sort the keys
	sort.Strings(commandKeys)

	e.ui.Say("usage: packer [--version] [--help] <command> [<args>]\n\n")
	e.ui.Say("Available commands are:\n")
	for _, key := range commandKeys {
		command := e.command[key]

		// Pad the key with spaces so that they're all the same width
		key = fmt.Sprintf("%v%v", key, strings.Repeat(" ", maxKeyLen-len(key)))

		// Output the command and the synopsis
		e.ui.Say("    %v     %v\n", key, command.Synopsis())
	}
}

// Returns the UI for the environment. The UI is the interface that should
// be used for all communication with the outside world.
func (e *Environment) Ui() Ui {
	return e.ui
}