package kingpin

import (
	"os"
	"path/filepath"
)

var (
	// CommandLine is the default Kingpin parser.
	CommandLine = New(filepath.Base(os.Args[0]), "")
)

// Command adds a new command to the default parser.
func Command(name, help string) *CmdClause {
	return CommandLine.Command(name, help)
}

// Flag adds a new flag to the default parser.
func Flag(name, help string) *FlagClause {
	return CommandLine.Flag(name, help)
}

// Arg adds a new argument to the top-level of the default parser.
func Arg(name, help string) *ArgClause {
	return CommandLine.Arg(name, help)
}

// Parse and return the selected command. Will exit with a non-zero status if
// an error was encountered.
func Parse() string {
	selected := MustParse(CommandLine.Parse(os.Args[1:]))
	if selected == "" && CommandLine.cmdGroup.have() {
		Usage()
		os.Exit(0)
	}
	return selected
}

// Fatalf prints an error message to stderr and exits.
func Fatalf(format string, args ...interface{}) {
	CommandLine.Fatalf(os.Stderr, format, args...)
}

// FatalIfError prints an error and exits if err is not nil. The error is printed
// with the given prefix.
func FatalIfError(err error, prefix string) {
	CommandLine.FatalIfError(os.Stderr, err, prefix)
}

// UsageErrorf prints an error message followed by usage information, then
// exits with a non-zero status.
func UsageErrorf(format string, args ...interface{}) {
	CommandLine.UsageErrorf(os.Stderr, format, args...)
}

// Usage prints usage to stderr.
func Usage() {
	CommandLine.Usage(os.Stderr)
}

// MustParse can be used with app.Parse(args) to exit with an error if parsing fails.
func MustParse(command string, err error) string {
	if err != nil {
		Fatalf("%s, try --help", err)
	}
	return command
}

// Version adds a flag for displaying the application version number.
func Version(version string) {
	CommandLine.Version(version)
}