option.go

package mybase

import (
	"fmt"
	"os"
	"runtime"
	"sort"
	"strings"
	"unicode"

	"github.com/mitchellh/go-wordwrap"
	terminal "golang.org/x/term"
)

// OptionType is an enum for representing the type of an option.
type OptionType int

// Constants representing different OptionType enumerated values.
// Note that there intentionally aren't separate types for int, comma-separated
// list, regex, etc. From the perspective of the CLI or an option file, these
// are all strings; callers may *process* a string value as a different Golang
// type at runtime using Config.GetInt, Config.GetSlice, etc.
const (
	OptionTypeString OptionType = iota // String-valued option
	OptionTypeBool                     // Boolean-valued option
)

// Option represents a flag/setting for a Command. Any Option present for a
// parent Command will automatically be available to all of its descendent
// subcommands, although subcommands may choose to override the exact semantics
// by providing another conflicting Option of same Name.
type Option struct {
	Name         string
	Shorthand    rune
	Type         OptionType
	Default      string
	Description  string
	RequireValue bool
	HiddenOnCLI  bool
	Group        string // Used in help information
}

// StringOption creates a string-type Option. By default, string options require
// a value, though this can be overridden via ValueOptional().
func StringOption(long string, short rune, defaultValue string, description string) *Option {
	return &Option{
		Name:         strings.Replace(long, "_", "-", -1),
		Shorthand:    short,
		Type:         OptionTypeString,
		Default:      defaultValue,
		Description:  description,
		RequireValue: true,
	}
}

// BoolOption creates a boolean-type Option. By default, boolean options do not
// require a value, though this can be overridden via ValueRequired().
func BoolOption(long string, short rune, defaultValue bool, description string) *Option {
	var defaultAsStr string
	if defaultValue {
		defaultAsStr = "1"
	} else {
		defaultAsStr = ""
	}
	return &Option{
		Name:         strings.Replace(long, "_", "-", -1),
		Shorthand:    short,
		Type:         OptionTypeBool,
		Default:      defaultAsStr,
		Description:  description,
		RequireValue: false,
	}
}

// Hidden prevents an Option from being displayed in a Command's help/usage
// text.
func (opt *Option) Hidden() *Option {
	opt.HiddenOnCLI = true
	return opt
}

// ValueRequired marks an Option as needing a value, so it will be an error if
// the option is supplied alone without any corresponding value.
func (opt *Option) ValueRequired() *Option {
	if opt.Type == OptionTypeBool {
		panic(fmt.Errorf("Option %s: boolean options cannot have required value", opt.Name))
	}
	opt.RequireValue = true
	return opt
}

// ValueOptional marks an Option as not needing a value, allowing the Option to
// appear without any value associated.
func (opt *Option) ValueOptional() *Option {
	opt.RequireValue = false
	return opt
}

// Usage displays one-line help information on the Option.
func (opt *Option) Usage(maxNameLength int) string {
	if opt.HiddenOnCLI {
		return ""
	}

	lineLen := 10000
	stdinFd := int(os.Stderr.Fd())
	if terminal.IsTerminal(stdinFd) {
		lineLen, _, _ = terminal.GetSize(stdinFd)
		if lineLen < 80 {
			lineLen = 80
		}
		// Avoid extra blank lines on Windows when output matches full line length
		if runtime.GOOS == "windows" {
			lineLen--
		}
	}

	var shorthand string
	if opt.Shorthand > 0 {
		shorthand = fmt.Sprintf("-%c,", opt.Shorthand)
	}
	head := fmt.Sprintf("  %3s --%*s  ", shorthand, -1*maxNameLength, opt.usageName())
	desc := fmt.Sprintf("%s%s", opt.Description, opt.DefaultUsage())
	if len(desc)+len(head) > lineLen {
		desc = wordwrap.WrapString(desc, uint(lineLen-len(head)))
		spacer := fmt.Sprintf("\n%s", strings.Repeat(" ", len(head)))
		desc = strings.Replace(desc, "\n", spacer, -1)
	}
	return fmt.Sprintf("%s%s\n", head, desc)
}

// DefaultUsage returns usage information relating to the Option's default
// value.
func (opt *Option) DefaultUsage() string {
	if opt.HiddenOnCLI || !opt.HasNonzeroDefault() {
		return ""
	} else if opt.Type == OptionTypeBool {
		return fmt.Sprintf(" (enabled by default; disable with --skip-%s)", opt.Name)
	}
	return fmt.Sprintf(" (default %s)", opt.PrintableDefault())
}

// usageName returns the option's name, potentially modified/annotated for
// display on help screen.
func (opt *Option) usageName() string {
	if opt.HiddenOnCLI {
		return ""
	} else if opt.Type == OptionTypeBool {
		if opt.HasNonzeroDefault() {
			return fmt.Sprintf("[skip-]%s", opt.Name)
		}
		return opt.Name
	} else if opt.RequireValue {
		return fmt.Sprintf("%s value", opt.Name)
	}
	return fmt.Sprintf("%s[=value]", opt.Name)
}

// HasNonzeroDefault returns true if the Option's default value differs from
// its type's zero/empty value.
func (opt *Option) HasNonzeroDefault() bool {
	switch opt.Type {
	case OptionTypeString:
		return opt.Default != ""
	case OptionTypeBool:
		return BoolValue(opt.Default)
	default:
		return false
	}
}

// PrintableDefault returns a human-friendly version of the Option's default
// value.
func (opt *Option) PrintableDefault() string {
	switch opt.Type {
	case OptionTypeBool:
		if BoolValue(opt.Default) {
			return "true"
		}
		return "false"
	default:
		return fmt.Sprintf(`"%s"`, opt.Default)
	}
}

// OptionGroup is a group of related Options, used in generation of usage
// instructions for a Command.
type OptionGroup struct {
	Name    string
	Options []*Option
}

func newOptionGroup(group string, options []*Option) *OptionGroup {
	grp := &OptionGroup{Name: group}
	lookup := make(map[string]*Option, len(options))
	names := make([]string, 0, len(options))
	for _, opt := range options {
		lookup[opt.Name] = opt
		names = append(names, opt.Name)
	}
	sort.Strings(names)
	for _, name := range names {
		grp.Options = append(grp.Options, lookup[name])
	}
	return grp
}

// NormalizeOptionToken takes a string of form "foo=bar" or just "foo", and
// parses it into separate key and value. It also returns whether the arg
// included a value (to tell "" vs no-value) and whether it had a "loose-"
// prefix, meaning that the calling parser shouldn't return an error if the key
// does not correspond to any existing option.
func NormalizeOptionToken(arg string) (key, value string, hasValue, loose bool) {
	tokens := strings.SplitN(arg, "=", 2)
	key = strings.TrimFunc(tokens[0], unicode.IsSpace)
	if key == "" {
		return
	}
	key = strings.ToLower(key)
	key = strings.Replace(key, "_", "-", -1)

	if strings.HasPrefix(key, "loose-") {
		key = key[6:]
		loose = true
	}

	var negated bool
	if strings.HasPrefix(key, "skip-") {
		key = key[5:]
		negated = true
	} else if strings.HasPrefix(key, "disable-") {
		key = key[8:]
		negated = true
	} else if strings.HasPrefix(key, "enable-") {
		key = key[7:]
	}

	if len(tokens) > 1 {
		hasValue = true
		value = strings.TrimFunc(tokens[1], unicode.IsSpace)
		// negated and value supplied: set to falsey value of "" UNLESS the value is
		// also falsey, in which case we have a double-negative, meaning enable
		if negated {
			if BoolValue(value) {
				value = ""
			} else {
				value = "1"
			}
		}
	} else if negated {
		// No value supplied and negated: set to falsey value of ""
		value = ""

		// But negation still satisfies "having a value" for RequireValue options
		hasValue = true
	}
	return
}

// BoolValue converts the supplied option value string to a boolean.
// The case-insensitive values "", "off", "false", and "0" are considered false;
// all other values are considered true.
func BoolValue(input string) bool {
	switch strings.ToLower(input) {
	case "", "off", "false", "0":
		return false
	default:
		return true
	}
}

// NormalizeOptionName is a convenience function that only returns the "key"
// portion of NormalizeOptionToken.
func NormalizeOptionName(name string) string {
	ret, _, _, _ := NormalizeOptionToken(name)
	return ret
}

// OptionNotDefinedError is an error returned when an unknown Option is used.
type OptionNotDefinedError struct {
	Name   string
	Source string
}

// Error satisfies golang's error interface.
func (ond OptionNotDefinedError) Error() string {
	var source string
	if ond.Source != "" {
		source = fmt.Sprintf("%s: ", ond.Source)
	}
	return fmt.Sprintf("%sUnknown option \"%s\"", source, ond.Name)
}

// OptionMissingValueError is an error returned when an Option requires a value,
// but no value was supplied.
type OptionMissingValueError struct {
	Name   string
	Source string
}

// Error satisfies golang's error interface.
func (omv OptionMissingValueError) Error() string {
	var source string
	if omv.Source != "" {
		source = fmt.Sprintf("%s: ", omv.Source)
	}
	return fmt.Sprintf("%sMissing required value for option %s", source, omv.Name)
}