tag.go

package kong

import (
	"errors"
	"fmt"
	"reflect"
	"strconv"
	"strings"
	"unicode/utf8"
)

// Tag represents the parsed state of Kong tags in a struct field tag.
type Tag struct {
	Ignored     bool // Field is ignored by Kong. ie. kong:"-"
	Cmd         bool
	Arg         bool
	Required    bool
	Optional    bool
	Name        string
	Help        string
	Type        string
	Default     string
	Format      string
	PlaceHolder string
	Env         string
	Short       rune
	Hidden      bool
	Sep         rune
	MapSep      rune
	Enum        string
	Group       string
	Xor         []string
	Vars        Vars
	Prefix      string // Optional prefix on anonymous structs. All sub-flags will have this prefix.
	EnvPrefix   string
	Embed       bool
	Aliases     []string
	Negatable   bool
	Passthrough bool

	// Storage for all tag keys for arbitrary lookups.
	items map[string][]string
}

type tagChars struct {
	sep, quote, assign rune
}

var kongChars = tagChars{sep: ',', quote: '\'', assign: '='}
var bareChars = tagChars{sep: ' ', quote: '"', assign: ':'}

func parseTagItems(tagString string, chr tagChars) (map[string][]string, error) {
	d := map[string][]string{}
	key := []rune{}
	value := []rune{}
	quotes := false
	inKey := true

	add := func() {
		d[string(key)] = append(d[string(key)], string(value))
		key = []rune{}
		value = []rune{}
		inKey = true
	}

	runes := []rune(tagString)
	for idx := 0; idx < len(runes); idx++ {
		r := runes[idx]
		next := rune(0)
		eof := false
		if idx < len(runes)-1 {
			next = runes[idx+1]
		} else {
			eof = true
		}
		if !quotes && r == chr.sep {
			add()
			continue
		}
		if r == chr.assign && inKey {
			inKey = false
			continue
		}
		if r == '\\' {
			if next == chr.quote {
				idx++
				r = chr.quote
			}
		} else if r == chr.quote {
			if quotes {
				quotes = false
				if next == chr.sep || eof {
					continue
				}
				return nil, fmt.Errorf("%v has an unexpected char at pos %v", tagString, idx)
			}
			quotes = true
			continue
		}
		if inKey {
			key = append(key, r)
		} else {
			value = append(value, r)
		}
	}
	if quotes {
		return nil, fmt.Errorf("%v is not quoted properly", tagString)
	}

	add()

	return d, nil
}

func getTagInfo(ft reflect.StructField) (string, tagChars) {
	s, ok := ft.Tag.Lookup("kong")
	if ok {
		return s, kongChars
	}

	return string(ft.Tag), bareChars
}

func newEmptyTag() *Tag {
	return &Tag{items: map[string][]string{}}
}

func tagSplitFn(r rune) bool {
	return r == ',' || r == ' '
}

func parseTagString(s string) (*Tag, error) {
	items, err := parseTagItems(s, bareChars)
	if err != nil {
		return nil, err
	}
	t := &Tag{
		items: items,
	}
	err = hydrateTag(t, "", false)
	if err != nil {
		return nil, fmt.Errorf("%s: %s", s, err)
	}
	return t, nil
}

func parseTag(parent reflect.Value, ft reflect.StructField) (*Tag, error) {
	if ft.Tag.Get("kong") == "-" {
		t := newEmptyTag()
		t.Ignored = true
		return t, nil
	}
	items, err := parseTagItems(getTagInfo(ft))
	if err != nil {
		return nil, err
	}
	t := &Tag{
		items: items,
	}
	err = hydrateTag(t, ft.Type.Name(), ft.Type.Kind() == reflect.Bool)
	if err != nil {
		return nil, failField(parent, ft, "%s", err)
	}
	return t, nil
}

func hydrateTag(t *Tag, typeName string, isBool bool) error {
	var err error
	t.Cmd = t.Has("cmd")
	t.Arg = t.Has("arg")
	required := t.Has("required")
	optional := t.Has("optional")
	if required && optional {
		return fmt.Errorf("can't specify both required and optional")
	}
	t.Required = required
	t.Optional = optional
	t.Default = t.Get("default")
	// Arguments with defaults are always optional.
	if t.Arg && t.Default != "" {
		t.Optional = true
	}
	t.Name = t.Get("name")
	t.Help = t.Get("help")
	t.Type = t.Get("type")
	t.Env = t.Get("env")
	t.Short, err = t.GetRune("short")
	if err != nil && t.Get("short") != "" {
		return fmt.Errorf("invalid short flag name %q: %s", t.Get("short"), err)
	}
	t.Hidden = t.Has("hidden")
	t.Format = t.Get("format")
	t.Sep, _ = t.GetSep("sep", ',')
	t.MapSep, _ = t.GetSep("mapsep", ';')
	t.Group = t.Get("group")
	for _, xor := range t.GetAll("xor") {
		t.Xor = append(t.Xor, strings.FieldsFunc(xor, tagSplitFn)...)
	}
	t.Prefix = t.Get("prefix")
	t.EnvPrefix = t.Get("envprefix")
	t.Embed = t.Has("embed")
	negatable := t.Has("negatable")
	if negatable && !isBool {
		return fmt.Errorf("negatable can only be set on booleans")
	}
	t.Negatable = negatable
	aliases := t.Get("aliases")
	if len(aliases) > 0 {
		t.Aliases = append(t.Aliases, strings.FieldsFunc(aliases, tagSplitFn)...)
	}
	t.Vars = Vars{}
	for _, set := range t.GetAll("set") {
		parts := strings.SplitN(set, "=", 2)
		if len(parts) == 0 {
			return fmt.Errorf("set should be in the form key=value but got %q", set)
		}
		t.Vars[parts[0]] = parts[1]
	}
	t.PlaceHolder = t.Get("placeholder")
	if t.PlaceHolder == "" {
		t.PlaceHolder = strings.ToUpper(dashedString(typeName))
	}
	t.Enum = t.Get("enum")
	if t.Enum != "" && !(t.Required || t.Default != "") {
		return fmt.Errorf("enum value is only valid if it is either required or has a valid default value")
	}
	passthrough := t.Has("passthrough")
	if passthrough && !t.Arg {
		return fmt.Errorf("passthrough only makes sense for positional arguments")
	}
	t.Passthrough = passthrough
	return nil
}

// Has returns true if the tag contained the given key.
func (t *Tag) Has(k string) bool {
	_, ok := t.items[k]
	return ok
}

// Get returns the value of the given tag.
//
// Note that this will return the empty string if the tag is missing.
func (t *Tag) Get(k string) string {
	values := t.items[k]
	if len(values) == 0 {
		return ""
	}
	return values[0]
}

// GetAll returns all encountered values for a tag, in the case of multiple occurrences.
func (t *Tag) GetAll(k string) []string {
	return t.items[k]
}

// GetBool returns true if the given tag looks like a boolean truth string.
func (t *Tag) GetBool(k string) (bool, error) {
	return strconv.ParseBool(t.Get(k))
}

// GetFloat parses the given tag as a float64.
func (t *Tag) GetFloat(k string) (float64, error) {
	return strconv.ParseFloat(t.Get(k), 64)
}

// GetInt parses the given tag as an int64.
func (t *Tag) GetInt(k string) (int64, error) {
	return strconv.ParseInt(t.Get(k), 10, 64)
}

// GetRune parses the given tag as a rune.
func (t *Tag) GetRune(k string) (rune, error) {
	value := t.Get(k)
	r, size := utf8.DecodeRuneInString(value)
	if r == utf8.RuneError || size < len(value) {
		return 0, errors.New("invalid rune")
	}
	return r, nil
}

// GetSep parses the given tag as a rune separator, allowing for a default or none.
// The separator is returned, or -1 if "none" is specified. If the tag value is an
// invalid utf8 sequence, the default rune is returned as well as an error. If the
// tag value is more than one rune, the first rune is returned as well as an error.
func (t *Tag) GetSep(k string, dflt rune) (rune, error) {
	tv := t.Get(k)
	if tv == "none" {
		return -1, nil
	} else if tv == "" {
		return dflt, nil
	}
	r, size := utf8.DecodeRuneInString(tv)
	if r == utf8.RuneError {
		return dflt, fmt.Errorf(`%v:"%v" has a rune error`, k, tv)
	} else if size != len(tv) {
		return r, fmt.Errorf(`%v:"%v" is more than a single rune`, k, tv)
	}
	return r, nil
}