box-o-sand/farse/farse.go

package farse

import "fmt"

type TokenType int

const (
	TokenLongFlag TokenType = iota
	TokenShortFlag
	TokenShortCompoundFlag
	TokenIdentifier
	TokenArgument
	TokenInvalid
	TokenSentinel
)

func (t TokenType) String() string {
	switch t {
	case TokenLongFlag:
		return "long flag"
	case TokenShortFlag:
		return "short flag"
	case TokenShortCompoundFlag:
		return "short compound"
	case TokenIdentifier:
		return "identifier"
	case TokenArgument:
		return "argument"
	case TokenInvalid:
		return "invalid"
	case TokenSentinel:
		return "sentinel"
	}
	return "(x___x)"
}

type Token struct {
	Value string
	Type  TokenType
}

type Farse struct {
	known map[string]TokenType
}

func New() *Farse {
	return &Farse{
		known: map[string]TokenType{},
	}
}

func (fl *Farse) Known() map[string]TokenType {
	return fl.known
}

func (fl *Farse) AddKnown(knownStrings ...string) error {
	for i, tok := range scan(knownStrings) {
		if tok.Type == TokenShortCompoundFlag {
			return fmt.Errorf("argument %d %q is invalid value for known identifier", i, tok.Value)
		}

		if len(tok.Value) == 0 {
			return fmt.Errorf("argument %d is empty", i)
		}

		if len(tok.Value) == 1 && tok.Value == "-" {
			return fmt.Errorf("argument %d %q is invalid value for known identifier", i, tok.Value)
		}

		if _, exists := fl.known[tok.Value]; exists {
			return fmt.Errorf("argument %d %s conflicts with known", i, tok.Value)
		}

		fl.known[tok.Value] = tok.Type
	}

	return nil
}

func (fl *Farse) Scan(args []string) []*Token {
	ret := []*Token{}
	passedSentinel := false

	for _, tok := range scan(args) {
		if tok.Type == TokenSentinel {
			ret = append(ret, tok)
			passedSentinel = true
			continue
		}

		if passedSentinel {
			tok.Type = TokenArgument
			ret = append(ret, tok)
			continue
		}

		if tok.Type == TokenShortCompoundFlag {
			ret = append(ret, fl.extractCompoundTokens(tok.Value)...)
			continue
		}

		if tok.Type == TokenIdentifier {
			if _, known := fl.known[tok.Value]; !known {
				tok.Type = TokenArgument
			}
			ret = append(ret, tok)
		}
	}

	return ret
}

func (fl *Farse) extractCompoundTokens(s string) []*Token {
	ret := []*Token{}

	for j, ch := range s {
		last := j == (len(s) - 1)

		if j == 0 && ch == '-' {
			continue
		}

		sf := string(append([]rune("-"), ch))

		if _, known := fl.known[sf]; known {
			ret = append(ret, &Token{Value: sf, Type: TokenShortFlag})

			if last {
				return ret
			}

			if _, nextKnown := fl.known[string(append([]rune("-"), rune(s[j+1])))]; !nextKnown {
				ret = append(ret, &Token{Value: s[j+1:], Type: TokenArgument})
				return ret
			}

		}
	}

	return ret
}

func scan(sl []string) []*Token {
	ret := []*Token{}

	for _, s := range sl {
		tok := scanToken(s)
		if tok != nil {
			ret = append(ret, tok)
		}
	}

	return ret
}

func scanToken(s string) *Token {
	switch len(s) {
	case 0, 1:
		return &Token{Value: s, Type: TokenIdentifier}
	case 2:
		if s == "--" {
			return &Token{Value: s, Type: TokenSentinel}
		}

		if s[0] == '-' {
			return &Token{Value: s, Type: TokenShortFlag}
		}
	default:
		if s[0] == '-' {
			if s[1] != '-' {
				return &Token{Value: s, Type: TokenShortCompoundFlag}
			}

			return &Token{Value: s, Type: TokenLongFlag}
		}

		return &Token{Value: s, Type: TokenIdentifier}
	}

	return nil
}