Refactor the option parsing code to use methods on a struct

command.go

@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 
@@ -67,14 +68,10 @@ func (c *Command) Execute(args []string) {
 		args = args[1:]
 	}
 
-	restArgs, err := c.opts.Parse(args)
-	if err != nil {
-		c.ShowHelp()
-		return
-	}
-
-	restArgs, err = opts.Globals().Parse(restArgs)
+	parser := opts.NewParser(args, c.opts)
+	restArgs, err := parser.Parse()
 	if err != nil {
+		fmt.Printf("Option error: %s\n", err.Error())
 		c.ShowHelp()
 		return
 	}

opts/bool.go

@@ -1,6 +1,8 @@
 package opts
 
-import "strconv"
+import (
+	"strconv"
+)
 
 type BoolOption struct {
 	name        string

opts/parser.go

@@ -2,7 +2,6 @@ package opts
 
 import (
 	"errors"
-	"fmt"
 	"strings"
 )
 
@@ -11,133 +10,136 @@ var (
 	ErrCannotChainOption  = errors.New("cannot chain option as it takes an argument")
 )
 
-func (s Set) Parse(args []string) (restArgs []string, err error) {
-	for i := 0; i < len(args); i++ {
-		arg := args[i]
-
-		// Handle regular argument
-		if !strings.HasPrefix(arg, "-") {
-			restArgs = append(restArgs, arg)
-			continue
+type Parser struct {
+	opts Set
+	args []string
+	curr int
+}
+
+func NewParser(args []string, opts []Option) *Parser {
+	return &Parser{
+		opts: append(opts, globalOpts...),
+		args: args,
+		curr: -1,
+	}
+}
+
+func (p *Parser) Parse() (restArgs []string, err error) {
+	for p.hasNext() {
+		arg := p.next()
+
+		if !strings.HasPrefix(arg, "-") { // Regular argument
+			restArgs = append(restArgs, arg)
+		} else if arg == "--" { // Options terminator
+			restArgs = append(restArgs, p.restArgs()...)
+			return
+		} else if strings.HasPrefix(arg, "--") { // Long option
+			longName := arg[2:]
+			if err = p.parseLongOption(longName); err != nil {
+				return
+			}
+		} else { // Short option
+			shortNames := arg[1:]
+			if err = p.parseShortOption(shortNames); err != nil {
+				return
+			}
+		}
 	}
 
-		// Handle options terminator
-		if arg == "--" {
-			restArgs = append(restArgs, args[i+1:]...)
 	return
 }
 
-		// Handle long option
-		if strings.HasPrefix(arg, "--") {
-			longName := arg[2:]
+func (p *Parser) hasNext() bool {
+	return (p.curr + 1) < len(p.args)
+}
+
+func (p *Parser) next() string {
+	p.curr++
+
+	if p.curr >= len(p.args) {
+		return ""
+	}
+
+	return p.args[p.curr]
+}
+
+func (p *Parser) value() string {
+	p.curr++
+
+	if p.curr >= len(p.args) {
+		return ""
+	}
+
+	arg := p.args[p.curr]
+	return arg
+}
+
+func (p *Parser) restArgs() []string {
+	rest := p.args[p.curr+1:]
+	p.curr = len(p.args)
+
+	return rest
+}
+
+func (p *Parser) parseLongOption(longName string) error {
 	value := ""
 
 	equals := strings.Index(longName, "=")
-			if equals > 0 {
+	if equals >= 0 {
 		longName = longName[:equals]
 		value = longName[equals+1:]
-			} else if i < len(args)-1 && !strings.HasPrefix(args[i+1], "-") {
-				value = args[i+1]
-				i++
+	} else {
+		value = p.value()
 	}
 
-			parsed := false
-			for _, opt := range s {
-				if opt.Name() != longName {
-					continue
+	opt, ok := p.opts.GetByLongName(longName)
+	if ok {
+		if err := opt.Parse(value); err != nil {
+			return err
+		}
 	}
 
-				if err = opt.Parse(value); err != nil {
-					return
+	return nil
 }
 
-				parsed = true
-				break
-			}
-
-			if !parsed {
-				restArgs = append(restArgs, arg)
-			}
-
-			continue
-		}
-
-		// Handle short option
-		shortNames := arg[1:]
+func (p *Parser) parseShortOption(shortNames string) error {
 	if len(shortNames) == 0 {
-			err = ErrInvalidShortOption
+		return ErrInvalidShortOption
 	} else if len(shortNames) == 1 {
-			parsed := false
-			value := ""
-			if i < len(args)-1 && !strings.HasPrefix(args[i+1], "-") {
-				value = args[i+1]
-				i++
-			}
+		value := p.value()
 
-			for _, opt := range s {
-				if opt.ShortName() != shortNames {
-					continue
+		opt, ok := p.opts.GetByShortName(shortNames)
+		if ok {
+			if err := opt.Parse(value); err != nil {
+				return err
 			}
-
-				if err = opt.Parse(value); err != nil {
-					return
-				}
-
-				parsed = true
-				break
-			}
-
-			if !parsed {
-				restArgs = append(restArgs, arg)
 		}
 	} else {
 		for j := 0; j < len(shortNames); j++ {
 			shortName := shortNames[j]
 			value := ""
-				takesValue := false
-				parsed := false
-
-				for _, opt := range s {
-					if opt.ShortName() != string(shortName) {
-						continue
-					}
 
+			opt, ok := p.opts.GetByShortName(string(shortName))
+			if ok {
 				if opt.TakesArg() {
 					if j > 0 {
-							err = ErrCannotChainOption
-							return
+						return ErrCannotChainOption
 					}
 
-						takesValue = true
-						value = shortNames[j+1:]
+					value = shortNames[1:]
 					value = strings.TrimPrefix(value, "=")
-						if len(value) == 0 && i < len(args)-1 && !strings.HasPrefix(args[i+1], "-") {
-							value = args[i+1]
-							i++
+					if len(value) == 0 {
+						value = p.value()
 					}
 					j = len(shortNames)
 				}
 
-					parsed = true
-
-					if err = opt.Parse(value); err != nil {
-						return
-					}
-
-					break
-				}
-
-				if !parsed {
-					if takesValue {
-						restArgs = append(restArgs, arg)
-						break
-					} else {
-						restArgs = append(restArgs, fmt.Sprintf("-%c", shortName))
-					}
+				if err := opt.Parse(value); err != nil {
+					return err
 				}
 			}
 		}
 	}
 
-	return
+	return nil
 }

opts/set.go

@@ -33,6 +33,24 @@ func (s Set) Get(name string) (Option, bool) {
 	return nil, false
 }
 
+func (s Set) GetByLongName(longName string) (Option, bool) {
+	for _, o := range s {
+		if o.Name() == longName {
+			return o, true
+		}
+	}
+	return nil, false
+}
+
+func (s Set) GetByShortName(shortName string) (Option, bool) {
+	for _, o := range s {
+		if o.ShortName() == shortName {
+			return o, true
+		}
+	}
+	return nil, false
+}
+
 func (s Set) GetBool(name string) (*BoolOption, bool) {
 	o, ok := s.Get(name)
 	if !ok {