1 files changed, 234 insertions, 0 deletions
diff --git a/v2/opts.go b/v2/opts.go
new file mode 100644
index 0000000..314acd8
--- /dev/null
+++ b/v2/opts.go
@@ -0,0 +1,234 @@
+// Package opts implements unicode-aware getopt(3)- and getopt_long(3)
+// flag parsing.
+//
+// The opts package aims to provide as simple an API as possible.  If
+// your usecase requires more advanced argument-parsing or a more robust
+// API, this may not be the ideal package for you.
+//
+// While the opts package aims to closely follow the POSIX getopt(3) and
+// GNU getopt_long(3) C functions, there are some notable differences.
+// This package properly supports unicode flags, but also does not
+// support a leading ‘:’ in the [Get] function’s option string; all
+// user-facing I/O is delegrated to the caller.
+package opts
+
+import (
+	"slices"
+	"strings"
+)
+
+// ArgMode represents whether or not a long-option takes an argument.
+type ArgMode int
+
+// These tokens can be used to specify whether or not a long-option takes
+// an argument.
+const (
+	None     ArgMode = iota // long opt takes no argument
+	Required                // long opt takes an argument
+	Optional                // long opt optionally takes an argument
+)
+
+// Flag represents a parsed command-line flag.  Key corresponds to the
+// rune that was passed on the command-line, and Value corresponds to the
+// flags argument if one was provided.  In the case of long-options Key
+// will map to the corresponding short-code, even if a long-option was
+// used.
+type Flag struct {
+	Key   rune   // the flag that was passed
+	Value string // the flags argument
+}
+
+// LongOpt represents a long-option to attempt to parse.  All long
+// options have a short-hand form represented by Short and a long-form
+// represented by Long.  Arg is used to represent whether or not the
+// long-option takes an argument.
+//
+// In the case that you want to parse a long-option which doesn’t have a
+// short-hand form, you can set Short to a negative integer.
+type LongOpt struct {
+	Short rune
+	Long  string
+	Arg   ArgMode
+}
+
+// Get parses the command-line arguments in args according to optstr.
+// Unlike POSIX-getopt(3), a leading ‘:’ in optstr is not supported and
+// will be ignored and no I/O is ever performed.
+//
+// Get will look for the flags listed in optstr (i.e., it will look for
+// ‘-a’, ‘-ß’, and ‘λ’ given optstr == "aßλ").  The optstr need not be
+// sorted in any particular order.  If an option takes a required
+// argument, it can be suffixed by a colon.  If an option takes an
+// optional argument, it can be suffixed by two colons.  As an example,
+// optstr == "a::ßλ:" will search for ‘-a’ with an optional argument,
+// ‘-ß’ with no argument, and ‘-λ’ with a required argument.
+//
+// A successful parse returns the flags in the flags slice and a slice of
+// the remaining non-option arguments in rest.  In the case of failure,
+// err will be one of [BadOptionError] or [NoArgumentError].
+func Get(args []string, optstr string) (flags []Flag, rest []string, err error) {
+	if len(args) == 0 {
+		return
+	}
+
+	optrs := []rune(optstr)
+	var i int
+	for i = 1; i < len(args); i++ {
+		arg := args[i]
+		if len(arg) == 0 || arg == "-" || arg[0] != '-' {
+			break
+		} else if arg == "--" {
+			i++
+			break
+		}
+
+		rs := []rune(arg[1:])
+		for j, r := range rs {
+			k := slices.Index(optrs, r)
+			if k == -1 {
+				return nil, nil, BadOptionError{r: r}
+			}
+
+			var s string
+			switch am := colonsToArgMode(optrs[k+1:]); {
+			case am != None && j < len(rs)-1:
+				s = string(rs[j+1:])
+			case am == Required:
+				i++
+				if i >= len(args) {
+					return nil, nil, NoArgumentError{r: r}
+				}
+				s = args[i]
+			default:
+				flags = append(flags, Flag{Key: r})
+				continue
+			}
+
+			flags = append(flags, Flag{r, s})
+			break
+		}
+	}
+
+	return flags, args[i:], nil
+}
+
+// GetLong parses the command-line arguments in args according to opts.
+//
+// This function is identical to [Get] except it parses according to a
+// [LongOpt] slice instead of an opt-string, and it parses long-options.
+// When parsing, GetLong will also accept incomplete long-options if they
+// are unambiguous.  For example, given the following definition of opts:
+//
+//	opts := []LongOpt{
+//		{Short: 'a', Long: "add", Arg: None},
+//		{Short: 'd', Long: "delete", Arg: None},
+//		{Short: 'D', Long: "defer", Arg: None},
+//	}
+//
+// The options ‘--a’ and ‘--ad’ will parse as ‘--add’.  The option ‘--de’
+// will not parse however as it is ambiguous.
+func GetLong(args []string, opts []LongOpt) (flags []Flag, rest []string, err error) {
+	if len(args) == 0 {
+		return
+	}
+
+	var i int
+	for i = 1; i < len(args); i++ {
+		arg := args[i]
+		if len(arg) == 0 || arg == "-" || arg[0] != '-' {
+			break
+		} else if arg == "--" {
+			i++
+			break
+		}
+
+		if strings.HasPrefix(arg, "--") {
+			arg = arg[2:]
+
+			n := arg
+			j := strings.IndexByte(n, '=')
+			if j != -1 {
+				n = arg[:j]
+			}
+
+			var s string
+			o, ok := optStruct(opts, n)
+
+			switch {
+			case !ok:
+				return nil, nil, BadOptionError{s: n}
+			case o.Arg != None && j != -1:
+				s = arg[j+1:]
+			case o.Arg == Required:
+				i++
+				if i >= len(args) {
+					return nil, nil, NoArgumentError{s: n}
+				}
+				s = args[i]
+			}
+
+			flags = append(flags, Flag{Key: o.Short, Value: s})
+		} else {
+			rs := []rune(arg[1:])
+			for j, r := range rs {
+				var s string
+
+				switch am, ok := getModeRune(opts, r); {
+				case !ok:
+					return nil, nil, BadOptionError{r: r}
+				case am != None && j < len(rs)-1:
+					s = string(rs[j+1:])
+				case am == Required:
+					i++
+					if i >= len(args) {
+						return nil, nil, NoArgumentError{r: r}
+					}
+					s = args[i]
+				default:
+					flags = append(flags, Flag{Key: r})
+					continue
+				}
+
+				flags = append(flags, Flag{r, s})
+				break
+			}
+		}
+	}
+
+	return flags, args[i:], nil
+}
+
+func getModeRune(os []LongOpt, r rune) (ArgMode, bool) {
+	for _, o := range os {
+		if o.Short == r {
+			return o.Arg, true
+		}
+	}
+	return 0, false
+}
+
+func optStruct(os []LongOpt, s string) (LongOpt, bool) {
+	i := -1
+	for j, o := range os {
+		if strings.HasPrefix(o.Long, s) {
+			if i != -1 {
+				return LongOpt{}, false
+			}
+			i = j
+		}
+	}
+	if i == -1 {
+		return LongOpt{}, false
+	}
+	return os[i], true
+}
+
+func colonsToArgMode(rs []rune) ArgMode {
+	if len(rs) >= 2 && rs[0] == ':' && rs[1] == ':' {
+		return Optional
+	}
+	if len(rs) >= 1 && rs[0] == ':' {
+		return Required
+	}
+	return None
+}