1 files changed, 134 insertions, 0 deletions
diff --git a/commands/parser.go b/commands/parser.go
new file mode 100644
index 00000000..e8146506
--- /dev/null
+++ b/commands/parser.go
@@ -0,0 +1,134 @@
+package commands
+
+import (
+	"strings"
+)
+
+type completionType int
+
+const (
+	NONE completionType = iota
+	COMMAND
+	OPERAND
+	SHORT_OPTION
+	OPTION_ARGUMENT
+)
+
+type parser struct {
+	tokens []string
+	optind int
+	spec   string
+	space  bool
+	kind   completionType
+	flag   string
+	arg    string
+	err    error
+}
+
+func newParser(cmd, spec string, spaceTerminated bool) (*parser, error) {
+	args, err := splitCmd(cmd)
+	if err != nil {
+		return nil, err
+	}
+
+	p := &parser{
+		tokens: args,
+		optind: 0,
+		spec:   spec,
+		space:  spaceTerminated,
+		kind:   NONE,
+		flag:   "",
+		arg:    "",
+		err:    nil,
+	}
+
+	state := command
+	for state != nil {
+		state = state(p)
+	}
+
+	return p, p.err
+}
+
+func (p *parser) empty() bool {
+	return len(p.tokens) == 0
+}
+
+func (p *parser) peek() string {
+	return p.tokens[0]
+}
+
+func (p *parser) advance() string {
+	if p.empty() {
+		return ""
+	}
+	tok := p.tokens[0]
+	p.tokens = p.tokens[1:]
+	p.optind++
+	return tok
+}
+
+func (p *parser) set(t completionType) {
+	p.kind = t
+}
+
+func (p *parser) hasArgument() bool {
+	n := len(p.flag)
+	if n > 0 {
+		s := string(p.flag[n-1]) + ":"
+		return strings.Contains(p.spec, s)
+	}
+	return false
+}
+
+type stateFn func(*parser) stateFn
+
+func command(p *parser) stateFn {
+	p.set(COMMAND)
+	p.advance()
+	return peek(p)
+}
+
+func peek(p *parser) stateFn {
+	if p.empty() {
+		if p.space {
+			return operand
+		}
+		return nil
+	}
+	if p.spec == "" {
+		return operand
+	}
+	s := p.peek()
+	switch {
+	case s == "--":
+		p.advance()
+	case strings.HasPrefix(s, "-"):
+		return short_option
+	}
+	return operand
+}
+
+func short_option(p *parser) stateFn {
+	p.set(SHORT_OPTION)
+	tok := p.advance()
+	p.flag = tok[1:]
+	if p.hasArgument() {
+		return option_argument
+	}
+	return peek(p)
+}
+
+func option_argument(p *parser) stateFn {
+	p.set(OPTION_ARGUMENT)
+	p.arg = p.advance()
+	if p.empty() && len(p.arg) == 0 {
+		return nil
+	}
+	return peek(p)
+}
+
+func operand(p *parser) stateFn {
+	p.set(OPERAND)
+	return nil
+}