*: parsing a spec to a Hierarchy struct

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

parse.go

@@ -0,0 +1,77 @@
+package mtree
+
+import (
+	"bufio"
+	"io"
+	"strings"
+)
+
+func ParseSpec(r io.Reader) (*DirectoryHierarchy, error) {
+	s := bufio.NewScanner(r)
+	i := int(0)
+	dh := DirectoryHierarchy{}
+	for s.Scan() {
+		str := s.Text()
+		e := Entry{Pos: i}
+		switch {
+		case strings.HasPrefix(str, "#"):
+			e.Raw = str
+			if strings.HasPrefix(str, "#mtree") {
+				e.Type = SignatureType
+			} else {
+				e.Type = CommentType
+				// from here, the comment could be "# key: value" metadata
+				// or a relative path hint
+			}
+		case str == "":
+			e.Type = BlankType
+			// nothing else to do here
+		case strings.HasPrefix(str, "/"):
+			e.Type = SpecialType
+			// collapse any escaped newlines
+			for {
+				if strings.HasSuffix(str, `\`) {
+					str = str[:len(str)-1]
+					s.Scan()
+					str += s.Text()
+				} else {
+					break
+				}
+			}
+			// parse the options
+			f := strings.Fields(str)
+			e.Name = f[0]
+			e.Keywords = f[1:]
+		case len(strings.Fields(str)) > 0 && strings.Fields(str)[0] == "..":
+			e.Type = DotDotType
+			e.Raw = str
+			// nothing else to do here
+		case len(strings.Fields(str)) > 0:
+			// collapse any escaped newlines
+			for {
+				if strings.HasSuffix(str, `\`) {
+					str = str[:len(str)-1]
+					s.Scan()
+					str += s.Text()
+				} else {
+					break
+				}
+			}
+			// parse the options
+			f := strings.Fields(str)
+			if strings.Contains(str, "/") {
+				e.Type = FullType
+			} else {
+				e.Type = RelativeType
+			}
+			e.Name = f[0]
+			e.Keywords = f[1:]
+		default:
+			// TODO(vbatts) log a warning?
+			continue
+		}
+		dh.Entries = append(dh.Entries, e)
+		i++
+	}
+	return &dh, s.Err()
+}