*: parsing a spec to a Hierarchy struct

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

hierarchy.go

@@ -0,0 +1,65 @@
+package mtree
+
+import (
+	"fmt"
+	"io"
+	"sort"
+	"strings"
+)
+
+// DirectoryHierarchy is the mapped structure for an mtree directory hierarchy
+// spec
+type DirectoryHierarchy struct {
+	Entries []Entry
+}
+
+// WriteTo simplifies the output of the resulting hierarchy spec
+func (dh DirectoryHierarchy) WriteTo(w io.Writer) (n int64, err error) {
+	sort.Sort(byPos(dh.Entries))
+	var sum int64
+	for _, e := range dh.Entries {
+		i, err := io.WriteString(w, e.String()+"\n")
+		if err != nil {
+			return sum, err
+		}
+		sum += int64(i)
+	}
+	return sum, nil
+}
+
+type byPos []Entry
+
+func (bp byPos) Len() int           { return len(bp) }
+func (bp byPos) Less(i, j int) bool { return bp[i].Pos < bp[j].Pos }
+func (bp byPos) Swap(i, j int)      { bp[i], bp[j] = bp[j], bp[i] }
+
+// Entry is each component of content in the mtree spec file
+type Entry struct {
+	Pos      int      // order in the spec
+	Raw      string   // file or directory name
+	Name     string   // file or directory name
+	Keywords []string // TODO(vbatts) maybe a keyword typed set of values?
+	Type     EntryType
+}
+
+func (e Entry) String() string {
+	if e.Raw != "" {
+		return e.Raw
+	}
+	// TODO(vbatts) if type is RelativeType and a keyword of not type=dir
+	return fmt.Sprintf("%s %s", e.Name, strings.Join(e.Keywords, " "))
+}
+
+// EntryType are the formats of lines in an mtree spec file
+type EntryType int
+
+// The types of lines to be found in an mtree spec file
+const (
+	SignatureType EntryType = iota // first line of the file, like `#mtree v2.0`
+	BlankType                      // blank lines are ignored
+	CommentType                    // Lines beginning with `#` are ignored
+	SpecialType                    // line that has `/` prefix issue a "special" command (currently only /set and /unset)
+	RelativeType                   // if the first white-space delimited word does not have a '/' in it. Options/keywords are applied.
+	DotDotType                     // .. - A relative path step. keywords/options are ignored
+	FullType                       // if the first word on the line has a `/` after the first character, it interpretted as a file pathname with options
+)