filelist: Add FileList type

This adds a new type, FileList, to manage another new type (File). File
contains the mapping of source --> dest for a file or directory.

internal/filelist/filelist.go

@@ -1,5 +1,57 @@
 package filelist
 
+import "sync"
+
 type FileLister interface {
-	List() ([]string, error)
+	List() (*FileList, error)
+}
+
+type File struct {
+	Source string
+	Dest   string
+}
+
+type FileList struct {
+	m map[string]string
+	sync.RWMutex
+}
+
+func NewFileList() *FileList {
+	return &FileList{
+		m: make(map[string]string),
+	}
+}
+
+func (f *FileList) Add(src string, dest string) {
+	f.Lock()
+	defer f.Unlock()
+
+	f.m[src] = dest
+}
+
+func (f *FileList) Get(src string) (string, bool) {
+	f.RLock()
+	defer f.RUnlock()
+
+	dest, found := f.m[src]
+	return dest, found
+}
+
+// iterate through the list and and send each one as a new File over the
+// returned channel
+func (f *FileList) IterItems() <-chan File {
+	ch := make(chan File)
+	go func() {
+		f.RLock()
+		defer f.RUnlock()
+
+		for src, dest := range f.m {
+			ch <- File{
+				Source: src,
+				Dest:   dest,
+			}
+		}
+		close(ch)
+	}()
+	return ch
 }