Break the fs package up into smaller parts.

The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.

The new code layout is documented in CONTRIBUTING.

fs/direntries.go

@@ -0,0 +1,81 @@
+package fs
+
+import "fmt"
+
+// DirEntries is a slice of Object or *Dir
+type DirEntries []DirEntry
+
+// Len is part of sort.Interface.
+func (ds DirEntries) Len() int {
+	return len(ds)
+}
+
+// Swap is part of sort.Interface.
+func (ds DirEntries) Swap(i, j int) {
+	ds[i], ds[j] = ds[j], ds[i]
+}
+
+// Less is part of sort.Interface.
+func (ds DirEntries) Less(i, j int) bool {
+	return ds[i].Remote() < ds[j].Remote()
+}
+
+// ForObject runs the function supplied on every object in the entries
+func (ds DirEntries) ForObject(fn func(o Object)) {
+	for _, entry := range ds {
+		o, ok := entry.(Object)
+		if ok {
+			fn(o)
+		}
+	}
+}
+
+// ForObjectError runs the function supplied on every object in the entries
+func (ds DirEntries) ForObjectError(fn func(o Object) error) error {
+	for _, entry := range ds {
+		o, ok := entry.(Object)
+		if ok {
+			err := fn(o)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// ForDir runs the function supplied on every Directory in the entries
+func (ds DirEntries) ForDir(fn func(dir Directory)) {
+	for _, entry := range ds {
+		dir, ok := entry.(Directory)
+		if ok {
+			fn(dir)
+		}
+	}
+}
+
+// ForDirError runs the function supplied on every Directory in the entries
+func (ds DirEntries) ForDirError(fn func(dir Directory) error) error {
+	for _, entry := range ds {
+		dir, ok := entry.(Directory)
+		if ok {
+			err := fn(dir)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// DirEntryType returns a string description of the DirEntry, either
+// "object", "directory" or "unknown type XXX"
+func DirEntryType(d DirEntry) string {
+	switch d.(type) {
+	case Object:
+		return "object"
+	case Directory:
+		return "directory"
+	}
+	return fmt.Sprintf("unknown type %T", d)
+}