Emit events (#11)

* Add event to protocol.

* Revert ids to strings until other stuff is merged into master.

* Add $event vertices for project and documents.

* Remove todo note.

* Collapse arg types.

export/exporter.go

@@ -75,6 +75,11 @@ func (e *exporter) export(info protocol.ToolInfo) error {
 		return fmt.Errorf(`emit "project": %v`, err)
 	}
 
+	_, err = e.emitBeginEvent("project", proID)
+	if err != nil {
+		return fmt.Errorf(`emit "begin": %v`, err)
+	}
+
 	for _, p := range e.pkgs {
 		if err := e.exportPkg(p, proID); err != nil {
 			return fmt.Errorf("export package %q: %v", p.Name, err)
@@ -114,6 +119,11 @@ func (e *exporter) export(info protocol.ToolInfo) error {
 		}
 	}
 
+	_, err = e.emitEndEvent("project", proID)
+	if err != nil {
+		return fmt.Errorf(`emit "end": %v`, err)
+	}
+
 	return nil
 }
 
@@ -133,6 +143,11 @@ func (e *exporter) exportPkg(p *packages.Package, proID string) (err error) {
 				return fmt.Errorf(`emit "document": %v`, err)
 			}
 
+			_, err = e.emitBeginEvent("document", docID)
+			if err != nil {
+				return fmt.Errorf(`emit "begin": %v`, err)
+			}
+
 			_, err = e.emitContains(proID, []string{docID})
 			if err != nil {
 				return fmt.Errorf(`emit "contains": %v`, err)
@@ -151,6 +166,13 @@ func (e *exporter) exportPkg(p *packages.Package, proID string) (err error) {
 		}
 	}
 
+	for _, info := range e.files {
+		_, err = e.emitEndEvent("document", info.docID)
+		if err != nil {
+			return fmt.Errorf(`emit "end": %v`, err)
+		}
+	}
+
 	return nil
 }
 
@@ -431,6 +453,16 @@ func (e *exporter) emitMetaData(root string, info protocol.ToolInfo) (string, er
 	return id, e.emit(protocol.NewMetaData(id, root, info))
 }
 
+func (e *exporter) emitBeginEvent(scope string, data string) (string, error) {
+	id := e.nextID()
+	return id, e.emit(protocol.NewEvent(id, "begin", scope, data))
+}
+
+func (e *exporter) emitEndEvent(scope string, data string) (string, error) {
+	id := e.nextID()
+	return id, e.emit(protocol.NewEvent(id, "end", scope, data))
+}
+
 func (e *exporter) emitProject() (string, error) {
 	id := e.nextID()
 	return id, e.emit(protocol.NewProject(id))

protocol/protocol.go

@@ -110,6 +110,35 @@ func NewMetaData(id, root string, info ToolInfo) *MetaData {
 	}
 }
 
+// Event is optional metadata emitted to give hints to consumers about
+// the beginning and ending of new "socpes" (e.g. a project or document).
+type Event struct {
+	Vertex
+	// The kind of event (begin or end).
+	Kind string `json:"kind"`
+	// The type of element this event describes (project or document).
+	Scope string `json:"scope"`
+	// The identifier of the data beginning or ending.
+	Data string `json:"data"`
+}
+
+// NewEvent returns a new Event object with the given ID, kind, scope,
+// and data information.
+func NewEvent(id, kind, scope, data string) *Event {
+	return &Event{
+		Vertex: Vertex{
+			Element: Element{
+				ID:   id,
+				Type: ElementVertex,
+			},
+			Label: VertexEvent,
+		},
+		Kind:  kind,
+		Scope: scope,
+		Data:  data,
+	}
+}
+
 // Project declares the language of the dump.
 type Project struct {
 	Vertex