Add filter, add READMES

backend_go/snapshot_service.go

@@ -0,0 +1,76 @@
+package main
+
+import (
+	"context"
+	"sync"
+)
+
+type snapshotKey struct {
+	NodeLimit      int
+	EdgeLimit      int
+	IncludeBNodes  bool
+	GraphQueryID   string
+}
+
+type snapshotInflight struct {
+	ready    chan struct{}
+	snapshot GraphResponse
+	err      error
+}
+
+type GraphSnapshotService struct {
+	sparql *AnzoGraphClient
+	cfg    Config
+
+	mu       sync.Mutex
+	cache    map[snapshotKey]GraphResponse
+	inflight map[snapshotKey]*snapshotInflight
+}
+
+func NewGraphSnapshotService(sparql *AnzoGraphClient, cfg Config) *GraphSnapshotService {
+	return &GraphSnapshotService{
+		sparql:    sparql,
+		cfg:      cfg,
+		cache:    make(map[snapshotKey]GraphResponse),
+		inflight: make(map[snapshotKey]*snapshotInflight),
+	}
+}
+
+func (s *GraphSnapshotService) Get(ctx context.Context, nodeLimit int, edgeLimit int, graphQueryID string) (GraphResponse, error) {
+	key := snapshotKey{NodeLimit: nodeLimit, EdgeLimit: edgeLimit, IncludeBNodes: s.cfg.IncludeBNodes, GraphQueryID: graphQueryID}
+
+	s.mu.Lock()
+	if snap, ok := s.cache[key]; ok {
+		s.mu.Unlock()
+		return snap, nil
+	}
+
+	if inf, ok := s.inflight[key]; ok {
+		ready := inf.ready
+		s.mu.Unlock()
+		select {
+		case <-ctx.Done():
+			return GraphResponse{}, ctx.Err()
+		case <-ready:
+			return inf.snapshot, inf.err
+		}
+	}
+
+	inf := &snapshotInflight{ready: make(chan struct{})}
+	s.inflight[key] = inf
+	s.mu.Unlock()
+
+	snap, err := fetchGraphSnapshot(ctx, s.sparql, s.cfg, nodeLimit, edgeLimit, graphQueryID)
+
+	s.mu.Lock()
+	inf.snapshot = snap
+	inf.err = err
+	delete(s.inflight, key)
+	if err == nil {
+		s.cache[key] = snap
+	}
+	close(inf.ready)
+	s.mu.Unlock()
+
+	return snap, err
+}