From 60d72f489acd2891e5ac69f6483e2800de4f3d38 Mon Sep 17 00:00:00 2001
From: Tonko Sabolcec <tonko.sabolcec@memgraph.io>
Date: Thu, 9 May 2019 14:24:00 +0200
Subject: [PATCH] Add DumpGenerator class

Summary: DumpGenerator dumps parts of query to stream.

Reviewers: teon.banek

Reviewed By: teon.banek

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D2023
---
 src/database/single_node/dump.cpp | 51 +++++++++++++++--------------
 src/database/single_node/dump.hpp | 53 +++++++++++++++++++++++++++++--
 2 files changed, 77 insertions(+), 27 deletions(-)

diff --git a/src/database/single_node/dump.cpp b/src/database/single_node/dump.cpp
index ce3d13bb0..2c44414a8 100644
--- a/src/database/single_node/dump.cpp
+++ b/src/database/single_node/dump.cpp
@@ -80,13 +80,6 @@ void DumpVertex(std::ostream *os, GraphDbAccessor *dba,
   *os << ")";
 }
 
-void DumpVertices(std::ostream *os, GraphDbAccessor *dba) {
-  auto vertices = dba->Vertices(false);
-  utils::PrintIterable(
-      os, vertices.begin(), vertices.end(), ", ",
-      [&dba](auto &os, const auto &vertex) { DumpVertex(&os, dba, vertex); });
-}
-
 void DumpEdge(std::ostream *os, GraphDbAccessor *dba,
               const EdgeAccessor &edge) {
   *os << "(n" << edge.from().gid() << ")-[";
@@ -99,29 +92,39 @@ void DumpEdge(std::ostream *os, GraphDbAccessor *dba,
   *os << "]->(n" << edge.to().gid() << ")";
 }
 
-void DumpEdges(std::ostream *os, GraphDbAccessor *dba) {
-  auto edges = dba->Edges(false);
-  utils::PrintIterable(
-      os, edges.begin(), edges.end(), ", ",
-      [&dba](auto &os, const auto &edge) { DumpEdge(&os, dba, edge); });
-}
-
 }  // namespace
 
-void DumpToCypher(std::ostream *os, GraphDbAccessor *dba) {
-  CHECK(os);
+DumpGenerator::DumpGenerator(GraphDbAccessor *dba) : dba_(dba), first_(true) {
   CHECK(dba);
+  vertices_state_.emplace(dba->Vertices(false));
+  edges_state_.emplace(dba->Edges(false));
+}
 
-  if (dba->VerticesCount() > 0) {
+bool DumpGenerator::NextQuery(std::ostream *os) {
+  if (vertices_state_->ReachedEnd() && edges_state_->ReachedEnd()) return false;
+
+  if (first_) {
+    first_ = false;
     *os << "CREATE ";
-    DumpVertices(os, dba);
-    if (dba->EdgesCount() > 0) {
-      *os << ", ";
-      DumpEdges(os, dba);
-    }
-    *os << ";";
+  } else {
+    *os << ", ";
   }
-  // TODO(tsabolcec): Dump other data as well.
+
+  if (!vertices_state_->ReachedEnd()) {
+    DumpVertex(os, dba_, *vertices_state_->GetCurrentAndAdvance());
+  } else if (!edges_state_->ReachedEnd()) {
+    DumpEdge(os, dba_, *edges_state_->GetCurrentAndAdvance());
+  }
+
+  if (vertices_state_->ReachedEnd() && edges_state_->ReachedEnd()) *os << ";";
+  return true;
+}
+
+void DumpToCypher(std::ostream *os, GraphDbAccessor *dba) {
+  CHECK(os && dba);
+
+  DumpGenerator dump(dba);
+  while (dump.NextQuery(os)) continue;
 }
 
 }  // namespace database
diff --git a/src/database/single_node/dump.hpp b/src/database/single_node/dump.hpp
index e2480204c..8e98a4304 100644
--- a/src/database/single_node/dump.hpp
+++ b/src/database/single_node/dump.hpp
@@ -6,13 +6,60 @@
 
 namespace database {
 
+/// Class which generates parts of openCypher query which can be used to dump
+/// the database state.
+///
+/// Currently, all parts combined form a single query which dumps an entire
+/// graph (vertices and edges). Since query can be quite long for larger graphs,
+/// the graph should be split in multiple queries in the future. Indexes,
+/// constraints, roles, etc. are currently not dumped.
+class DumpGenerator {
+ public:
+  explicit DumpGenerator(GraphDbAccessor *dba);
+
+  bool NextQuery(std::ostream *os);
+
+ private:
+  // A helper class that keeps container and its iterators.
+  template <typename TContainer>
+  class ContainerState {
+   public:
+    explicit ContainerState(TContainer container)
+        : container_(std::move(container)),
+          current_(container_.begin()),
+          end_(container_.end()) {}
+
+    auto GetCurrentAndAdvance() {
+      auto to_be_returned = current_;
+      if (current_ != end_) ++current_;
+      return to_be_returned;
+    }
+
+    bool ReachedEnd() const { return current_ == end_; }
+
+   private:
+    TContainer container_;
+
+    using TIterator = decltype(container_.begin());
+    TIterator current_;
+    TIterator end_;
+  };
+
+  GraphDbAccessor *dba_;
+
+  // Boolean which indicates if the `NextQuery` method is called for the first
+  // time.
+  bool first_;
+
+  std::optional<ContainerState<decltype(dba_->Vertices(false))>>
+      vertices_state_;
+  std::optional<ContainerState<decltype(dba_->Edges(false))>> edges_state_;
+};
+
 /// Dumps database state to output stream as openCypher queries.
 ///
 /// Currently, it only dumps vertices and edges of the graph. In the future,
 /// it should also dump indexes, constraints, roles, etc.
-///
-/// @param os Output stream
-/// @param dba Database accessor
 void DumpToCypher(std::ostream *os, GraphDbAccessor *dba);
 
 }  // namespace database