From 0ef6f1f73948c581a8479d26bf40824d733f2a03 Mon Sep 17 00:00:00 2001
From: Arnaud Mimart <33665250+amimart@users.noreply.github.com>
Date: Mon, 22 May 2023 17:56:55 +0200
Subject: [PATCH] feat(cognitarium): build query plan from basic graph pattern

---
 .../src/querier/plan_builder.rs               | 21 +++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/contracts/okp4-cognitarium/src/querier/plan_builder.rs b/contracts/okp4-cognitarium/src/querier/plan_builder.rs
index b18f3eb7..93195ce0 100644
--- a/contracts/okp4-cognitarium/src/querier/plan_builder.rs
+++ b/contracts/okp4-cognitarium/src/querier/plan_builder.rs
@@ -26,6 +26,27 @@ impl<'a> PlanBuilder<'a> {
     pub fn build_plan(&mut self, where_clause: WhereClause) -> StdResult<QueryPlan> {
         Err(StdError::generic_err("not implemented"))
 
+    fn build_from_bgp(&self, bgp: Vec<QueryNode::TriplePattern>) -> StdResult<QueryPlan> {
+        bgp.iter()
+            .reduce(|left: QueryNode, right: QueryNode| -> QueryNode {
+                if left
+                    .bound_variables()
+                    .union(&right.bound_variables())
+                    .next()
+                    .is_some()
+                {
+                    return QueryNode::ForLoopJoin { left, right };
+                }
+                QueryNode::CartesianProductJoin { left, right }
+            })
+            .map(Ok)
+            .unwrap_or(Err(StdError::generic_err("Empty basic graph pattern")))
+            .map(|query_node: QueryNode| QueryPlan {
+                entrypoint: query_node,
+                variables: self.variables.clone(),
+            })
+    }
+
     fn build_triple_pattern(
         &mut self,
         pattern: &TriplePattern,