feat(cognitarium): add plan builder structure

contracts/okp4-cognitarium/src/querier/plan_builder.rs

@@ -0,0 +1,36 @@
+use crate::msg::{
+    Literal, Node, Prefix, SimpleWhereCondition, TriplePattern, VarOrNode, VarOrNodeOrLiteral,
+    WhereClause, WhereCondition, IRI,
+};
+use crate::querier::plan::{PatternValue, QueryNode, QueryPlan};
+use crate::state::{namespaces, Object, Predicate, Subject};
+use crate::{rdf, state};
+use cosmwasm_std::{StdError, StdResult, Storage};
+use std::collections::HashMap;
+
+pub struct PlanBuilder<'a> {
+    storage: &'a dyn Storage,
+    prefixes: HashMap<String, String>,
+    variables: Vec<String>,
+}
+
+impl<'a> PlanBuilder<'a> {
+    pub fn new(storage: &'a dyn Storage, prefixes: Vec<Prefix>) -> Self {
+        Self {
+            storage,
+            prefixes: Self::make_prefixes(prefixes),
+            variables: Vec::new(),
+        }
+    }
+
+    pub fn build_plan(&mut self, where_clause: WhereClause) -> StdResult<QueryPlan> {
+        Err(StdError::generic_err("not implemented"))
+    }
+
+    fn make_prefixes(as_list: Vec<Prefix>) -> HashMap<String, String> {
+        as_list.iter().fold(HashMap::new(), |mut map, prefix| {
+            map.insert(prefix.prefix.clone(), prefix.namespace.clone());
+            map
+        })
+    }
+}