From f0d22976c74611d35b270ba90bbea0892c3dc758 Mon Sep 17 00:00:00 2001
From: Hassan Abedi <cogitator.tech@gmail.com>
Date: Fri, 10 Apr 2026 16:07:26 +0200
Subject: [PATCH] WIP

---
 src/execution/table_store.rs | 72 ++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 src/execution/table_store.rs

diff --git a/src/execution/table_store.rs b/src/execution/table_store.rs
new file mode 100644
index 0000000..33711e7
--- /dev/null
+++ b/src/execution/table_store.rs
@@ -0,0 +1,72 @@
+//! An in-memory table store backed by hash maps.
+
+use std::collections::HashMap;
+
+use crate::relational::{ResultSet, Row, Schema};
+
+use super::{DataSource, ExecutionError};
+
+/// A simple in-memory data source backed by named tables of rows.
+///
+/// Unlike [`Instance`](crate::chase::Instance), which stores chase-level atoms,
+/// `TableStore` holds typed relational rows directly. This makes it useful for
+/// testing and for scenarios where data does not originate from the chase engine.
+#[derive(Debug, Clone, Default)]
+pub struct TableStore {
+    tables: HashMap<String, (Schema, Vec<Row>)>,
+}
+
+impl TableStore {
+    /// Create an empty table store.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Register a table with its schema and initial rows.
+    pub fn insert(&mut self, name: impl Into<String>, schema: Schema, rows: Vec<Row>) {
+        self.tables.insert(name.into(), (schema, rows));
+    }
+}
+
+impl DataSource for TableStore {
+    fn scan(&self, table: &str, schema: &Schema) -> Result<ResultSet, ExecutionError> {
+        match self.tables.get(table) {
+            Some((_, rows)) => Ok(ResultSet::new(schema.clone(), rows.clone())),
+            None => Ok(ResultSet::new(schema.clone(), Vec::new())),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::relational::{DataType, Field, Value};
+
+    #[test]
+    fn scans_registered_table() {
+        let schema = Schema::new(vec![
+            Field::new("name", DataType::Text, false),
+            Field::new("age", DataType::Integer, false),
+        ]);
+
+        let rows = vec![
+            Row::new(vec![Value::text("alice"), Value::Integer(30)]),
+            Row::new(vec![Value::text("bob"), Value::Integer(25)]),
+        ];
+
+        let mut store = TableStore::new();
+        store.insert("people", schema.clone(), rows);
+
+        let result = store.scan("people", &schema).unwrap();
+        assert_eq!(result.rows().len(), 2);
+        assert_eq!(result.schema().fields()[0].name(), "name");
+    }
+
+    #[test]
+    fn returns_empty_for_missing_table() {
+        let store = TableStore::new();
+        let schema = Schema::new(vec![]);
+        let result = store.scan("missing", &schema).unwrap();
+        assert_eq!(result.rows().len(), 0);
+    }
+}