1 files changed, 56 insertions, 0 deletions
diff --git a/server/src/play.rs b/server/src/play.rs
new file mode 100644
index 0000000..8fe1872
--- /dev/null
+++ b/server/src/play.rs
@@ -0,0 +1,56 @@
+use async_trait::async_trait;
+
+use crate::error::BridgeError;
+
+#[async_trait]
+pub trait Journal {
+    // Append payload to the journal at sequence number `seq`.
+    async fn append(&mut self, seq: i64, payload: serde_json::Value) -> Result<(), BridgeError>;
+
+    // Fetch all journal entries with sequence number greater or equal to `seq`.
+    async fn replay(&mut self, seq: i64) -> Result<Vec<serde_json::Value>, BridgeError>;
+}
+
+pub struct Table {}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[derive(Default)]
+    pub struct TestJournal {
+        log: Vec<Option<serde_json::Value>>,
+    }
+
+    #[async_trait]
+    impl Journal for TestJournal {
+        async fn append(
+            &mut self,
+            seq: i64,
+            payload: serde_json::Value,
+        ) -> Result<(), BridgeError> {
+            if seq != self.log.len() as i64 {
+                return Err(BridgeError::UpdateConflict(self.log.len() as i64, seq));
+            }
+            self.log.push(Some(payload));
+            Ok(())
+        }
+
+        async fn replay(&mut self, seq: i64) -> Result<Vec<serde_json::Value>, BridgeError> {
+            Ok(self.log[seq as usize..]
+                .into_iter()
+                .filter_map(|e| e.clone())
+                .collect())
+        }
+    }
+
+    #[tokio::test]
+    async fn test_journal() {
+        use serde_json::json;
+        let mut jnl: TestJournal = Default::default();
+        assert_eq!(jnl.append(0, json!(10)).await.unwrap(), ());
+        assert!(jnl.append(0, json!(0)).await.is_err());
+        assert_eq!(jnl.append(1, json!(20)).await.unwrap(), ());
+        assert_eq!(jnl.replay(1).await.unwrap(), vec!(json!(20)));
+    }
+}