Add crsql changes metadata status

crates/geth-db/src/lib.rs

@@ -12,9 +12,43 @@ pub struct DbResource {
     pub path_exists: bool,
     pub size_bytes: Option<u64>,
     pub schema_metadata: String,
+    pub crsqlite_changes: CrSqliteChangeMetadata,
     pub sync_status: String,
 }
 
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub struct CrSqliteChangeMetadata {
+    pub available: bool,
+    pub change_count: Option<u64>,
+    pub max_db_version: Option<i64>,
+    pub columns: Vec<String>,
+    pub error: Option<String>,
+}
+
+impl CrSqliteChangeMetadata {
+    #[must_use]
+    pub fn unavailable() -> Self {
+        Self {
+            available: false,
+            change_count: None,
+            max_db_version: None,
+            columns: Vec::new(),
+            error: None,
+        }
+    }
+
+    #[must_use]
+    pub fn error(error: impl Into<String>) -> Self {
+        Self {
+            available: false,
+            change_count: None,
+            max_db_version: None,
+            columns: Vec::new(),
+            error: Some(error.into()),
+        }
+    }
+}
+
 #[derive(Debug, thiserror::Error)]
 pub enum DbError {
     #[error("invalid db resource name: {0}")]
@@ -78,6 +112,43 @@ pub fn schema_metadata(path: &Path) -> Result<String, DbError> {
     ))
 }
 
+pub fn crsqlite_change_metadata(path: &Path) -> Result<CrSqliteChangeMetadata, DbError> {
+    let conn = Connection::open_with_flags(path, OpenFlags::SQLITE_OPEN_READ_ONLY)?;
+    let available: bool = conn.query_row(
+        r#"SELECT EXISTS(
+            SELECT 1 FROM sqlite_master
+            WHERE name = 'crsql_changes' AND type IN ('table', 'view')
+        )"#,
+        [],
+        |row| row.get(0),
+    )?;
+    if !available {
+        return Ok(CrSqliteChangeMetadata::unavailable());
+    }
+
+    let mut columns_stmt = conn.prepare("PRAGMA table_info('crsql_changes')")?;
+    let columns = columns_stmt
+        .query_map([], |row| row.get::<_, String>(1))?
+        .collect::<Result<Vec<_>, _>>()?;
+    let change_count: u64 =
+        conn.query_row("SELECT COUNT(*) FROM crsql_changes", [], |row| row.get(0))?;
+    let max_db_version = if columns.iter().any(|column| column == "db_version") {
+        conn.query_row("SELECT MAX(db_version) FROM crsql_changes", [], |row| {
+            row.get(0)
+        })?
+    } else {
+        None
+    };
+
+    Ok(CrSqliteChangeMetadata {
+        available: true,
+        change_count: Some(change_count),
+        max_db_version,
+        columns,
+        error: None,
+    })
+}
+
 #[must_use]
 pub fn crsqlite_sync_roadmap() -> &'static str {
     "future db sync reads crsql_changes, exchanges changes over Iroh, and applies through crsql_changes"
@@ -119,4 +190,39 @@ mod tests {
         assert!(first.contains("indexes=1"));
         assert!(first.contains("schema_hash="));
     }
+
+    #[test]
+    fn crsqlite_change_metadata_reports_mock_change_table() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let path = dir.path().join("notes.sqlite");
+        let conn = Connection::open(&path).expect("open sqlite");
+        conn.execute(
+            r#"CREATE TABLE crsql_changes(
+                table_name TEXT NOT NULL,
+                pk TEXT NOT NULL,
+                cid TEXT NOT NULL,
+                val BLOB,
+                col_version INTEGER NOT NULL,
+                db_version INTEGER NOT NULL,
+                site_id BLOB,
+                cl INTEGER,
+                seq INTEGER
+            )"#,
+            [],
+        )
+        .expect("create crsql_changes table");
+        conn.execute(
+            "INSERT INTO crsql_changes(table_name, pk, cid, val, col_version, db_version) VALUES ('notes', '1', 'body', 'hello', 1, 7)",
+            [],
+        )
+        .expect("insert change");
+        drop(conn);
+
+        let metadata = crsqlite_change_metadata(&path).expect("change metadata");
+
+        assert!(metadata.available);
+        assert_eq!(metadata.change_count, Some(1));
+        assert_eq!(metadata.max_db_version, Some(7));
+        assert!(metadata.columns.contains(&"db_version".to_owned()));
+    }
 }