added initial roadmap and implementation

migrations/20260311000000_realtime_history.sql

@@ -0,0 +1,71 @@
+-- Create History Table
+CREATE TABLE IF NOT EXISTS madbase_realtime.messages (
+    id bigserial PRIMARY KEY,
+    topic text NOT NULL, -- schema:table
+    payload jsonb NOT NULL,
+    created_at timestamptz DEFAULT now()
+);
+
+CREATE INDEX IF NOT EXISTS idx_realtime_messages_topic_id ON madbase_realtime.messages (topic, id);
+
+-- Update Trigger Function
+CREATE OR REPLACE FUNCTION madbase_realtime.broadcast_changes()
+RETURNS trigger AS $$
+DECLARE
+    base_payload jsonb;
+    final_payload jsonb;
+    topic text;
+    msg_id bigint;
+BEGIN
+    -- Construct topic
+    topic = TG_TABLE_SCHEMA || ':' || TG_TABLE_NAME;
+
+    -- Construct base payload
+    base_payload = jsonb_build_object(
+        'schema', TG_TABLE_SCHEMA,
+        'table', TG_TABLE_NAME,
+        'type', TG_OP,
+        'timestamp', now()
+    );
+
+    IF (TG_OP = 'INSERT') THEN
+        base_payload = base_payload || jsonb_build_object('record', row_to_json(NEW)::jsonb);
+    ELSIF (TG_OP = 'UPDATE') THEN
+        base_payload = base_payload || jsonb_build_object(
+            'record', row_to_json(NEW)::jsonb,
+            'old_record', row_to_json(OLD)::jsonb
+        );
+    ELSIF (TG_OP = 'DELETE') THEN
+        base_payload = base_payload || jsonb_build_object('old_record', row_to_json(OLD)::jsonb);
+    END IF;
+
+    -- Insert into history
+    INSERT INTO madbase_realtime.messages (topic, payload)
+    VALUES (topic, base_payload)
+    RETURNING id INTO msg_id;
+
+    -- Add ID to payload
+    final_payload = base_payload || jsonb_build_object('id', msg_id);
+
+    -- Send notification
+    -- Payload limit is 8000 bytes. Larger payloads will fail or need truncation.
+    -- If payload is too large, we can send a "payload too large" message with ID, 
+    -- and client can fetch it from history.
+    -- For MVP, we assume it fits or fail silently on notify (but insert succeeds).
+    BEGIN
+        PERFORM pg_notify('madbase_realtime', final_payload::text);
+    EXCEPTION WHEN string_data_right_truncation OR others THEN
+        -- If notification fails, client can still rely on history if they poll or reconnect.
+        -- We could notify just the ID.
+        PERFORM pg_notify('madbase_realtime', jsonb_build_object(
+            'id', msg_id, 
+            'schema', TG_TABLE_SCHEMA, 
+            'table', TG_TABLE_NAME, 
+            'type', TG_OP,
+            'truncated', true
+        )::text);
+    END;
+    
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;