Introduce an observer

In a larger refactor of the sidebar, this piece decouples message
production from their handlers. Introduces an observer pattern to
subscribe to notifications. When the server receives a notification it
notifies any subscribers

Author: tomgeorge

lua/eca/observer.lua

@@ -0,0 +1,24 @@
+local observer = {}
+
+---@type { [integer]: fun(message: table) }
+local subscriptions = {}
+
+---@param id integer
+---@param on_update fun(message: table)
+function observer.subscribe(id, on_update)
+  subscriptions[id] = on_update
+end
+
+function observer.unsubscribe(id)
+  if subscriptions[id] then
+    subscriptions[id] = nil
+  end
+end
+
+function observer.notify(message)
+  for _, fn in pairs(subscriptions) do
+    fn(message)
+  end
+end
+
+return observer

lua/eca/server.lua

@@ -12,8 +12,8 @@ local Logger = require("eca.logger")
 ---@field on_start? function Callback when the server process starts
 ---@field on_stop function Callback when the server stops
 ---Called when a notification is received(message without an ID)
----@field on_notification fun(server: eca.Server, method: string, params: table)
----@field capabilities table Server capabilities
+---@field on_notification fun(server: eca.Server, message: table)
+---@field capabilities eca.ServerCapabilities Server capabilities
 ---@field private path_finder eca.PathFinder Server path finder
 ---@field pending_requests {id: fun(err, data)} -- outgoing requests with callbacks
 local M = {}
@@ -31,12 +31,11 @@ function M.new(opts)
     on_stop = function()
       require("eca.logger").notify("Server stopped", vim.log.levels.INFO)
     end,
-    ---@param server eca.Server
-    ---@param method string
-    ---@param params table
-    on_notification = function(server, method, params)
+    ---@param _ eca.Server
+    ---@param message table
+    on_notification = function(_, message)
       return vim.schedule(function()
-        server:handle_content(method, params)
+        require("eca.observer").notify(message)
       end)
     end,
     path_finder = PathFinder:new(),
@@ -237,7 +236,7 @@ function M:handle_message(message)
     end
   elseif message.method and not message.id then
     if self.on_notification then
-      self.on_notification(self, message.method, message.params)
+      self:on_notification(message)
     end
   end
 end

lua/eca/sidebar.lua

@@ -33,6 +33,14 @@ local WINDOW_MARGIN = 3 -- Additional margin for window borders and spacing
 local UI_ELEMENTS_HEIGHT = 2 -- Reserve space for statusline and tabline
 local SAFETY_MARGIN = 2 -- Extra margin to prevent "Not enough room" errors
 
+---@param sidebar eca.Sidebar
+---@return fun(message: table)
+local function make_handler(sidebar)
+  return function(message)
+    sidebar:handle_chat_content(message)
+  end
+end
+
 ---@param id integer Tab ID
 ---@return eca.Sidebar
 function M.new(id)
@@ -55,6 +63,8 @@ function M.new(id)
   instance._augroup = vim.api.nvim_create_augroup("eca_sidebar_" .. id, { clear = true })
   instance._response_start_time = 0
   instance._max_response_length = 50000 -- 50KB max response
+
+  require("eca.observer").subscribe(id, make_handler(instance))
   return instance
 end
 
@@ -1180,6 +1190,12 @@ function M:_send_message(message)
   end
 end
 
+function M:handle_chat_content(message)
+  if message.params then
+    self:handle_chat_content_received(message.params)
+  end
+end
+
 ---@param params table Server content notification
 function M:handle_chat_content_received(params)
   if not params or not params.content then