Fix loading history when multiple buffers in config

When starting the RingLogger backend, the `RingLogger.Server` loads any
history from a persistence file during init, then configures the Server
after successfully starting up. However, the configure action was
destructive and would reset all the buffers which were just loaded if you
happened to have buffer configuration.

This fixes that to reload any existing buffer back into the newly configured
ones so that history would not be lost when adjusting minor configuration

lib/ring_logger/server.ex

@@ -137,6 +137,8 @@ defmodule RingLogger.Server do
   end
 
   def handle_call({:configure, opts}, _from, state) do
+    logs = merge_buffers(state)
+
     state =
       case Keyword.get(opts, :max_size) do
         nil ->
@@ -155,6 +157,9 @@ defmodule RingLogger.Server do
           %__MODULE__{state | buffers: reset_buffers(buffers)}
       end
 
+    # Reinsert old buffers to let new max size filter out
+    state = Enum.reduce(logs, state, &insert_log(&2, &1))
+
     {:reply, :ok, state}
   end
 

test/ring_logger_test.exs

@@ -759,6 +759,60 @@ defmodule RingLoggerTest do
       File.rm!("test/persistence.log")
     end
 
+    test "loading the log with multiple buffers", %{io: io} do
+      Logger.remove_backend(RingLogger)
+
+      logs = [
+        %{
+          level: :debug,
+          module: Logger,
+          message: "Foo",
+          timestamp: {{2023, 2, 8}, {13, 58, 31, 343}},
+          metadata: []
+        },
+        %{
+          level: :debug,
+          module: Logger,
+          message: "Bar",
+          timestamp: {{2023, 2, 8}, {13, 58, 31, 344}},
+          metadata: []
+        },
+        %{
+          level: :info,
+          module: Logger,
+          message: "Baz",
+          timestamp: {{2023, 2, 8}, {13, 58, 31, 345}},
+          metadata: []
+        }
+      ]
+
+      :ok = Persistence.save("test/persistence.log", logs)
+
+      # Start the backend with _just_ the persist_path and restore old
+      # config to allow other tests to run without loading a log file
+      old_env = Application.get_env(:logger, RingLogger)
+
+      new_env = [
+        persist_path: "test/persistence.log",
+        max_size: 3,
+        buffers: %{debug: %{levels: [:debug], max_size: 2}}
+      ]
+
+      Application.put_env(:logger, RingLogger, new_env)
+      Logger.add_backend(RingLogger)
+      Application.put_env(:logger, RingLogger, old_env)
+
+      Logger.add_backend(RingLogger)
+
+      :ok = RingLogger.attach(io: io)
+
+      buffer = RingLogger.get(0, 0)
+
+      assert Enum.count(buffer) == 3
+
+      File.rm!("test/persistence.log")
+    end
+
     test "loading a corrupted file", %{io: io} do
       Logger.remove_backend(RingLogger)