Adding before_disconnect hook (#271)

Allows consumers to specify a function or MFA to call before
the database is disconnected.

Author: jeregrine

lib/exqlite/connection.ex

@@ -36,15 +36,18 @@ defmodule Exqlite.Connection do
     :path,
     :transaction_status,
     :status,
-    :chunk_size
+    :chunk_size,
+    :before_disconnect
   ]
 
   @type t() :: %__MODULE__{
           db: Sqlite3.db(),
           directory: String.t() | nil,
           path: String.t(),
           transaction_status: :idle | :transaction,
-          status: :idle | :busy
+          status: :idle | :busy,
+          chunk_size: integer(),
+          before_disconnect: (t -> any) | {module, atom, [any]} | nil
         }
 
   @type journal_mode() :: :delete | :truncate | :persist | :memory | :wal | :off
@@ -73,6 +76,7 @@ defmodule Exqlite.Connection do
           | {:hard_heap_limit, integer()}
           | {:key, String.t()}
           | {:custom_pragmas, [{keyword(), integer() | boolean() | String.t()}]}
+          | {:before_disconnect, (t -> any) | {module, atom, [any]} | nil}
 
   @impl true
   @doc """
@@ -155,6 +159,9 @@ defmodule Exqlite.Connection do
             "./priv/sqlite/\#{arch_dir}/vss0"
           ]
       ```
+    * `:before_disconnect` - A function to run before disconnect, either a 
+      2-arity fun or `{module, function, args}` with the close reason and 
+      `t:Exqlite.Connection.t/0` prepended to `args` or `nil` (default: `nil`)
 
   For more information about the options above, see [sqlite documentation][1]
 
@@ -190,7 +197,11 @@ defmodule Exqlite.Connection do
   end
 
   @impl true
-  def disconnect(_err, %__MODULE__{db: db}) do
+  def disconnect(err, %__MODULE__{db: db} = state) do
+    if state.before_disconnect != nil do
+      apply(state.before_disconnect, [err, state])
+    end
+
     case Sqlite3.close(db) do
       :ok -> :ok
       {:error, reason} -> {:error, %Error{message: to_string(reason)}}
@@ -539,7 +550,8 @@ defmodule Exqlite.Connection do
         path: database,
         transaction_status: :idle,
         status: :idle,
-        chunk_size: Keyword.get(options, :chunk_size)
+        chunk_size: Keyword.get(options, :chunk_size),
+        before_disconnect: Keyword.get(options, :before_disconnect, nil)
       }
 
       {:ok, state}

test/exqlite/connection_test.exs

@@ -184,6 +184,23 @@ defmodule Exqlite.ConnectionTest do
 
       assert :ok == Connection.disconnect(nil, conn)
     end
+
+    test "executes before_disconnect before disconnecting" do
+      {:ok, pid} = Agent.start_link(fn -> 0 end)
+
+      {:ok, conn} =
+        Connection.connect(
+          database: :memory,
+          before_disconnect: fn err, db ->
+            Agent.update(pid, fn count -> count + 1 end)
+            assert err == true
+            assert db
+          end
+        )
+
+      assert :ok == Connection.disconnect(true, conn)
+      assert Agent.get(pid, &Function.identity/1) == 1
+    end
   end
 
   describe ".handle_execute/4" do