From ab5d442d9f87c1f19731b5b6cb52e4a65bd4f51c Mon Sep 17 00:00:00 2001
From: Fabio Salvini <salvini.fabio001@gmail.com>
Date: Mon, 26 Jun 2017 11:39:16 +0200
Subject: [PATCH] Save emails to send to Mnesia

---
 TODO.md                                  |  7 +++
 apps/log_monitor/src/log_monitor_app.erl | 16 ++++++-
 apps/log_monitor/src/mailer.erl          | 59 +++++++++++++++++++++---
 apps/log_monitor/src/mnesia_tables.hrl   |  1 +
 4 files changed, 75 insertions(+), 8 deletions(-)
 create mode 100644 TODO.md

diff --git a/TODO.md b/TODO.md
new file mode 100644
index 0000000..5789005
--- /dev/null
+++ b/TODO.md
@@ -0,0 +1,7 @@
+TODO
+=====
+
+  - Manage problem of "infinite" consecutive errors.
+  - Limit number of emails that can be sent in a period of time.
+  - Store the logfiles in a configuration file.
+  - gen_fsm for gatherer?
diff --git a/apps/log_monitor/src/log_monitor_app.erl b/apps/log_monitor/src/log_monitor_app.erl
index 5631820..b798e4e 100644
--- a/apps/log_monitor/src/log_monitor_app.erl
+++ b/apps/log_monitor/src/log_monitor_app.erl
@@ -31,7 +31,7 @@ stop(_State) ->
 
 start_mnesia() ->
     Nodes = [node()],
-    %% Stop Mnesia if is running, cannot create schema otherwise.
+    %% Stop Mnesia if it is running, cannot create schema otherwise.
     mnesia:stop(),
     mnesia:create_schema(Nodes),
     mnesia:start(),
@@ -46,4 +46,16 @@ start_mnesia() ->
                          {index, [#log_monitor_file.group]},
                          {disc_copies, Nodes}
                         ]),
-    ok = mnesia:wait_for_tables([log_monitor_group, log_monitor_file], 30000).
+    mnesia:create_table(log_monitor_error,
+                        [
+                         {attributes, record_info(fields, log_monitor_error)},
+                         {disc_copies, Nodes}
+                        ]),
+    ok = mnesia:wait_for_tables(
+           [
+            log_monitor_group,
+            log_monitor_file,
+            log_monitor_error
+           ],
+           30000
+          ).
diff --git a/apps/log_monitor/src/mailer.erl b/apps/log_monitor/src/mailer.erl
index c47d950..8e0e71f 100644
--- a/apps/log_monitor/src/mailer.erl
+++ b/apps/log_monitor/src/mailer.erl
@@ -1,6 +1,8 @@
 -module(mailer).
 -behaviour(gen_server).
 
+-include_lib("mnesia_tables.hrl").
+
 -export([start_link/0, init/1, terminate/2]).
 -export([handle_info/2, handle_cast/2, handle_call/3]).
 -export([code_change/3]).
@@ -10,15 +12,27 @@ start_link() ->
 
 init([]) ->
     register(mailer, self()),
+    timer:send_after(1000, {send_emails}),
     {ok, []}.
 
-handle_info({error, File, Text}, []) ->
-    case send_email(File, Text) of
-        {error, Reason, Message} ->
-            error_logger:error_msg("Error sending email: ~s ~p~n", [Reason, Message]);
-        _ -> ok
+handle_info({error, File, Text}, State) ->
+    mnesia:activity(
+      transaction,
+      fun() ->
+              Id = erlang:monotonic_time(),
+              mnesia:write(#log_monitor_error{id = Id, file = File, text = Text})
+      end),
+    {noreply, State};
+handle_info({send_emails}, State) ->
+    Emails = emails_to_send(),
+    try send_emails(Emails) of
+        _ -> timer:send_after(1000, {send_emails})
+    catch
+        _Throw ->
+            error_logger:info_msg("Waiting 60s before sending new emails~n"),
+            timer:send_after(60000, {send_emails})
     end,
-    {noreply, []}.
+    {noreply, State}.
 
 handle_cast(_Msg, State) ->
     {noreply, State}.
@@ -32,6 +46,31 @@ terminate(_Reason, _State) ->
 code_change(_OldVsn, State, _Extra) ->
     {ok, State}.
 
+emails_to_send() ->
+    mnesia:activity(
+      transaction,
+      fun() ->
+              mnesia:foldl(
+                fun(#log_monitor_error{id = Id, file = File, text = Text}, Acc) ->
+                        [{Id, File, Text}] ++ Acc
+                end, [], log_monitor_error)
+      end).
+
+send_emails(Emails) ->
+    case Emails of
+        [] -> {ok};
+        [{Id, File, Text} | Others] ->
+            case send_email(File, Text) of
+                {error, Reason, Message} ->
+                    error_logger:error_msg("Error sending email: ~s ~p~n", [Reason, Message]),
+                    throw(cannot_send_email);
+                _ ->
+                    remove_email(Id),
+                    send_emails(Others),
+                    {ok}
+            end
+    end.
+
 send_email(File, Text) ->
     {ok, EmailConfig} = application:get_env(log_monitor, email_config),
     Sender = proplists:get_value(sender, EmailConfig),
@@ -43,3 +82,11 @@ send_email(File, Text) ->
        io_lib:format("Subject: Error notification\r\nFrom: Fabio\r\n\r\nLogfile: ~s~nError: ~n~s~n", [File, Text])},
       Connection
      ).
+
+remove_email(Id) ->
+    mnesia:activity(
+      transaction,
+      fun() ->
+              mnesia:delete({log_monitor_error, Id})
+      end),
+    ok.
diff --git a/apps/log_monitor/src/mnesia_tables.hrl b/apps/log_monitor/src/mnesia_tables.hrl
index ecf98ab..9b907ee 100644
--- a/apps/log_monitor/src/mnesia_tables.hrl
+++ b/apps/log_monitor/src/mnesia_tables.hrl
@@ -4,5 +4,6 @@
 %% Mnesia tables
 -record(log_monitor_group, {name, email_receivers=[]}).
 -record(log_monitor_file, {file, error_regex, status, group}).
+-record(log_monitor_error, {id, file, text}).
 
 -endif.