From 77b2d1b44a13ccf726109d1881ded79d4d4d45b0 Mon Sep 17 00:00:00 2001
From: Robbert van der Helm <mail@robbertvanderhelm.nl>
Date: Sat, 7 Mar 2020 16:48:41 +0100
Subject: [PATCH] Add a function for formatting log messages

---
 src/common/logging.cpp | 28 ++++++++++++++++++++++++++++
 src/common/logging.h   | 19 +++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/src/common/logging.cpp b/src/common/logging.cpp
index c1d4122b..f9e776c9 100644
--- a/src/common/logging.cpp
+++ b/src/common/logging.cpp
@@ -1,6 +1,9 @@
 #include "logging.h"
 
+#include <chrono>
+#include <ctime>
 #include <fstream>
+#include <iomanip>
 #include <iostream>
 
 #ifdef __WINE__
@@ -52,3 +55,28 @@ Logger Logger::create_from_environment(std::string prefix) {
         return Logger(std::move(std::cerr), verbosity_level, prefix);
     }
 }
+
+void Logger::log(const std::string& message) {
+    const auto current_time = std::chrono::system_clock::now();
+    const std::time_t timestamp =
+        std::chrono::system_clock::to_time_t(current_time);
+
+    // How did C++ manage to get time formatting libraries without a way to
+    // actually get a timestamp in a threadsafe way? `localtime_r` in C++ is not
+    // portable but luckily we only have to support GCC anyway.
+    std::tm tm;
+    localtime_r(&timestamp, &tm);
+
+    std::ostringstream formatted_message;
+    formatted_message << "[" << std::put_time(&tm, "%T") << "]";
+    formatted_message << prefix;
+    formatted_message << message;
+    // Flushing a stringstream doesn't do anything, but we need to put a
+    // linefeed in this string stream rather writing it sprightly to the output
+    // stream to prevent two messages from being put on the same row
+    formatted_message << std::endl;
+
+    // No flush. Should technically be necessary, but it decreases throughput by
+    // a lot and it seems to work fine without.
+    stream << formatted_message.str();
+}
diff --git a/src/common/logging.h b/src/common/logging.h
index 00065512..b2534df4 100644
--- a/src/common/logging.h
+++ b/src/common/logging.h
@@ -76,11 +76,30 @@ class Logger {
      */
     static Logger create_from_environment(std::string prefix = "");
 
+    /**
+     * Write a message to the log, prefixing it with a timestamp and this
+     * logger's prefix string.
+     *
+     * @param message The message to write.
+     */
+    void log(const std::string& message);
+
     // TODO: Add dedicated logging functions for events and the Wine process's
     //       STDOUT and STDERR
 
    private:
+    /**
+     * The output stream to write the log messages to. Typically either STDERR
+     * or a file stream.
+     */
     std::ostream& stream;
+    /**
+     * The verbosity level of this logger instance. Based on this certain
+     * messages may or may not be shown.
+     */
     Verbosity verbosity;
+    /**
+     * A prefix that gets prepended before every message.
+     */
     std::string prefix;
 };