Rudimentary logging!

src/log.hh

@@ -0,0 +1,147 @@
+/* log.hh
+ * vim: set tw=80:
+ * Eryn Wells <eryn@erynwells.me>
+ */
+
+#ifndef __LOG_HH__
+#define __LOG_HH__
+
+#include <cassert>
+#include <cstddef>
+
+#include <chrono>
+#include <iomanip>
+#include <map>
+#include <fstream>
+#include <string>
+
+
+namespace charles {
+namespace log {
+
+/** Useful predefined levels. */
+namespace level {
+    unsigned int Error = 10;
+    unsigned int Warning = 20;
+    unsigned int Info = 30;
+    unsigned int Debug = 40;
+    unsigned int Trace = 50;
+};
+
+
+struct Log
+{
+    static void Init(const std::string& filename);
+    static void Close();
+
+    Log(const std::string& name = "root", unsigned int level = level::Info);
+    ~Log();
+
+    template<typename T> Log& operator<<(const T& item);
+
+private:
+    struct Logger
+    {
+        Logger(unsigned int level = level::Info);
+
+        unsigned int level;
+    };
+
+    typedef std::map<std::string, Logger> LoggerMap;
+
+    static std::ostream* sOutput;
+    static LoggerMap sLoggers;
+
+    static Logger& GetLogger(const std::string& name);
+
+    const std::string& mName;
+    unsigned int mLevel;
+    Logger& mOutput;
+};
+
+
+std::ostream* Log::sOutput = nullptr;
+Log::LoggerMap Log::sLoggers;
+
+
+/* static */ void
+Log::Init(const std::string& filename)
+{
+    assert(sOutput == nullptr);
+    sOutput = new std::ofstream(filename);
+
+    Log("root", level::Error) << "Opening log file: " << filename;
+}
+
+
+/* static */ void
+Log::Close()
+{
+    assert(sOutput != nullptr);
+    delete sOutput;
+    sOutput = nullptr;
+}
+
+
+/**
+ * Construct a Log object.
+ *
+ * @param [in] name     The name of the log stream. If this name hasn't been
+ *                      seen before, a new one will be created for you.
+ * @param [in] level    The level. If this is higher than the level of the log
+ *                      stream, nothing will be output.
+ */
+Log::Log(const std::string& name,
+         unsigned int level)
+    : mName(name),
+      mLevel(level),
+      mOutput(Log::GetLogger(name))
+{
+    using namespace std::chrono;
+
+    /* Write a log message leader: "<time> - <name>:<level>: ". */
+    auto now = system_clock::to_time_t(system_clock::now());
+    *this << std::put_time(std::localtime(&now), "%F %T")
+          << " - " << mName << ":" << mLevel << " - ";
+}
+
+
+Log::~Log()
+{
+    /* Add a newline at the end of this log message. */
+    *this << "\n";
+}
+
+
+template<typename T>
+Log&
+Log::operator<<(const T& item)
+{
+    if (mLevel <= mOutput.level) {
+        assert(sOutput != nullptr);
+        *sOutput << item;
+    }
+    return *this;
+}
+
+
+/* static */ Log::Logger&
+Log::GetLogger(const std::string& name)
+{
+    /*
+     * TODO: For now, output is always the same: sOutput. In the future, figure
+     * out a way to set different outputs for different streams.
+     */
+    auto pair = sLoggers.emplace(name, level::Info);
+    return pair.first->second;
+}
+
+
+Log::Logger::Logger(unsigned int l)
+    : level(l)
+{ }
+
+} /* namespace log */
+} /* namespace charles */
+
+#endif /* __LOG_HH__ */