Split src/common/* into headers and definitions

src/common/logging.cpp

@@ -0,0 +1,54 @@
+#include "logging.h"
+
+#include <fstream>
+#include <iostream>
+
+#ifdef __WINE__
+#include "../wine-host/boost-fix.h"
+#endif
+#include <boost/process/environment.hpp>
+
+/**
+ * The environment variable indicating whether to log to a file. Will log to
+ * STDERR if not specified.
+ */
+constexpr char logging_file_environment_variable[] = "YABRIDGE_DEBUG_FILE";
+
+/**
+ * The verbosity of the logging, defaults to `Logger::Verbosity::events` if
+ * `logging_file_environment_variable` has been set and
+ * `Logger::Verbosity::basic` otherwise.
+ *
+ * @see Logger::Verbosity
+ */
+constexpr char logging_verbosity_environment_variable[] =
+    "YABRIDGE_DEBUG_VERBOSITY";
+
+Logger::Logger(std::ostream&& stream,
+               Verbosity verbosity_level,
+               std::string prefix)
+    : stream(stream), verbosity(verbosity_level), prefix(prefix) {}
+
+Logger Logger::create_from_environment(std::string prefix) {
+    auto env = boost::this_process::environment();
+    std::string file_path = env.get(logging_file_environment_variable);
+    std::string verbosity = env.get(logging_verbosity_environment_variable);
+
+    // Default to `Verbosity::basic` if the environment variable has not
+    // been set or if it is not an integer.
+    Verbosity verbosity_level;
+    try {
+        verbosity_level = static_cast<Verbosity>(std::stoi(verbosity));
+    } catch (const std::invalid_argument&) {
+        verbosity_level = Verbosity::basic;
+    }
+
+    // If `file` points to a valid location then use create/truncate the
+    // file and write all of the logs there, otherwise use STDERR
+    std::ofstream log_file(file_path, std::fstream::out);
+    if (log_file.is_open()) {
+        return Logger(std::move(log_file), verbosity_level, prefix);
+    } else {
+        return Logger(std::move(std::cerr), verbosity_level, prefix);
+    }
+}