Default to XDG dir for configuration

This patch changes the default configuration directory, internally
referred to as 'ApplicationDir', to comply with XDG's Base Directory
Specification.

Most Unix tools already operate on the specification. By adhering it,
Nchat becomes more intuitive and integrated with the system.

More information about the spec can be found at:
    https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html

The '--confdir' flag doesn't cover this scenario as it's directed at
customization at invokation and not at defaults.

Signed-off-by: Carlos Torres <torr.ca@mailgw.com>

src/main.cpp

@@ -37,6 +37,10 @@
 #include "wmchat.h"
 #endif
 
+static const char *EnvXdgConf = "XDG_CONFIG_HOME";
+static const std::string DefaultXdgConfDir = ".config";
+
+
 static void RemoveProfile();
 static std::shared_ptr<Protocol> SetupProfile();
 static void ShowHelp();
@@ -121,12 +125,20 @@ static std::vector<ProtocolBaseFactory*> GetProtocolFactorys()
   return protocolFactorys;
 }
 
+static std::string GetConfDir()
+{
+  char *confDir = getenv(EnvXdgConf);
+  if (confDir != NULL && confDir[0] != '\0') {
+    return std::string(confDir) + std::string("/nchat");
+  }
+  return std::string(getenv("HOME")) + "/" + DefaultXdgConfDir + "/" + std::string("nchat");
+}
 
 int main(int argc, char* argv[])
 {
   // Defaults
   umask(S_IRWXG | S_IRWXO);
-  FileUtil::SetApplicationDir(std::string(getenv("HOME")) + std::string("/.nchat"));
+  FileUtil::SetApplicationDir(GetConfDir());
   Log::SetVerboseLevel(Log::INFO_LEVEL);
 
   // Argument handling
@@ -534,7 +546,7 @@ void ShowHelp()
     "Usage: nchat [OPTION]\n"
     "\n"
     "Command-line Options:\n"
-    "    -d, --confdir <DIR>    use a different directory than ~/.nchat\n"
+    "    -d, --confdir <DIR>    use a different directory than ~/.config/nchat\n"
     "    -e, --verbose          enable verbose logging\n"
     "    -ee, --extra-verbose   enable extra verbose logging\n"
     "    -h, --help             display this help and exit\n"

src/nchat.1

@@ -10,7 +10,7 @@ nchat is a terminal\-based telegram / whatsapp client.
 .SS "Command-line Options:"
 .TP
 \fB\-d\fR, \fB\-\-confdir\fR <DIR>
-use a different directory than ~/.nchat
+use a different directory than \fB$XDG_CONFIG_HOME\fR/nchat
 .TP
 \fB\-e\fR, \fB\-\-verbose\fR
 enable verbose logging