stdlib: Add filename:basedir/2,3

3 files changed, 495 insertions, 3 deletions

diff --git a/lib/stdlib/doc/src/filename.xml b/lib/stdlib/doc/src/filename.xml
index 77e262dbe6..65009753f3 100644
--- a/lib/stdlib/doc/src/filename.xml
+++ b/lib/stdlib/doc/src/filename.xml
@@ -47,7 +47,12 @@
     <p>The module supports raw file names in the way that if a binary is present, or the file name cannot be interpreted according to the return value of 
     <seealso marker="kernel:file#native_name_encoding/0">file:native_name_encoding/0</seealso>, a raw file name will also be returned. For example filename:join/1 provided with a path component being a binary (and also not being possible to interpret under the current native file name encoding) will result in a raw file name being returned (the join operation will have been performed of course). For more information about raw file names, see the <seealso marker="kernel:file">file</seealso> module.</p>
   </description>
-
+  <datatypes>
+      <datatype>
+          <name name="basedir_type"/>
+      </datatype>
+  </datatypes>
+ 
   <funcs>
     <func>
       <name name="absname" arity="1"/>
@@ -102,6 +107,155 @@
       </desc>
     </func>
     <func>
+      <name name="basedir" arity="2"/>
+      <fsummary>Equivalent to <c>basedir(<anno>Type</anno>,<anno>Application</anno>,#{})</c>.</fsummary>
+      <desc>
+          <p>
+              Equivalent to <seealso marker="#basedir-3">
+                  basedir(<anno>Type</anno>, <anno>Application</anno>, #{})</seealso>.
+          </p>
+      </desc>
+    </func>
+    <func>
+      <name name="basedir" arity="3"/>
+      <fsummary></fsummary>
+      <desc><marker id="basedir-3"/>
+          <p>
+              Returns a suitable path, or paths, for a given type.
+              If <c>os</c> is not set in <c><anno>Opts</anno></c> the function will default to
+              the native option, i.e. <c>'linux'</c>, <c>'darwin'</c> or <c>'windows'</c>, as understood
+              by <c>os:type/0</c>. Anything not recognized as <c>'darwin'</c> or <c>'windows'</c> is
+              interpreted as <c>'linux'</c>.</p>
+          <p>
+              The options <c>'author'</c> and <c>'version'</c> are only used with <c>'windows'</c> option mode.
+          </p>
+        <list type="bulleted">
+            <item><c>user_cache</c>
+                <p>The path location is intended for transient data files on a local machine.</p>
+                <p>
+                    On Linux:
+                    Respects the os environment variable <c>XDG_CACHE_HOME</c>.
+                </p>
+                <pre>
+1> <input>filename:basedir(user_cache, "my_application", #{os=>linux}).</input>
+"/home/otptest/.cache/my_application"</pre>
+                On Darwin: <pre>
+1> <input>filename:basedir(user_cache, "my_application", #{os=>darwin}).</input>
+"/home/otptest/Library/Caches/my_application"</pre>
+                On Windows: <pre>
+1> <input>filename:basedir(user_cache, "My App").</input>
+"c:/Users/otptest/AppData/Local/My App/Cache"
+2> <input>filename:basedir(user_cache, "My App").</input>
+"c:/Users/otptest/AppData/Local/My App/Cache"
+3> <input>filename:basedir(user_cache, "My App", #{author=>"Erlang"}).</input>
+"c:/Users/otptest/AppData/Local/Erlang/My App/Cache"
+4> <input>filename:basedir(user_cache, "My App", #{version=>"1.2"}).</input>
+"c:/Users/otptest/AppData/Local/My App/1.2/Cache"
+5> <input>filename:basedir(user_cache, "My App", #{author=>"Erlang",version=>"1.2"}).</input>
+"c:/Users/otptest/AppData/Local/Erlang/My App/1.2/Cache"</pre>
+            </item>
+            <item><c>user_config</c>
+                <p>
+                    The path location is intended for persistent configuration files.
+                </p>
+                <p>
+                    On Linux:
+                    Respects the os environment variable <c>XDG_CONFIG_HOME</c>.
+                </p>
+                <pre>
+2> <input>filename:basedir(user_config, "my_application", #{os=>linux}).</input>
+"/home/otptest/.config/my_application"</pre>
+                On Darwin:<pre>
+2> <input>filename:basedir(user_config, "my_application", #{os=>darwin}).</input>
+"/home/otptest/Library/Application Support/my_application"</pre>
+                On Windows:<pre>
+1> <input>filename:basedir(user_config, "My App").</input>
+"c:/Users/otptest/AppData/Roaming/My App"
+2> <input>filename:basedir(user_config, "My App", #{author=>"Erlang", version=>"1.2"}).</input>
+"c:/Users/otptest/AppData/Roaming/Erlang/My App/1.2"</pre>
+            </item>
+            <item><c>user_data</c>
+                <p>
+                    The path location is intended for persistent data files.
+                </p>
+                <p>
+                    On Linux:
+                    Respects the os environment variable <c>XDG_DATA_HOME</c>.
+                </p>
+                <pre>
+3> <input>filename:basedir(user_data, "my_application", #{os=>linux}).</input>
+"/home/otptest/.local/my_application"</pre>
+                On Darwin:<pre>
+3> <input>filename:basedir(user_data, "my_application", #{os=>darwin}).</input>
+"/home/otptest/Library/Application Support/my_application"</pre>
+                On Windows:<pre>
+8> <input>filename:basedir(user_data, "My App").</input>
+"c:/Users/otptest/AppData/Local/My App"
+9> <input>filename:basedir(user_data, "My App",#{author=>"Erlang",version=>"1.2"}).</input>
+"c:/Users/otptest/AppData/Local/Erlang/My App/1.2"</pre>
+            </item>
+            <item><c>user_log</c>
+                <p>The path location is intended for transient log files on a local machine.</p>
+                <p>
+                On Linux:
+                Respects the os environment variable <c>XDG_CACHE_HOME</c>.</p>
+                <pre>
+4> <input>filename:basedir(user_log, "my_application", #{os=>linux}).</input>
+"/home/otptest/.cache/my_application/log"</pre>
+                On Darwin:<pre>
+4> <input>filename:basedir(user_log, "my_application", #{os=>darwin}).</input>
+"/home/otptest/Library/Caches/my_application"</pre>
+                On Windows:<pre>
+12> <input>filename:basedir(user_log, "My App").</input>
+"c:/Users/otptest/AppData/Local/My App/Logs"
+13> <input>filename:basedir(user_log, "My App",#{author=>"Erlang",version=>"1.2"}).</input>
+"c:/Users/otptest/AppData/Local/Erlang/My App/1.2/Logs"</pre>
+            </item>
+            <item><c>site_config</c><p>
+                On Linux:
+                Respects the os environment variable <c>XDG_CONFIG_DIRS</c>.</p>
+<pre>
+5> <input>filename:basedir(site_data, "my_application", #{os=>linux}).</input>
+["/usr/local/share/my_application",
+ "/usr/share/my_application"]
+6> <input>os:getenv("XDG_CONFIG_DIRS").</input>
+"/etc/xdg/xdg-ubuntu:/usr/share/upstart/xdg:/etc/xdg"
+7> <input>filename:basedir(site_config, "my_application", #{os=>linux}).</input>
+["/etc/xdg/xdg-ubuntu/my_application",
+ "/usr/share/upstart/xdg/my_application",
+ "/etc/xdg/my_application"]
+8> <input>os:unsetenv("XDG_CONFIG_DIRS").</input>
+true
+9> <input>filename:basedir(site_config, "my_application", #{os=>linux}).</input>
+["/etc/xdg/my_application"]</pre>
+                On Darwin:<pre>
+5> <input>filename:basedir(site_config, "my_application", #{os=>darwin}).</input>
+["/Library/Application Support/my_application"]</pre>
+            </item>
+            <item><c>site_data</c><p>
+                    On Linux:
+                    Respects the os environment variable <c>XDG_DATA_DIRS</c>.</p>
+                <pre>
+10> <input>os:getenv("XDG_DATA_DIRS").</input>
+"/usr/share/ubuntu:/usr/share/gnome:/usr/local/share/:/usr/share/"
+11> <input>filename:basedir(site_data, "my_application", #{os=>linux}).</input>
+["/usr/share/ubuntu/my_application",
+ "/usr/share/gnome/my_application",
+ "/usr/local/share/my_application",
+ "/usr/share/my_application"]
+12> <input>os:unsetenv("XDG_DATA_DIRS").</input>
+true
+13> <input>filename:basedir(site_data, "my_application", #{os=>linux}).</input>
+["/usr/local/share/my_application",
+ "/usr/share/my_application"]</pre>
+                On Darwin:<pre>
+5> <input>filename:basedir(site_data, "my_application", #{os=>darwin}).</input>
+["/Library/Application Support/my_application"]</pre>
+            </item>
+        </list>
+      </desc>
+    </func>
+    <func>
       <name name="basename" arity="1"/>
       <fsummary>Return the last component of a filename</fsummary>
       <desc>
diff --git a/lib/stdlib/src/filename.erl b/lib/stdlib/src/filename.erl
index 008beb8b67..d921a69108 100644
--- a/lib/stdlib/src/filename.erl
+++ b/lib/stdlib/src/filename.erl
@@ -36,6 +36,7 @@
 	 extension/1, join/1, join/2, pathtype/1,
 	 rootname/1, rootname/2, split/1, nativename/1]).
 -export([find_src/1, find_src/2, flatten/1]).
+-export([basedir/2, basedir/3]).
 
 %% Undocumented and unsupported exports.
 -export([append/2]).
@@ -139,6 +140,7 @@ absname_join(AbsBase, Name) ->
 
 -spec basename(Filename) -> file:filename_all() when
       Filename :: file:name_all().
+
 basename(Name) when is_binary(Name) ->
     case os:type() of
 	{win32,_} ->
@@ -954,3 +956,161 @@ filename_string_to_binary(List) ->
 	    Bin
     end.
 
+%% Application Base Directories
+%% basedir
+%% http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
+
+-type basedir_type() :: 'user_cache' | 'user_config' | 'user_data'
+                      | 'user_log'
+                      | 'site_config' | 'site_data'.
+
+-spec basedir(Type,Application) -> file:filename_all() when
+      Type :: basedir_type(),
+      Application :: string() | binary().
+
+basedir(Type,Application) when is_atom(Type), is_list(Application) orelse
+                                              is_binary(Application) ->
+    basedir(Type, Application, #{}).
+
+-spec basedir(Type,Application,Opts) -> file:filename_all() when
+      Type :: basedir_type(),
+      Application :: string() | binary(),
+      Opts :: #{author => string() | binary(),
+                os => 'windows' | 'darwin' | 'linux',
+                version => string() | binary()}.
+
+basedir(Type,Application,Opts) when is_atom(Type), is_map(Opts),
+                                    is_list(Application) orelse
+                                    is_binary(Application) ->
+    Os   = basedir_os_from_opts(Opts),
+    Name = basedir_name_from_opts(Os,Application,Opts),
+    Base = basedir_from_os(Type,Os),
+    case {Type,Os} of
+        {user_log,linux} ->
+            filename:join([Base,Name,"log"]);
+        {user_log,windows} ->
+            filename:join([Base,Name,"Logs"]);
+        {user_cache,windows} ->
+            filename:join([Base,Name,"Cache"]);
+        {Type,_} when Type =:= site_config orelse Type =:= site_data ->
+            [filename:join([B,Name]) || B <- Base];
+        _ ->
+            filename:join([Base,Name])
+    end.
+
+basedir_os_from_opts(#{os := linux}) -> linux;
+basedir_os_from_opts(#{os := windows}) -> windows;
+basedir_os_from_opts(#{os := darwin}) -> darwin;
+basedir_os_from_opts(#{}) -> basedir_os_type().
+
+basedir_name_from_opts(windows,App,#{author:=Author,version:=Vsn}) ->
+    filename:join([Author,App,Vsn]);
+basedir_name_from_opts(windows,App,#{author:=Author}) ->
+    filename:join([Author,App]);
+basedir_name_from_opts(_,App,#{version:=Vsn}) ->
+    filename:join([App,Vsn]);
+basedir_name_from_opts(_,App,_) ->
+    App.
+
+basedir_from_os(Type,Os) ->
+    case Os of
+        linux   -> basedir_linux(Type);
+        darwin  -> basedir_darwin(Type);
+        windows -> basedir_windows(Type)
+    end.
+
+-define(basedir_linux_user_data,   ".local/share").
+-define(basedir_linux_user_config, ".config").
+-define(basedir_linux_user_cache,  ".cache").
+-define(basedir_linux_user_log,    ".cache"). %% .cache/App/log
+-define(basedir_linux_site_data,   "/usr/local/share/:/usr/share/").
+-define(basedir_linux_site_config, "/etc/xdg").
+
+basedir_linux(Type) ->
+    case Type of
+        user_data   -> getenv("XDG_DATA_HOME",  ?basedir_linux_user_data,  true);
+        user_config -> getenv("XDG_CONFIG_HOME",?basedir_linux_user_config,true);
+        user_cache  -> getenv("XDG_CACHE_HOME", ?basedir_linux_user_cache, true);
+        user_log    -> getenv("XDG_CACHE_HOME", ?basedir_linux_user_log,   true);
+        site_data   ->
+            Base = getenv("XDG_DATA_DIRS",?basedir_linux_site_data,false),
+            string:tokens(Base,":");
+        site_config ->
+            Base = getenv("XDG_CONFIG_DIRS",?basedir_linux_site_config,false),
+            string:tokens(Base,":")
+    end.
+
+-define(basedir_darwin_user_data,   "Library/Application Support").
+-define(basedir_darwin_user_config, "Library/Application Support").
+-define(basedir_darwin_user_cache,  "Library/Caches").
+-define(basedir_darwin_user_log,    "Library/Logs").
+-define(basedir_darwin_site_data,   "/Library/Application Support").
+-define(basedir_darwin_site_config, "/Library/Application Support").
+
+basedir_darwin(Type) ->
+    case Type of
+        user_data   -> basedir_join_home(?basedir_darwin_user_data);
+        user_config -> basedir_join_home(?basedir_darwin_user_config);
+        user_cache  -> basedir_join_home(?basedir_darwin_user_cache);
+        user_log    -> basedir_join_home(?basedir_darwin_user_log);
+        site_data   -> [?basedir_darwin_site_data];
+        site_config -> [?basedir_darwin_site_config]
+    end.
+
+%% On Windows:
+%% ex. C:\Users\egil\AppData\Local\Ericsson\Erlang
+%% %LOCALAPPDATA% is defined on Windows 7 and onwards
+%% %APPDATA% is used instead of %LOCALAPPDATA% if it's not defined.
+%% %APPDATA% is used for roaming, i.e. for user_config on Windows 7 and beyond.
+%%
+%% user_data    %LOCALAPPDATA%[/$author]/$appname[/$version]
+%% user_config  %APPDATA%[/$author]/$appname[/$version]
+%% user_cache   %LOCALAPPDATA%[/$author]/$appname[/$version]/Cache
+%% user_log     %LOCALAPPDATA%[/$author]/$appname[/$version]/Logs
+
+basedir_windows(Type) ->
+    %% If LOCALAPPDATA is not defined we are likely on an
+    %% XP machine. Use APPDATA instead.
+    AppData = basedir_windows_appdata(),
+    case Type of
+        user_data   -> getenv("LOCALAPPDATA", AppData);
+        user_config -> AppData;
+        user_cache  -> getenv("LOCALAPPDATA", AppData);
+        user_log    -> getenv("LOCALAPPDATA", AppData);
+        site_data   -> [];
+        site_config -> []
+    end.
+
+basedir_windows_appdata() ->
+    case os:getenv("APPDATA") of
+        Invalid when Invalid =:= false orelse Invalid =:= [] ->
+            erlang:error(noappdata);
+        Val   -> Val
+    end.
+
+%% basedir aux
+
+getenv(K,Def,false) -> getenv(K,Def);
+getenv(K,Def,true)  -> getenv(K,basedir_join_home(Def)).
+
+getenv(K,Def) ->
+    case os:getenv(K) of
+        []    -> Def;
+        false -> Def;
+        Val   -> Val
+    end.
+
+basedir_join_home(Dir) ->
+    case os:getenv("HOME") of
+        false ->
+            {ok,[[Home]]} = init:get_argument(home),
+            filename:join(Home,Dir);
+        Home  -> filename:join(Home,Dir)
+    end.
+
+basedir_os_type() ->
+    case os:type() of
+        {unix,darwin} -> darwin;
+        {win32,_}     -> windows;
+        _             -> linux
+    end.
diff --git a/lib/stdlib/test/filename_SUITE.erl b/lib/stdlib/test/filename_SUITE.erl
index ad7206ceae..7f2e4771f3 100644
--- a/lib/stdlib/test/filename_SUITE.erl
+++ b/lib/stdlib/test/filename_SUITE.erl
@@ -28,6 +28,7 @@
 	 basename_bin_1/1, basename_bin_2/1,
 	 dirname_bin/1, extension_bin/1, join_bin/1, t_nativename_bin/1]).
 -export([pathtype_bin/1,rootname_bin/1,split_bin/1]).
+-export([t_basedir_api/1, t_basedir_xdg/1, t_basedir_windows/1]).
 
 -include_lib("common_test/include/ct.hrl").
 
@@ -37,7 +38,8 @@ all() ->
     [absname, absname_2,
      find_src,
      absname_bin, absname_bin_2,
-     {group,p}].
+     {group,p},
+     t_basedir_xdg, t_basedir_windows].
 
 groups() -> 
     [{p, [parallel],
@@ -47,7 +49,8 @@ groups() ->
        basename_1, basename_2,
        basename_bin_1, basename_bin_2, dirname_bin,
        join_bin, pathtype_bin, rootname_bin, split_bin,
-       t_nativename_bin]}].
+       t_nativename_bin,
+       t_basedir_api]}].
 
 init_per_suite(Config) ->
     Config.
@@ -770,3 +773,178 @@ t_nativename_bin(Config) when is_list(Config) ->
             <<"/usr/tmp/arne">> =
                 filename:nativename(<<"/usr/tmp//arne/">>)
     end.
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% basedirs
+t_basedir_api(Config) when is_list(Config) ->
+    true = is_list(filename:basedir(site_data, "My App")),
+    true = is_list(filename:basedir(site_config, "My App")),
+    true = is_list(filename:basedir(user_data, "My App")),
+    true = is_list(filename:basedir(user_log, "My App")),
+    true = is_list(filename:basedir(user_config, "My App")),
+    true = is_list(filename:basedir(user_cache, "My App")),
+
+    true = is_list(filename:basedir(site_data, <<"My App">>)),
+    true = is_list(filename:basedir(site_config, <<"My App">>)),
+    true = is_binary(filename:basedir(user_data, <<"My App">>)),
+    true = is_binary(filename:basedir(user_log, <<"My App">>)),
+    true = is_binary(filename:basedir(user_config, <<"My App">>)),
+    true = is_binary(filename:basedir(user_cache, <<"My App">>)),
+
+    %% simulate for windows
+    case os:type() of
+        {win32,_} -> ok;
+        _ ->
+            os:putenv("APPDATA", "C:\\Documents and Settings\\otptest\\Application Data")
+    end,
+
+    true = is_list(filename:basedir(site_data, "My App", #{})),
+    true = is_list(filename:basedir(site_config, "My App", #{os=>linux})),
+    true = is_list(filename:basedir(user_data, "My App", #{os=>darwin})),
+    true = is_list(filename:basedir(user_log, "My App", #{os=>windows})),
+    true = is_list(filename:basedir(user_config, "My App",#{author=>"Erl"})),
+    true = is_list(filename:basedir(user_config, "My App",#{os=>darwin,
+                                                            author=>"Erl"})),
+    true = is_list(filename:basedir(user_config, "My App",#{os=>linux,
+                                                            author=>"Erl"})),
+    true = is_list(filename:basedir(user_cache, "My App",#{os=>windows,
+                                                           author=>"Erl"})),
+    true = is_list(filename:basedir(user_config, "My App",#{os=>darwin,
+                                                            author=>"Erla",
+                                                            version=>"1.0"})),
+    true = is_list(filename:basedir(user_config, "My App",#{os=>linux,
+                                                            version=>"2.0.1",
+                                                            author=>"Erl"})),
+    true = is_list(filename:basedir(user_cache, "My App",#{os=>windows,
+                                                           version=>"3.1.2",
+                                                           author=>"Erl"})),
+    true = is_binary(filename:basedir(user_config, "My App",#{os=>darwin,
+                                                              author=>"Erla",
+                                                              version=><<"1.0">>})),
+    true = is_binary(filename:basedir(user_config, "My App",#{os=>windows,
+                                                              version=>"2.0.1",
+                                                              author=><<"Erl">>})),
+    true = is_binary(filename:basedir(user_cache, "My App",#{os=>linux,
+                                                             version=><<"3.1.2">>,
+                                                             author=>"Erl"})),
+    %% simulate for windows
+    case os:type() of
+        {win32,_} -> ok;
+        _ -> os:unsetenv("APPDATA")
+    end,
+
+    {'EXIT', _} = (catch filename:basedir(wrong_config, "My App")),
+    {'EXIT', _} = (catch filename:basedir(user_cache, {bad,name})),
+    {'EXIT', _} = (catch filename:basedir(user_cache, "My App", badopts)),
+    {'EXIT', _} = (catch filename:basedir(user_cache, "My App", [])),
+    ok.
+
+t_basedir_windows(Config) when is_list(Config) ->
+    Types = [user_data,user_log,user_config,user_cache],
+    case os:type() of
+        {win32,_} ->
+            ok = check_basedir_windows(Types, #{});
+        _ ->
+            %% Windows 7 and beyond
+            os:putenv("APPDATA", "C:\\Users\\otptest\\AppData\\Roaming"),
+            os:putenv("LOCALAPPDATA", "C:\\Users\\otptest\\AppData\\Local"),
+            io:format("APPDATA ~p~n", [os:getenv("APPDATA")]),
+            io:format("LOCALAPPDATA ~p~n", [os:getenv("LOCALAPPDATA")]),
+            ok = check_basedir_windows(Types,#{os=>windows}),
+            %% Windows XP
+            os:unsetenv("LOCALAPPDATA"),
+            os:putenv("APPDATA", "C:\\Documents and Settings\\otptest\\Application Data"),
+            io:format("APPDATA ~p~n", [os:getenv("APPDATA")]),
+            io:format("APPLOCALDATA ~p~n", [os:getenv("APPLOCALDATA")]),
+            ok = check_basedir_windows(Types,#{os=>windows}),
+            os:unsetenv("APPDATA")
+    end,
+    ok.
+
+check_basedir_windows([],_) -> ok;
+check_basedir_windows([Type|Types],Opt) ->
+    Name = "Some Application",
+    io:format("type: ~p~n", [Type]),
+    ok = check_basedir_windows_path(Type,
+                                    [Name],
+                                    filename:basedir(Type, Name, Opt)),
+    ok = check_basedir_windows_path(Type,
+                                    ["Erl",Name],
+                                    filename:basedir(Type, Name, Opt#{author=>"Erl"})),
+    ok = check_basedir_windows_path(Type,
+                                    [Name,"1.0"],
+                                    filename:basedir(Type, Name, Opt#{version=>"1.0"})),
+    ok = check_basedir_windows_path(Type,
+                                    ["Erl",Name,"1.0"],
+                                    filename:basedir(Type, Name, Opt#{author=>"Erl",
+                                                                      version=>"1.0"})),
+    check_basedir_windows(Types, Opt).
+
+check_basedir_windows_path(Type,Check0,Basedir) ->
+    BDR = lists:reverse(filename:split(Basedir)),
+    Check = lists:reverse(Check0),
+    io:format("~w: ~p ~p~n", [Type,Check,BDR]),
+    case Type of
+        user_log -> check_basedir_windows_path_split(["Logs"|Check],BDR);
+        user_cache -> check_basedir_windows_path_split(["Cache"|Check],BDR);
+        _ -> check_basedir_windows_path_split(Check,BDR)
+    end.
+
+check_basedir_windows_path_split([],_) -> ok;
+check_basedir_windows_path_split([Same|Check],[Same|BDR]) ->
+    check_basedir_windows_path_split(Check,BDR).
+
+
+t_basedir_xdg(Config) when is_list(Config) ->
+    check_basedir_xdg([user_data,user_log,user_config,user_cache,
+                       site_data,site_config]),
+    ok.
+
+check_basedir_xdg([]) -> ok;
+check_basedir_xdg([Type|Types]) ->
+    Name = "some_app",
+    Opt  = #{os=>linux},
+    Key  = basedir_xdg_env(Type),
+    io:format("type: ~p~n", [Type]),
+    Home = os:getenv("HOME"),
+    NDir = "/some/absolute/path",
+    DefPath = basedir_xdg_def(Type,Home,Name),
+    EnvPath = case Type of
+                  user_log    -> filename:join([NDir,Name,"log"]);
+                  site_data   -> [filename:join([NDir,Name])];
+                  site_config -> [filename:join([NDir,Name])];
+                  _           -> filename:join([NDir,Name])
+              end,
+    os:unsetenv(Key),
+    ok = check_basedir(Type, DefPath, filename:basedir(Type, Name, Opt)),
+    os:putenv(Key, NDir),
+    ok = check_basedir(Type, EnvPath, filename:basedir(Type, Name, Opt)),
+    os:unsetenv(Key),
+    ok = check_basedir(Type, DefPath, filename:basedir(Type, Name, Opt)),
+    check_basedir_xdg(Types).
+
+check_basedir(Type, Path, Basedir) ->
+    io:format("~w: ~p = ~p~n", [Type,Path,Basedir]),
+    Path = Basedir,
+    ok.
+
+basedir_xdg_env(Type) ->
+    case Type of
+        user_data   -> "XDG_DATA_HOME";
+        user_config -> "XDG_CONFIG_HOME";
+        user_cache  -> "XDG_CACHE_HOME";
+        user_log    -> "XDG_CACHE_HOME";
+        site_data   -> "XDG_DATA_DIRS";
+        site_config -> "XDG_CONFIG_DIRS"
+    end.
+
+basedir_xdg_def(Type,Home,Name) ->
+    case Type of
+        user_data   -> filename:join([Home,".local","share",Name]);
+        user_config -> filename:join([Home,".config",Name]);
+        user_cache  -> filename:join([Home,".cache",Name]);
+        user_log    -> filename:join([Home,".cache",Name,"log"]);
+        site_data   -> [filename:join([Dir,Name]) ||
+                        Dir <- ["/usr/local/share/","/usr/share/"]];
+        site_config -> [filename:join(["/etc/xdg",Name])]
+    end.