core: auto-detect terminal background and apply light theme on first start

Detect the terminal background (via COLORFGBG or an OSC 11 query) before
GUI init and, on the first start, automatically apply the built-in
"light" theme when a light terminal is detected.

The function gui_term_theme_is_light returns an int (1 if light, 0 otherwise,
0 being the safe value when detection is unsure).

src/core/weechat.c

@@ -135,10 +135,13 @@ int weechat_auto_load_scripts = 1;     /* auto-load scripts                 */
 
 /*
  * Display WeeChat startup message.
+ *
+ * If "term_theme_light" is set, a notice about the automatic "light" theme is
+ * displayed on first start.
  */
 
 void
-weechat_startup_message (void)
+weechat_startup_message (int term_theme_light)
 {
     if (weechat_headless)
     {
@@ -183,22 +186,34 @@ weechat_startup_message (void)
     if (weechat_first_start)
     {
         /* message on first run (when weechat.conf is created) */
-        gui_chat_printf (NULL, "");
+        gui_chat_printf (NULL, _("Welcome to WeeChat!"));
         gui_chat_printf (
             NULL,
-            _("Welcome to WeeChat!\n"
-              "\n"
-              "If you are discovering WeeChat, it is recommended to read at "
-              "least the quickstart guide, and the user's guide if you have "
-              "some time; they explain main WeeChat concepts.\n"
-              "All WeeChat docs are available at: https://weechat.org/doc/\n"
-              "\n"
-              "Moreover, there is inline help with /help on all commands and "
-              "options (use Tab key to complete the name).\n"
-              "The command /fset can help to customize WeeChat.\n"
-              "\n"
-              "You can add and connect to an IRC server with /server and "
+            _("If you are discovering WeeChat, it is recommended to "
+              "read at least the quickstart guide, and the user's guide if "
+              "you have some time; they explain main WeeChat concepts."));
+        gui_chat_printf (
+            NULL,
+            _("All WeeChat docs are available at: %s"),
+            WEECHAT_WEBSITE_DOC);
+        gui_chat_printf (
+            NULL,
+            _("Moreover, there is inline help with /help on all commands and "
+              "options (use Tab key to complete the name)."));
+        gui_chat_printf (
+            NULL,
+            _("The command /fset can help to customize WeeChat."));
+        gui_chat_printf (
+            NULL,
+            _("You can add and connect to an IRC server with /server and "
               "/connect commands (see /help server)."));
+        if (term_theme_light)
+        {
+            gui_chat_printf (
+                NULL,
+                _("The \"light\" theme will be automatically applied. "
+                "Use /theme reset to switch back to the default dark theme."));
+        }
         gui_chat_printf (NULL, "");
         gui_chat_printf (NULL, "---");
         gui_chat_printf (NULL, "");
@@ -361,6 +376,8 @@ weechat_init_gettext (void)
 void
 weechat_init (int argc, char *argv[], void (*gui_init_cb)(void))
 {
+    int term_theme_light;               /* 1 if a light terminal detected   */
+
     weechat_first_start_time = time (NULL); /* initialize start time        */
     gettimeofday (&weechat_current_start_timeval, NULL);
 
@@ -369,6 +386,9 @@ weechat_init (int argc, char *argv[], void (*gui_init_cb)(void))
             * weechat_current_start_timeval.tv_usec)
            ^ getpid ());
 
+    /* detect the terminal theme, before initializing the GUI */
+    term_theme_light = gui_term_theme_is_light ();
+
     weeurl_init ();                     /* initialize URL                   */
     string_init ();                     /* initialize string                */
     signal_init ();                     /* initialize signals               */
@@ -408,7 +428,7 @@ weechat_init (int argc, char *argv[], void (*gui_init_cb)(void))
             weechat_upgrading = 0;
     }
     if (!weechat_doc_gen)
-        weechat_startup_message ();     /* display WeeChat startup message  */
+        weechat_startup_message (term_theme_light); /* startup message       */
     gui_chat_print_lines_waiting_buffer (NULL); /* display lines waiting    */
     weechat_term_check ();              /* warning about wrong $TERM        */
     weechat_locale_check ();            /* warning about wrong locale       */
@@ -426,6 +446,13 @@ weechat_init (int argc, char *argv[], void (*gui_init_cb)(void))
         weechat_doc_gen_ok = doc_generate (weechat_doc_gen_path);
         weechat_quit = 1;
     }
+
+    if (weechat_first_start && isatty (STDOUT_FILENO) && !weechat_headless && !weechat_doc_gen)
+    {
+        /* switch to "light" theme if terminal background was detected as "light" */
+        if (term_theme_light)
+            theme_apply ("light");
+    }
 }
 
 /*

src/core/weechat.h

@@ -55,6 +55,7 @@
 
 #define WEECHAT_COPYRIGHT_DATE   "(C) 2003-2026"
 #define WEECHAT_WEBSITE          "https://weechat.org/"
+#define WEECHAT_WEBSITE_DOC      "https://weechat.org/doc/"
 #define WEECHAT_WEBSITE_DOWNLOAD "https://weechat.org/download/"
 #define WEECHAT_AUTHOR_NAME      "Sébastien Helleu"
 #define WEECHAT_AUTHOR_EMAIL     "flashcode@flashtux.org"