[balsa/75-html-display-printing] fix wrong display/printout if the user overrides HTML preferences

[Albrecht Dreß <albrecht src gnome org>]

commit ed340fce8c99f7f4aef14af8a2fba040c548ed16
Author: Albrecht Dreß <albrecht dress netcologne de>
Date:   Wed May 4 21:17:23 2022 +0200

    fix wrong display/printout if the user overrides HTML preferences
    
    See https://gitlab.gnome.org/GNOME/balsa/-/issues/75#note_1444507 for a
    description of the issue.
    
    Changes:
    - libbalsa/body.[ch]: replace multipart/alternative selection state by a
    tri-state enum
    - src/balsa-message.c: use the automatic selection (settings, HTML prefs
    db) of the multipart/alternative subpart only initially
    - src/print-gtk.c: eval tri-state enum
    
    Signed-off-by: Albrecht Dreß <albrecht dress netcologne de>

 libbalsa/body.c     | 15 ++++++++++-----
 libbalsa/body.h     | 14 +++++++++++---
 src/balsa-message.c | 35 ++++++++++++++++++++++++-----------
 src/print-gtk.c     |  4 ++--
 4 files changed, 47 insertions(+), 21 deletions(-)
---
diff --git a/libbalsa/body.c b/libbalsa/body.c
index a3410497c..0dcb5f243 100644
--- a/libbalsa/body.c
+++ b/libbalsa/body.c
@@ -1007,7 +1007,11 @@ libbalsa_message_body_set_html_selected(LibBalsaMessageBody *body)
                        gchar *conttype;
 
                        conttype = libbalsa_message_body_get_mime_type(body);
-                       mp_alt_body->html_selected = libbalsa_html_type(conttype) != LIBBALSA_HTML_TYPE_NONE;
+                       if (libbalsa_html_type(conttype) != LIBBALSA_HTML_TYPE_NONE) {
+                               mp_alt_body->mp_alt_selection = LIBBALSA_MP_ALT_HTML;
+                       } else {
+                               mp_alt_body->mp_alt_selection = LIBBALSA_MP_ALT_PLAIN;
+                       }
                        g_free(conttype);
                }
        }
@@ -1017,19 +1021,20 @@ libbalsa_message_body_set_html_selected(LibBalsaMessageBody *body)
 /** @brief Check if a multipart/alternative HTML or plain part is selected
  *
  * @param[in] body message body
- * @return TRUE iff body is a child of a multipart/alternative for which the HTML part is selected
+ * @return which part of a multipart/alternative is selected, @ref LIBBALSA_MP_ALT_AUTO if @em body id not 
part of a
+ *         multipart/alternative or if the selection shall be done automatically
  * @sa find_mp_alt_parent()
  */
-gboolean
+LibBalsaMpAltSelection
 libbalsa_message_body_get_html_selected(LibBalsaMessageBody *body)
 {
        LibBalsaMessageBody *mp_alt_body;
-       gboolean result = FALSE;
+       LibBalsaMpAltSelection result = LIBBALSA_MP_ALT_AUTO;
 
        g_return_val_if_fail(body != NULL, FALSE);
        mp_alt_body = find_mp_alt_parent(body);
        if (mp_alt_body != NULL) {
-               result = mp_alt_body->html_selected;
+               result = mp_alt_body->mp_alt_selection;
        }
        return result;
 }
diff --git a/libbalsa/body.h b/libbalsa/body.h
index 4fb6adc0b..58a03dd68 100644
--- a/libbalsa/body.h
+++ b/libbalsa/body.h
@@ -57,6 +57,14 @@ enum _LibBalsaAttachMode {
     LIBBALSA_ATTACH_AS_EXTBODY
 };
 
+typedef enum _LibBalsaMpAltSelection LibBalsaMpAltSelection;
+
+enum _LibBalsaMpAltSelection {
+       LIBBALSA_MP_ALT_AUTO = 0,                       /**< Automatically select text/plain or text/html. */
+       LIBBALSA_MP_ALT_PLAIN,                          /**< User selected text/plain.  */
+       LIBBALSA_MP_ALT_HTML                            /**< User selected text/html. */
+};
+
 #define LIBBALSA_MESSAGE_BODY_SAFE (S_IRUSR | S_IWUSR)
 #define LIBBALSA_MESSAGE_BODY_UNSAFE \
     (S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH)
@@ -85,7 +93,7 @@ struct _LibBalsaMessageBody {
 
 #ifdef HAVE_HTML_WIDGET
     gboolean html_ext_loaded;  /* if external HTML content was loaded */
-    gboolean html_selected;            /* if the HTML part of a multipart/alternative is selected */
+    LibBalsaMpAltSelection mp_alt_selection;   /* which part of a multipart/alternative is selected */
 #endif /* HAVE_HTML_WIDGET */
 
     LibBalsaMessageBody *parent;       /* Parent part in the message */
@@ -140,10 +148,10 @@ LibBalsaMessageBody *libbalsa_message_body_mp_related_root(LibBalsaMessageBody *
 
 #ifdef HAVE_HTML_WIDGET
 void libbalsa_message_body_set_html_selected(LibBalsaMessageBody *body);
-gboolean libbalsa_message_body_get_html_selected(LibBalsaMessageBody *body);
+LibBalsaMpAltSelection libbalsa_message_body_get_html_selected(LibBalsaMessageBody *body);
 #else
 #define libbalsa_message_body_set_html_selected(x)
-#define libbalsa_message_body_get_html_selected(x)     FALSE
+#define libbalsa_message_body_get_html_selected(x)     LIBBALSA_MP_ALT_AUTO
 #endif /*HAVE_HTML_WIDGET*/
 
 guint libbalsa_message_body_protect_mode(const LibBalsaMessageBody * body);
diff --git a/src/balsa-message.c b/src/balsa-message.c
index 7b9163542..e69c4bf95 100644
--- a/src/balsa-message.c
+++ b/src/balsa-message.c
@@ -2013,17 +2013,30 @@ balsa_message_has_previous_part(BalsaMessage * balsa_message)
 static gboolean
 libbalsa_can_display(LibBalsaMessageBody *part, InternetAddressList *from)
 {
-    gchar *content_type = libbalsa_message_body_get_mime_type(part);
-    gboolean res = FALSE;
-    if ((!balsa_app.display_alt_plain || libbalsa_html_get_prefer_html(from) ||
-         libbalsa_message_body_get_html_selected(part)) &&
-       (libbalsa_html_type(content_type) != LIBBALSA_HTML_TYPE_NONE))
-       res = TRUE;
-    else if(strcmp(content_type, "multipart/related") == 0 &&
-           part->parts)
-       res = libbalsa_can_display(part->parts, from);
-    g_free(content_type);
-    return res;
+       gchar *content_type = libbalsa_message_body_get_mime_type(part);
+       gboolean res;
+
+       if (strcmp(content_type, "multipart/related") == 0) {
+               res = (part->parts != NULL) ? libbalsa_can_display(part->parts, from) : FALSE;
+       } else {
+               switch (libbalsa_message_body_get_html_selected(part)) {
+               case LIBBALSA_MP_ALT_AUTO:
+                       res = (!balsa_app.display_alt_plain || libbalsa_html_get_prefer_html(from)) &&
+                               (libbalsa_html_type(content_type) != LIBBALSA_HTML_TYPE_NONE);
+                       break;
+               case LIBBALSA_MP_ALT_PLAIN:
+                       res = FALSE;
+                       break;
+               case LIBBALSA_MP_ALT_HTML:
+                       res = (libbalsa_html_type(content_type) != LIBBALSA_HTML_TYPE_NONE);
+                       break;
+               default:
+                       g_assert_not_reached();         /* paranoid check... */
+               }
+       }
+
+       g_free(content_type);
+       return res;
 }
 #endif                          /* HAVE_HTML_WIDGET */
 
diff --git a/src/print-gtk.c b/src/print-gtk.c
index d2b4d54c2..521d0662d 100644
--- a/src/print-gtk.c
+++ b/src/print-gtk.c
@@ -249,7 +249,7 @@ scan_body(GList *bpo_list, GtkPrintContext * context, BalsaPrintSetup * psetup,
 
                if (strcmp(conttype, "multipart/alternative") == 0) {
 #ifdef HAVE_HTML_WIDGET
-                       print_part = select_from_mp_alt(body->parts, body->html_selected);
+                       print_part = select_from_mp_alt(body->parts, body->mp_alt_selection == 
LIBBALSA_MP_ALT_HTML);
 #else
                        print_part = select_from_mp_alt(body->parts, FALSE);
 #endif
@@ -262,7 +262,7 @@ scan_body(GList *bpo_list, GtkPrintContext * context, BalsaPrintSetup * psetup,
                        mp_rel_root_type = libbalsa_message_body_get_mime_type(mp_rel_root);
                        if (strcmp(mp_rel_root_type, "multipart/alternative") == 0) {
 #ifdef HAVE_HTML_WIDGET
-                               print_part = select_from_mp_alt(mp_rel_root->parts, 
mp_rel_root->html_selected);
+                               print_part = select_from_mp_alt(mp_rel_root->parts, 
mp_rel_root->mp_alt_selection == LIBBALSA_MP_ALT_HTML);
 #else
                                print_part = select_from_mp_alt(mp_rel_root->parts, FALSE);
 #endif