From cc185bae4eac6322b5c4151d46f7aea637e50b76 Mon Sep 17 00:00:00 2001
From: poire-z <poire-z@users.noreply.github.com>
Date: Sat, 11 Jun 2022 11:08:42 +0200
Subject: [PATCH] Embedded fonts toggle: disabled if no embedded font

Have the enabled/disabled state of the toggle show the
presence or not of embedded fonts in the current book.
Also show the names of the embedded fonts in the
help_text InfoMessage.
---
 frontend/document/credocument.lua |  4 ++++
 frontend/ui/data/creoptions.lua   | 17 +++++++++++++++--
 frontend/ui/data/optionsutil.lua  |  5 ++++-
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/frontend/document/credocument.lua b/frontend/document/credocument.lua
index 23ab1daa2..64b2cae05 100644
--- a/frontend/document/credocument.lua
+++ b/frontend/document/credocument.lua
@@ -797,6 +797,10 @@ function CreDocument:getFontFace()
     return self._document:getFontFace()
 end
 
+function CreDocument:getEmbeddedFontList()
+    return self._document:getEmbeddedFontList()
+end
+
 function CreDocument:getCurrentPos()
     return self._document:getCurrentPos()
 end
diff --git a/frontend/ui/data/creoptions.lua b/frontend/ui/data/creoptions.lua
index 459f68018..924edaa07 100644
--- a/frontend/ui/data/creoptions.lua
+++ b/frontend/ui/data/creoptions.lua
@@ -1,9 +1,10 @@
 local Device = require("device")
 local Screen = Device.screen
+local ffiUtil = require("ffi/util")
 local optionsutil = require("ui/data/optionsutil")
 local _ = require("gettext")
 local C_ = _.pgettext
-local T = require("ffi/util").template
+local T = ffiUtil.template
 
 -- Get font size numbers as a table of strings
 local tableOfNumbersToTableOfStrings = function(numbers)
@@ -700,12 +701,24 @@ Whether enabled or disabled, KOReader's own status bar at the bottom of the scre
                 args = {false, true},
                 default_arg = nil,
                 event = "ToggleEmbeddedFonts",
-                enabled_func = function(configurable)
+                enabled_func = function(configurable, document)
                     return optionsutil.enableIfEquals(configurable, "embedded_css", 1)
+                            and next(document:getEmbeddedFontList()) ~= nil
                 end,
                 name_text_hold_callback = optionsutil.showValues,
                 help_text = _([[Enable or disable the use of the fonts embedded in the book.
 (Disabling the fonts specified in the publisher stylesheets can also be achieved via Style Tweaks in the main menu.)]]),
+                help_text_func = function(configurable, document)
+                    local font_list = document:getEmbeddedFontList()
+                    if next(font_list) then
+                        local font_details = {}
+                        table.insert(font_details, _("Embedded fonts provided by the current book:"))
+                        for name in ffiUtil.orderedPairs(font_list) do
+                            table.insert(font_details, name .. (font_list[name] and "" or T("  (%1)", _("not used"))))
+                        end
+                        return table.concat(font_details, "\n")
+                    end
+                end,
             },
             {
                 name = "smooth_scaling",
diff --git a/frontend/ui/data/optionsutil.lua b/frontend/ui/data/optionsutil.lua
index aa6074739..d0f131308 100644
--- a/frontend/ui/data/optionsutil.lua
+++ b/frontend/ui/data/optionsutil.lua
@@ -101,7 +101,10 @@ function optionsutil.showValues(configurable, option, prefix, document)
     end
     if option.help_text_func then
         -- Allow for concatenating a dynamic help_text_func to a static help_text
-        help_text = T("%1\n%2\n", help_text, option.help_text_func(configurable, document))
+        local more_text = option.help_text_func(configurable, document)
+        if more_text and more_text ~= "" then
+            help_text = T("%1\n%2\n", help_text, more_text)
+        end
     end
     local text
     local name_text = option.name_text_func