[UX] Implement back_to_exit option (#3838)

Also goes back to File Manager as default view first.

frontend/apps/filemanager/filemanager.lua

@@ -363,16 +363,31 @@ function FileManager:init()
 
     if Device:hasKeys() then
         self.key_events.Home = { {"Home"}, doc = "go home" }
-        if not Device:isSDL() then
-            --if not in the desktop emulator
-            --remove the old Back key to exit koreader
-            self.file_chooser.key_events.Close = nil
-        end
+        --Override the menu.lua way of handling the back key
+        self.file_chooser.key_events.Back = { {"Back"}, doc = "go back" }
     end
 
     self:handleEvent(Event:new("SetDimensions", self.dimen))
 end
 
+function FileChooser:onBack()
+    local back_to_exit = G_reader_settings:readSetting("back_to_exit") or "prompt"
+    if back_to_exit == "always" then
+        return self:onClose()
+    elseif back_to_exit == "disable" then
+        return true
+    elseif back_to_exit == "prompt" then
+            UIManager:show(ConfirmBox:new{
+                text = _("Exit KOReader?"),
+                ok_text = _("Exit"),
+                ok_callback = function()
+                    self:onClose()
+                end
+            })
+        return true
+    end
+end
+
 function FileManager:tapPlus()
     local buttons = {
         {

frontend/apps/reader/modules/readerback.lua

@@ -3,6 +3,7 @@ local Event = require("ui/event")
 local EventListener = require("ui/widget/eventlistener")
 local logger = require("logger")
 local util = require("util")
+local _ = require("gettext")
 
 local ReaderBack = EventListener:new{
     location_stack = {},
@@ -74,7 +75,7 @@ function ReaderBack:onBack()
         end
     else
         logger.dbg("[ReaderBack] no location history, closing")
-        self.ui:handleEvent(Event:new("Close"))
+        self.ui:handleEvent(Event:new("Home"))
     end
 end
 

frontend/apps/reader/readerui.lua

@@ -634,7 +634,9 @@ function ReaderUI:dealWithLoadDocumentFailure()
 end
 
 function ReaderUI:onHome()
-    return self:showFileManager()
+    self:onClose()
+    self:showFileManager()
+    return true
 end
 
 return ReaderUI

frontend/ui/elements/common_settings_menu_table.lua

@@ -125,6 +125,48 @@ if Device:isAndroid() then
     table.insert(common_settings.screen.sub_item_table, require("ui/elements/screen_fullscreen_menu_table"))
 end
 
+if Device:hasKeys() then
+    common_settings.navigation = {
+        text = _("Navigation"),
+        sub_item_table = {
+            {
+                text = _("Back key to exit KOReader"),
+                sub_item_table = {
+                    {
+                        text = _("Prompt"),
+                        checked_func = function()
+                            local setting = G_reader_settings:readSetting("back_to_exit")
+                            return setting == "prompt" or setting == nil
+                        end,
+                        callback = function()
+                            G_reader_settings:saveSetting("back_to_exit", "prompt")
+                        end,
+                    },
+                    {
+                        text = _("Always"),
+                        checked_func = function()
+                            return G_reader_settings:readSetting("back_to_exit")
+                                       == "always"
+                        end,
+                        callback = function()
+                            G_reader_settings:saveSetting("back_to_exit", "always")
+                        end,
+                    },
+                    {
+                        text = _("Disable"),
+                        checked_func = function()
+                            return G_reader_settings:readSetting("back_to_exit")
+                                       == "disable"
+                        end,
+                        callback = function()
+                            G_reader_settings:saveSetting("back_to_exit", "disable")
+                        end,
+                    },
+                },
+            },
+        }
+    }
+end
 common_settings.document = {
     text = _("Document"),
     sub_item_table = {

frontend/ui/elements/filemanager_menu_order.lua

@@ -27,6 +27,7 @@ local order = {
         "screen",
         "screensaver",
         "document",
+        "navigation",
         "----------------------------",
         "language",
         "time",

frontend/ui/elements/reader_menu_order.lua

@@ -43,6 +43,7 @@ local order = {
         "screen",
         "screensaver",
         "document",
+        "navigation",
         "----------------------------",
         "language",
         "time",