register opened document in documentregistry

so that when calling getCoverPageImage in screensaver mode
the document won't be opened again. This should avoid a lot of
problem such as messing up style and options described in #863.

frontend/document/credocument.lua

@@ -17,6 +17,7 @@ local CreDocument = Document:new{
     PAGE_VIEW_MODE = 1,
 
     _document = false,
+    _loaded = false,
     engine_initilized = false,
 
     line_space_percent = 100,
@@ -120,9 +121,16 @@ function CreDocument:init()
     self.info.configurable = true
 end
 
+function CreDocument:loadDocument()
+    if not self._loaded then
+        self._document:loadDocument(self.file)
+        self._loaded = true
+    end
+end
+
 function CreDocument:render()
     -- load document before rendering
-    self._document:loadDocument(self.file)
+    self:loadDocument()
     self._document:renderDocument()
     if not self.info.has_pages then
         self.info.doc_height = self._document:getFullHeight()
@@ -139,7 +147,7 @@ end
 
 function CreDocument:getCoverPageImage()
     -- don't need to render document in order to get cover image
-    self._document:loadDocument(self.file)
+    self:loadDocument()
     local data, size = self._document:getCoverPageImageData()
     if data and size then
         local image = Image:fromData(data, size)

frontend/document/document.lua

@@ -81,7 +81,8 @@ end
 
 -- this might be overridden by a document implementation
 function Document:close()
-    if self.is_open then
+    local DocumentRegistry = require("document/documentregistry")
+    if self.is_open and DocumentRegistry:closeDocument(self.file) == 0 then
         self.is_open = false
         self._document:close()
     end

frontend/document/documentregistry.lua

@@ -2,7 +2,8 @@
 This is a registry for document providers
 ]]--
 local DocumentRegistry = {
-    providers = { }
+    registry = {},
+    providers = {},
 }
 
 function DocumentRegistry:addProvider(extension, mimetype, provider)
@@ -20,9 +21,31 @@ function DocumentRegistry:getProvider(file)
 end
 
 function DocumentRegistry:openDocument(file)
-    local provider = self:getProvider(file)
-    if provider ~= nil then
-        return provider:new{file = file}
+    if not self.registry[file] then
+        local provider = self:getProvider(file)
+        if provider ~= nil then
+            self.registry[file] = {
+                doc = provider:new{file = file},
+                refs = 1,
+            }
+        end
+    else
+        self.registry[file].refs = self.registry[file].refs + 1
+    end
+    return self.registry[file].doc
+end
+
+function DocumentRegistry:closeDocument(file)
+    if self.registry[file] then
+        self.registry[file].refs = self.registry[file].refs - 1
+        if self.registry[file].refs == 0 then
+            self.registry[file] = nil
+            return 0
+        else
+            return self.registry[file].refs
+        end
+    else
+        error("Try to close unregistered file.")
     end
 end