imagebox: Support a CSS file.

Before, the CSS had to be inline. Now that the border container uses
this code, it makes sense to make it more flexible.

lib/wibox/widget/imagebox.lua

@@ -31,12 +31,17 @@ local base = require("wibox.widget.base")
 local surface = require("gears.surface")
 local gtable = require("gears.table")
 local gdebug = require("gears.debug")
+local gfs = require("gears.filesystem")
 local setmetatable = setmetatable
 local type = type
 local math = math
 
 local unpack = unpack or table.unpack -- luacheck: globals unpack (compatibility with Lua 5.1)
 
+-- Placeholder table to represent an emty stylesheet.
+-- It has to be defined here to avoid being GCed
+local empty_stylesheet = {}
+
 local policies_to_extents = {
     ["pad"]     = cairo.Extend.PAD,
     ["repeat"]  = cairo.Extend.REPEAT,
@@ -55,18 +60,25 @@ end
 local imagebox = { mt = {} }
 
 local rsvg_handle_cache = setmetatable({}, { __mode = 'k' })
+local stylesheet_cache = {}
 
 --Load rsvg handle form image file
 -- @tparam string file Path to svg file.
 -- @return Rsvg handle
 -- @treturn table A table where cached data can be stored.
-function imagebox._load_rsvg_handle(file)
+function imagebox._load_rsvg_handle(file, style)
+    -- Make sure this is called in the right order.
+    assert((not style) or (style and stylesheet_cache[style]))
+
+    local style_ref = style and stylesheet_cache[style] or empty_stylesheet
+
     if not Rsvg then return end
 
-    local cache = (rsvg_handle_cache[file] or {})["handle"]
+    local bucket = rsvg_handle_cache[file] or {}
+    local cache = (bucket[style_ref] or {})["handle"]
 
     if cache then
-        return cache, rsvg_handle_cache[file]
+        return cache, bucket[style_ref]
     end
 
     local handle, err
@@ -78,9 +90,10 @@ function imagebox._load_rsvg_handle(file)
     end
 
     if not err then
-        rsvg_handle_cache[file] = rsvg_handle_cache[file] or {}
-        rsvg_handle_cache[file]["handle"] = handle
-        return handle, rsvg_handle_cache[file]
+        rsvg_handle_cache[file] = rsvg_handle_cache[file] or setmetatable({}, {__mode = "k"})
+        rsvg_handle_cache[file][style_ref] = rsvg_handle_cache[file][style_ref] or {}
+        rsvg_handle_cache[file][style_ref]["handle"] = handle
+        return handle, rsvg_handle_cache[file][style_ref]
     end
 end
 
@@ -117,7 +130,7 @@ end
 ---@treturn boolean True if image was successfully applied
 local function load_and_apply(ib, file, image_loader, image_setter)
     local image_applied
-    local object, cache = image_loader(file)
+    local object, cache = image_loader(file, ib._private.stylesheet_og)
 
     if object then
         image_applied = image_setter(ib, object, cache)
@@ -125,6 +138,38 @@ local function load_and_apply(ib, file, image_loader, image_setter)
     return image_applied
 end
 
+--- Support both CSS data and filepath for the stylsheet.
+function imagebox._get_stylesheet(self, content_or_path)
+    if not content_or_path then return nil end
+
+    -- Always set the entry because the image cache uses it.
+    stylesheet_cache[content_or_path] = stylesheet_cache[content_or_path]
+        or setmetatable({}, {__mode = "v"})
+
+    if gfs.file_readable(content_or_path) then
+        local ret
+
+        local _, obj = next(stylesheet_cache[content_or_path])
+
+        if obj then
+            ret = obj._private.stylesheet
+            table.insert(stylesheet_cache[content_or_path], self)
+        else
+            local f = io.open(content_or_path, 'r')
+
+            if not f then return nil end
+
+            ret = f:read("*all")
+            f:close()
+            table.insert(stylesheet_cache[content_or_path], self)
+        end
+
+        return ret
+    else
+        return content_or_path
+    end
+end
+
 ---Update the cached size depending on the stylesheet and dpi.
 --
 -- It's necessary because a single RSVG handle can be used by
@@ -443,8 +488,7 @@ end
 -- If the image is an SVG (vector graphics), this property allows to set
 -- a CSS stylesheet. It can be used to set colors and much more.
 --
--- Note that this property is a string, not a path. If the stylesheet is
--- stored on disk, read the content first.
+-- The value can be either CSS data or a file path.
 --
 --@DOC_wibox_widget_imagebox_stylesheet_EXAMPLE@
 --
@@ -483,18 +527,47 @@ end
 -- @propemits true false
 -- @see dpi
 
-for _, prop in ipairs {"stylesheet", "dpi", "auto_dpi"} do
+for _, prop in ipairs {"dpi", "auto_dpi"} do
     imagebox["set_" .. prop] = function(self, value)
+        local old = self._private[prop]
+
         -- It will be set in :fit and :draw. The handle is shared
         -- by multiple imagebox, so it cannot be set just once.
         self._private[prop] = value
 
         self:emit_signal("widget::redraw_needed")
         self:emit_signal("widget::layout_changed")
-        self:emit_signal("property::" .. prop)
+        self:emit_signal("property::" .. prop, value, old)
     end
 end
 
+function imagebox:set_stylesheet(value)
+    if value == self._private.stylesheet_og then return end
+
+    local old = self._private.stylesheet_og
+
+    if old and stylesheet_cache[old] then
+        for k, v in ipairs(stylesheet_cache[old]) do
+            if self == v then
+                table.remove(stylesheet_cache[old], k)
+                break
+            end
+        end
+    end
+
+    local content = imagebox._get_stylesheet(self, value)
+
+    self._private.stylesheet    = content
+    self._private.stylesheet_og = value
+
+    -- Refresh the pixmap.
+    self.image = self._private.original_image
+
+    self:emit_signal("widget::redraw_needed")
+    self:emit_signal("widget::layout_changed")
+    self:emit_signal("property::stylesheet", value)
+end
+
 function imagebox:set_resize(allowed)
     self._private.resize = allowed