awful: implement tag history

Signed-off-by: Julien Danjou <julien@danjou.info>

awesomerc.lua.in

@@ -187,6 +187,7 @@ end
 
 keybinding({ modkey }, "Left", awful.tag.viewprev):add()
 keybinding({ modkey }, "Right", awful.tag.viewnext):add()
+keybinding({ modkey }, "Escape", awful.tag.history.restore):add()
 
 -- Standard program
 keybinding({ modkey }, "Return", function () awful.spawn(terminal) end):add()
@@ -346,8 +347,11 @@ end
 -- Hook function to execute when arranging the screen
 -- (tag switch, new client, etc)
 function hook_arrange(screen)
-    local layout = awful.layout.get(screen)
-    mylayoutbox[screen].text = "<bg image=\"@AWESOME_ICON_PATH@/layouts/" .. layout .. "w.png\" resize=\"true\"/>"
+    mylayoutbox[screen].text =
+        "<bg image=\"@AWESOME_ICON_PATH@/layouts/" .. awful.layout.get(screen) .. "w.png\" resize=\"true\"/>"
+
+    -- Update tag history
+    awful.tag.history.update(screen)
 
     -- Uncomment if you want mouse warping
     --[[

lib/awful.lua.in

@@ -45,6 +45,10 @@ P.screen = {}
 P.layout = {}
 P.client = {}
 P.tag = {}
+P.tag.history = {}
+P.tag.history.data = {}
+P.tag.history.data.past = {}
+P.tag.history.data.current = {}
 P.titlebar = {}
 P.widget = {}
 P.widget.taglist = {}
@@ -174,6 +178,54 @@ function P.screen.focus(i)
     mouse.coords = screen.coords_get(s)
 end
 
+--- Compare 2 tables of tags.
+-- @param a The first table.
+-- @param b The second table of tags.
+-- @return True if the tables are identical, false otherwise.
+local function tag_compare_select(a, b)
+    if not a or not b then
+        return false
+    end
+    -- Quick size comparison
+    if #a ~= #b then
+        return false
+    end
+    for ka, va in pairs(a) do
+        if b[ka] ~= va.selected then
+            return false
+        end
+    end
+    for kb, vb in pairs(b) do
+        if a[kb].selected ~= vb then
+            return false
+        end
+    end
+    return true
+end
+
+--- Update the tag history.
+-- @param screen The screen number.
+function P.tag.history.update(screen)
+    local curtags = tag.geti(screen)
+    if not tag_compare_select(curtags, P.tag.history.data.current[screen]) then
+        P.tag.history.data.past[screen] = P.tag.history.data.current[screen]
+        P.tag.history.data.current[screen] = {}
+        for k, v in ipairs(curtags) do
+            P.tag.history.data.current[screen][k] = v.selected
+        end
+    end
+end
+
+-- Revert tag history.
+-- @param screen The screen number.
+function P.tag.history.restore(screen)
+    local s = screen or mouse.screen
+    local tags = tag.geti(s)
+    for k, t in pairs(tags) do
+        t.selected = P.tag.history.data.past[s][k]
+    end
+end
+
 --- Return a table with all visible tags
 -- @param s Screen number.
 -- @return A table with all selected tags.