From 086da474d2729c627d0472e9f2e64e48a3968d0a Mon Sep 17 00:00:00 2001
From: Adrian Cochrane <adrian@openwork.nz>
Date: Wed, 22 Apr 2020 19:42:17 +1200
Subject: [PATCH] Rewrite trivial cases of :where & :is.

This is mostly for the psuedoselector rewrites performed in Data.CSS.Preprocessor.PsuedoClasses
---
 src/Data/CSS/Style.hs                     |  5 +++-
 src/Data/CSS/Style/Selector/LowerWhere.hs | 32 +++++++++++++++++++++++
 stylist.cabal                             |  3 ++-
 3 files changed, 38 insertions(+), 2 deletions(-)
 create mode 100644 src/Data/CSS/Style/Selector/LowerWhere.hs

diff --git a/src/Data/CSS/Style.hs b/src/Data/CSS/Style.hs
index 30381e7..654f4da 100644
--- a/src/Data/CSS/Style.hs
+++ b/src/Data/CSS/Style.hs
@@ -12,6 +12,7 @@ module Data.CSS.Style(
 import Data.CSS.Style.Selector.Index
 import Data.CSS.Style.Selector.Interpret
 import Data.CSS.Style.Selector.Specificity
+import Data.CSS.Style.Selector.LowerWhere
 import Data.CSS.Style.Importance
 import Data.CSS.Style.Common
 import qualified Data.CSS.Style.Cascade as Cascade
@@ -25,7 +26,9 @@ import Data.List (elemIndex)
 
 -- | A parsed CSS stylesheet from which you can query styles to match an element.
 type QueryableStyleSheet parser = QueryableStyleSheet' (ImportanceSplitter (
-        PropertyExpander parser (OrderedRuleStore (InterpretedRuleStore StyleIndex))
+        PropertyExpander parser (
+            OrderedRuleStore (WhereLowerer (InterpretedRuleStore StyleIndex))
+        )
     )) parser
 
 -- | More generic version of `QueryableStyleSheet`.
diff --git a/src/Data/CSS/Style/Selector/LowerWhere.hs b/src/Data/CSS/Style/Selector/LowerWhere.hs
new file mode 100644
index 0000000..fc3e024
--- /dev/null
+++ b/src/Data/CSS/Style/Selector/LowerWhere.hs
@@ -0,0 +1,32 @@
+{-# LANGUAGE OverloadedStrings #-}
+module Data.CSS.Style.Selector.LowerWhere(
+        WhereLowerer(..)
+    ) where
+
+import Data.CSS.Syntax.Selector
+import Data.CSS.Style.Common
+
+lowerSelector :: Selector -> Selector
+lowerSelector (Element sel) = Element $ lowerSelector' sel
+lowerSelector (Child sel x) = Child (lowerSelector sel) x
+lowerSelector (Descendant sel x) = Descendant (lowerSelector sel) x
+lowerSelector (Adjacent sel x) = Adjacent (lowerSelector sel) x
+lowerSelector (Sibling sel x) = Sibling (lowerSelector sel) x
+
+lowerSelector' :: [SimpleSelector] -> [SimpleSelector]
+lowerSelector' (Psuedoclass c args:sel)
+    | c `elem` ["is", "where"], ([Element arg'], []) <- parseSelectors args =
+        arg' ++ lowerSelector' sel
+lowerSelector' (test:tests) = test : lowerSelector' tests
+lowerSelector' [] = []
+
+data WhereLowerer s = WhereLowerer s
+
+instance RuleStore s => RuleStore (WhereLowerer s) where
+    new = WhereLowerer new
+    addStyleRule (WhereLowerer self) priority rule =
+        WhereLowerer $ addStyleRule self priority $ rule {
+            inner = StyleRule (lowerSelector sel) props psuedo
+        }
+      where StyleRule sel props psuedo = inner rule
+    lookupRules (WhereLowerer self) el = lookupRules self el
diff --git a/stylist.cabal b/stylist.cabal
index 1b759e0..6ac2109 100644
--- a/stylist.cabal
+++ b/stylist.cabal
@@ -61,7 +61,8 @@ library
   -- Modules included in this library but not exported.
   other-modules:       Data.CSS.Syntax.StylishUtil,
                        Data.CSS.Style.Importance, Data.CSS.Style.Common, Data.CSS.Style.Cascade,
-                       Data.CSS.Style.Selector.Index, Data.CSS.Style.Selector.Interpret, Data.CSS.Style.Selector.Specificity
+                       Data.CSS.Style.Selector.Index, Data.CSS.Style.Selector.Interpret,
+                           Data.CSS.Style.Selector.Specificity, Data.CSS.Style.Selector.LowerWhere
   
   -- LANGUAGE extensions used by modules in this package.
   -- other-extensions:    
-- 
2.30.2