{-# LANGUAGE
    OverloadedStrings
  , FlexibleInstances
  , GeneralizedNewtypeDeriving
  , StandaloneDeriving
  , UndecidableInstances
  , ViewPatterns
  , PatternGuards
  #-}
module Clay.Selector where

import Control.Applicative
import Data.Semigroup
import Data.String
import Data.Text (Text)

import qualified Data.Text as Text

-- | The star selector applies to all elements. Maps to @*@ in CSS.

star :: Selector
star = In (SelectorF (Refinement []) Star)

-- | Select elements by name. The preferred syntax is to enable
-- @OverloadedStrings@ and actually just use @\"element-name\"@ or use one of
-- the predefined elements from "Clay.Elements".

element :: Text -> Selector
element e = In (SelectorF (Refinement []) (Elem e))

-- | Named alias for `**`.

deep :: Selector -> Selector -> Selector
deep a b = In (SelectorF (Refinement []) (Deep a b))

-- | The deep selector composer. Maps to @sel1 sel2@ in CSS.

(**) :: Selector -> Selector -> Selector
(**) = deep

-- | Named alias for `|>`.

child :: Selector -> Selector -> Selector
child a b = In (SelectorF (Refinement []) (Child a b))

-- | The child selector composer. Maps to @sel1 > sel2@ in CSS.

(|>) :: Selector -> Selector -> Selector
(|>) = child

-- | The adjacent selector composer. Maps to @sel1 + sel2@ in CSS.

(|+) :: Selector -> Selector -> Selector
(|+) a b = In (SelectorF (Refinement []) (Adjacent a b))

-- | Named alias for `#`.

with :: Selector -> Refinement -> Selector
with (In (SelectorF (Refinement fs) e)) (Refinement ps) = In (SelectorF (Refinement (fs ++ ps)) e)

-- | The filter selector composer, adds a filter to a selector. Maps to
-- something like @sel#filter@ or @sel.filter@ in CSS, depending on the filter.

(#) :: Selector -> Refinement -> Selector
(#) = with

-- | Filter elements by id. The preferred syntax is to enable
-- @OverloadedStrings@ and use @\"#id-name\"@.

byId :: Text -> Refinement
byId = Refinement . pure . Id

-- | Filter elements by class. The preferred syntax is to enable
-- @OverloadedStrings@ and use @\".class-name\"@.

byClass :: Text -> Refinement
byClass = Refinement . pure . Class

-- | Filter elements by pseudo selector or pseudo class. The preferred syntax
-- is to enable @OverloadedStrings@ and use @\":pseudo-selector\"@ or use one
-- of the predefined ones from "Clay.Pseudo".

pseudo :: Text -> Refinement
pseudo = Refinement . pure . Pseudo

-- | Filter elements by pseudo selector functions. The preferred way is to use
-- one of the predefined functions from "Clay.Pseudo".

func :: Text -> [Text] -> Refinement
func f = Refinement . pure . PseudoFunc f

-- | Filter elements based on the presence of a certain attribute. The
-- preferred syntax is to enable @OverloadedStrings@ and use
-- @\"\@attr\"@ or use one of the predefined ones from "Clay.Attributes".

attr :: Text -> Refinement
attr = Refinement . pure . Attr

-- | Filter elements based on the presence of a certain attribute with the
-- specified value.

(@=) :: Text -> Text -> Refinement
(@=) a = Refinement . pure . AttrVal a

-- | Filter elements based on the presence of a certain attribute that begins
-- with the selected value.

(^=) :: Text -> Text -> Refinement
(^=) a = Refinement . pure . AttrBegins a

-- | Filter elements based on the presence of a certain attribute that ends
-- with the specified value.

($=) :: Text -> Text -> Refinement
($=) a = Refinement . pure . AttrEnds a

-- | Filter elements based on the presence of a certain attribute that contains
-- the specified value as a substring.

(*=) :: Text -> Text -> Refinement
(*=) a = Refinement . pure . AttrContains a

-- | Filter elements based on the presence of a certain attribute that have the
-- specified value contained in a space separated list.

(~=) :: Text -> Text -> Refinement
(~=) a = Refinement . pure . AttrSpace a

-- | Filter elements based on the presence of a certain attribute that have the
-- specified value contained in a hyphen separated list.

(|=) :: Text -> Text -> Refinement
(|=) a = Refinement . pure . AttrHyph a


-------------------------------------------------------------------------------

data Predicate
  = Id           Text
  | Class        Text
  | Attr         Text
  | AttrVal      Text Text
  | AttrBegins   Text Text
  | AttrEnds     Text Text
  | AttrContains Text Text
  | AttrSpace    Text Text
  | AttrHyph     Text Text
  | Pseudo       Text
  | PseudoFunc   Text [Text]
  | PseudoElem   Text
  deriving (Eq, Ord, Show)

newtype Refinement = Refinement { unFilter :: [Predicate] }
  deriving (Show, Semigroup, Monoid)

instance IsString Refinement where
  fromString = refinementFromText . fromString

refinementFromText :: Text -> Refinement
refinementFromText t = Refinement $
  case Text.uncons t of
    Just ('#', s) -> [Id     s]
    Just ('.', s) -> [Class  s]
    Just (':', s)
      | Just (':',s') <- Text.uncons s
                  -> [PseudoElem s']
      | otherwise -> [Pseudo s]
    Just ('@', s) -> [Attr   s]
    _             -> [Attr   t]

-------------------------------------------------------------------------------

data Path f
  = Star
  | Elem      Text
  | Child     f f
  | Deep      f f
  | Adjacent  f f
  | Combined  f f
  deriving Show

newtype Fix f = In { out :: f (Fix f) }

deriving instance Show (f (Fix f)) => Show (Fix f)

data SelectorF a = SelectorF Refinement (Path a)
  deriving Show

type Selector = Fix SelectorF

instance IsString (Fix SelectorF) where
  fromString = selectorFromText . fromString

selectorFromText :: Text -> Selector
selectorFromText t =
  case Text.uncons t of
    Just (c, _) | elem c ("#.:@" :: [Char])
      -> with star (refinementFromText t)
    _ -> In $ SelectorF (Refinement []) (Elem t)

instance Semigroup (Fix SelectorF) where
  a <> b = In (SelectorF (Refinement []) (Combined a b))

instance Monoid (Fix SelectorF) where
  mempty  = error "Selector is a semigroup"
  mappend = (<>)