{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE ImpredicativeTypes #-}
{-# OPTIONS_HADDOCK hide #-}
module Text.HTML.Scalpel.Internal.Select.Types (
    Selector (..)
,   Selectable (..)
,   AttributePredicate (..)
,   checkPred
,   Any (..)
,   AttributeName (..)
,   TagName (..)

,   SelectNode (..)
) where

import qualified Text.HTML.TagSoup as TagSoup
import qualified Text.StringLike as TagSoup


-- | The 'Selectable' class defines a class of types that are capable of being
-- cast into a 'Selector' which in turns describes a section of an HTML DOM
-- tree.
class Selectable s where
    toSelector :: s -> Selector

-- | The 'AttributeName' class defines a class of types that can be used when
-- creating 'Selector's to specify the name of an attribute of a tag.  Currently
-- the only types of this class are 'String' for matching attributes exactly,
-- and 'Any' for matching attributes with any name.
class AttributeName k where
    matchKey :: TagSoup.StringLike str => k -> str -> Bool

-- | The 'TagName' class defines a class of types that can be used when creating
-- 'Selector's to specify the name of a tag. Currently the only types of this
-- class are 'String' for matching tags exactly, and 'Any' for matching tags
-- with any name.
class TagName t where
    toSelectNode :: t -> [AttributePredicate] -> SelectNode

-- | An 'AttributePredicate' is a method that takes a 'TagSoup.Attribute' and
-- returns a 'Bool' indicating if the given attribute matches a predicate.
data AttributePredicate
        = MkAttributePredicate
                (TagSoup.StringLike str => TagSoup.Attribute str -> Bool)

checkPred :: TagSoup.StringLike str
          => AttributePredicate -> TagSoup.Attribute str -> Bool
checkPred (MkAttributePredicate p) = p

-- | 'Any' can be used as a wildcard when constructing selectors to match tags
-- and attributes with any name.
--
-- For example, the selector @Any \@: [Any \@= \"foo\"]@ matches all tags that
-- have any attribute where the value is @\"foo\"@.
data Any = Any

-- | 'Selector' defines a selection of an HTML DOM tree to be operated on by
-- a web scraper. The selection includes the opening tag that matches the
-- selection, all of the inner tags, and the corresponding closing tag.
newtype Selector = MkSelector [SelectNode]

data SelectNode = SelectNode String [AttributePredicate]
                | SelectAny [AttributePredicate]

instance Selectable Selector where
    toSelector = id

instance Selectable String where
    toSelector node = MkSelector [SelectNode node []]

instance Selectable Any where
    toSelector = const (MkSelector [SelectAny []])

instance AttributeName Any where
    matchKey = const . const True

instance AttributeName String where
    matchKey = (==) . TagSoup.fromString

instance TagName Any where
    toSelectNode = const SelectAny

instance TagName String where
    toSelectNode = SelectNode . TagSoup.fromString