Html.Shorthand.Internal

module Html.Shorthand.Internal exposing (..)
{-| Internals for Html.Shorthand See [Html.Shorthand](http://package.elm-lang.org/packages/circuithub/elm-html-shorthand/latest/Html-Shorthand)

@docs encodeId, encodeClass, class', id'
-}

import Maybe
import List
import Char
import String
import Html exposing (..)
import Html.Attributes as A
import Html.Shorthand.Type exposing (..)
import Html.Shorthand.Event exposing (..)

{-| -}
encodeId : IdString -> IdString
encodeId =
  let hu = ['-','_']
      isAlpha c = let cc = Char.toCode <| Char.toLower c
                  in cc >= Char.toCode 'a' && cc <= Char.toCode 'z'
      -- Note that : and . are also allowed in HTML 4, but since these need to be escaped in selectors we exclude them
      -- HTML 5 includes many more characters, but we'll exclude these for now
      isIdChar c = Char.isDigit c
                    || isAlpha c
                    || (c `List.member` hu)
      startWithAlpha s = case String.uncons s of
                          Just (c, s') -> if not (isAlpha c) then 'x' `String.cons` s else s
                          Nothing      -> s
      smartTrimLeft s = case String.uncons s of
                          Just (c, s') -> if c `List.member` hu then s' else s
                          Nothing      -> s
      smartTrimRight s = case String.uncons (String.reverse s) of
                          Just (c, s') -> if c `List.member` hu then String.reverse s' else s
                          Nothing      -> s
      smartTrim = smartTrimLeft >> smartTrimRight
  in  String.words
      >> List.map
        ( String.toLower
        >> String.filter isIdChar
        >> smartTrim
        )
      >> String.join "-"
      >> startWithAlpha

{-| -}
encodeClass : ClassString -> ClassString
encodeClass =
  let hu = ['-','_']
      isAlpha c = let cc = Char.toCode <| Char.toLower c
                  in cc >= Char.toCode 'a' && cc <= Char.toCode 'z'
      -- Note that : and . are also allowed in HTML 4, but since these need to be escaped in selectors we exclude them
      -- HTML 5 includes many more characters, but we'll exclude these for now
      isClassChar c = Char.isDigit c
                      || isAlpha c
                      || (c `List.member` hu)
      startWithAlpha s = case String.uncons s of
                          Just (c, s') -> if not (isAlpha c) then 'x' `String.cons` s else s
                          Nothing      -> s
      smartTrimLeft s = case String.uncons s of
                          Just (c, s') -> if c `List.member` hu then s' else s
                          Nothing      -> s
      smartTrimRight s = case String.uncons (String.reverse s) of
                          Just (c, s') -> if c `List.member` hu then String.reverse s' else s
                          Nothing      -> s
      smartTrim = smartTrimLeft >> smartTrimRight
  in  String.words
      >> List.map
        ( String.toLower
        >> String.filter isClassChar
        >> smartTrim
        >> startWithAlpha
        )
      >> String.join " "

{-| -}
id' : IdString -> Attribute msg
id' = A.id << encodeId

{-| -}
class' : ClassString -> Attribute msg
class' = A.class << encodeClass