-- |A simple feed generator: HTML generator
--
--  Copyright (c) 2006 Manuel M T Chakravarty
--
--  License: <http://www.gnu.org/licenses/gpl.html>
--
--- Description ---------------------------------------------------------------
--
--  Language: Haskell 98
--
--  Docs ----------------------------------------------------------------------
--
--  Introduction to Text.Html: <http://www.cse.ogi.edu/~andy/html/intro.htm>
--

module HTML (
  channelToHTML
) where

-- hierachical libraries
import Control.Monad (
  mplus, liftM2)
import Data.Maybe (
  isJust)
import Text.Html

-- lambdaFeed
import Config (
  Config(..))
import Date (
  Date, addMinutes)
import Feed (
  URL, Channel(..), Image(..), Category(..), Item(..), Enclosure(..),
  GUID(..), Source(..))


-- Render a channel to HTML.
--
channelToHTML :: Config -> Channel [Item] -> String
channelToHTML config chan = 
  renderHtml $
    header << concatHtml
      [ thetitle <<
          titleChan chan
      , primHtml "<link rel=\"stylesheet\" type=\"text/css\" \
	         \href=\"channel.css\"/>"
      , meta ! [httpequiv "Content-Type", 
	        content "text/html; charset=iso-8859-1"]
		-- FIXME: We should be able to parametrise the charset!!
      , languageChan chan `optional`
          \lang -> meta ! [httpequiv "Content-Language", content lang]
      , (liftM2 addMinutes (lastBuildDateChan chan) (ttlChan chan)) `optional` 
          \expiryDate -> meta ! [httpequiv "expires", 
				 content (show expiryDate)]
      , generatorChan chan `optional` 
          \gen -> meta ! [name "generator", content gen]
      , copyrightChan chan `optional` 
          \cr -> meta ! [name "copyright", content cr]
      , (pubDateChan chan `mplus` lastBuildDateChan chan) `optional`
          \date -> meta ! [name "date", content (show date)]
	  -- NB: `pubDate' takes preference
      ]
    +++ 
    body << concatHtml
      [ imageChan chan `optional` imageToHTML
      , h1 << titleChan chan
      , p << descriptionChan chan
      ]
      +++
      map itemToHTML (itemsChan chan)

-- Render an channel image element in HTML.
--
imageToHTML :: Image -> Html
imageToHTML img =
  anchor ! ([href (linkImage img)] ++ 
	    descriptionImage img `optionalAttr` title) <<
    image ! ([ theclass "channel"
	     , src (urlImage   img)
	     , alt (titleImage img)
             ] ++
	     ((widthImage  img `mplus` Just 88) `optionalAttr` (width.show))++
	     ((heightImage img `mplus` Just 31) `optionalAttr` height))
	      -- defaults from RSS 2.0 spec

-- Render an item in HTML.
--
itemToHTML :: Item -> Html
itemToHTML item = 
  thediv ! [theclass "item"] << concatHtml
    [ titleItem item `optional`
        \title -> linkItem item `optionalHrefFor` (h2 << title)
    , descriptionItem item `optional` (p <<)
    , thediv ! [theclass "authorDate"]  << concatHtml
        [ authorItem item `optional` toHtml
	, if isJust (authorItem item) && isJust (authorItem item)
   	  then bulletWithSpace else noHtml
	, pubDateItem item `optional` (toHtml . show)
	]
    , thediv ! [theclass "commentsEnclosure"]  << concatHtml
        [ enclosureItem item `optional` enclosureToHtml
	, if isJust (enclosureItem item) && 
	     isJust (commentsItem item)
   	  then bulletWithSpace else noHtml
	, commentsItem item `optional`
	    \commentsLink -> anchor ! [href commentsLink] << "Comments"
	]
    ]
  where bulletWithSpace = spaceHtml +++ bullet +++ spaceHtml

-- Render an enclosure to HTML.
--
enclosureToHtml :: Enclosure -> Html
enclosureToHtml enc =
  anchor ! [href (urlEnclosure enc), thetype (typeEnclosure enc) ] << 
    "Enclosure"

-- Render an optional element.
--
optional :: Maybe a -> (a -> Html) -> Html
optional = flip (maybe noHtml)

-- Render an optional attribute.
--
optionalAttr :: Maybe a -> (a -> HtmlAttr) -> [HtmlAttr]
optionalAttr Nothing  _    = []
optionalAttr (Just x) attr = [attr x]

-- An optional enclosing href.
--
optionalHrefFor :: Maybe String -> Html -> Html
optionalHrefFor Nothing     inner = inner
optionalHrefFor (Just link) inner = anchor ! [href link] << inner