Link.hs

--------------------------------------------------------------------
-- |
-- Module    : Text.Atom.Feed.Link
-- Copyright : (c) Galois, Inc. 2008
-- License   : BSD3
--
-- Maintainer: Don Stewart <dons@galois.com>
-- Stability : provisional
-- Portability:
--
--------------------------------------------------------------------

module Text.Atom.Feed.Link
       ( LinkRelation(..)
       , showLinkRelation
       , showLinkAttr
       ) where

-- | Atom feeds uses typed IRI links to represent
-- information \/ metadata that is of interest to the
-- consumers (software, in the main) of feeds. For instance,
-- the edit link relation attached to an atom:entry element
-- points to the IRI to use to update\/edit it.
--
-- The Atom standard encourages that such typed links to
-- be registered with IANA if they have wider applicability,
-- and the 'LinkRelation' data type encodes the currently
-- registered link types (derived from: 
--  http:\/\/www.iana.org\/assignments\/link-relations.html
-- on 2007-10-28]
--
data LinkRelation               -- relevant RFC:
 = LinkAlternate                -- http://www.rfc-editor.org/rfc/rfc4287.txt
 | LinkCurrent                  -- http://www.rfc-editor.org/rfc/rfc5005.txt
 | LinkEnclosure                -- http://www.rfc-editor.org/rfc/rfc4287.txt
 | LinkEdit                     -- http://www.rfc-editor.org/rfc/rfc5023.txt
 | LinkEditMedia                -- http://www.rfc-editor.org/rfc/rfc5023.txt
 | LinkFirst                    -- http://www.iana.org/assignments/link-relations/first
 | LinkLast                     -- http://www.iana.org/assignments/link-relations/last
 | LinkLicense                  -- http://www.rfc-editor.org/rfc/rfc4946.txt
 | LinkNext                     -- http://www.rfc-editor.org/rfc/rfc5005.txt
 | LinkNextArchive              -- http://www.rfc-editor.org/rfc/rfc5005.txt
 | LinkPayment                  -- http://www.iana.org/assignments/link-relations/payment
 | LinkPrevArchive              -- http://www.rfc-editor.org/rfc/rfc5005.txt
 | LinkPrevious                 -- http://www.rfc-editor.org/rfc/rfc5005.txt
 | LinkRelated                  -- http://www.rfc-editor.org/rfc/rfc4287.txt
 | LinkReplies                  -- http://www.rfc-editor.org/rfc/rfc4685.txt
 | LinkSelf                     -- http://www.rfc-editor.org/rfc/rfc4287.txt
 | LinkVia                      -- http://www.rfc-editor.org/rfc/rfc4287.txt
 | LinkOther String
     deriving (Eq, Show)

showLinkRelation :: LinkRelation -> String
showLinkRelation lr = 
  case lr of
   LinkAlternate   -> "alternate"
   LinkCurrent     -> "current"
   LinkEnclosure   -> "enclosure"
   LinkEdit        -> "edit"
   LinkEditMedia   -> "edit-media"
   LinkFirst       -> "first"
   LinkLast        -> "last"
   LinkLicense     -> "license"
   LinkNext        -> "next"
   LinkNextArchive -> "next-archive"
   LinkPayment     -> "payment"
   LinkPrevArchive -> "prev-archive"
   LinkPrevious    -> "previous"
   LinkRelated     -> "related"
   LinkReplies     -> "replies"
   LinkSelf        -> "self"
   LinkVia         -> "via"
   LinkOther s     -> s

showLinkAttr :: LinkRelation -> String{-URI-} -> String
showLinkAttr lr s = showLinkRelation lr ++ '=':'"':concatMap escQ s ++ "\""
 where
  escQ '"' = "&dquot;"
  escQ x   = [x]