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|
-- | A Module that allows easy rendering of RSS feeds.
--
-- The main rendering functions (@renderRss@, @renderAtom@) all assume that
-- you pass the list of items so that the most recent entry in the feed is the
-- first item in the list.
--
-- Also note that the pages should have (at least) the following fields to
-- produce a correct feed:
--
-- - @$title@: Title of the item
--
-- - @$description@: Description to appear in the feed
--
-- - @$url@: URL to the item - this is usually set automatically.
--
-- In addition, the posts should be named according to the rules for
-- 'Hakyll.Page.Metadata.renderDateField'.
--
module Hakyll.Web.Feed
( FeedConfiguration (..)
, renderRss
, renderAtom
) where
import Prelude hiding (id)
import Control.Category (id)
import Control.Arrow ((>>>), arr, (&&&))
import Control.Monad ((<=<))
import Data.Maybe (fromMaybe, listToMaybe)
import Hakyll.Core.Compiler
import Hakyll.Web.Page
import Hakyll.Web.Page.Metadata
import Hakyll.Web.Template
import Hakyll.Web.Template.Read.Hakyll (readTemplate)
import Hakyll.Web.Urls
import Paths_hakyll
-- | This is a data structure to keep the configuration of a feed.
data FeedConfiguration = FeedConfiguration
{ -- | Title of the feed.
feedTitle :: String
, -- | Description of the feed.
feedDescription :: String
, -- | Name of the feed author.
feedAuthorName :: String
, -- | Absolute root URL of the feed site (e.g. @http://jaspervdj.be@)
feedRoot :: String
} deriving (Show, Eq)
-- | This is an auxiliary function to create a listing that is, in fact, a feed.
-- The items should be sorted on date. The @$updated@ field should be set for
-- each item.
--
createFeed :: Template -- ^ Feed template
-> Template -- ^ Item template
-> String -- ^ URL of the feed
-> FeedConfiguration -- ^ Feed configuration
-> [Page String] -- ^ Items to include
-> String -- ^ Resulting feed
createFeed feedTemplate itemTemplate url configuration items =
pageBody $ applyTemplate feedTemplate
$ trySetField "updated" updated
$ trySetField "title" (feedTitle configuration)
$ trySetField "description" (feedDescription configuration)
$ trySetField "authorName" (feedDescription configuration)
$ trySetField "root" (feedRoot configuration)
$ trySetField "url" url
$ fromBody body
where
-- Preprocess items
items' = flip map items $ applyTemplate itemTemplate
. trySetField "root" (feedRoot configuration)
-- Body: concatenated items
body = concat $ map pageBody items'
-- Take the first updated, which should be the most recent
updated = fromMaybe "Unknown" $ do
p <- listToMaybe items
return $ getField "updated" p
-- | Abstract function to render any feed.
--
renderFeed :: FilePath -- ^ Feed template
-> FilePath -- ^ Item template
-> FeedConfiguration -- ^ Feed configuration
-> Compiler [Page String] String -- ^ Feed compiler
renderFeed feedTemplate itemTemplate configuration =
id &&& getRoute >>> renderFeed'
where
-- Arrow rendering the feed from the items and the URL
renderFeed' = unsafeCompiler $ \(items, url) -> do
feedTemplate' <- loadTemplate feedTemplate
itemTemplate' <- loadTemplate itemTemplate
let url' = toUrl $ fromMaybe noUrl url
return $ createFeed feedTemplate' itemTemplate' url' configuration items
-- Auxiliary: load a template from a datafile
loadTemplate = fmap readTemplate . readFile <=< getDataFileName
-- URL is required to have a valid field
noUrl = error "Hakyll.Web.Feed.renderFeed: no route specified"
-- | Render an RSS feed with a number of items.
--
renderRss :: FeedConfiguration -- ^ Feed configuration
-> Compiler [Page String] String -- ^ Feed compiler
renderRss configuration = arr (map (addUpdated . renderDate))
>>> renderFeed "templates/rss.xml" "templates/rss-item.xml" configuration
where
renderDate = renderDateField "published" "%a, %d %b %Y %H:%M:%S UT"
"No date found."
-- | Render an Atom feed with a number of items.
--
renderAtom :: FeedConfiguration -- ^ Feed configuration
-> Compiler [Page String] String -- ^ Feed compiler
renderAtom configuration = arr (map (addUpdated . renderDate))
>>> renderFeed "templates/atom.xml" "templates/atom-item.xml" configuration
where
renderDate = renderDateField "published" "%Y-%m-%dT%H:%M:%SZ"
"No date found."
-- | Copies @$updated$@ from @$published$@ if it is not already set.
--
addUpdated :: Page a -> Page a
addUpdated page = trySetField "updated" (getField "published" page) page
|
