Merge pull request #147 from adubovik/master

Pagination support

1 files changed, 206 insertions, 0 deletions

diff --git a/src/Hakyll/Web/Paginator.hs b/src/Hakyll/Web/Paginator.hs
new file mode 100644
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+++ b/src/Hakyll/Web/Paginator.hs
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+{-# LANGUAGE OverloadedStrings          #-}
+
+module Hakyll.Web.Paginator
+   ( Paginator(..)
+   , PagState(..)
+   , NavigationLinkType(..)
+   , buildPaginator
+   , buildPaginatorWith
+   , paginatorRules
+   , renderPaginator
+   , renderPaginatorWith
+
+   , paginatorFields
+  ) where
+
+--------------------------------------------------------------------------------
+import           Control.Monad                   (forM, forM_)
+import           Data.List                       (intercalate, unfoldr)
+import           Data.Monoid                     ((<>))
+import           Data.Maybe                      (fromMaybe)
+import qualified Data.Map                        as M
+import           Text.Blaze.Html                 (toHtml, toValue, (!))
+import           Text.Printf                     (printf)
+import           Text.Blaze.Html.Renderer.String (renderHtml)
+import qualified Text.Blaze.Html5                as H
+import qualified Text.Blaze.Html5.Attributes     as A
+
+
+--------------------------------------------------------------------------------
+import           Hakyll.Core.Compiler
+import           Hakyll.Core.Identifier
+import           Hakyll.Core.Identifier.Pattern
+import           Hakyll.Core.Metadata
+import           Hakyll.Core.Rules
+import           Hakyll.Web.Template.Context
+import           Hakyll.Core.Item
+import           Hakyll.Web.Html
+
+-- | Data about paginators
+data Paginator = Paginator
+    { pagPages  :: M.Map Int [Identifier]
+    , pagPlaces :: M.Map Identifier Int
+    , pagMakeId :: PagState -> Identifier
+    , pagDependency :: Dependency
+    } deriving (Show)
+
+data PagState = PagState { pagPos :: Int
+                         , pagLen :: Int }
+
+buildPaginatorWith :: MonadMetadata m
+                   => Int
+                   -> (PagState -> Identifier)
+                   -> Pattern
+                   -> m Paginator
+buildPaginatorWith n makeId pattern = do
+  -- TODO: there is no sensible order for `ids` here, for now it's random;
+  -- but it should be `resectFirst` order because most recent posts should
+  -- correspond to 1st paginator page and oldest one to last page
+  idents <- getMatches pattern
+  let pages = unfoldr f idents
+        where
+          f [] = Nothing
+          f x  = Just $ splitAt n x
+      nPages     = length pages
+      pagPages'  = zip [1..] pages
+      pagPlaces' = [(ident, idx) | (idx,ids) <- pagPages', ident <- ids] ++
+                   [(makeId (PagState i nPages), i) | i <- [1 .. nPages]]
+  return $ Paginator (M.fromList pagPages') (M.fromList pagPlaces') makeId
+                     (PatternDependency pattern idents)
+
+--------------------------------------------------------------------------------
+
+buildPaginator :: MonadMetadata m => Pattern -> m Paginator
+buildPaginator = buildPaginatorWith 5 makeId
+  where
+    makeId (PagState pos n) = fromFilePath $ "index" ++ makeIndex pos n ++ ".html"
+    makeIndex i n = let nils = replicate (length (show n) - length (show i)) '0'
+                    in  nils ++ show i
+
+--------------------------------------------------------------------------------
+
+paginatorRules :: Paginator -> (PagState -> Pattern -> Rules ()) -> Rules ()
+paginatorRules paginator rules =
+    forM_ (M.toList $ pagPages paginator) $ \(idx, identifiers) ->
+        let pagState = PagState idx (M.size $ pagPages paginator)
+        in  create [pagMakeId paginator pagState] $
+                rulesExtraDependencies [pagDependency paginator] $
+                    rules pagState $ fromList identifiers
+
+--------------------------------------------------------------------------------
+
+data NavigationLinkType = NFirst | NPrev | NNext | NLast
+
+instance Show NavigationLinkType where
+  show NFirst = "first"
+  show NPrev  = "prev"
+  show NNext  = "next"
+  show NLast  = "last"
+
+renderPaginatorWith :: (String -> Int -> Int -> Int -> String)
+                    -- ^ Produce a paginator menu item: url, index of menu element,
+                    --   index of current page, amount of pages
+                    -> (String -> NavigationLinkType -> Int -> String)
+                    -- ^ Produce fast navigation links: url, type of navigation
+                    --   element (e.g. last, prev...), index of corresponding page
+                    -> ([String] -> String)
+                    -- ^ Join items
+                    -> Paginator
+                    -> PagState
+                    -> Compiler String
+renderPaginatorWith makeHtml navigationHtml concatHtml paginator (PagState i n) = do
+    pags' <- forM (M.toList $ pagPages paginator) $ \(idx,_) -> do
+        let pagState = PagState idx (M.size $ pagPages paginator)
+            
+        url <- getRoute $ pagMakeId paginator pagState
+        return (url, idx)
+
+    let -- Create a link for one item
+        makeHtml' (url, idx) =
+            makeHtml (toUrl $ fromMaybe "/" url) idx i n
+
+        -- Fast-travel links logic: first, prev, next, last (<< < > >>)
+        navIdxs = [1, max 1 (i-1), min (i+1) n, n]
+        navIds  = [NFirst, NPrev, NNext, NLast]
+        navUrls = map (\idx -> toFilePath $ pagMakeId paginator (PagState idx n))
+                     navIdxs
+        navHtmlCode = zipWith3 navigationHtml navUrls navIds navIdxs
+        navLefts = if i==1
+                   then []
+                   else take 2 navHtmlCode
+        navRights= if i==n
+                   then []
+                   else drop 2 navHtmlCode
+
+    return $ concatHtml $ navLefts ++ map makeHtml' pags' ++ navRights
+
+renderPaginator :: Paginator -> PagState -> Compiler String
+renderPaginator =
+  renderPaginatorWith makeHtml navigationHtml concatHtml
+  where
+    navigationHtml url navType _idx =
+      let (caption, alt) = arrow navType
+      in  renderHtml $ H.a ! (A.href  (toValue url) <>
+                              A.title (toValue alt))
+                           $ toHtml caption
+      where
+        arrow :: NavigationLinkType -> (String, String)
+        arrow NPrev  = ("<" , "prev")
+        arrow NNext  = (">" , "next")
+        arrow NFirst = ("<<", "first")
+        arrow NLast  = (">>", "last")
+    concatHtml = intercalate " " . filter (not . null)
+    makeHtml url menuItemIdx pageIdx nPages
+      | menuItemIdx == pageIdx = show menuItemIdx
+      | not shouldBeDisplayed = ""
+      | otherwise =
+        let caption = show menuItemIdx
+        in  renderHtml $ H.a ! (A.href  (toValue url) <>
+                                A.title (toValue caption))
+                             $ toHtml caption
+      where
+        shouldBeDisplayed =
+          let leg = 2
+              width = 1 + 2*leg
+          in    abs (menuItemIdx - pageIdx) <= leg
+             || pageIdx - leg <= 0      && menuItemIdx - width <= 0
+             || pageIdx + leg >= nPages && menuItemIdx + width >= nPages
+
+
+paginatorField :: Paginator -> String -> NavigationLinkType -> Context a
+paginatorField pag fieldName arrowType = field fieldName $ \item -> do
+    let identifier = itemIdentifier item
+        nPages     = M.size (pagPages pag)
+        
+        neededPage NNext pos | pos+1 > nPages = Nothing
+        neededPage NNext pos = Just (pos + 1)
+        
+        neededPage NPrev pos | pos-1 < 1 = Nothing
+        neededPage NPrev pos = Just (pos - 1)
+
+        neededPage NFirst pos | pos == 1 = Nothing
+        neededPage NFirst  _  = Just 1
+
+        neededPage NLast pos | pos == nPages = Nothing
+        neededPage NLast  _  = Just nPages
+    
+    case M.lookup identifier (pagPlaces pag) of
+      Nothing -> error $ printf "Hakyll.Web.Paginator: there is no page %s in paginator map."
+                         (show identifier)
+      Just pos -> case neededPage arrowType pos of
+        Nothing   -> fail $ printf "There is no %s page for page %s in position %s."
+                            (show arrowType) (show identifier) (show pos)
+        Just pos' -> do
+          let nextId = pagMakeId pag (PagState pos' nPages)
+          mroute <- getRoute nextId
+          case mroute of
+            Nothing -> error $ printf "Hakyll.Web.Paginator: unable to get route of identifier %s."
+                               (show nextId)
+            Just rt -> return $ toUrl rt
+
+paginatorFields :: Paginator -> Context a
+paginatorFields pag =    paginatorField pag "firstPage" NFirst
+                      <> paginatorField pag "prevPage"  NPrev
+                      <> paginatorField pag "nextPage"  NNext
+                      <> paginatorField pag "lastPage"  NLast
+                      
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