Add renderTagCloud prototype

1 files changed, 69 insertions, 1 deletions

diff --git a/src/Hakyll/Web/Tags.hs b/src/Hakyll/Web/Tags.hs
index cf0d9a5..14aaab5 100644
--- a/src/Hakyll/Web/Tags.hs
+++ b/src/Hakyll/Web/Tags.hs
@@ -1,17 +1,52 @@
-{-# LANGUAGE DeriveDataTypeable #-}
+-- | Module containing some specialized functions to deal with tags.
+-- This Module follows certain conventions. My advice is to stick with them if
+-- possible.
+--
+-- More concrete: all functions in this module assume that the tags are
+-- located in the @tags@ field, and separated by commas. An example file
+-- @foo.markdown@ could look like:
+--
+-- > ---
+-- > author: Philip K. Dick
+-- > title: Do androids dream of electric sheep?
+-- > tags: future, science fiction, humanoid
+-- > ---
+-- > The novel is set in a post-apocalyptic near future, where the Earth and
+-- > its populations have been damaged greatly by Nuclear...
+--
+-- All the following functions would work with such a format. In addition to
+-- tags, Hakyll also supports categories. The convention when using categories
+-- is to place pages in subdirectories.
+--
+-- An example, the page @posts\/coding\/2010-01-28-hakyll-categories.markdown@
+-- Tags or categories are read using the @readTags@ and @readCategories@
+-- functions. This module only provides functions to work with tags:
+-- categories are represented as tags. This is perfectly possible: categories
+-- only have an additional restriction that a page can only have one category
+-- (instead of multiple tags).
+--
+{-# LANGUAGE DeriveDataTypeable, OverloadedStrings #-}
 module Hakyll.Web.Tags
     ( Tags (..)
     , readTagsWith
     , readTags
     , readCategories
+    , renderTagCloud
     ) where
 
 import Control.Applicative ((<$>))
 import Data.Map (Map)
 import qualified Data.Map as M
+import Data.List (intersperse)
+import Control.Arrow (second, (&&&))
 
 import Data.Typeable (Typeable)
 import Data.Binary (Binary, get, put)
+import Data.Monoid (mconcat)
+import Text.Blaze.Renderer.String (renderHtml)
+import Text.Blaze (Html, (!), toHtml, toValue)
+import qualified Text.Blaze.Html5 as H
+import qualified Text.Blaze.Html5.Attributes as A
 
 import Hakyll.Web.Page
 import Hakyll.Web.Util.String
@@ -53,3 +88,36 @@ readTags = readTagsWith $ map trim . splitAll "," . getField "tags"
 --
 readCategories :: [Page a] -> Tags a
 readCategories = readTagsWith $ return . getField "category"
+
+-- | Render a tag cloud in HTML
+--
+renderTagCloud :: (String -> String)  -- ^ Function to produce an url for a tag
+               -> Double              -- ^ Smallest font size, in percent
+               -> Double              -- ^ Biggest font size, in percent
+               -> Tags a              -- ^ Tags structure to render
+               -> String              -- ^ Resulting HTML
+renderTagCloud urlFunction minSize maxSize (Tags tags) = renderHtml $
+    mconcat $ intersperse " " $ map (uncurry renderTag) withCount
+  where
+    -- Tags composed with their count
+    withCount = map (second $ fromIntegral . length) $ M.toList tags
+
+    -- Render one tag, given it's count
+    renderTag :: String -> Int -> Html
+    renderTag tag count =
+        H.a ! A.style (toValue $ "font-size: " ++ size count)
+            ! A.href (toValue $ urlFunction tag)
+            $ toHtml tag
+
+    -- Show the relative size of one 'count' in percent
+    size count =
+        let size' = floor $ minSize + relative count * (maxSize - minSize)
+        in show (size' :: Int) ++ "%"
+
+    -- Find out the relative count of a tag: on a scale from 0 to 1
+    relative count = (fromIntegral count - minCount) / (maxCount - minCount)
+
+    -- The minimum and maximum count found, as doubles
+    (minCount, maxCount)
+        | null withCount = (0, 1)
+        | otherwise = (minimum &&& maximum) $ map (fromIntegral . snd) withCount