content: {-
  Copyright (C) 2009 John MacFarlane <jgm@berkeley.edu>
  
  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.
  
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.
  
  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  -}
  
  {- | Interface for plugins.
  
  A plugin is a Haskell module that is dynamically loaded by gitit.
  
  There are three kinds of plugins: 'PageTransform's,
  'PreParseTransform's, and 'PreCommitTransform's. These plugins differ
  chiefly in where they are applied. 'PreCommitTransform' plugins are
  applied just before changes to a page are saved and may transform
  the raw source that is saved. 'PreParseTransform' plugins are applied
  when a page is viewed and may alter the raw page source before it
  is parsed as a 'Pandoc' document. Finally, 'PageTransform' plugins
  modify the 'Pandoc' document that results after a page's source is
  parsed, but before it is converted to HTML:
  
  >                 +--------------------------+
  >                 | edited text from browser |
  >                 +--------------------------+
  >                              ||         <----  PreCommitTransform plugins
  >                              \/
  >                              ||         <----  saved to repository
  >                              \/
  >              +---------------------------------+
  >              | raw page source from repository |
  >              +---------------------------------+
  >                              ||         <----  PreParseTransform plugins
  >                              \/
  >                              ||         <----  markdown or RST reader
  >                              \/
  >                     +-----------------+
  >                     | Pandoc document |
  >                     +-----------------+
  >                              ||         <---- PageTransform plugins
  >                              \/
  >                   +---------------------+
  >                   | new Pandoc document |
  >                   +---------------------+
  >                              ||         <---- HTML writer
  >                              \/
  >                   +----------------------+
  >                   | HTML version of page |
  >                   +----------------------+
  
  Note that 'PreParseTransform' and 'PageTransform' plugins do not alter
  the page source stored in the repository. They only affect what is
  visible on the website.  Only 'PreCommitTransform' plugins can
  alter what is stored in the repository.
  
  Note also that 'PreParseTransform' and 'PageTransform' plugins will
  not be run when the cached version of a page is used.  Plugins can
  use the 'doNotCache' command to prevent a page from being cached,
  if their behavior is sensitive to things that might change from
  one time to another (such as the time or currently logged-in user).
  
  You can use the helper functions 'mkPageTransform' and 'mkPageTransformM'
  to create 'PageTransform' plugins from a transformation of any
  of the basic types used by Pandoc (for example, @Inline@, @Block@,
  @[Inline]@, even @String@). Here is a simple (if silly) example:
  
  > -- Deprofanizer.hs
  > module Deprofanizer (plugin) where
  >
  > -- This plugin replaces profane words with "XXXXX".
  >
  > import Network.Gitit.Interface
  > import Data.Char (toLower)
  >
  > plugin :: Plugin
  > plugin = mkPageTransform deprofanize
  >
  > deprofanize :: Inline -> Inline
  > deprofanize (Str x) | isBadWord x = Str "XXXXX"
  > deprofanize x                     = x
  >
  > isBadWord :: String -> Bool
  > isBadWord x = (map toLower x) `elem` ["darn", "blasted", "stinker"]
  > -- there are more, but this is a family program
  
  Further examples can be found in the @plugins@ directory in
  the source distribution.  If you have installed gitit using Cabal,
  you can also find them in the directory
  @CABALDIR\/share\/gitit-X.Y.Z\/plugins@, where @CABALDIR@ is the cabal
  install directory and @X.Y.Z@ is the version number of gitit.
  
  -}
  
  module Network.Gitit.Interface ( Plugin(..)
                                 , PluginM
                                 , mkPageTransform
                                 , mkPageTransformM
                                 , Config(..)
                                 , Request(..)
                                 , User(..)
                                 , Context(..)
                                 , PageType(..)
                                 , PageLayout(..)
                                 , askConfig
                                 , askUser
                                 , askRequest
                                 , askFileStore
                                 , askMeta
                                 , doNotCache
                                 , getContext
                                 , modifyContext
                                 , inlinesToURL
                                 , inlinesToString
                                 , liftIO
                                 , withTempDir
                                 , module Text.Pandoc.Definition
                                 , module Text.Pandoc.Generic
                                 )
  where
  import Text.Pandoc.Definition
  import Text.Pandoc.Generic
  import Data.Data
  import Network.Gitit.Types
  import Network.Gitit.ContentTransformer
  import Network.Gitit.Util (withTempDir)
  import Network.Gitit.Server (Request(..))
  import Control.Monad.Reader (ask)
  import Control.Monad.Trans (liftIO)
  import Control.Monad (liftM)
  import Data.FileStore (FileStore)
  
  -- | Returns the current wiki configuration.
  askConfig :: PluginM Config
  askConfig = liftM pluginConfig ask
  
  -- | Returns @Just@ the logged in user, or @Nothing@ if nobody is logged in.
  askUser :: PluginM (Maybe User)
  askUser = liftM pluginUser ask
  
  -- | Returns the complete HTTP request.
  askRequest :: PluginM Request
  askRequest = liftM pluginRequest ask
  
  -- | Returns the wiki filestore.
  askFileStore :: PluginM FileStore
  askFileStore = liftM pluginFileStore ask
  
  -- | Returns the page meta data
  askMeta :: PluginM [(String, String)]
  askMeta = liftM ctxMeta getContext
  
  -- | Indicates that the current page or file is not to be cached.
  doNotCache :: PluginM ()
  doNotCache = modifyContext (\ctx -> ctx{ ctxCacheable = False })
  
  -- | Lifts a function from @a -> a@ (for example, @Inline -> Inline@,
  -- @Block -> Block@, @[Inline] -> [Inline]@, or @String -> String@)
  -- to a 'PageTransform' plugin.
  mkPageTransform :: Data a => (a -> a) -> Plugin
  mkPageTransform fn = PageTransform $ return . bottomUp fn
  
  -- | Monadic version of 'mkPageTransform'.
  -- Lifts a function from @a -> m a@ to a 'PageTransform' plugin.
  mkPageTransformM :: Data a => (a -> PluginM a) -> Plugin
  mkPageTransformM =  PageTransform . bottomUpM
  
  