From 7f83d88a656eff36b070fec0958bd2687c35c146 Mon Sep 17 00:00:00 2001
From: John MacFarlane <fiddlosopher@gmail.com>
Date: Mon, 1 Jul 2013 20:49:22 -0700
Subject: Added Text.Pandoc.Writers.Shared to repository.

This should have been in last commit.
---
 src/Text/Pandoc/Writers/Shared.hs | 121 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 121 insertions(+)
 create mode 100644 src/Text/Pandoc/Writers/Shared.hs

diff --git a/src/Text/Pandoc/Writers/Shared.hs b/src/Text/Pandoc/Writers/Shared.hs
new file mode 100644
index 000000000..c6c30d070
--- /dev/null
+++ b/src/Text/Pandoc/Writers/Shared.hs
@@ -0,0 +1,121 @@
+{-
+Copyright (C) 2013 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
+-}
+
+{- |
+   Module      : Text.Pandoc.Writers.Shared
+   Copyright   : Copyright (C) 2013 John MacFarlane
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : John MacFarlane <jgm@berkeley.edu>
+   Stability   : alpha
+   Portability : portable
+
+Shared utility functions for pandoc writers.
+-}
+module Text.Pandoc.Writers.Shared (
+                       metaToJSON
+                     , getField
+                     , setField
+                     , defField
+                     )
+where
+import Text.Pandoc.Definition
+import Control.Monad (liftM)
+import Text.Pandoc.Options (WriterOptions(..))
+import qualified Data.HashMap.Strict as H
+import qualified Data.Map as M
+import qualified Data.Text as T
+import Data.Aeson (FromJSON(..), fromJSON, ToJSON (..), Value(Object), Result(..))
+import qualified Data.Traversable as Traversable
+
+-- | Create JSON value for template from a 'Meta' and an association list
+-- of variables, specified at the command line or in the writer.
+-- Variables overwrite metadata fields with the same names.
+-- If multiple variables are set with the same name, a list is
+-- assigned.
+metaToJSON :: Monad m
+           => WriterOptions
+           -> ([Block] -> m String)
+           -> ([Inline] -> m String)
+           -> Meta
+           -> m Value
+metaToJSON opts blockWriter inlineWriter (Meta metamap)
+  | writerStandalone opts = do
+    let baseContext = foldl (\acc (x,y) -> setField x y acc) (Object H.empty)
+                      $ writerVariables opts
+    renderedMap <- Traversable.mapM
+                   (metaValueToJSON blockWriter inlineWriter)
+                   metamap
+    return $ M.foldWithKey (\key val obj -> defField key val obj)
+                   baseContext renderedMap
+  | otherwise = return (Object H.empty)
+
+metaValueToJSON :: Monad m
+                => ([Block] -> m String)
+                -> ([Inline] -> m String)
+                -> MetaValue
+                -> m Value
+metaValueToJSON blockWriter inlineWriter (MetaMap metamap) = liftM toJSON $
+  Traversable.mapM (metaValueToJSON blockWriter inlineWriter) metamap
+metaValueToJSON blockWriter inlineWriter (MetaList xs) = liftM toJSON $
+  Traversable.mapM (metaValueToJSON blockWriter inlineWriter) xs
+metaValueToJSON _ _ (MetaString s) = return $ toJSON s
+metaValueToJSON blockWriter _ (MetaBlocks bs) = liftM toJSON $ blockWriter bs
+metaValueToJSON _ inlineWriter (MetaInlines bs) = liftM toJSON $ inlineWriter bs
+
+-- | Retrieve a field value from a JSON object.
+getField :: FromJSON a
+         => String
+         -> Value
+         -> Maybe a
+getField field (Object hashmap) = do
+  result <- H.lookup (T.pack field) hashmap
+  case fromJSON result of
+       Success x -> return x
+       _         -> fail "Could not convert from JSON"
+getField _ _ = fail "Not a JSON object"
+
+setField :: ToJSON a
+         => String
+         -> a
+         -> Value
+         -> Value
+-- | Set a field of a JSON object.  If the field already has a value,
+-- convert it into a list with the new value appended to the old value(s).
+-- This is a utility function to be used in preparing template contexts.
+setField field val (Object hashmap) =
+  Object $ H.insertWith combine (T.pack field) (toJSON val) hashmap
+  where combine newval oldval =
+          case fromJSON oldval of
+                Success xs  -> toJSON $ xs ++ [newval]
+                _           -> toJSON [oldval, newval]
+setField _ _  x = x
+
+defField :: ToJSON a
+         => String
+         -> a
+         -> Value
+         -> Value
+-- | Set a field of a JSON object if it currently has no value.
+-- If it has a value, do nothing.
+-- This is a utility function to be used in preparing template contexts.
+defField field val (Object hashmap) =
+  Object $ H.insertWith f (T.pack field) (toJSON val) hashmap
+    where f _newval oldval = oldval
+defField _ _  x = x
+
-- 
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