From 6cf0ca7f96a3fba72bf42dab0e1add1b62e3f580 Mon Sep 17 00:00:00 2001
From: Igor Pashev <pashev.igor@gmail.com>
Date: Wed, 3 Jun 2020 22:14:24 +0200
Subject: Allow specifying a metadata provider

In addition to parsing metadata header & metadata files it will
allow any custom routine to extract metadata from the resource files,
for example with Pandoc
---
 lib/Hakyll/Core/Provider/Internal.hs | 10 +++++++---
 lib/Hakyll/Core/Provider/Metadata.hs |  5 +++--
 2 files changed, 10 insertions(+), 5 deletions(-)

(limited to 'lib/Hakyll/Core/Provider')

diff --git a/lib/Hakyll/Core/Provider/Internal.hs b/lib/Hakyll/Core/Provider/Internal.hs
index c298653..777decb 100644
--- a/lib/Hakyll/Core/Provider/Internal.hs
+++ b/lib/Hakyll/Core/Provider/Internal.hs
@@ -45,6 +45,7 @@ import           System.Time            (formatCalendarTime, toCalendarTime)
 
 --------------------------------------------------------------------------------
 import           Hakyll.Core.Identifier
+import           Hakyll.Core.Metadata
 import           Hakyll.Core.Store      (Store)
 import qualified Hakyll.Core.Store      as Store
 import           Hakyll.Core.Util.File
@@ -95,16 +96,19 @@ data Provider = Provider
       providerOldFiles  :: Map Identifier ResourceInfo
     , -- | Underlying persistent store for caching
       providerStore     :: Store
-    } deriving (Show)
+      -- | A custom function to extract metadata from files
+    , providerMetadata  :: FilePath -> IO Metadata
+    }
 
 
 --------------------------------------------------------------------------------
 -- | Create a resource provider
 newProvider :: Store                  -- ^ Store to use
             -> (FilePath -> IO Bool)  -- ^ Should we ignore this file?
+            -> (FilePath -> IO Metadata)  -- ^ Metadata provider
             -> FilePath               -- ^ Search directory
             -> IO Provider            -- ^ Resulting provider
-newProvider store ignore directory = do
+newProvider store ignore metadata directory = do
     list <- map fromFilePath <$> getRecursiveContents ignore directory
     let universe = S.fromList list
     files <- fmap (maxmtime . M.fromList) $ forM list $ \identifier -> do
@@ -116,7 +120,7 @@ newProvider store ignore directory = do
     oldFiles <- fromMaybe mempty . Store.toMaybe <$> Store.get store oldKey
     oldFiles `deepseq` Store.set store oldKey files
 
-    return $ Provider directory files oldFiles store
+    return $ Provider directory files oldFiles store metadata
   where
     oldKey = ["Hakyll.Core.Provider.Internal.newProvider", "oldFiles"]
 
diff --git a/lib/Hakyll/Core/Provider/Metadata.hs b/lib/Hakyll/Core/Provider/Metadata.hs
index c74627b..1630b0c 100644
--- a/lib/Hakyll/Core/Provider/Metadata.hs
+++ b/lib/Hakyll/Core/Provider/Metadata.hs
@@ -27,7 +27,7 @@ import           Hakyll.Core.Identifier
 import           Hakyll.Core.Metadata
 import           Hakyll.Core.Provider.Internal
 import           System.IO                     as IO
-import           System.IO.Error               (modifyIOError, ioeSetLocation)
+import           System.IO.Error               (ioeSetLocation, modifyIOError)
 
 
 --------------------------------------------------------------------------------
@@ -42,7 +42,8 @@ loadMetadata p identifier = do
         Nothing  -> return mempty
         Just mi' -> loadMetadataFile $ resourceFilePath p mi'
 
-    return (md <> emd, body)
+    mdp <- providerMetadata p fp
+    return (md <> emd <> mdp, body)
   where
     normal = setVersion Nothing identifier
     fp     = resourceFilePath p identifier
-- 
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