Make CommonState opaque.

Text.Pandoc.Class now exports CommonState as an opaque object,
without its fields. [API change]

The internal module Text.Pandoc.Class.CommonState still exports
the fields.

Text.Pandoc.Class now exports the following new functions:
`getRequestHeaders`, `setRequestHeaders`, `getSourceURL`,
`getTrace`. [API change]

3 files changed, 31 insertions, 9 deletions

diff --git a/src/Text/Pandoc/Class.hs b/src/Text/Pandoc/Class.hs
index a1e51e0cf..7df67236b 100644
--- a/src/Text/Pandoc/Class.hs
+++ b/src/Text/Pandoc/Class.hs
@@ -23,7 +23,9 @@ module Text.Pandoc.Class
   , Translations
   ) where
 
-import Text.Pandoc.Class.CommonState (CommonState (..))
+-- We export CommonState as an opaque object.  Accessors for
+-- its fields are provided in Text.Pandoc.Class.PandocMonad.
+import Text.Pandoc.Class.CommonState (CommonState)
 import Text.Pandoc.Class.PandocMonad
 import Text.Pandoc.Class.PandocIO
 import Text.Pandoc.Class.PandocPure
diff --git a/src/Text/Pandoc/Class/PandocMonad.hs b/src/Text/Pandoc/Class/PandocMonad.hs
index 850aff584..7fc89bdab 100644
--- a/src/Text/Pandoc/Class/PandocMonad.hs
+++ b/src/Text/Pandoc/Class/PandocMonad.hs
@@ -28,12 +28,13 @@ module Text.Pandoc.Class.PandocMonad
   , getZonedTime
   , readFileFromDirs
   , report
-  , setTrace
   , setRequestHeader
   , setNoCheckCertificate
   , getLog
   , setVerbosity
   , getVerbosity
+  , setTrace
+  , getTrace
   , getMediaBag
   , setMediaBag
   , insertMedia
@@ -47,6 +48,9 @@ module Text.Pandoc.Class.PandocMonad
   , setOutputFile
   , setResourcePath
   , getResourcePath
+  , setRequestHeaders
+  , getRequestHeaders
+  , getSourceURL
   , readMetadataFile
   , toTextM
   , fillMediaBag
@@ -164,6 +168,15 @@ setVerbosity verbosity =
 getVerbosity :: PandocMonad m => m Verbosity
 getVerbosity = getsCommonState stVerbosity
 
+-- | Set tracing. This affects the behavior of 'trace'. If tracing
+-- is not enabled, 'trace' does nothing.
+setTrace :: PandocMonad m => Bool -> m ()
+setTrace enabled = modifyCommonState $ \st -> st{ stTrace = enabled }
+
+-- | Get tracing status.
+getTrace :: PandocMonad m => m Bool
+getTrace = getsCommonState stTrace
+
 -- | Get the accumulated log messages (in temporal order).
 getLog :: PandocMonad m => m [LogMessage]
 getLog = reverse <$> getsCommonState stLog
@@ -179,12 +192,6 @@ report msg = do
   when (level <= verbosity) $ logOutput msg
   modifyCommonState $ \st -> st{ stLog = msg : stLog st }
 
--- | Determine whether tracing is enabled.  This affects
--- the behavior of 'trace'.  If tracing is not enabled,
--- 'trace' does nothing.
-setTrace :: PandocMonad m => Bool -> m ()
-setTrace useTracing = modifyCommonState $ \st -> st{stTrace = useTracing}
-
 -- | Set request header to use in HTTP requests.
 setRequestHeader :: PandocMonad m
                  => T.Text  -- ^ Header name
@@ -248,6 +255,18 @@ getResourcePath = getsCommonState stResourcePath
 setResourcePath :: PandocMonad m => [FilePath] -> m ()
 setResourcePath ps = modifyCommonState $ \st -> st{stResourcePath = ps}
 
+-- | Retrieve the request headers to add for HTTP requests.
+getRequestHeaders :: PandocMonad m => m [(T.Text, T.Text)]
+getRequestHeaders = getsCommonState stRequestHeaders
+
+-- | Set the request headers to add for HTTP requests.
+setRequestHeaders :: PandocMonad m => [(T.Text, T.Text)] -> m ()
+setRequestHeaders hs = modifyCommonState $ \st -> st{ stRequestHeaders = hs }
+
+-- | Get the absolute UL or directory of first source file.
+getSourceURL :: PandocMonad m => m (Maybe T.Text)
+getSourceURL = getsCommonState stSourceURL
+
 -- | Get the current UTC time. If the @SOURCE_DATE_EPOCH@ environment
 -- variable is set to a unix time (number of seconds since midnight
 -- Jan 01 1970 UTC), it is used instead of the current time, to support
diff --git a/src/Text/Pandoc/Translations.hs b/src/Text/Pandoc/Translations.hs
index 3be76335e..00562e189 100644
--- a/src/Text/Pandoc/Translations.hs
+++ b/src/Text/Pandoc/Translations.hs
@@ -20,7 +20,8 @@ module Text.Pandoc.Translations (
                          )
 where
 import Text.Pandoc.Translations.Types
-import Text.Pandoc.Class (PandocMonad(..), CommonState(..), toTextM, report)
+import Text.Pandoc.Class (PandocMonad(..), toTextM, report)
+import Text.Pandoc.Class.CommonState (CommonState(..))
 import Text.Pandoc.Data (readDataFile)
 import Text.Pandoc.Error (PandocError(..))
 import Text.Pandoc.Logging (LogMessage(..))