Lua: add `pandoc.template` module

The module provides a `compile` function to use strings as templates.

2 files changed, 62 insertions, 1 deletions

diff --git a/src/Text/Pandoc/Lua/Module/Pandoc.hs b/src/Text/Pandoc/Lua/Module/Pandoc.hs
index c0127cdfe..9864da0db 100644
--- a/src/Text/Pandoc/Lua/Module/Pandoc.hs
+++ b/src/Text/Pandoc/Lua/Module/Pandoc.hs
@@ -29,6 +29,7 @@ import HsLua hiding (pushModule)
 import HsLua.Class.Peekable (PeekError)
 import System.Exit (ExitCode (..))
 import Text.Pandoc.Definition
+import Text.Pandoc.Error (PandocError (..))
 import Text.Pandoc.Lua.Orphans ()
 import Text.Pandoc.Lua.Marshal.AST
 import Text.Pandoc.Lua.Marshal.Filter (peekFilter)
@@ -50,7 +51,6 @@ import qualified Data.ByteString.Lazy.Char8 as BSL
 import qualified Data.Text as T
 import qualified Text.Pandoc.Lua.Util as LuaUtil
 import qualified Text.Pandoc.UTF8 as UTF8
-import Text.Pandoc.Error
 
 -- | Push the "pandoc" package to the Lua stack. Requires the `List`
 -- module to be loadable.
diff --git a/src/Text/Pandoc/Lua/Module/Template.hs b/src/Text/Pandoc/Lua/Module/Template.hs
new file mode 100644
index 000000000..cd66ce1c1
--- /dev/null
+++ b/src/Text/Pandoc/Lua/Module/Template.hs
@@ -0,0 +1,61 @@
+{-# LANGUAGE OverloadedStrings #-}
+{- |
+   Module      : Text.Pandoc.Lua.Module.Template
+   Copyright   : Copyright © 2022 Albert Krewinkel, John MacFarlane
+   License     : GNU GPL, version 2 or above
+   Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+
+Lua module to handle pandoc templates.
+-}
+module Text.Pandoc.Lua.Module.Template
+  ( documentedModule
+  ) where
+
+import HsLua
+import Text.Pandoc.Error (PandocError)
+import Text.Pandoc.Lua.Marshal.Template (pushTemplate)
+import Text.Pandoc.Lua.PandocLua (PandocLua (unPandocLua), liftPandocLua)
+import Text.Pandoc.Templates
+  (compileTemplate, getDefaultTemplate, runWithPartials, runWithDefaultPartials)
+
+import qualified Data.Text as T
+
+-- | The "pandoc.template" module.
+documentedModule :: Module PandocError
+documentedModule = Module
+  { moduleName = "pandoc.template"
+  , moduleDescription = T.unlines
+    [ "Lua functions for pandoc templates."
+    ]
+  , moduleFields = []
+  , moduleOperations = []
+  , moduleFunctions = functions
+  }
+
+-- | Template module functions.
+functions :: [DocumentedFunction PandocError]
+functions =
+  [ defun "compile"
+     ### (\template mfilepath -> unPandocLua $
+           case mfilepath of
+             Just fp -> runWithPartials (compileTemplate fp template)
+             Nothing -> runWithDefaultPartials
+                        (compileTemplate "templates/default" template))
+     <#> parameter peekText "string" "template" "template string"
+     <#> optionalParameter peekString "string" "templ_path" "template path"
+     =#> functionResult (either failLua pushTemplate) "pandoc Template"
+           "compiled template"
+
+  , defun "default"
+     ### (\mformat -> unPandocLua $ do
+           let getFORMAT = liftPandocLua $ do
+                 getglobal "FORMAT"
+                 forcePeek $ peekText top `lastly` pop 1
+           format <- maybe getFORMAT pure mformat
+           getDefaultTemplate format)
+     <#> optionalParameter peekText "string" "writer"
+           "writer for which the template should be returned."
+     =#> functionResult pushText "string"
+           "string representation of the writer's default template"
+
+  ]