1 files changed, 30 insertions, 0 deletions
diff --git a/plugins/DotPlugin.hs b/plugins/DotPlugin.hs
new file mode 100644
index 000000000..db1a02e1c
--- /dev/null
+++ b/plugins/DotPlugin.hs
@@ -0,0 +1,30 @@
+module DotPlugin (transform) where
+import Text.Pandoc
+import Text.Pandoc.Shared
+import System.Process (readProcess)
+import Data.Char (ord)
+-- from the utf8-string package on HackageDB:
+import Data.ByteString.Lazy.UTF8 (fromString)
+-- from the SHA package on HackageDB:
+import Data.Digest.Pure.SHA
+
+-- This plugin allows you to include a graphviz "dot" diagram
+-- in a document like this:
+--
+-- ~~~ {.dot name="diagram1"}
+-- digraph G {Hello->World}
+-- ~~~
+
+transform :: Block -> IO Block
+transform (CodeBlock (id, classes, namevals) contents) | "dot" `elem` classes = do
+  let (name, outfile) =  case lookup "name" namevals of
+                                Just fn   -> ([Str fn], fn ++ ".png")
+                                Nothing   -> ([], uniqueName contents ++ ".png")
+  result <- readProcess "dot" ["-Tpng"] contents
+  writeFile outfile result
+  return $ Para [Image name (outfile, "")]
+transform x = return x
+
+-- | Generate a unique filename given the file's contents.
+uniqueName :: String -> String
+uniqueName = showDigest . sha1 . fromString