Add fallbacks to image conversion

camelot/backends/image_conversion.py

@@ -1,15 +1,41 @@
 # -*- coding: utf-8 -*-
 
+import logging
+
 from .poppler_backend import PopplerBackend
 from .ghostscript_backend import GhostscriptBackend
 
+logger = logging.getLogger("camelot")
 backends = {"poppler": PopplerBackend, "ghostscript": GhostscriptBackend}
 
 
 class ImageConversionBackend(object):
-    def __init__(self, backend="poppler"):
+    def __init__(self, backend="poppler", use_fallback=True):
+        if backend not in backends.keys():
+            raise ValueError(f"Image conversion backend '{backend}' not supported")
+
         self.backend = backend
+        self.use_fallback = use_fallback
+        self.fallbacks = list(filter(lambda x: x != backend, backends.keys()))
 
     def convert(self, pdf_path, png_path):
-        converter = backends[self.backend]()
-        converter.convert(pdf_path, png_path)
+        try:
+            converter = backends[self.backend]()
+            converter.convert(pdf_path, png_path)
+        except Exception as e:
+            logger.info(f"Image conversion backend '{self.backend}' failed with {str(e)}")
+
+            if self.use_fallback:
+                for fallback in self.fallbacks:
+                    logger.info(f"Falling back on '{fallback}'")
+
+                    try:
+                        converter = backends[self.backend]()
+                        converter.convert(pdf_path, png_path)
+                    except Exception as e:
+                        logger.info(f"Image conversion backend '{fallback}' failed with {str(e)}")
+
+                        continue
+                    else:
+                        logger.info(f"Image conversion backend '{fallback}' succeeded")
+                        break