Add epub support

image_cache.py

@@ -0,0 +1,34 @@
+from urllib.parse import urlparse
+from os.path import exists, join, dirname
+from os import makedirs
+from config import Config
+import requests
+
+
+def try_fetch(url):
+    for _ in range(5):
+        try:
+            re = requests.get(url=url)
+            if re.status_code == 200:
+                return re.content
+        except Exception:
+            pass
+        raise ValueError(f'HTTP ERROR {re.status_code} {re.reason}.')
+    raise ValueError('Failed to fetch the image.')
+
+
+def get_cache(cfg: Config, url: str):
+    u = urlparse(url)
+    path = u.path
+    if path.endswith('/'):
+        path = path[:-1]
+    path = join(cfg.img_cache_dir, path[1:])
+    if exists(path):
+        return path
+    else:
+        img = try_fetch(url)
+        d = dirname(path)
+        makedirs(d, exist_ok=True)
+        with open(path, 'wb') as f:
+            f.write(img)
+        return path