image loader working but messy

image_manager.py

@@ -0,0 +1,83 @@
+# -*- encoding: utf-8 -*-
+
+import os.path
+from threading import Thread
+import urllib.request
+import base64
+import sublime
+
+CACHE_FILE = os.path.join(os.path.dirname(__file__), 'cache.txt')
+TIMEOUT = 20
+
+SEPARATOR = '---%cache%--'
+
+class InternalError(Exception): pass
+
+def to_base64(path=None, content=None):
+    if content is None and path is not None:
+        try:
+            with open(path, 'rb') as fp:
+                content = fp.read()
+        except FileNotFoundError:
+            return to_base64(os.path.join(os.path.dirname(__file__), '404.png'))
+
+    return 'data:image/png;base64,' + ''.join([chr(el) for el in list(base64.standard_b64encode(content))])
+
+def load_and_save_image(url, user_callback):
+    def callback(content):
+        content = to_base64(content=content)
+        with open(CACHE_FILE, 'a') as fp:
+            fp.write(url + SEPARATOR + content)
+            user_callback(content)
+    thread = ImageLoader(url, callback)
+    thread.start()
+    sublime.set_timeout_async(lambda: thread.join(), TIMEOUT)
+
+class ImageLoader(Thread):
+
+    def __init__(self, url, callback):
+        Thread.__init__(self)
+        self.url = url
+        self.callback = callback
+
+    def run(self):
+        page = urllib.request.urlopen(self.url, None, TIMEOUT)
+        self.callback(page.read())
+
+
+class ImageManager(object):
+
+    currently_loading = []
+
+    @staticmethod
+    def get(imageurl, user_callback):
+        if imageurl in ImageManager.currently_loading:
+            return None
+        def callback(content):
+            try:
+                ImageManager.currently_loading.remove(imageurl)
+            except ValueError:
+                sublime.error_message('Internal error: Trying to remove an URL'
+                                      'from loading_url, but not found. Please'
+                                      'report to the issue tracker.')
+                sublime.run_command('open_url', {
+                    'url': 'https://github.com/math2001/MarkdownLivePreview/'
+                           'issues/new'     
+                })
+
+            user_callback(content)
+
+        ImageManager.currently_loading.append(imageurl)
+        try:
+            with open(CACHE_FILE, 'r') as fp:
+                lines = fp.readlines()
+        except FileNotFoundError:
+            pass
+        else:
+            for line in lines:
+                url, base64 = line.split(SEPARATOR, 1)
+                if url == imageurl:
+                    return callback(base64)
+                else:
+                    print(url + '\n' + imageurl)
+        load_and_save_image(imageurl, callback)