main: add image hashing

build md5 sum over the resulting assembled image(s) and
check against a stored hash file to determine if we really need
to update the screen.
Option can be controlled by new image_hash global option.

If info_section is enabled while image_hash is on,
the time of update will be stripped from the section,
as it is clearly not hashable.

In the end this enables us to update the information in the
background way more frequent without increasing the stress
caused to the display

Signed-off-by: Konrad Weihmann <kweihmann@outlook.com>

inkycal/main.py

@@ -6,7 +6,10 @@ Main class for inkycal Project
 Copyright by aceisace
 """
 
+import glob
+import hashlib
 import json
+import os
 import traceback
 from logging.handlers import RotatingFileHandler
 
@@ -168,6 +171,9 @@ class Inkycal:
         # Path to store images
         self.image_folder = image_folder
 
+        # Remove old hashes
+        self._remove_hashes(self.image_folder)
+
         # Give an OK message
         print('loaded inkycal')
 
@@ -235,6 +241,45 @@ class Inkycal:
 
         self._assemble()
 
+    def _image_hash(self, _in):
+        """Create a md5sum of a path or a bytes stream."""
+        if not isinstance(_in, str):
+            image_bytes = _in.tobytes()
+        else:
+            try:
+                with open(_in) as i:
+                    return i.read()
+            except FileNotFoundError:
+                image_bytes = None
+        return hashlib.md5(image_bytes).hexdigest() if image_bytes else ""
+
+    def _remove_hashes(self, basepath):
+        for _file in glob.glob(f"{basepath}/*.hash"):
+            try:
+                os.remove(_file)
+            except:
+                pass
+
+    def _write_image_hash(self, path, _in):
+        """Write hash to a file."""
+        with open(path, "w") as o:
+            o.write(self._image_hash(_in))
+
+    def _needs_image_update(self, _list):
+        """Check if any image has been updated or not.
+        Input a list of tuples(str, image)."""
+        res = False
+        for item in _list:
+            _a = self._image_hash(item[0])
+            _b = self._image_hash(item[1])
+            print("{f1}:{h1} -> {h2}".format(f1=item[0], h1=_a, h2=_b))
+            if _a != _b:
+                res = True
+                self._write_image_hash(item[0], item[1])
+            print("Refresh needed: {a}".format(a=res))
+        return res
+
+
     def run(self):
         """Runs main program in nonstop mode.
 
@@ -264,7 +309,10 @@ class Inkycal:
             errors = []  # store module numbers in here
 
             # short info for info-section
-            self.info = f"{current_time.format('D MMM @ HH:mm')}  "
+            if not self.settings.get('image_hash', False):
+                self.info = f"{current_time.format('D MMM @ HH:mm')}  "
+            else:
+                self.info = ""
 
             for number in range(1, self._module_number):
 
@@ -299,6 +347,9 @@ class Inkycal:
                 display = self.Display
 
                 self._calibration_check()
+                if self._calibration_state:
+                    # after calibration we have to forcefully rewrite the screen
+                    self._remove_hashes(self.image_folder)
 
                 if self.supports_colour:
                     im_black = Image.open(f"{self.image_folder}canvas.png")
@@ -310,7 +361,12 @@ class Inkycal:
                         im_colour = upside_down(im_colour)
 
                     # render the image on the display
-                    display.render(im_black, im_colour)
+                    if not self.settings.get('image_hash', False) or self._needs_image_update([
+                      (f"{self.image_folder}/canvas.png.hash", im_black),
+                      (f"{self.image_folder}/canvas_colour.png.hash", im_colour)
+                    ]):
+                        # render the image on the display
+                        display.render(im_black, im_colour)
 
                 # Part for black-white ePapers
                 elif not self.supports_colour:
@@ -321,7 +377,10 @@ class Inkycal:
                     if self.settings['orientation'] == 180:
                         im_black = upside_down(im_black)
 
-                    display.render(im_black)
+                    if not self.settings.get('image_hash', False) or self._needs_image_update([
+                      (f"{self.image_folder}/canvas.png.hash", im_black),
+                    ]):
+                        display.render(im_black)
 
             print(f'\nNo errors since {counter} display updates \n'
                   f'program started {runtime.humanize()}')