add main algorithm

config.conf

 [main]
-active_set_size = 2
-header_size =10 
+header_size = 10 
 
 [translation]
 service = libretranslate

protocol_translation_live/__main__.py

 import json
 import time
 from configparser import ConfigParser
-from pathlib import Path
-from difflib import Differ
+from difflib import SequenceMatcher
+from itertools import takewhile
 from math import ceil
+from pathlib import Path
+import atexit
 
 import requests
 
@@ -14,9 +16,10 @@ from translation import DeepL, LibreTranslate, Translation
 # TODO: scheint nur bei fem-instanz zu funktionieren. bei libretranslate.de kackt das ab
 # TODO: implement possibility to execute this package for multiple pairs of protocols (see matterbridge)
 # TODO: work on appending text:
-# idea: 2 states:
-# * detection of active line (using diff)
-# * translation of active line
+
+# write termination message on exit
+atexit.register(lambda: dst_pad.write(
+    "[PROTOCOL TRANSLATION HAS BEEN TERMINATED]\n" + dst_pad.read()))
 
 if __name__ == "__main__":
     # read config files
@@ -28,7 +31,6 @@ if __name__ == "__main__":
     config.read(Path(__file__).parent.parent / "config.conf")
 
     # read main
-    active_set_size = int(config["main"]["active_set_size"])
     header_size = int(config["main"]["header_size"])
 
     # create src pad
@@ -71,23 +73,88 @@ if __name__ == "__main__":
         raise ValueError(
             "config.conf: 'service' in [translation] is not valid")
 
-    # do translation
-    # ..initial translation
+    # initial translation
+    dst_pad.write("initializing...")
+
     initial_text = src_pad.read().split('\n')
-    header = '\n'.join(initial_text[0:header_size])
-    body = '\n'.join(initial_text[header_size:])
+    header = initial_text[0:header_size]
+    body = initial_text[header_size:]
+
+    # ..only include line break after header if header size > 0
+    joined_header = '\n'.join(header) + '\n' if len(header) > 0 else ""
 
-    translated_body = t.translate(body, src_lang, dst_lang)
-    dst_pad.write(header + '\n' + translated_body)
+    # ..strip leading lines consisting of whitespace
+    # ..add them when writing to dst_pad
+    # ..this has to be done, because libretranslate ignores leading whitespace,
+    # ..leading to incorrect order of the translated lines
+    leading_space_lines = list(
+        takewhile(lambda line: line.isspace() or not line, body))
+    # ..only include line break after lines if size > 0
+    joined_leading_space_lines = '\n'.join(
+        leading_space_lines) + '\n' if len(leading_space_lines) > 0 else ""
+
+    body = body[len(leading_space_lines):]
+
+    joined_translated_body = t.translate(
+        '\n'.join(body), src_lang, dst_lang)
+
+    dst_pad.write(joined_header + joined_leading_space_lines +
+                  joined_translated_body)
 
     # ..further translation
-    d = Differ()
+    s = SequenceMatcher()
+    translated_body = joined_translated_body.split('\n')
+
     while True:
+        # TODO: it is assumed, that libretranslate definitely translates the protocol line by line
+        # this is to be tested
+
+        # [old_]body and [old_]translated_body are lists of lines
         old_body = body
-        body = src_pad.read()[header_size:]
 
-        # TODO: use diff to find changes of protocol, extract them, translate them, insert them, post them
+        # read body (without header)
+        body = src_pad.read().split('\n')[header_size:]
+
+        # again, handle leading space lines
+        leading_space_lines = list(
+            takewhile(lambda line: line.isspace() or not line, body))
+        joined_leading_space_lines = '\n'.join(
+            leading_space_lines) + '\n' if len(leading_space_lines) > 0 else ""
+
+        body = body[len(leading_space_lines):]
+
         # sequence matcher get_opcodes
+        s.set_seqs(old_body, body)
+        opcodes = s.get_opcodes()
+
+        # this line does a couple of things:
+        # ..create a generator
+        # ..add all elements of 'opcodes' to it except those with the 'equal'-tag
+        # ..compute the text in the lines that have been changed and translate it
+        # ..except for the case, that the tag is 'delete' which is trivial
+        translated_opcodes = (
+            (e[0], e[1], e[2], e[3], e[4], (lambda: t.translate('\n'.join(body[e[3]:e[4]]), src_lang, dst_lang).split('\n') if e[0] != "delete" else None)()) for e in opcodes if e[0] != "equal")
+
+        # insert the translated text into the old_translated_body, thus creating translated_body
+        added_lines = 0
+        for e in translated_opcodes:
+            if e[0] == "delete":
+                del translated_body[e[1] +
+                                    added_lines: e[2] + added_lines]
+                added_lines -= e[2] - e[1]
+
+            elif e[0] == "replace":
+                translated_body[e[1] +
+                                added_lines: e[2] + added_lines] = e[5]
+
+            elif e[0] == "insert":
+                translated_body[e[1] +
+                                added_lines: e[2] + added_lines] = e[5]
+                added_lines += e[4] - e[3]
+
+            else:
+                assert False
 
-        # dst_pad.write(src_pad.read())
-        pass
+        # write
+        dst_pad.write(joined_header + joined_leading_space_lines +
+                      '\n'.join(translated_body))