Ensure that the chat prompt will always contain < 2048 tokens

This way, we can keep the context string at the top of the prompt
even if you keep talking to the bot for hours.

Before this commit, the prompt would be simply truncated and the
context string would eventually be lost.

server.py

@@ -116,6 +116,14 @@ def fix_galactica(s):
     s = s.replace(r'$$', r'$')
     return s
 
+def encode(prompt, tokens):
+    if not args.cpu:
+        torch.cuda.empty_cache()
+        input_ids = tokenizer.encode(str(prompt), return_tensors='pt', truncation=True, max_length=2048-tokens).cuda()
+    else:
+        input_ids = tokenizer.encode(str(prompt), return_tensors='pt', truncation=True, max_length=2048-tokens)
+    return input_ids
+
 def generate_reply(question, tokens, inference_settings, selected_model, eos_token=None):
     global model, tokenizer, model_name, loaded_preset, preset
 
@@ -131,14 +139,9 @@ def generate_reply(question, tokens, inference_settings, selected_model, eos_tok
             preset = infile.read()
         loaded_preset = inference_settings
 
-    if not args.cpu:
-        torch.cuda.empty_cache()
-        input_ids = tokenizer.encode(str(question), return_tensors='pt', truncation=True, max_length=2048-tokens).cuda()
-        cuda = ".cuda()"
-    else:
-        input_ids = tokenizer.encode(str(question), return_tensors='pt', truncation=True, max_length=2048-tokens)
-        cuda = ""
+    input_ids = encode(question, tokens)
 
+    cuda = ".cuda()" if args.cpu else ""
     if eos_token is None:
         output = eval(f"model.generate(input_ids, {preset}){cuda}")
     else:
@@ -217,16 +220,20 @@ elif args.chat or args.cai_chat:
     def chatbot_wrapper(text, tokens, inference_settings, selected_model, name1, name2, context, check):
         text = chat_response_cleaner(text)
 
-        question = f"{context}\n\n"
-        for i in range(len(history)):
-            if args.cai_chat:
-                question += f"{name1}: {history[i][0].strip()}\n"
-                question += f"{name2}: {history[i][1].strip()}\n"
-            else:
-                question += f"{name1}: {history[i][0][3:-5].strip()}\n"
-                question += f"{name2}: {history[i][1][3:-5].strip()}\n"
-        question += f"{name1}: {text}\n"
-        question += f"{name2}:"
+        rows = [f"{context}\n\n"]
+        i = len(history)-1
+        while i >= 0 and len(encode(''.join(rows), tokens)[0]) < 2048-tokens:
+            rows.insert(1, f"{name2}: {history[i][1].strip()}\n")
+            rows.insert(1, f"{name1}: {history[i][0].strip()}\n")
+            i -= 1
+        rows.append(f"{name1}: {text}\n")
+        rows.append(f"{name2}:")
+
+        while len(rows) > 3 and len(encode(''.join(rows), tokens)[0]) >= 2048-tokens:
+            rows.pop(1)
+            rows.pop(1)
+
+        question = ''.join(rows)
 
         if check:
             reply = generate_reply(question, tokens, inference_settings, selected_model, eos_token='\n')[0]