fix organize agent's history messages without recalculating tokens (#4324)

Co-authored-by: chenyongzhao <chenyz@mama.cn>

api/core/prompt/agent_history_prompt_transform.py

@@ -0,0 +1,82 @@
+from typing import Optional, cast
+
+from core.app.entities.app_invoke_entities import (
+    ModelConfigWithCredentialsEntity,
+)
+from core.memory.token_buffer_memory import TokenBufferMemory
+from core.model_runtime.entities.message_entities import (
+    PromptMessage,
+    SystemPromptMessage,
+    UserPromptMessage,
+)
+from core.model_runtime.model_providers.__base.large_language_model import LargeLanguageModel
+from core.prompt.prompt_transform import PromptTransform
+
+
+class AgentHistoryPromptTransform(PromptTransform):
+    """
+    History Prompt Transform for Agent App
+    """
+    def __init__(self,
+                 model_config: ModelConfigWithCredentialsEntity,
+                 prompt_messages: list[PromptMessage],
+                 history_messages: list[PromptMessage],
+                 memory: Optional[TokenBufferMemory] = None,
+                 ):
+        self.model_config = model_config
+        self.prompt_messages = prompt_messages
+        self.history_messages = history_messages
+        self.memory = memory
+
+    def get_prompt(self) -> list[PromptMessage]:
+        prompt_messages = []
+        num_system = 0
+        for prompt_message in self.history_messages:
+            if isinstance(prompt_message, SystemPromptMessage):
+                prompt_messages.append(prompt_message)
+                num_system += 1
+
+        if not self.memory:
+            return prompt_messages
+
+        max_token_limit = self._calculate_rest_token(self.prompt_messages, self.model_config)
+
+        model_type_instance = self.model_config.provider_model_bundle.model_type_instance
+        model_type_instance = cast(LargeLanguageModel, model_type_instance)
+
+        curr_message_tokens = model_type_instance.get_num_tokens(
+            self.memory.model_instance.model,
+            self.memory.model_instance.credentials,
+            self.history_messages
+        )
+        if curr_message_tokens <= max_token_limit:
+            return self.history_messages
+
+        # number of prompt has been appended in current message
+        num_prompt = 0
+        # append prompt messages in desc order
+        for prompt_message in self.history_messages[::-1]:
+            if isinstance(prompt_message, SystemPromptMessage):
+                continue
+            prompt_messages.append(prompt_message)
+            num_prompt += 1
+            # a message is start with UserPromptMessage
+            if isinstance(prompt_message, UserPromptMessage):
+                curr_message_tokens = model_type_instance.get_num_tokens(
+                    self.memory.model_instance.model,
+                    self.memory.model_instance.credentials,
+                    prompt_messages
+                )
+                # if current message token is overflow, drop all the prompts in current message and break
+                if curr_message_tokens > max_token_limit:
+                    prompt_messages = prompt_messages[:-num_prompt]
+                    break
+                num_prompt = 0
+        # return prompt messages in asc order
+        message_prompts = prompt_messages[num_system:]
+        message_prompts.reverse()
+
+        # merge system and message prompt
+        prompt_messages = prompt_messages[:num_system]
+        prompt_messages.extend(message_prompts)
+        return prompt_messages