Update LLM logic for pure text input (opea-project#40)

* fix requirement issue

Signed-off-by: letonghan <[email protected]>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* update llm codes

Signed-off-by: letonghan <[email protected]>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Signed-off-by: letonghan <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

comps/llms/langchain/llm_tgi.py

@@ -36,19 +36,22 @@ def llm_generate(input: Union[TextDoc, RerankedDoc]) -> GeneratedDoc:
         repetition_penalty=params.repetition_penalty,
         streaming=params.streaming,
     )
+    final_prompt = None
     if isinstance(input, RerankedDoc):
         template = """Answer the question based only on the following context:
         {context}
         Question: {question}
         """
         prompt = ChatPromptTemplate.from_template(template)
         chain = prompt | llm | StrOutputParser()
+        final_prompt = input.query
         response = chain.invoke({"question": input.query, "context": input.doc.text})
     elif isinstance(input, TextDoc):
+        final_prompt = input.text
         response = llm.invoke(input.text)
     else:
         raise TypeError("Invalid input type. Expected TextDoc or RerankedDoc.")
-    res = GeneratedDoc(text=response, prompt=input.query)
+    res = GeneratedDoc(text=response, prompt=final_prompt)
     return res