app.py

# PDFs
from langchain_community.document_loaders import PyPDFLoader
from langchain.vectorstores import FAISS
from langchain.embeddings import HuggingFaceEmbeddings as HFE
from langchain.schema import Document

# Groq
from langchain_groq import ChatGroq
from langchain_core.messages import HumanMessage
from langchain_community.chat_message_histories import ChatMessageHistory
from langchain_core.chat_history import BaseChatMessageHistory
from langchain_core.runnables.history import RunnableWithMessageHistory
from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
from groq import Groq

# Expanded Queries
import ast

# Cross Encoder
from sentence_transformers import CrossEncoder

# BM25
from rank_bm25 import BM25Okapi
import numpy as np

# Gradio
import gradio as gr

# GROQ_API = userdata.get('GROQ_API')
embed_model = "sentence-transformers/all-MiniLM-L6-v2"
cross_encoder = CrossEncoder('cross-encoder/ms-marco-MiniLM-L-12-v2')

prompt = ChatPromptTemplate.from_messages(
    [
        ("system", """
        You are a helpful HR assistant specializing in the resume screening phase.
        Your goal is to identify the best, most suitable, or highest-potential
        candidates whose qualifications align well with the provided job title
        and job description. If a question or request falls outside the scope
        of resume screening and candidate alignment,
        please respond with 'I don't know'.
        """),
        MessagesPlaceholder(variable_name="history", optional=True),
        ("system", "Context: {context}"),
        ("human", "{question}"),
    ]
)

query_expansion_prompt = ChatPromptTemplate([
    ("system", """
    You are an expert HR assistant. Given a job description and a user query,
    generate 3 alternative, diverse search queries that capture different
    aspects of what makes a great candidate for this role. Each query should
    focus on a different facet (e.g., skills, leadership, hands-on experience,
                                        certifications, unique achievements).

    If the job description is empty, generate a general job description for the role
    mentioned in the user query and then create the 3 alternative search queries based on that.

    Return ONLY the generated queries as a Python list of strings. Do not include
    any other explanatory text or formatting.
    """),
    ("human", "Job Description: {job_description}\nUser Query: {user_query}")
])

JUDGE_PROMPT = """
You are an expert recruiter. Given the job description, the user query, and the system's answer, rate:

Faithfulness: Does the answer accurately reflect the resume(s) provided? (1-5)
Relevance: Does the answer address the job requirements and user query? (1-5)

Provide your feedback as follows:

Faithfulness: <score>
Relevance: <score>
Justification: <brief explanation>

Job Description:
{job_description}

User Query:
{user_query}

System Answer:
{system_answer}
"""

def load_single_pdf(path):
  loader = PyPDFLoader(path)
  pages = loader.load()
  full_text = "\n".join([page.page_content for page in pages])
  return Document(page_content=full_text)

def chunks_embed(chunks, model_name):
  """Create embeds for doc chunks and store in FAISS"""
  embeds = HFE(model_name=model_name)
  # Create FAISS index
  db = FAISS.from_documents(chunks, embeds)
  print(f"Created FAISS Index with {len(chunks)} documents.")
  return db

def search_docs_mmr(db, query, k, fetch_k, lambda_mult):
  """
  Retrieve the most similar docs to the query using MMR
  (Maximum Marginal Relevance)
  """
  if not db:
    print("Error: No document database available")
    return []

  docs = db.max_marginal_relevance_search(
      query, k=fetch_k, lambda_mult=lambda_mult
  )
  return docs

def combine_results(results):
  # Combine the content from results to create context
  context = ""
  for doc in results:
    context += doc.page_content + "\n"
  return context

# 1. Prepare corpus for BM25
def prepare_bm25_corpus(docs):
  # Tokenize for BM25 (simple whitespace split, can improve)
  return [doc.page_content.lower().split() for doc in docs]

# 2. Initialize BM25
def init_bm25(docs):
  corpus = prepare_bm25_corpus(docs)
  return BM25Okapi(corpus)

# 3. BM25 Search
def bm25_search(bm25, query, docs, top_k=10):
  query_tokens = query.lower().split()
  scores = bm25.get_scores(query_tokens)
  top_indices = np.argsort(scores)[::-1][:top_k]
  return [docs[i] for i in top_indices], [scores[i] for i in top_indices]

# Hybrid Merge Functino
def hybrid_merge(semantic_results, bm25_results):
  # Merge by union, keeping order (semantic first, then BM25 if not already present)
  seen = set()
  merged = []
  for doc in semantic_results + bm25_results:
      if doc.page_content not in seen:
          merged.append(doc)
          seen.add(doc.page_content)
  return merged

def llm_judge_groq(api_key, job_description, user_query, system_answer):
  judge_prompt = JUDGE_PROMPT.format(
      job_description=job_description,
      user_query=user_query,
      system_answer=system_answer
  )
  client = Groq(api_key=api_key)
  completion = client.chat.completions.create(
      model="deepseek-r1-distill-llama-70b",
      messages=[{"role": "user", "content": judge_prompt}],
      max_tokens=512
  )
  return completion.choices[0].message.content

def screen_resumes(api_key, job_description, user_query, files):
  embed_model = "sentence-transformers/all-MiniLM-L6-v2"
  cross_encoder = CrossEncoder('cross-encoder/ms-marco-MiniLM-L-12-v2')

  # Model and prompt setup (inside function, using user API key)
  model = ChatGroq(model="llama-3.1-8b-instant", api_key=api_key)
  history = {}
  def get_session_history(session_id: str):
      if session_id not in history:
          history[session_id] = ChatMessageHistory()
      return history[session_id]
  with_message_history = RunnableWithMessageHistory(model, get_session_history)
  chain = prompt | model
  with_message_history = RunnableWithMessageHistory(
      chain,
      get_session_history,
      input_messages_key="question",
      history_messages_key="history"
  )

  # Load and process resumes
  resume_paths = [file.name for file in files]
  chunks = [load_single_pdf(path) for path in resume_paths]
  embeds = chunks_embed(chunks, embed_model)
  bm25 = init_bm25(chunks)

  # Query Expansion
  prompt_value = query_expansion_prompt.invoke({
      "job_description": job_description,
      "user_query": user_query,
  })
  expanded_queries_response = model.invoke(prompt_value.messages)
  expanded_queries = ast.literal_eval(expanded_queries_response.content)

  # Hybrid Retrieval
  all_semantic = []
  all_bm25 = []
  for q in expanded_queries:
      semantic_docs = search_docs_mmr(embeds, q, 10, 100, 0.7)
      bm25_docs, _ = bm25_search(bm25, q, chunks, top_k=10)
      all_semantic.extend(semantic_docs)
      all_bm25.extend(bm25_docs)
  merged_results = hybrid_merge(all_semantic, all_bm25)
  unique_results_list = merged_results

  # Cross-encoder Re-ranking
  pairs = [(user_query, doc.page_content) for doc in unique_results_list]
  scores = cross_encoder.predict(pairs)
  ranked = sorted(zip(scores, unique_results_list), key=lambda x: x[0], reverse=True)
  top_n = min(5, len(ranked))
  ranked_top_n = [doc for score, doc in ranked[:top_n]]
  context = "\n\n".join([doc.page_content for doc in ranked_top_n])

  # LLM Final Reasoning
  inputs = {
      "context": context,
      "question": user_query,
  }
  config = {"configurable": {"session_id": "GradioSession"}}
  response = with_message_history.invoke(inputs, config=config)
  system_output = response.content

  # LLM-as-a-Judge Evaluation
  judge_feedback = llm_judge_groq(api_key, job_description, user_query, system_output)

  return system_output, context, judge_feedback

demo = gr.Interface(
    fn=screen_resumes,
    inputs=[
        gr.Textbox(label="Groq API Key", type="password", lines=1, placeholder="sk..."),
        gr.Textbox(lines=4, label="Job Description"),
        gr.Textbox(lines=2, label="User Query"),
        gr.File(file_count="multiple", label="Upload Resume PDFs")
    ],
    outputs=[
        gr.Textbox(label="Screening Result (LLM Output)"),
        gr.Textbox(label="Top Ranked Resumes (Raw Text)"),
        gr.Textbox(label="LLM-as-a-Judge Evaluation (DeepSeek)")
    ],
    title="Resume Screening Assistant (Hybrid + LLM-as-a-Judge)",
    description="Enter your Groq API key, upload resumes, enter a job description and query, get the best candidates with explanations, and see an automated evaluation."
)

demo.launch(share=True)