app.py

import os
import shutil
import PyPDF2
import gradio as gr
from PIL import Image

# Unstructured for rich PDF parsing
from unstructured.partition.pdf import partition_pdf
from unstructured.partition.utils.constants import PartitionStrategy

# Vision-language captioning (BLIP)
from transformers import BlipProcessor, BlipForConditionalGeneration

# LangChain vectorstore and embeddings
from langchain_community.vectorstores import FAISS
from langchain_community.embeddings import HuggingFaceEmbeddings

# HF Inference client for chat completions
from huggingface_hub import InferenceClient

# ── Globals ───────────────────────────────────────────────────────────────────
retriever = None               # FAISS retriever for multimodal content
current_pdf_name = None        # Name of the currently loaded PDF
combined_texts = None          # Combined text + image captions corpus

# ── Setup: directories ─────────────────────────────────────────────────────────
FIGURES_DIR = "figures"
if os.path.exists(FIGURES_DIR):
    shutil.rmtree(FIGURES_DIR)
os.makedirs(FIGURES_DIR, exist_ok=True)

# ── Models & Clients ───────────────────────────────────────────────────────────
# Chat model (Mistral-7B-Instruct)
chat_client = InferenceClient(model="mistralai/Mistral-7B-Instruct-v0.3")
# Text embeddings (BAAI BGE)
embeddings = HuggingFaceEmbeddings(model_name="BAAI/bge-base-en-v1.5")
# Image captioning (BLIP)
blip_processor = BlipProcessor.from_pretrained("Salesforce/blip-image-captioning-base")
blip_model = BlipForConditionalGeneration.from_pretrained("Salesforce/blip-image-captioning-base")


def generate_caption(image_path: str) -> str:
    """
    Generates a natural-language caption for an image using BLIP.
    """
    image = Image.open(image_path).convert('RGB')
    inputs = blip_processor(image, return_tensors="pt")
    out = blip_model.generate(**inputs)
    caption = blip_processor.decode(out[0], skip_special_tokens=True)
    return caption


def process_pdf(pdf_file) -> str:
    """
    Parses the uploaded PDF into text chunks and image captions,
    builds a FAISS index, and prepares the retriever.
    Returns status message.
    """
    global current_pdf_name, retriever, combined_texts
    if pdf_file is None:
        return "❌ Please upload a PDF file."

    # Save PDF locally for unstructured
    pdf_path = pdf_file.name
    current_pdf_name = os.path.basename(pdf_path)

    # Extract text, table, and image blocks
    elements = partition_pdf(
        filename=pdf_path,
        strategy=PartitionStrategy.HI_RES,
        extract_image_block_types=["Image", "Table"],
        extract_image_block_output_dir=FIGURES_DIR
    )

    # Separate text and image elements
    text_elements = [el.text for el in elements if el.category not in ["Image", "Table"] and el.text]
    image_files = [os.path.join(FIGURES_DIR, f)
                   for f in os.listdir(FIGURES_DIR)
                   if f.lower().endswith((".png", ".jpg", ".jpeg"))]

    # Generate captions for each image
    captions = []
    for img in image_files:
        cap = generate_caption(img)
        captions.append(cap)

    # Combine all pieces for indexing
    combined_texts = text_elements + captions

    # Create FAISS index and retriever
    index = FAISS.from_texts(combined_texts, embeddings)
    retriever = index.as_retriever(search_kwargs={"k": 2})

    status = f"✅ Indexed '{current_pdf_name}' — {len(text_elements)} text blocks + {len(captions)} image captions"
    return status


def ask_question(question: str) -> str:
    """
    Retrieves relevant chunks from the FAISS index and generates an answer via chat model.
    """
    global retriever
    if retriever is None:
        return "❌ Please upload and process a PDF first."
    if not question.strip():
        return "❌ Please enter a question."

    docs = retriever.get_relevant_documents(question)
    context = "\n\n".join(doc.page_content for doc in docs)

    prompt = (
        "Use the following document excerpts to answer the question.\n\n"
        f"{context}\n\n"
        f"Question: {question}\n"
        "Answer:"
    )

    response = chat_client.chat_completion(
        messages=[{"role": "user", "content": prompt}],
        max_tokens=128,
        temperature=0.5
    )
    answer = response["choices"][0]["message"]["content"].strip()
    return answer


def clear_interface():
    """Resets global state and clears the figures directory."""
    global retriever, current_pdf_name, combined_texts
    retriever = None
    current_pdf_name = None
    combined_texts = None
    shutil.rmtree(FIGURES_DIR)
    os.makedirs(FIGURES_DIR, exist_ok=True)
    return ""

# ── Gradio UI ────────────────────────────────────────────────────────────────
theme = gr.themes.Soft(primary_hue="indigo", secondary_hue="blue")
with gr.Blocks(theme=theme, css="""
    .container { border-radius: 10px; padding: 15px; }
    .pdf-active { border-left: 3px solid #6366f1; padding-left: 10px; background-color: rgba(99,102,241,0.1); }
    .footer { text-align: center; margin-top: 30px; font-size: 0.8em; color: #666; }
    .main-title { text-align: center; font-size: 64px; font-weight: bold; margin-bottom: 20px; }
""") as demo:
    gr.Markdown("<div class='main-title'>DocQueryAI (Multimodal)</div>")

    with gr.Row():
        with gr.Column():
            gr.Markdown("## 📄 Document Input")
            pdf_display = gr.Textbox(label="Active Document", interactive=False, elem_classes="pdf-active")
            pdf_file = gr.File(file_types=[".pdf"], type="file")
            process_btn = gr.Button("📤 Process Document", variant="primary")
            status_box = gr.Textbox(label="Status", interactive=False)

        with gr.Column():
            gr.Markdown("## ❓ Ask Questions")
            question_input = gr.Textbox(lines=3, placeholder="Enter your question here…")
            ask_btn = gr.Button("🔍 Ask Question", variant="primary")
            answer_output = gr.Textbox(label="Answer", lines=8, interactive=False)

    clear_btn = gr.Button("🗑️ Clear All", variant="secondary")
    gr.Markdown("<div class='footer'>Powered by LangChain + Mistral 7B + FAISS + BLIP | Gradio</div>")

    process_btn.click(fn=process_pdf, inputs=[pdf_file], outputs=[status_box])
    ask_btn.click(fn=ask_question, inputs=[question_input], outputs=[answer_output])
    clear_btn.click(fn=clear_interface, outputs=[status_box, answer_output])

if __name__ == "__main__":
    demo.launch(debug=True, share=True)