import streamlit as st
from transformers import AutoModelForSeq2SeqLM, AutoTokenizer
import difflib

# Load model and tokenizer
@st.cache_resource

def load_model():
    model_name = "vennify/t5-base-grammar-correction"
    tokenizer = AutoTokenizer.from_pretrained(model_name)
    model = AutoModelForSeq2SeqLM.from_pretrained(model_name)
    return tokenizer, model

tokenizer, model = load_model()

# Function to correct grammar
def correct_text(text):
    input_text = "gec: " + text
    inputs = tokenizer.encode(input_text, return_tensors="pt", truncation=True)
    outputs = model.generate(inputs, max_length=512, num_beams=4, early_stopping=True)
    corrected_text = tokenizer.decode(outputs[0], skip_special_tokens=True)
    return corrected_text

# Word-by-word diff
def get_word_diffs(original, corrected):
    orig_words = original.split()
    corr_words = corrected.split()
    diff = list(difflib.ndiff(orig_words, corr_words))
    return diff

# Streamlit UI
st.set_page_config(page_title="Grammar Agent", layout="wide")
st.title("📝 Grammar Agent – Like Grammarly, Powered by AI")

st.markdown("""
This AI grammar agent helps you:
- ✅ Correct grammar, spelling, and punctuation
- ✅ Improve sentence clarity
- ✅ See word-by-word differences
- ✅ Get suggestions on how to rewrite
""")

text_input = st.text_area("Enter your sentence, paragraph, or essay:", height=200)

if st.button("Correct Grammar") and text_input.strip():
    corrected = correct_text(text_input)
    diffs = get_word_diffs(text_input, corrected)

    st.subheader("🔧 Corrected Version")
    st.success(corrected)

    st.subheader("🔍 Word-by-Word Differences")
    diff_text = []
    for word in diffs:
        if word.startswith("-"):
            diff_text.append(f"❌ {word[2:]}")
        elif word.startswith("+"):
            diff_text.append(f"✅ {word[2:]}")
    st.markdown(" ".join(diff_text))

    st.subheader("💡 Writing Suggestion")
    if len(text_input.split()) > len(corrected.split()):
        st.info("Try simplifying your sentences for better clarity.")
    elif len(corrected.split()) > len(text_input.split()):
        st.info("The AI added helpful detail – good for formal writing.")
    else:
        st.info("The AI cleaned grammar and punctuation with minimal changes.")