app.py

# app.py - Gradio version (much simpler for HF Spaces)
import unsloth
from unsloth import FastModel

import gradio as gr
import logging
import spaces

import torch
import torch.nn as nn
from transformers import AutoTokenizer, AutoModelForSequenceClassification, AutoModelForCausalLM, AutoTokenizer, BitsAndBytesConfig


from peft import PeftModel
from huggingface_hub import hf_hub_download

import json
import re
import math

DEVICE = torch.device("cuda" if torch.cuda.is_available() else "cpu")





# Set up logging
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)

# Global variables for model and tokenizer
label_mapping = {0: "✅ Correct", 1: "🤔 Conceptually Flawed", 2: "🔢 Computationally Flawed"}


# ===================================================================
# 1. DEFINE CUSTOM CLASSIFIER (Required for Phi-4)
# ===================================================================
class GPTSequenceClassifier(nn.Module):
    def __init__(self, base_model, num_labels):
        super().__init__()
        self.base = base_model
        hidden_size = base_model.config.hidden_size
        self.classifier = nn.Linear(hidden_size, num_labels, bias=True)
        self.num_labels = num_labels

    def forward(self, input_ids=None, attention_mask=None, labels=None, **kwargs):
        outputs = self.base(input_ids=input_ids, attention_mask=attention_mask, output_hidden_states=True, **kwargs)
        last_hidden_state = outputs.hidden_states[-1]
        pooled_output = last_hidden_state[:, -1, :]
        logits = self.classifier(pooled_output)
        loss = None
        if labels is not None:
            loss = nn.functional.cross_entropy(logits.view(-1, self.num_labels), labels.view(-1))
        return {"loss": loss, "logits": logits} if loss is not None else {"logits": logits}
        
        
# ===================================================================
# 3. HELPERS
# ===================================================================

# --- Helper Functions ---
def extract_equation_from_response(response: str) -> str | None:
    """Extracts content from between <eq> and </eq> tags."""
    match = re.search(r'<eq>(.*?)</eq>', response, re.DOTALL)
    return match.group(1) if match else None

def sanitize_equation_string(expression: str) -> str:
    """

    Enhanced version with your requested simplified parenthesis logic.

    """
    if not isinstance(expression, str):
        return ""

    # Your requested parenthesis logic:
    if expression.count('(') > expression.count(')') and expression.startswith('('):
        expression = expression[1:]
    elif expression.count(')') > expression.count('(') and expression.endswith(')'):
        expression = expression[:-1]

    sanitized = expression.replace(' ', '')
    sanitized = sanitized.replace('x', '*').replace('×', '*')
    sanitized = re.sub(r'/([a-zA-Z]+)', '', sanitized)
    sanitized = re.sub(r'[^\d.()+\-*/=]', '', sanitized)
    return sanitized

def evaluate_equations(eq_dict: dict, sol_dict: dict):
    """

    Evaluates extracted equations and returns a more detailed dictionary for

    building clearer explanations.

    """
    for key, eq_str in eq_dict.items():
        if not eq_str or "=" not in eq_str:
            continue
        try:
            sanitized_eq = sanitize_equation_string(eq_str)

            if not sanitized_eq or "=" not in sanitized_eq:
                continue

            lhs, rhs_str = sanitized_eq.split('=', 1)

            if not lhs or not rhs_str:
                continue

            lhs_val = eval(lhs, {"__builtins__": None}, {})
            rhs_val = eval(rhs_str, {"__builtins__": None}, {})

            if not math.isclose(lhs_val, rhs_val, rel_tol=1e-2):
                correct_rhs_val = round(lhs_val, 4)
                correct_rhs_str = f"{correct_rhs_val:.4f}".rstrip('0').rstrip('.')

                # Return a more detailed dictionary for better explanations
                return {
                    "error": True,
                    "line_key": key,
                    "line_text": sol_dict.get(key, "N/A"),
                    "original_flawed_calc": eq_str, # The raw model output
                    "sanitized_lhs": lhs,           # The clean left side
                    "original_rhs": rhs_str,        # The clean right side
                    "correct_rhs": correct_rhs_str, # The correct right side
                }
        except Exception:
            continue

    return {"error": False}

# --- Prompts ---
EXTRACTOR_SYSTEM_PROMPT = \
"""[ROLE]

You are an expert at parsing mathematical solutions.



[TASK]

You are given a single line from a mathematical solution. Your task is to extract the calculation from this line.



**This is a literal transcription task. Follow these rules with extreme precision:**

- **RULE 1: Transcribe EXACTLY.** Do not correct mathematical errors. If a line implies `2+2=5`, your output for that line must be `2+2=5`.

- **RULE 2: Isolate the Equation.** Your output must contain ONLY the equation, with no surrounding text, units, or currency symbols. Always use `*` for multiplication.



[RESPONSE FORMAT]

Your response must ONLY contain the extracted equation, wrapped in <eq> and </eq> tags.

If the line contains no calculation, respond with empty tags: <eq></eq>.

"""
CLASSIFIER_SYSTEM_PROMPT = \
"""You are a mathematics tutor.

You will be given a math word problem and a solution written by a student.

Carefully analyze the problem and solution LINE-BY-LINE and determine whether there are any errors in the solution."""


        
gemma_model = None
gemma_tokenizer = None
classifier_model = None
classifier_tokenizer = None

def load_model():
    """Load your trained model here"""
    global gemma_model, gemma_tokenizer, classifier_model, classifier_tokenizer
    
    try:
        device = DEVICE

        # --- Model 1: Equation Extractor (Gemma-3 with Unsloth) ---
        extractor_adapter_repo = "arvindsuresh-math/gemma-3-1b-equation-line-extractor-aug-10"
        base_gemma_model = "unsloth/gemma-3-1b-it-unsloth-bnb-4bit"

        gemma_model, gemma_tokenizer = FastModel.from_pretrained(
            model_name=base_gemma_model,
            max_seq_length=350,
            dtype=None,
            load_in_4bit=True,
        )
        gemma_model = PeftModel.from_pretrained(gemma_model, extractor_adapter_repo)

        # --- Model 2: Conceptual Error Classifier (Phi-4) ---
        classifier_adapter_repo = "arvindsuresh-math/phi-4-error-binary-classifier"
        base_phi_model = "microsoft/Phi-4-mini-instruct"

        DTYPE = torch.float16
        quantization_config = BitsAndBytesConfig(
            load_in_4bit=True,
            bnb_4bit_quant_type="nf4",
            bnb_4bit_compute_dtype=DTYPE
            )
        classifier_backbone_base = AutoModelForCausalLM.from_pretrained(
            base_phi_model,
            quantization_config=quantization_config,
            device_map="auto",
            trust_remote_code=True,
            )

        classifier_tokenizer = AutoTokenizer.from_pretrained(
            base_phi_model,
            trust_remote_code=True
            )
        classifier_tokenizer.padding_side = "left"
        if classifier_tokenizer.pad_token is None:
            classifier_tokenizer.pad_token = classifier_tokenizer.eos_token

        classifier_backbone_peft = PeftModel.from_pretrained(
            classifier_backbone_base,
            classifier_adapter_repo
            )
        classifier_model = GPTSequenceClassifier(classifier_backbone_peft, num_labels=2)

        # Download and load the custom classifier head's state dictionary
        classifier_head_path = hf_hub_download(repo_id=classifier_adapter_repo, filename="classifier_head.pth")
        classifier_model.classifier.load_state_dict(torch.load(classifier_head_path, map_location=device))

        classifier_model.to(device)
        classifier_model = classifier_model.to(torch.float16)

        classifier_model.eval() # Set model to evaluation mode
        
    except Exception as e:
        logger.error(f"Error loading model: {e}")
        return f"Error loading model: {e}"
        
def models_ready() -> bool:
    ready = all(x is not None for x in [
        gemma_model, gemma_tokenizer, classifier_model, classifier_tokenizer
    ])
    if not ready:
        logger.warning(
            "models_ready=False  gemma_model=%s gemma_tok=%s phi_model=%s phi_tok=%s",
            type(gemma_model).__name__ if gemma_model is not None else None,
            type(gemma_tokenizer).__name__ if gemma_tokenizer is not None else None,
            type(classifier_model).__name__ if classifier_model is not None else None,
            type(classifier_tokenizer).__name__ if classifier_tokenizer is not None else None,
        )
    return ready

# Load model on startup
msg = load_model()
logger.info("load_model(): %s", msg)
    
    
# ===================================================================
# 4. PIPELINE COMPONENTS
# ===================================================================

def run_conceptual_check(question: str, solution: str, model, tokenizer) -> dict:
    """

    STAGE 1: Runs the Phi-4 classifier with memory optimizations.

    """
    device = DEVICE
    
    input_text = f"{CLASSIFIER_SYSTEM_PROMPT}\n\n### Problem:\n{question}\n\n### Answer:\n{solution}"
    inputs = tokenizer(
        input_text,
        return_tensors="pt",
        truncation=True,
        max_length=512).to(device)

    # Use inference_mode and disable cache for better performance and memory management
    with torch.inference_mode():
        outputs = model(**inputs, use_cache=False)

        # Explicitly cast logits to float32 for stable downstream processing
        logits = outputs["logits"].to(torch.float32)
        probs = torch.softmax(logits, dim=-1).squeeze().tolist()

    is_flawed_prob = probs[1]
    prediction = "flawed" if is_flawed_prob > 0.5 else "correct"

    return {
        "prediction": prediction,
        "probabilities": {"correct": probs[0], "flawed": probs[1]}
    }


def run_computational_check(solution: str, model, tokenizer, batch_size: int = 32) -> dict:
    """

    STAGE 2: Splits a solution into lines and performs a batched computational check.

    (Corrected to handle PEMDAS/parentheses)

    """
    device = DEVICE
    
    lines = [line.strip() for line in solution.strip().split('\n') if line.strip() and "FINAL ANSWER:" not in line.upper()]
    if not lines:
        return {"error": False}

    # Create a batch of prompts, one for each line
    prompts = []
    for line in lines:
        messages = [{"role": "user", "content": f"{EXTRACTOR_SYSTEM_PROMPT}\n\n### Solution Line:\n{line}"}]
        prompts.append(tokenizer.apply_chat_template(messages, tokenize=False, add_generation_prompt=True))

    # Run batched inference
    tokenizer.padding_side = "left"
    inputs = tokenizer(prompts, return_tensors="pt", padding=True).to(device)
    tokenizer.padding_side = "left"
    outputs = model.generate(**inputs, max_new_tokens=64, use_cache=True, pad_token_id=tokenizer.pad_token_id)
    tokenizer.padding_side = "left"
    decoded_outputs = tokenizer.batch_decode(outputs[:, inputs.input_ids.shape[1]:], skip_special_tokens=True)

    # Evaluate each line's extracted equation
    for i, raw_output in enumerate(decoded_outputs):
        equation = extract_equation_from_response(raw_output)
        if not equation or "=" not in equation:
            continue

        try:
            # Sanitize the full equation string, preserving parentheses
            sanitized_eq = sanitize_equation_string(equation)
            if "=" not in sanitized_eq:
                continue

            lhs, rhs_str = sanitized_eq.split('=', 1)

            # Evaluate the sanitized LHS, which now correctly includes parentheses
            lhs_val = eval(lhs, {"__builtins__": None}, {})

            # Compare with the RHS
            if not math.isclose(lhs_val, float(rhs_str), rel_tol=1e-2):
                return {
                    "error": True,
                    "line_text": lines[i],
                    "correct_calc": f"{lhs} = {round(lhs_val, 4)}"
                }
        except Exception:
            continue # Skip lines where evaluation fails

    return {"error": False}


def analyze_solution(question: str, solution: str):
    """

    Main orchestrator that runs the full pipeline and generates the final explanation.

    """
    # STAGE 1: Conceptual Check (Fast)
    conceptual_result = run_conceptual_check(question, solution, classifier_model, classifier_tokenizer)
    confidence = conceptual_result['probabilities'][conceptual_result['prediction']]

    # STAGE 2: Computational Check (Slower, Batched)
    computational_result = run_computational_check(solution, gemma_model, gemma_tokenizer)

    # FINAL VERDICT LOGIC
    if computational_result["error"]:
        classification = "computational_error"
        explanation = (
            f"A calculation error was found.\n"
            f"On the line: \"{computational_result['line_text']}\"\n"
            f"The correct calculation should be: {computational_result['correct_calc']}"
        )
    else:
        # If calculations are fine, the final verdict is the conceptual one.
        if conceptual_result['prediction'] == 'correct':
            classification = 'correct'
            explanation = "All calculations are correct and the overall logic appears to be sound."
        else: # This now correctly corresponds to 'flawed'
            classification = 'conceptual_error' # Produce the user-facing label
            explanation = "All calculations are correct, but there appears to be a conceptual error in the logic or setup of the solution."
    final_verdict = {
        "classification": classification,
        "explanation": explanation
    }

    return final_verdict    
     



def classify_solution(question: str, solution: str):
    """

    Classify the math solution

    Returns: (classification_label, confidence_score, explanation)

    """
    if not question.strip() or not solution.strip():
        return "Please fill in both fields", 0.0, ""
    
    if not models_ready():
        return "Models not loaded", 0.0, ""
    
    try:
        res = analyze_solution(question, solution)
        
        return res["classification"], res["explanation"]
    except Exception:
        logger.exception("inference failed")
        
        
        



# Create Gradio interface
with gr.Blocks(title="Math Solution Classifier", theme=gr.themes.Soft()) as app:
    gr.Markdown("# 🧮 Math Solution Classifier")
    gr.Markdown("Classify math solutions as correct, conceptually flawed, or computationally flawed.")
    
    with gr.Row():
        with gr.Column():
            question_input = gr.Textbox(
                label="Math Question",
                placeholder="e.g., Solve for x: 2x + 5 = 13",
                lines=3
            )
            
            solution_input = gr.Textbox(
                label="Proposed Solution", 
                placeholder="e.g., 2x + 5 = 13\n2x = 13 - 5\n2x = 8\nx = 4",
                lines=5
            )
            
            classify_btn = gr.Button("Classify Solution", variant="primary")
        
        with gr.Column():
            classification_output = gr.Textbox(label="Classification", interactive=False)
            confidence_output = gr.Textbox(label="Confidence", interactive=False)
            explanation_output = gr.Textbox(label="Explanation", interactive=False, lines=3)
    
    # Examples
    gr.Examples(
        examples=[
            [
                "Solve for x: 2x + 5 = 13",
                "2x + 5 = 13\n2x = 13 - 5\n2x = 8\nx = 4"
            ],
            [
                "John has three apples and Mary has seven, how many apples do they have together?", 
                "They have 7 + 3 = 11 apples."  # This should be computationally flawed
            ],
            [
                "What is 15% of 200?",
                "15% = 15/100 = 0.15\n0.15 × 200 = 30"
            ]
        ],
        inputs=[question_input, solution_input]
    )
    
    classify_btn.click(
        fn=classify_solution,
        inputs=[question_input, solution_input],
        outputs=[classification_output, explanation_output]
    )

if __name__ == "__main__":
    app.launch()