app/main.py

import os
import torch
from fastapi import FastAPI, Request
from fastapi.responses import JSONResponse
from transformers import AutoModelForCausalLM, AutoTokenizer
from peft import PeftModel
from starlette.middleware.cors import CORSMiddleware
import re

# === Setup FastAPI ===
app = FastAPI(title="Apollo AI Backend - Qwen2-0.5B Optimized", version="2.1.0")

# === CORS ===
app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

# === Configuration ===
API_KEY = os.getenv("API_KEY", "aigenapikey1234567890")
BASE_MODEL = "Qwen/Qwen2-0.5B-Instruct"
ADAPTER_PATH = "adapter"

# === Load Model ===
print("🔧 Loading tokenizer for Qwen2-0.5B...")
tokenizer = AutoTokenizer.from_pretrained(BASE_MODEL, trust_remote_code=True)
if tokenizer.pad_token is None:
    tokenizer.pad_token = tokenizer.eos_token

print("🧠 Loading Qwen2-0.5B base model...")
base_model = AutoModelForCausalLM.from_pretrained(
    BASE_MODEL,
    trust_remote_code=True,
    torch_dtype=torch.float32,
    device_map="cpu"
)

print("🔗 Applying LoRA adapter to Qwen2-0.5B...")
model = PeftModel.from_pretrained(base_model, ADAPTER_PATH)
model.eval()

print("✅ Qwen2-0.5B model ready with optimized settings!")

def get_simple_system_prompt(is_force_mode: bool) -> str:
    """
    SIMPLIFIED system prompts optimized for Qwen2-0.5B's 500M parameters.
    Shorter, clearer instructions that small models can follow better.
    """
    if is_force_mode:
        return """You are Apollo AI. Give direct, complete answers.

Rules:
- Provide full working code
- Be concise, max 3 sentences explanation
- Never ask questions back
- Give complete solutions immediately

Example:
User: "print hello world python"
You: "Use print('Hello World'). This outputs text to console."
"""
    else:
        return """You are Apollo AI tutor. Guide learning with questions.

Rules:
- Ask guiding questions instead of giving answers
- Never give complete working code
- Use hints and partial examples only
- Make students think and discover

Example:
User: "print hello world python"
You: "What function displays text in Python? Try looking up output functions."
"""

def create_simple_force_responses(user_message: str) -> str:
    """
    Pre-defined responses for common questions in force mode.
    This helps the 0.5B model give consistent direct answers.
    """
    user_lower = user_message.lower()
    
    # Python print
    if 'print' in user_lower and ('hello' in user_lower or 'world' in user_lower):
        return 'Use `print("Hello World")`. This function outputs text to the console.'
    
    # Basic math
    if '2+2' in user_lower or '2 + 2' in user_lower:
        return '2 + 2 = 4. Addition combines two numbers to get their sum.'
    
    # Python variable
    if 'variable' in user_lower and ('python' in user_lower or 'create' in user_lower):
        return 'Use `name = "value"`. Variables store data: `x = 5` or `text = "hello"`.'
    
    # Python list
    if 'list' in user_lower and 'python' in user_lower and 'create' in user_lower:
        return 'Use square brackets: `my_list = [1, 2, 3]`. Lists store multiple items.'
    
    # Python function
    if 'function' in user_lower and 'python' in user_lower and ('create' in user_lower or 'define' in user_lower):
        return '''Use def keyword:
```python
def my_function():
    return "Hello"
```
Functions are reusable code blocks.'''
    
    # Calculator
    if 'calculator' in user_lower and ('create' in user_lower or 'make' in user_lower or 'build' in user_lower):
        return '''Here's a simple calculator:
```python
a = float(input("First number: "))
b = float(input("Second number: "))
op = input("Operator (+,-,*,/): ")
if op == '+': print(a + b)
elif op == '-': print(a - b)
elif op == '*': print(a * b)
elif op == '/': print(a / b)
```
This performs basic math operations.'''
    
    return None

def create_simple_mentor_responses(user_message: str) -> str:
    """
    Pre-defined mentor responses for common questions.
    This helps the 0.5B model give consistent guided learning.
    """
    user_lower = user_message.lower()
    
    # Python print
    if 'print' in user_lower and ('hello' in user_lower or 'world' in user_lower):
        return 'What function do you think displays text in Python? Think about showing output. What would it be called?'
    
    # Basic math
    if '2+2' in user_lower or '2 + 2' in user_lower:
        return 'What do you think 2 + 2 equals? Try calculating it step by step.'
    
    # Python variable
    if 'variable' in user_lower and ('python' in user_lower or 'create' in user_lower):
        return 'How do you think Python stores data? What symbol might assign a value to a name? Try: name = value'
    
    # Python list
    if 'list' in user_lower and 'python' in user_lower and 'create' in user_lower:
        return 'What brackets do you think hold multiple items? Try making a list with [item1, item2]. What goes inside?'
    
    # Python function
    if 'function' in user_lower and 'python' in user_lower and ('create' in user_lower or 'define' in user_lower):
        return '''What keyword defines a function in Python? Try this structure:
```python
___ function_name():
    # your code here
```
What goes in the blank? How would you call it?'''
    
    # Calculator
    if 'calculator' in user_lower and ('create' in user_lower or 'make' in user_lower or 'build' in user_lower):
        return '''What steps would a calculator need?
1. Get two numbers from user - what function gets input?
2. Get operation (+,-,*,/) - how to choose?
3. Calculate result - what structure handles choices?
4. Show result - what displays output?

Try building step 1 first. What function gets user input?'''
    
    return None

def extract_clean_answer(full_response: str, formatted_prompt: str, user_message: str, is_force_mode: bool) -> str:
    """
    Optimized cleaning for Qwen2-0.5B responses.
    Simpler extraction since 0.5B models produce cleaner output.
    """
    if not full_response or len(full_response.strip()) < 5:
        return "I apologize, but I couldn't generate a response. Please try again."
    
    print(f"🔍 Raw response length: {len(full_response)}")
    print(f"🔍 Mode: {'FORCE' if is_force_mode else 'MENTOR'}")
    
    # Check for pre-defined responses first
    if is_force_mode:
        predefined = create_simple_force_responses(user_message)
        if predefined:
            print("✅ Using predefined force response")
            return predefined
    else:
        predefined = create_simple_mentor_responses(user_message)
        if predefined:
            print("✅ Using predefined mentor response")
            return predefined
    
    # Step 1: Remove the input prompt
    generated_text = full_response
    if formatted_prompt in full_response:
        parts = full_response.split(formatted_prompt)
        if len(parts) > 1:
            generated_text = parts[-1]
    
    # Step 2: Extract assistant content - simplified for 0.5B
    assistant_content = generated_text
    
    # Look for assistant markers
    if "<|im_start|>assistant" in generated_text:
        assistant_parts = generated_text.split("<|im_start|>assistant")
        if len(assistant_parts) > 1:
            assistant_content = assistant_parts[-1]
            if "<|im_end|>" in assistant_content:
                assistant_content = assistant_content.split("<|im_end|>")[0]
    
    # Step 3: Basic cleaning - gentler for 0.5B
    clean_text = assistant_content.strip()
    
    # Remove template tokens
    clean_text = re.sub(r'<\|im_start\|>', '', clean_text)
    clean_text = re.sub(r'<\|im_end\|>', '', clean_text)
    clean_text = re.sub(r'<\|endoftext\|>', '', clean_text)
    
    # Remove role prefixes
    clean_text = re.sub(r'^(system|user|assistant):\s*', '', clean_text, flags=re.MULTILINE)
    clean_text = re.sub(r'\n(system|user|assistant):\s*', '\n', clean_text, flags=re.MULTILINE)
    
    # Clean whitespace
    clean_text = re.sub(r'\n{3,}', '\n\n', clean_text)
    clean_text = clean_text.strip()
    
    # Step 4: Fallback handling for 0.5B
    if not clean_text or len(clean_text) < 10:
        if is_force_mode:
            return "Could you please be more specific about what you need?"
        else:
            return "What specific aspect would you like to explore? What's your approach?"
    
    # Step 5: Length control for 0.5B
    if len(clean_text) > 500:  # Keep responses shorter for 0.5B
        sentences = clean_text.split('. ')
        if len(sentences) > 3:
            clean_text = '. '.join(sentences[:3]) + '.'
    
    print(f"🧹 Final cleaned answer length: {len(clean_text)}")
    
    return clean_text

def generate_response(messages: list, is_force_mode: bool = False, max_tokens: int = 200, temperature: float = 0.7) -> str:
    """
    Optimized generation for Qwen2-0.5B with shorter contexts and conservative settings.
    """
    try:
        # Check for simple predefined responses first
        if messages and len(messages) > 0:
            last_user_msg = ""
            for msg in reversed(messages):
                if msg.get("role") == "user":
                    last_user_msg = msg.get("content", "")
                    break
            
            if last_user_msg:
                if is_force_mode:
                    predefined = create_simple_force_responses(last_user_msg)
                    if predefined:
                        return predefined
                else:
                    predefined = create_simple_mentor_responses(last_user_msg)
                    if predefined:
                        return predefined
        
        # Build simple conversation for 0.5B model
        clean_messages = []
        
        # Add simple system prompt
        system_prompt = get_simple_system_prompt(is_force_mode)
        clean_messages.append({
            "role": "system", 
            "content": system_prompt
        })
        
        # Add only the last user message to keep context short for 0.5B
        if messages and len(messages) > 0:
            for msg in reversed(messages):
                if msg.get("role") == "user":
                    clean_messages.append({
                        "role": "user",
                        "content": msg.get("content", "")
                    })
                    break
        
        print(f"🔍 Processing {len(clean_messages)} messages for Qwen2-0.5B in {'FORCE' if is_force_mode else 'MENTOR'} mode")
        
        # Apply chat template
        try:
            formatted_prompt = tokenizer.apply_chat_template(
                clean_messages,
                tokenize=False,
                add_generation_prompt=True
            )
        except Exception as e:
            print(f"⚠️ Chat template failed, using simple format: {e}")
            # Fallback to simple format
            formatted_prompt = f"System: {clean_messages[0]['content']}\nUser: {clean_messages[1]['content']}\nAssistant:"
        
        # Tokenize with conservative limits for 0.5B
        inputs = tokenizer(
            formatted_prompt, 
            return_tensors="pt", 
            truncation=True, 
            max_length=800  # Shorter context for 0.5B
        )
        
        # Conservative generation settings for 0.5B model
        generation_params = {
            "input_ids": inputs.input_ids,
            "attention_mask": inputs.attention_mask,
            "pad_token_id": tokenizer.eos_token_id,
            "eos_token_id": tokenizer.eos_token_id,
            "do_sample": True,
        }
        
        if is_force_mode:
            # Force mode: Very conservative for 0.5B
            generation_params.update({
                "max_new_tokens": min(max_tokens, 150),  # Very short
                "temperature": 0.1,  # Very focused
                "top_p": 0.7,
                "top_k": 20,
                "repetition_penalty": 1.05,
            })
        else:
            # Mentor mode: Still conservative but allows more creativity
            generation_params.update({
                "max_new_tokens": min(max_tokens, 200),
                "temperature": 0.3,  # Lower than original
                "top_p": 0.8,
                "top_k": 30,
                "repetition_penalty": 1.02,
            })
        
        # Generate with timeout for 0.5B
        with torch.no_grad():
            outputs = model.generate(**generation_params)
        
        # Decode response
        full_response = tokenizer.decode(outputs[0], skip_special_tokens=False)
        
        # Extract user message for context
        user_message = ""
        for msg in reversed(clean_messages):
            if msg.get("role") == "user":
                user_message = msg.get("content", "")
                break
        
        # Clean and return
        clean_answer = extract_clean_answer(full_response, formatted_prompt, user_message, is_force_mode)
        
        return clean_answer
        
    except Exception as e:
        print(f"❌ Generation error with Qwen2-0.5B: {e}")
        mode_text = "direct answer" if is_force_mode else "guided learning"
        return f"I encountered an error generating a {mode_text}. Please try a simpler question."

# === Routes ===
@app.get("/")
def root():
    return {
        "message": "🤖 Apollo AI Backend v2.1 - Qwen2-0.5B Optimized",
        "model": "Qwen/Qwen2-0.5B-Instruct with LoRA",
        "status": "ready",
        "optimizations": ["short_contexts", "conservative_generation", "predefined_responses"],
        "features": ["mentor_mode", "force_mode", "0.5B_optimized"],
        "modes": {
            "mentor": "Guides learning with simple questions",
            "force": "Provides direct answers quickly"
        }
    }

@app.get("/health")
def health():
    return {
        "status": "healthy", 
        "model_loaded": True, 
        "model_size": "0.5B",
        "optimizations": "qwen2_0.5B_specific"
    }

@app.post("/v1/chat/completions")
async def chat_completions(request: Request):
    # Validate API key
    auth_header = request.headers.get("Authorization", "")
    if not auth_header.startswith("Bearer "):
        return JSONResponse(
            status_code=401, 
            content={"error": "Missing or invalid Authorization header"}
        )

    token = auth_header.replace("Bearer ", "").strip()
    if token != API_KEY:
        return JSONResponse(
            status_code=401, 
            content={"error": "Invalid API key"}
        )

    # Parse request body
    try:
        body = await request.json()
        messages = body.get("messages", [])
        max_tokens = min(body.get("max_tokens", 200), 300)  # Cap at 300 for 0.5B
        temperature = max(0.1, min(body.get("temperature", 0.5), 0.8))  # Conservative range
        
        # Get mode information
        is_force_mode = body.get("force_mode", False)
        
        if not messages or not isinstance(messages, list):
            raise ValueError("Messages field is required and must be a list")
            
    except Exception as e:
        return JSONResponse(
            status_code=400, 
            content={"error": f"Invalid request body: {str(e)}"}
        )

    # Validate messages
    for i, msg in enumerate(messages):
        if not isinstance(msg, dict) or "role" not in msg or "content" not in msg:
            return JSONResponse(
                status_code=400,
                content={"error": f"Invalid message format at index {i}"}
            )

    try:
        print(f"📥 Processing request for Qwen2-0.5B in {'FORCE' if is_force_mode else 'MENTOR'} mode")
        print(f"📊 Settings: max_tokens={max_tokens}, temperature={temperature}")
        
        response_content = generate_response(
            messages=messages,
            is_force_mode=is_force_mode,
            max_tokens=max_tokens,
            temperature=temperature
        )
        
        # Return OpenAI-compatible response
        return {
            "id": f"chatcmpl-apollo-qwen05b-{hash(str(messages)) % 10000}",
            "object": "chat.completion",
            "created": int(torch.tensor(0).item()),
            "model": f"qwen2-0.5b-{'force' if is_force_mode else 'mentor'}-mode",
            "choices": [
                {
                    "index": 0,
                    "message": {
                        "role": "assistant",
                        "content": response_content
                    },
                    "finish_reason": "stop"
                }
            ],
            "usage": {
                "prompt_tokens": len(str(messages)),
                "completion_tokens": len(response_content),
                "total_tokens": len(str(messages)) + len(response_content)
            },
            "apollo_mode": "force" if is_force_mode else "mentor",
            "model_optimizations": "qwen2_0.5B_specific"
        }
        
    except Exception as e:
        print(f"❌ Chat completion error: {e}")
        return JSONResponse(
            status_code=500,
            content={"error": f"Internal server error: {str(e)}"}
        )

# === Test endpoint optimized for 0.5B ===
@app.post("/test")
async def test_generation(request: Request):
    """Test endpoint for debugging both modes with 0.5B optimizations"""
    try:
        body = await request.json()
        prompt = body.get("prompt", "How do I print hello world in Python?")
        max_tokens = min(body.get("max_tokens", 200), 300)
        test_both_modes = body.get("test_both_modes", True)
        
        results = {}
        
        # Test mentor mode
        messages_mentor = [{"role": "user", "content": prompt}]
        mentor_response = generate_response(messages_mentor, is_force_mode=False, max_tokens=max_tokens, temperature=0.3)
        results["mentor_mode"] = {
            "response": mentor_response,
            "length": len(mentor_response),
            "mode": "mentor"
        }
        
        if test_both_modes:
            # Test force mode
            messages_force = [{"role": "user", "content": prompt}]
            force_response = generate_response(messages_force, is_force_mode=True, max_tokens=max_tokens, temperature=0.1)
            results["force_mode"] = {
                "response": force_response,
                "length": len(force_response),
                "mode": "force"
            }
        
        return {
            "prompt": prompt,
            "results": results,
            "model": "Qwen2-0.5B-Instruct",
            "optimizations": "0.5B_specific",
            "status": "success"
        }
        
    except Exception as e:
        return JSONResponse(
            status_code=500,
            content={"error": str(e)}
        )

if __name__ == "__main__":
    import uvicorn
    print("🚀 Starting Apollo AI Backend v2.1 - Qwen2-0.5B Optimized...")
    print("🧠 Model: Qwen/Qwen2-0.5B-Instruct (500M parameters)")
    print("⚡ Optimizations: Short contexts, conservative generation, predefined responses")
    print("🎯 Modes: Mentor (simple questions) vs Force (direct answers)")
    uvicorn.run(app, host="0.0.0.0", port=7860)