```python
import requests
import json

# Build model mapping
original_models = [
    # OpenAI Models
    "gpt-3.5-turbo",
    "gpt-3.5-turbo-202201",
    "gpt-4o",
    "gpt-4o-2024-05-13",
    "o1-preview",

    # Claude Models
    "claude",
    "claude-3-5-sonnet",
    "claude-sonnet-3.5",
    "claude-3-5-sonnet-20240620",

    # Meta/LLaMA Models
    "@cf/meta/llama-2-7b-chat-fp16",
    "@cf/meta/llama-2-7b-chat-int8",
    "@cf/meta/llama-3-8b-instruct",
    "@cf/meta/llama-3.1-8b-instruct",
    "@cf/meta-llama/llama-2-7b-chat-hf-lora",
    "llama-3.1-405b",
    "llama-3.1-70b",
    "llama-3.1-8b",
    "meta-llama/Llama-2-7b-chat-hf",
    "meta-llama/Llama-3.1-70B-Instruct",
    "meta-llama/Llama-3.1-8B-Instruct",
    "meta-llama/Llama-3.2-11B-Vision-Instruct",
    "meta-llama/Llama-3.2-1B-Instruct",
    "meta-llama/Llama-3.2-3B-Instruct",
    "meta-llama/Llama-3.2-90B-Vision-Instruct",
    "meta-llama/Llama-Guard-3-8B",
    "meta-llama/Meta-Llama-3-70B-Instruct",
    "meta-llama/Meta-Llama-3-8B-Instruct",
    "meta-llama/Meta-Llama-3.1-70B-Instruct-Turbo",
    "meta-llama/Meta-Llama-3.1-8B-Instruct",
    "meta-llama/Meta-Llama-3.1-8B-Instruct-Turbo",

    # Mistral Models
    "mistral",
    "mistral-large",
    "@cf/mistral/mistral-7b-instruct-v0.1",
    "@cf/mistral/mistral-7b-instruct-v0.2-lora",
    "@hf/mistralai/mistral-7b-instruct-v0.2",
    "mistralai/Mistral-7B-Instruct-v0.2",
    "mistralai/Mistral-7B-Instruct-v0.3",
    "mistralai/Mixtral-8x22B-Instruct-v0.1",
    "mistralai/Mixtral-8x7B-Instruct-v0.1",

    # Qwen Models
    "@cf/qwen/qwen1.5-0.5b-chat",
    "@cf/qwen/qwen1.5-1.8b-chat",
    "@cf/qwen/qwen1.5-7b-chat-awq",
    "@cf/qwen/qwen1.5-14b-chat-awq",
    "Qwen/Qwen2.5-3B-Instruct",
    "Qwen/Qwen2.5-72B-Instruct",
    "Qwen/Qwen2.5-Coder-32B-Instruct",

    # Google/Gemini Models
    "@cf/google/gemma-2b-it-lora",
    "@cf/google/gemma-7b-it-lora",
    "@hf/google/gemma-7b-it",
    "google/gemma-1.1-2b-it",
    "google/gemma-1.1-7b-it",
    "gemini-pro",
    "gemini-1.5-pro",
    "gemini-1.5-pro-latest",
    "gemini-1.5-flash",

    # Cohere Models
    "c4ai-aya-23-35b",
    "c4ai-aya-23-8b",
    "command",
    "command-light",
    "command-light-nightly",
    "command-nightly",
    "command-r",
    "command-r-08-2024",
    "command-r-plus",
    "command-r-plus-08-2024",
    "rerank-english-v2.0",
    "rerank-english-v3.0",
    "rerank-multilingual-v2.0",
    "rerank-multilingual-v3.0",

    # Microsoft Models
    "@cf/microsoft/phi-2",
    "microsoft/DialoGPT-medium",
    "microsoft/Phi-3-medium-4k-instruct",
    "microsoft/Phi-3-mini-4k-instruct",
    "microsoft/Phi-3.5-mini-instruct",
    "microsoft/WizardLM-2-8x22B",

    # Yi Models
    "01-ai/Yi-1.5-34B-Chat",
    "01-ai/Yi-34B-Chat",
]

# Create mapping from simplified model names to original model names
model_mapping = {}
simplified_models = []

for original_model in original_models:
    simplified_name = original_model.split('/')[-1]
    if simplified_name in model_mapping:
        # Conflict detected, handle as per instructions
        print(f"Conflict detected for model name '{simplified_name}'. Excluding '{original_model}' from available models.")
        continue
    model_mapping[simplified_name] = original_model
    simplified_models.append(simplified_name)

def generate(
    model,
    messages,
    temperature=0.7,
    top_p=1.0,
    n=1,
    stream=False,
    stop=None,
    max_tokens=None,
    presence_penalty=0.0,
    frequency_penalty=0.0,
    logit_bias=None,
    user=None,
    timeout=30,
):
    """
    Generates a chat completion using the provided model and messages.
    """
    # Use the simplified model names
    models = simplified_models

    if model not in models:
        raise ValueError(f"Invalid model: {model}. Choose from: {', '.join(models)}")
    
    # Map simplified model name to original model name
    original_model = model_mapping[model]

    api_endpoint = "https://chat.typegpt.net/api/openai/v1/chat/completions"
    
    headers = {
        "authority": "chat.typegpt.net",
        "accept": "application/json, text/event-stream",
        "accept-language": "en-US,en;q=0.9",
        "content-type": "application/json",
        "origin": "https://chat.typegpt.net",
        "referer": "https://chat.typegpt.net/",
        "user-agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36"
    }
    
    # Payload
    payload = {
        "messages": messages,
        "stream": stream,
        "model": original_model,
        "temperature": temperature,
        "presence_penalty": presence_penalty,
        "frequency_penalty": frequency_penalty,
        "top_p": top_p,
    }

    # Only include max_tokens if it's not None
    if max_tokens is not None:
        payload["max_tokens"] = max_tokens

    # Only include 'stop' if it's not None
    if stop is not None:
        payload["stop"] = stop

    # Check if logit_bias is provided
    if logit_bias is not None:
        payload["logit_bias"] = logit_bias

    # Include 'user' if provided
    if user is not None:
        payload["user"] = user

    # Start the request
    session = requests.Session()
    response = session.post(
        api_endpoint, headers=headers, json=payload, stream=stream, timeout=timeout
    )
    
    if not response.ok:
        raise Exception(f"Failed to generate response - ({response.status_code}, {response.reason}) - {response.text}")
    
    def stream_response():
        for line in response.iter_lines():
            if line:
                line = line.decode("utf-8")
                if line.startswith("data: "):
                    line = line[6:]  # Remove "data: " prefix
                    if line.strip() == "[DONE]":
                        break
                    try:
                        data = json.loads(line)
                        yield data
                    except json.JSONDecodeError:
                        continue

    if stream:
        return stream_response()
    else:
        return response.json()

if __name__ == "__main__":
    # Example usage
    # model = "claude-3-5-sonnet-20240620"
    # model = "qwen1.5-0.5b-chat"
    # model = "llama-2-7b-chat-fp16"
    model = "gpt-3.5-turbo"
    messages = [
        {"role": "system", "content": "Be Detailed"},
        {"role": "user", "content": "What is the knowledge cut off? Be specific and also specify the month, year and date. If not sure, then provide approximate."}
    ]

    # try:
    #     # For non-streamed response
    #     response = generate(
    #         model=model,
    #         messages=messages,
    #         temperature=0.5,
    #         max_tokens=4000,
    #         stream=False  # Change to True for streaming
    #     )
    #     if 'choices' in response:
    #         reply = response['choices'][0]['message']['content']
    #         print(reply)
    #     else:
    #         print("No response received.")
    # except Exception as e:
    #     print(e)


    try:
        # For streamed response
        response = generate(
            model=model,
            messages=messages,
            temperature=0.5,
            max_tokens=4000,
            stream=True,  # Change to False for non-streamed response
        )
        for data in response:
            if 'choices' in data:
                reply = data['choices'][0]['delta']['content']
                print(reply, end="", flush=True)
            else:
                print("No response received.")
    except Exception as e:
        print(e)
```

```python
from fastapi import FastAPI, Request, Response
from fastapi.responses import JSONResponse, StreamingResponse
from fastapi.middleware.cors import CORSMiddleware
import uvicorn
import asyncio
import json
import requests

from TYPEGPT.typegpt_api import generate, model_mapping, simplified_models
from api_info import developer_info

app = FastAPI()

# Set up CORS middleware if needed
app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

@app.get("/health_check")
async def health_check():
    return {"status": "OK"}

@app.get("/models")
async def get_models():
    # Retrieve models from TypeGPT API and forward the response
    api_endpoint = "https://chat.typegpt.net/api/openai/v1/models"
    try:
        response = requests.get(api_endpoint)
        # return response.text
        return JSONResponse(content=response.json(), status_code=response.status_code)
    except Exception as e:
        return JSONResponse(content={"error": str(e)}, status_code=500)

@app.post("/chat/completions")
async def chat_completions(request: Request):
    # Receive the JSON payload
    try:
        body = await request.json()
    except Exception as e:
        return JSONResponse(content={"error": "Invalid JSON payload"}, status_code=400)

    # Extract parameters
    model = body.get("model")
    messages = body.get("messages")
    temperature = body.get("temperature", 0.7)
    top_p = body.get("top_p", 1.0)
    n = body.get("n", 1)
    stream = body.get("stream", False)
    stop = body.get("stop")
    max_tokens = body.get("max_tokens")
    presence_penalty = body.get("presence_penalty", 0.0)
    frequency_penalty = body.get("frequency_penalty", 0.0)
    logit_bias = body.get("logit_bias")
    user = body.get("user")
    timeout = 30  # or set based on your preference

    # Validate required parameters
    if not model:
        return JSONResponse(content={"error": "The 'model' parameter is required."}, status_code=400)
    if not messages:
        return JSONResponse(content={"error": "The 'messages' parameter is required."}, status_code=400)

    # Call the generate function
    try:
        if stream:
            async def generate_stream():
                response = generate(
                    model=model,
                    messages=messages,
                    temperature=temperature,
                    top_p=top_p,
                    n=n,
                    stream=True,
                    stop=stop,
                    max_tokens=max_tokens,
                    presence_penalty=presence_penalty,
                    frequency_penalty=frequency_penalty,
                    logit_bias=logit_bias,
                    user=user,
                    timeout=timeout,
                )
                
                for chunk in response:
                    yield f"data: {json.dumps(chunk)}\n\n"
                yield "data: [DONE]\n\n"

            return StreamingResponse(
                generate_stream(),
                media_type="text/event-stream",
                headers={
                    "Cache-Control": "no-cache",
                    "Connection": "keep-alive",
                    "Transfer-Encoding": "chunked"
                }
            )
        else:
            response = generate(
                model=model,
                messages=messages,
                temperature=temperature,
                top_p=top_p,
                n=n,
                stream=False,
                stop=stop,
                max_tokens=max_tokens,
                presence_penalty=presence_penalty,
                frequency_penalty=frequency_penalty,
                logit_bias=logit_bias,
                user=user,
                timeout=timeout,
            )
            return JSONResponse(content=response)
    except Exception as e:
        return JSONResponse(content={"error": str(e)}, status_code=500)

@app.get("/developer_info")
async def get_developer_info():
    return JSONResponse(content=developer_info)

if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=8000)
```