main.py

from datetime import datetime, timezone

from fastapi import FastAPI, HTTPException
from typing import List, Dict
from pydantic import BaseModel, Field

app = FastAPI()

class Message(BaseModel):
    role:str
    content:str

class ChatSession(BaseModel):
    session_id:int
    session_user:str
    created_at:datetime
    messages: List[Message]= Field(default_factory=list)

class CreateSessionRequest(BaseModel):
    username: str

# In-memory data structure to store chat sessions and messages
session_store: Dict[int, ChatSession] = {}
chat_store: Dict[int, List[Message]] = {}


@app.post("/sessions/", response_model=ChatSession)
def create_session(req: CreateSessionRequest):
    username = req.username.strip().lower()

    # Validation
    if not username:
        raise HTTPException(status_code=400, detail="Username cannot be empty or whitespace.")

    # Generate session_id
    session_id = len(session_store) + 1
    created_at = datetime.now(timezone.utc)

    # Create session and initialize chat
    new_session = ChatSession(
        session_id=session_id,
        session_user=username,
        created_at=created_at,
        messages=[]
    )

    session_store[session_id] = new_session
    chat_store[session_id] = []  # Initialize empty chat list

    return new_session

@app.post("/sessions/{session_id}/messages", response_model=ChatSession)
def add_message(session_id: int, message: Message):
    if session_id not in session_store:
        raise HTTPException(status_code=404, detail="Session not found")

    chat_store[session_id].append(message)
    session_store[session_id].messages = chat_store[session_id]

    return session_store[session_id]


@app.get("/sessions/{session_id}/messages", response_model=ChatSession)
def get_session(session_id: int):
    if session_id not in session_store:
        raise HTTPException(status_code=404, detail="Session not found")
    return session_store[session_id]