import json
import secrets
import hashlib
from datetime import datetime, timezone
from typing import Dict

from fastapi import FastAPI, WebSocket, WebSocketDisconnect, HTTPException, Request
from fastapi.responses import HTMLResponse
from fastapi.templating import Jinja2Templates
from pydantic import BaseModel

app = FastAPI(title="Private Chat")
templates = Jinja2Templates(directory="templates")

users: Dict[str, dict] = {}
connections: Dict[str, WebSocket] = {}

def generate_token() -> str:
    return secrets.token_urlsafe(48)

def room_id(a: str, b: str) -> str:
    return hashlib.sha256("".join(sorted([a, b])).encode()).hexdigest()[:16]

class JoinRequest(BaseModel):
    display_name: str

@app.get("/", response_class=HTMLResponse)
async def index(request: Request):
    return templates.TemplateResponse("index.html", {"request": request})

@app.post("/api/join")
async def join(body: JoinRequest):
    name = body.display_name.strip()
    if not name or len(name) > 32:
        raise HTTPException(400, "Display name must be 1-32 characters")
    uid = generate_token()
    users[uid] = {"name": name, "online": True, "joined": datetime.now(timezone.utc).isoformat()}
    return {"user_id": uid, "display_name": name}

@app.get("/api/users/{user_id}")
async def list_users(user_id: str):
    if user_id not in users:
        raise HTTPException(401, "Invalid session")
    return {
        "users": [
            {"id": uid, "name": u["name"]}
            for uid, u in users.items() if u["online"] and uid != user_id
        ]
    }

@app.post("/api/rename")
async def rename(data: dict):
    uid = data.get("user_id", "")
    name = data.get("display_name", "").strip()
    if uid not in users:
        raise HTTPException(401, "Invalid session")
    if not name or len(name) > 32:
        raise HTTPException(400, "Display name must be 1-32 characters")
    old = users[uid]["name"]
    users[uid]["name"] = name
    return {"display_name": name, "previous_name": old}

@app.websocket("/ws/{user_id}")
async def ws(websocket: WebSocket, user_id: str):
    if user_id not in users:
        await websocket.close(code=4001)
        return
    await websocket.accept()
    connections[user_id] = websocket
    users[user_id]["online"] = True

    for cid, conn in connections.items():
        if cid != user_id:
            try:
                await conn.send_text(json.dumps({
                    "type": "user_online", "id": user_id, "name": users[user_id]["name"]
                }))
            except Exception:
                pass

    try:
        while True:
            raw = await websocket.receive_text()
            msg = json.loads(raw)
            t = msg.get("type")

            if t == "message":
                target = msg.get("target_id", "")
                content = msg.get("content", "").strip()
                if not content or len(content) > 4000:
                    continue
                if target not in users:
                    await websocket.send_text(json.dumps({"type": "error", "msg": "User not found"}))
                    continue

                rid = room_id(user_id, target)
                payload = json.dumps({
                    "type": "message",
                    "from_id": user_id,
                    "from_name": users[user_id]["name"],
                    "content": content,
                    "room_id": rid,
                    "ts": datetime.now(timezone.utc).isoformat()
                })

                if target in connections:
                    try:
                        await connections[target].send_text(payload)
                    except Exception:
                        pass
                await websocket.send_text(payload)

            elif t == "typing":
                target = msg.get("target_id", "")
                if target in connections:
                    try:
                        await connections[target].send_text(json.dumps({
                            "type": "typing", "from_id": user_id,
                            "from_name": users[user_id]["name"]
                        }))
                    except Exception:
                        pass

            elif t == "rename":
                new_name = msg.get("name", "").strip()
                if new_name and len(new_name) <= 32:
                    users[user_id]["name"] = new_name
                    for cid, conn in connections.items():
                        if cid != user_id:
                            try:
                                await conn.send_text(json.dumps({
                                    "type": "user_renamed", "id": user_id, "name": new_name
                                }))
                            except Exception:
                                pass

    except WebSocketDisconnect:
        pass
    finally:
        connections.pop(user_id, None)
        if user_id in users:
            users[user_id]["online"] = False
        for cid, conn in connections.items():
            try:
                await conn.send_text(json.dumps({
                    "type": "user_offline", "id": user_id
                }))
            except Exception:
                pass