"""chart.amow.com FastAPI backend."""
import asyncio
from contextlib import asynccontextmanager
from pathlib import Path

import re
from hashlib import sha256

from fastapi import FastAPI
from fastapi.responses import HTMLResponse
from fastapi.staticfiles import StaticFiles

from app.api.meta import router as meta_router
from app.api.routes import router as api_router
from app.api.schwab_auth import router as schwab_auth_router
from app.api.ws import router as ws_router
from app.config import Settings
from app.runtime import Runtime

BASE_DIR = Path(__file__).parent
STATIC_DIR = BASE_DIR / "static"

@asynccontextmanager
async def lifespan(app: FastAPI):
    runtime = Runtime(Settings())
    app.state.runtime = runtime
    task = await runtime.start()
    yield
    runtime.stream.stop()
    task.cancel()
    try:
        await task
    except asyncio.CancelledError:
        pass


app = FastAPI(title="chart", lifespan=lifespan)

app.mount("/static", StaticFiles(directory=STATIC_DIR), name="static")
app.include_router(meta_router)
app.include_router(schwab_auth_router)
app.include_router(api_router)
app.include_router(ws_router)


ASSET_REF = re.compile(r'((?:src|href)="/static/[^"?]+)"')


def asset_version() -> str:
    """A digest of the served assets, so the URL changes iff the content does.

    StaticFiles sends an ETag but no Cache-Control, so a browser is free to keep
    using the copy it already has — and a tab left open simply never fetches
    again. That turned a fixed bug into a bug that still reproduced, because the
    page was running the JavaScript it had loaded hours earlier.

    Hashing rather than stamping mtimes: a deploy checks every file out fresh,
    which would otherwise invalidate assets that never changed.
    """
    digest = sha256()
    for path in sorted(STATIC_DIR.glob("*.*")):
        digest.update(path.read_bytes())
    return digest.hexdigest()[:12]


@app.get("/")
def index():
    html = (STATIC_DIR / "index.html").read_text(encoding="utf-8")
    html = ASSET_REF.sub(rf'\1?v={asset_version()}"', html)
    # The document itself must never be cached, or the versioned URLs inside it
    # are the stale thing instead.
    return HTMLResponse(html, headers={"Cache-Control": "no-store"})