"""
MeshBay Hub — FastAPI application factory.

Usage:
    from meshbay_hub.app import create_app
    from meshbay_hub.config import load_config

    cfg = load_config()
    app = create_app(cfg)
"""

import asyncio
from contextlib import asynccontextmanager
from pathlib import Path

from fastapi import FastAPI
from slowapi import _rate_limit_exceeded_handler
from slowapi.errors import RateLimitExceeded

from meshbay_hub import __version__
from meshbay_hub.auth import generate_hub_keypair, load_hub_keypair
from meshbay_hub.config import HubConfig
from meshbay_hub.db.engine import close_db, init_db
from meshbay_hub.api.hub        import router as hub_router, set_config as hub_set_config
from meshbay_hub.api.users      import router as users_router, set_config as users_set_config
from meshbay_hub.api.deps       import set_admin_usernames
from meshbay_hub.api.nodes      import router as nodes_router
from meshbay_hub.api.groups     import router as groups_router, swarm_router
from meshbay_hub.api.revocation  import router as revocation_router
from meshbay_hub.api.moderation  import router as moderation_router
from meshbay_hub.api.federation  import router as federation_router
from meshbay_hub.csam            import csam_router
from meshbay_hub.api.health      import router as health_router
from meshbay_hub.api.relay       import router as relay_router
from meshbay_hub.api.signaling   import router as signaling_router
from meshbay_hub.api.admin       import router as admin_router
from meshbay_hub.api.notifications import router as notifications_router
from meshbay_hub.api.webapp     import router as webapp_router, STATIC_DIR, ASSET_V, CSP
from meshbay_hub.api.middleware import limiter


async def _sync_admin_roles(admin_usernames: list[str]) -> None:
    """Ensure config-listed admin usernames have role='admin' in the DB."""
    from sqlalchemy import select, update
    from meshbay_hub.db.engine import get_session_factory
    from meshbay_hub.db.models import User

    factory = get_session_factory()
    async with factory() as session:
        result = await session.execute(
            select(User).where(User.username.in_(admin_usernames))
        )
        for user in result.scalars().all():
            if user.role != "admin":
                user.role = "admin"
        await session.commit()


async def _backfill_email_hashes() -> None:
    """One-time backfill: compute email_hash for users that don't have one yet."""
    import logging

    from sqlalchemy import select

    from meshbay_hub.auth import decrypt_email, hash_email_blind
    from meshbay_hub.db.engine import get_session_factory
    from meshbay_hub.db.models import User

    log = logging.getLogger(__name__)
    factory = get_session_factory()
    async with factory() as session:
        result = await session.execute(
            select(User).where(User.email_hash.is_(None), User.email.isnot(None))
        )
        users = list(result.scalars().all())
        if not users:
            return
        count = 0
        for user in users:
            try:
                plain = decrypt_email(user.email)
                user.email_hash = hash_email_blind(plain)
                count += 1
            except Exception:
                log.warning("Could not backfill email_hash for user %s", user.id)
        await session.commit()
        log.info("Backfilled email_hash for %d users", count)


def create_app(cfg: HubConfig | None = None) -> FastAPI:
    from meshbay_hub.config import load_config
    if cfg is None:
        cfg = load_config()

    @asynccontextmanager
    async def lifespan(app: FastAPI):
        # Startup
        await init_db(cfg.db.url)

        kp = cfg.identity.private_key_path
        if not kp.exists():
            generate_hub_keypair(kp)
        load_hub_keypair(kp, cfg.identity.id)
        users_set_config(cfg)
        hub_set_config(cfg)
        set_admin_usernames(cfg.identity.admin_usernames)

        await _backfill_email_hashes()

        from meshbay_hub import hub_settings as _hub_settings
        from meshbay_hub import mail as _mail
        _mail.configure(cfg.identity.id)
        # What `hub.toml` says the mail bounds are. The live values are read
        # from `hub_settings` at each use, so an admin can change them from the
        # panel while the hub is serving; these are what a missing row falls
        # back to.
        _hub_settings.set_mail_defaults(cfg.mail)

        if cfg.identity.admin_usernames:
            await _sync_admin_roles(cfg.identity.admin_usernames)

        from meshbay_hub.csam import get_csam_checker
        get_csam_checker().load()

        from meshbay_hub.tasks.cleanup import cleanup_loop
        from meshbay_hub.db.engine import get_session_factory
        cleanup_task = asyncio.create_task(cleanup_loop(get_session_factory()))

        yield

        cleanup_task.cancel()
        try:
            await cleanup_task
        except asyncio.CancelledError:
            pass

        # Shutdown
        await close_db()

    app = FastAPI(
        title="MeshBay Hub",
        version=__version__,
        description="MeshBay identity authority and group registry",
        lifespan=lifespan,
        # No interactive docs and no schema. The full description of the
        # identity authority's API is a map for whoever probes it, and nothing
        # in the tree reads it. meshbay.org hid these in its Caddyfile (S18),
        # which protects exactly one deployment: a hub installed from the
        # package, behind any other proxy, published all three.
        docs_url=None,
        redoc_url=None,
        openapi_url=None,
    )

    # Rate limiting
    app.state.limiter = limiter
    app.add_exception_handler(RateLimitExceeded, _rate_limit_exceeded_handler)

    @app.middleware("http")
    async def _security_headers(request, call_next):
        """
        Second-review L5, third-review M5: the SPA shell and its assets went out
        with no CSP and no other protective headers. This adds them everywhere —
        `webapp.CSP` is the same policy the desktop client already enforces on
        these exact files. `setdefault` so a route that sets its own wins.
        """
        response = await call_next(request)
        response.headers.setdefault("Content-Security-Policy", CSP)
        response.headers.setdefault("X-Content-Type-Options", "nosniff")
        response.headers.setdefault("Referrer-Policy", "strict-origin-when-cross-origin")
        # SAMEORIGIN, matching `frame-ancestors 'self'` in the CSP above.
        #
        # The two say the same thing to different generations of browser, and
        # they were saying different things: CSP allowed this origin to frame
        # itself, this header forbade all framing. The spec says a browser must
        # ignore X-Frame-Options when the CSP carries frame-ancestors — but
        # relying on that while shipping a header that contradicts our own
        # policy is asking to be surprised, and we were: the streamed download
        # (a hidden iframe onto `/_mbdl/<id>`, the only way to write a large
        # file to disk on Firefox and Safari) stayed blocked after the CSP was
        # fixed, and this header was why it looked like the fix had not worked.
        #
        # No foreign origin may frame this page under either spelling. That is
        # the property; DENY was one notch stricter than the property needed and
        # broke a feature to get there.
        response.headers.setdefault("X-Frame-Options", "SAMEORIGIN")
        return response

    # Routers (webapp last — catches / before API routes)
    app.include_router(hub_router)
    app.include_router(users_router)
    app.include_router(nodes_router)
    app.include_router(groups_router)
    app.include_router(swarm_router)
    app.include_router(revocation_router)
    app.include_router(moderation_router)
    app.include_router(federation_router)
    app.include_router(csam_router)
    app.include_router(health_router)
    app.include_router(relay_router)
    app.include_router(signaling_router)
    app.include_router(admin_router)
    app.include_router(notifications_router)
    app.include_router(webapp_router)

    from starlette.staticfiles import StaticFiles

    class RevalidatingStatics(StaticFiles):
        """Static assets that must be revalidated, never served blind from cache.

        The SPA is a module graph that has to agree with itself: `app.js` imports
        `i18n.js`, which imports a catalogue from `locales/`. Serving one of them
        from cache while fetching another is not a stale page, it is a broken
        one — a browser holding the previous `i18n.js` fails to link the new
        `app.js` ("does not provide an export named 'initLocale'") before any
        code runs, and the reverse pairing renders every string as its own key.

        Starlette sends only `etag` and `last-modified`, and with no explicit
        freshness a browser is entitled to guess one. `no-cache` does not
        disable caching: it requires a conditional request, which the existing
        ETag answers with a 304 and no body.
        """

        async def get_response(self, path, scope):
            response = await super().get_response(path, scope)
            response.headers.setdefault("Cache-Control", "no-cache")
            return response

    class VersionedStatics(StaticFiles):
        """The same files under a URL that changes when they do.

        `no-cache` above only binds a browser that asks. One that cached the SPA
        before that header existed applies heuristic freshness and does not ask
        at all, so it runs an old player against a new node — a fix that is
        deployed, served, and not running, which looks exactly like a fix that
        does not work. Measured: a phone kept a player without the read-ahead
        bound and filled the browser's buffer ceiling at 106 MB, while the
        server had been serving the bounded one for an hour.

        Serving the graph under /a/<fingerprint>/ solves it for every file at
        once, because relative imports inherit the prefix: `app.js` reaching for
        `./i18n.js` gets the version it was built against, and never a mixture.
        The URL changes with the content, so these may be cached hard.
        """

        async def get_response(self, path, scope):
            response = await super().get_response(path, scope)
            response.headers["Cache-Control"] = (
                "public, max-age=31536000, immutable")
            return response

    # Before "/", which would otherwise swallow it.
    app.mount(f"/a/{ASSET_V}", VersionedStatics(directory=STATIC_DIR),
              name="static-versioned")
    # Still served unversioned: sw.js must stay at the root or its scope stops
    # covering the pages it intercepts downloads for, and old bookmarks of
    # /style.css and the like should not 404.
    app.mount("/", RevalidatingStatics(directory=STATIC_DIR), name="static")

    return app