"""
Hub web application — serves the MeshBay SPA and static assets.

The SPA (Preact + htm) handles:
  - Authentication (login, register, token refresh)
  - Group discovery and browsing
  - WebRTC connection to nodes for P2P file transfer
  - Dark/light theme with system preference detection

Static files are served from meshbay_hub/static/ via Starlette StaticFiles.
The root route (/) returns the SPA HTML shell.
"""

import hashlib
from pathlib import Path

from fastapi import APIRouter
from fastapi.responses import HTMLResponse

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

router = APIRouter(tags=["webapp"])

# Assets the shell pulls in, in load order. Everything else is imported by
# app.js from a relative path, which inherits the `/a/<hash>/` prefix the shell
# loaded app.js under — so the whole module graph moves together.
# Every module the page loads. A file missing from here is a file whose change
# does not move the URL, so a browser holding the old one never asks for it —
# which is the failure this list exists to prevent, and it is silent.
_ASSETS = ("style.css", "keyderive.js", "crypto.js", "transport.js", "app.js",
           "i18n.js", "downloads.js", "transfers.js", "zipstream.js",
           "platform.js", "meshbay-m.png",
           # Split out of app.js by the group-page refactor — each imported by
           # app.js or group-page.js, so a change to any of them is a change
           # to what the browser must fetch.
           "icon.js", "file-utils.js", "hub-client.js", "apps.js",
           "source-merge.js", "sticky.js",
           "chat-app.js", "files-app.js", "video-player.js", "video-app.js",
           "music-app.js", "music-player.js", "photos-app.js",
           "group-settings.js", "group-page.js",
           # The per-app settings architecture (docs/refactor-groups.md §3):
           # the shared widgets, the folder picker, and one settings pane per
           # app. Reached through the `apps.js` registry rather than imported
           # by name anywhere, which is exactly why they have to be listed —
           # nothing else would notice one of them changing.
           "settings-ui.js", "folder-tree.js",
           "chat-app-settings.js", "video-app-settings.js",
           "music-app-settings.js", "photos-app-settings.js",
           # The reference app (docs/refactor-groups.md §4.1). Hidden behind
           # `?dev=1` client-side, but it is still served and still cached, so
           # it participates in the hash like anything else here.
           "helloworld-app.js", "helloworld-app-settings.js",
           # Pages extracted from app.js — statically imported or lazy-loaded,
           # but all must participate in the content hash.
           "auth-page.js", "explore-page.js", "create-group-page.js",
           "admin-page.js", "node-page.js", "group-name.js",
           "search-page.js", "settings-page.js", "profile-page.js")


def _asset_version() -> str:
    """A fingerprint of what we are actually serving.

    `Cache-Control: no-cache` only binds a browser that asks. One that cached
    app.js *before* that header existed applies heuristic freshness — a
    fraction of the file's age, which for a file dated weeks ago is days — and
    never asks at all. It then runs last week's player against this week's node
    for as long as that lasts, which is indistinguishable from the fix not
    working. Changing the URL is the only thing that reaches such a browser,
    and a content hash changes it exactly when the content changes.
    """
    h = hashlib.sha256()
    for name in _ASSETS:
        path = STATIC_DIR / name
        if path.exists():
            h.update(path.read_bytes())
    return h.hexdigest()[:12]


ASSET_V = _asset_version()


# No Cache-Control here meant no explicit signal either way, and a browser
# left to its own heuristics can decide this is fresh enough without asking
# — which nothing about a subsequent reload, pull-to-refresh included,
# is guaranteed to override. `{v}` only reaches the browser at all if this
# shell itself is refetched; a heuristically-cached copy of it re-serves the
# OLD hash and therefore the old JS forever, indistinguishable from a fix not
# working. `no-store` forces every navigation here to hit the network, which
# is the only way `{v}` can ever change what a browser holding an old page
# actually asks for next.
_NO_STORE = {"Cache-Control": "no-store"}


# Content-Security-Policy for the whole hub, applied by a middleware in app.py.
#
# This is the desktop client's policy for these exact UI files
# (`meshbay-client/src/main.js`), which serves the same interface, and the two
# have to be changed together — a directive added here and not there breaks the
# app, and the reverse leaves the browser behind. They differ in two places, on
# purpose: `frame-ancestors` is `'self'` here and `'none'` there (nothing frames
# an `app://` page), and `frame-src` carries `'self'` here for the streamed
# download's hidden iframe, which the client has no service worker for.
# `'unsafe-inline'` is style-only — htm/preact set inline `style=` attributes
# everywhere; nothing inline executes, and the shell below carries no inline
# `<script>`. `'wasm-unsafe-eval'` is required for the Argon2id WASM. The hub's
# own origin is deliberately absent from `script-src`: a response it returns is
# never executed, which is the point of T3.
_RECAPTCHA_SRC = "https://www.google.com https://www.gstatic.com"
CSP = "; ".join([
    "default-src 'none'",
    f"script-src 'self' 'wasm-unsafe-eval' {_RECAPTCHA_SRC}",
    "style-src 'self' 'unsafe-inline'",
    f"img-src 'self' data: blob: {_RECAPTCHA_SRC}",
    "media-src 'self' blob:",
    "font-src 'self'",
    "connect-src 'self' https: wss:",
    "worker-src 'self'",
    # `object-src` exists for one thing, and `frame-src`'s `blob:` for the same
    # thing: previewing a PDF without writing it anywhere.
    #
    # `files-app.js` decrypts the file in the page, wraps it in a Blob and hands
    # it to `<object type="application/pdf">`. Chromium renders that with its own
    # viewer, which needs TWO permissions — the resource is loaded as plugin data
    # (`object-src`) and then rendered in an internal frame (`frame-src`). This
    # policy had neither: `object-src` was absent, so it fell back to
    # `default-src 'none'`, and the fallback message ("this browser will not
    # display the PDF inline") was shown on every platform from the day this CSP
    # shipped. It read as a desktop-client limitation because the client has sent
    # a CSP since its first launch and the hub had none before this file.
    #
    # `'self'` does not cover a same-origin `blob:` URL in either directive —
    # measured, not assumed, in Chrome 152 against the deployed page — so the
    # token is `blob:` and it is needed in both. Widening `object-src` from
    # `'none'` admits only what page script minted itself, at a type this code
    # sets: PDFium parsing bytes that came from a node, which is what any
    # browser does with the same file once it is downloaded.
    "object-src blob:",
    # `'self'` is not decoration: the streamed-download path works by navigating
    # a hidden iframe to `/_mbdl/<id>` so the service worker is asked for the
    # response it is holding. Without it Chrome refuses the frame, the worker is
    # never asked, and the page waits out its timeout for a download that cannot
    # happen — on Firefox and Safari that is the *only* way to write a large
    # file to disk, so the whole path was dead. Added when reCAPTCHA needed a
    # frame, which is why nobody connected the two.
    f"frame-src 'self' blob: {_RECAPTCHA_SRC}",
    # `'self'`, not `'none'`, and the difference is one same-origin iframe.
    #
    # The threat frame-ancestors answers is clickjacking: a *foreign* page
    # framing this one and stealing clicks. `'self'` refuses every foreign
    # origin exactly as `'none'` does — what it additionally allows is this
    # origin framing itself, which is precisely how a streamed download works
    # (a hidden iframe navigates to `/_mbdl/<id>` so the service worker is
    # asked for the response it holds).
    #
    # Under `'none'` Firefox blocked that frame, the worker was never asked,
    # and every large download waited out two 15-second timeouts and then fell
    # through — on Firefox and Safari that is the only way to write a large
    # file to disk. Chrome did not show it: its worker intercepts the
    # navigation before the network response and its CSP are ever considered,
    # which is why this looked like a Firefox-only problem for an afternoon.
    "frame-ancestors 'self'",
    "base-uri 'none'",
    "form-action 'none'",
])


@router.get("/app", response_class=HTMLResponse)
async def app_root():
    return HTMLResponse(_HTML, headers=_NO_STORE)


@router.get("/app/{path:path}", response_class=HTMLResponse)
async def app_catchall(path: str):
    return HTMLResponse(_HTML, headers=_NO_STORE)


@router.get("/", response_class=HTMLResponse)
async def index():
    return HTMLResponse(_HTML, headers=_NO_STORE)


_HTML = """\
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <!-- `interactive-widget=resizes-content`: on Android the soft keyboard
       shrinks the visual viewport and leaves the layout viewport alone, which
       is the platform default. `position: sticky` anchors to the layout
       viewport, so with a keyboard up the pinned header of a group or of
       Search sits at a coordinate the reader can no longer see — it reads as
       though it had scrolled away. This asks for the keyboard to resize the
       layout viewport instead, so what is pinned stays where it is looked at.
       Ignored by browsers that do not know it. -->
  <meta name="viewport" content="width=device-width, initial-scale=1, interactive-widget=resizes-content">
  <title>MeshBay</title>
  <link rel="stylesheet" href="/a/{v}/style.css">
</head>
<body>
  <div id="app"></div>
  <!-- Everything below is loaded from a path that carries the fingerprint of
       what we are serving, so a browser holding a heuristically-cached copy of
       an older build fetches this one instead of deciding it need not ask —
       and app.js's own relative imports inherit the prefix, which is the only
       way the module graph is guaranteed not to be a mixture of two builds.
       See _asset_version() and VersionedStatics. -->
  <!-- Argon2id (WebAssembly, inlined) — WebCrypto has no memory-hard KDF, and the
       keypair bundle needs one: it is protected by the passphrase alone and sits
       on every node its owner joins (C4). Vendored, see static/vendor/PROVENANCE.md -->
  <script src="/a/{v}/vendor/argon2.min.js"></script>
  <script src="/a/{v}/keyderive.js"></script>
  <script src="/a/{v}/crypto.js"></script>
  <script src="/a/{v}/transport.js"></script>
  <script type="module" src="/a/{v}/app.js"></script>
</body>
</html>
""".replace("{v}", ASSET_V)