openslide/app/routes/api.py

from datetime import datetime, timedelta
import hashlib
import json
import time

from flask import Blueprint, Response, abort, jsonify, request, stream_with_context, url_for

from ..extensions import db
from ..models import Display, DisplaySession

bp = Blueprint("api", __name__, url_prefix="/api")


MAX_ACTIVE_SESSIONS_PER_DISPLAY = 2
SESSION_TTL_SECONDS = 90


def _enforce_and_touch_display_session(display: Display, sid: str | None):
    """Enforce concurrent display viewer limit and touch last_seen.

    Returns:
        (ok, response)
        - ok=True: caller may proceed
        - ok=False: response is a Flask response tuple to return
    """

    sid = (sid or "").strip()
    if not sid:
        return True, None

    cutoff = datetime.utcnow() - timedelta(seconds=SESSION_TTL_SECONDS)
    # Cleanup old sessions. Avoid committing if nothing was deleted (saves write locks on SQLite).
    deleted = (
        DisplaySession.query.filter(
            DisplaySession.display_id == display.id,
            DisplaySession.last_seen_at < cutoff,
        ).delete(synchronize_session=False)
    )
    if deleted:
        db.session.commit()

    existing = DisplaySession.query.filter_by(display_id=display.id, sid=sid).first()
    if existing:
        existing.last_seen_at = datetime.utcnow()
        db.session.commit()
        return True, None

    active_count = (
        DisplaySession.query.filter(
            DisplaySession.display_id == display.id,
            DisplaySession.last_seen_at >= cutoff,
        ).count()
    )
    if active_count >= MAX_ACTIVE_SESSIONS_PER_DISPLAY:
        return (
            False,
            (
                jsonify(
                    {
                        "error": "display_limit_reached",
                        "message": f"This display URL is already open on {MAX_ACTIVE_SESSIONS_PER_DISPLAY} displays.",
                    }
                ),
                429,
            ),
        )

    s = DisplaySession(
        display_id=display.id,
        sid=sid,
        last_seen_at=datetime.utcnow(),
        ip=request.headers.get("X-Forwarded-For", request.remote_addr),
        user_agent=(request.headers.get("User-Agent") or "")[:300],
    )
    db.session.add(s)
    db.session.commit()
    return True, None


def _playlist_signature(display: Display) -> tuple[int | None, str]:
    """Compute a stable hash for what the player should be showing.

    We include enough information so that changing the assigned playlist, reordering,
    duration changes, and item adds/deletes trigger an update.
    """

    playlist = display.assigned_playlist
    if not playlist:
        raw = "no-playlist"
        return None, hashlib.sha1(raw.encode("utf-8")).hexdigest()

    payload = {
        "playlist_id": playlist.id,
        "items": [
            {
                "id": it.id,
                "pos": it.position,
                "type": it.item_type,
                "title": it.title,
                "duration": it.duration_seconds,
                "file_path": it.file_path,
                "url": it.url,
            }
            for it in playlist.items
        ],
    }
    raw = json.dumps(payload, sort_keys=True, separators=(",", ":"))
    return playlist.id, hashlib.sha1(raw.encode("utf-8")).hexdigest()


@bp.get("/display/<token>/playlist")
def display_playlist(token: str):
    display = Display.query.filter_by(token=token).first()
    if not display:
        abort(404)

    # Enforce: a display URL/token can be opened by max 2 concurrently active sessions.
    # Player sends a stable `sid` via querystring.
    sid = request.args.get("sid")
    ok, resp = _enforce_and_touch_display_session(display, sid)
    if not ok:
        return resp

    playlist = display.assigned_playlist
    if not playlist:
        return jsonify({"display": display.name, "playlist": None, "items": []})

    items = []
    for item in playlist.items:
        payload = {
            "id": item.id,
            "type": item.item_type,
            "title": item.title,
            "duration": item.duration_seconds,
        }
        if item.item_type in ("image", "video") and item.file_path:
            payload["src"] = url_for("static", filename=item.file_path)
        if item.item_type in ("webpage", "youtube"):
            payload["url"] = item.url
        items.append(payload)

    return jsonify(
        {
            "display": display.name,
            "playlist": {"id": playlist.id, "name": playlist.name},
            "items": items,
        }
    )


@bp.get("/display/<token>/events")
def display_events(token: str):
    """Server-Sent Events stream to notify the player when its playlist changes."""

    display = Display.query.filter_by(token=token).first()
    if not display:
        abort(404)

    sid = request.args.get("sid")
    ok, resp = _enforce_and_touch_display_session(display, sid)
    if not ok:
        return resp

    display_id = display.id
    sid = (sid or "").strip() or None

    @stream_with_context
    def _gen():
        last_hash = None
        last_touch = 0.0
        keepalive_counter = 0

        while True:
            try:
                # Refresh from DB each loop so changes become visible.
                d = Display.query.filter_by(id=display_id).first()
                if not d:
                    yield "event: closed\ndata: {}\n\n"
                    return

                playlist_id, h = _playlist_signature(d)
                if h != last_hash:
                    last_hash = h
                    payload = json.dumps({"playlist_id": playlist_id, "hash": h})
                    yield f"event: changed\ndata: {payload}\n\n"

                # Touch session periodically so SSE-only viewers don't time out.
                now = time.time()
                if sid and (now - last_touch) >= 30:
                    last_touch = now
                    existing = DisplaySession.query.filter_by(display_id=display_id, sid=sid).first()
                    if existing:
                        existing.last_seen_at = datetime.utcnow()
                        db.session.commit()

                # Keep-alive comment (prevents some proxies from closing idle streams).
                keepalive_counter += 1
                if keepalive_counter >= 10:  # ~20s with the sleep below
                    keepalive_counter = 0
                    yield ": keep-alive\n\n"

                # Release DB connections between iterations.
                db.session.remove()

                time.sleep(2)
            except GeneratorExit:
                return
            except Exception:
                # Avoid tight error loops.
                try:
                    db.session.remove()
                except Exception:
                    pass
                time.sleep(2)

    return Response(
        _gen(),
        mimetype="text/event-stream",
        headers={
            "Cache-Control": "no-cache",
            "X-Accel-Buffering": "no",
            "Connection": "keep-alive",
        },
    )