Jul 28 - Update schedule page's referred time

app.py

@@ -9,7 +9,9 @@ from logging.handlers import RotatingFileHandler
 
 import bleach
 from bleach.css_sanitizer import CSSSanitizer
-from flask import Flask, flash, redirect, render_template, request, url_for
+from flask import (
+    Flask, flash, jsonify, redirect, render_template, request, url_for,
+)
 from flask_sqlalchemy import SQLAlchemy
 from flask_wtf import CSRFProtect
 from markupsafe import Markup
@@ -200,6 +202,40 @@ def demo_slots(config):
     return slots
 
 
+def taken_slots(day):
+    """Times already booked on `day`. Cancelled requests free their slot."""
+    rows = (
+        DemoRequest.query
+        .with_entities(DemoRequest.preferred_time)
+        .filter(DemoRequest.preferred_date == day,
+                DemoRequest.status != "cancelled")
+        .all()
+    )
+    return {row[0] for row in rows}
+
+
+def available_slots(config, day):
+    """Bookable times left on `day` — the full grid minus what's taken."""
+    if day is None:
+        return demo_slots(config)
+    booked = taken_slots(day)
+    return [slot for slot in demo_slots(config) if slot not in booked]
+
+
+def demo_day_status(config, day):
+    """Why a date can't be booked, or None if it's open. Shared by the form and
+    the /demo/slots endpoint so both give the same answer."""
+    today = date.today()
+    if day < today:
+        return "That date has already passed."
+    if day > today + timedelta(days=config["DEMO_MAX_DAYS_AHEAD"]):
+        return (f"Please pick a date within the next "
+                f"{config['DEMO_MAX_DAYS_AHEAD']} days.")
+    if day.weekday() >= 5:
+        return "Demonstrations run Monday through Friday."
+    return None
+
+
 def _rate_limited(ip, limit):
     """True if `ip` has already submitted `limit` requests in the last hour."""
     if limit <= 0:
@@ -350,15 +386,9 @@ def create_app():
                 wanted = None
                 errors.append("Please pick a date for the demonstration.")
             if wanted:
-                if wanted < today:
-                    errors.append("Please pick a date that hasn't passed yet.")
-                elif wanted > max_date:
-                    errors.append(
-                        f"Please pick a date within the next "
-                        f"{cfg['DEMO_MAX_DAYS_AHEAD']} days."
-                    )
-                elif wanted.weekday() >= 5:
-                    errors.append("Demonstrations run Monday through Friday.")
+                closed = demo_day_status(cfg, wanted)
+                if closed:
+                    errors.append(closed)
 
             if form["preferred_time"] not in slots:
                 errors.append("Please pick an available time.")
@@ -395,9 +425,19 @@ def create_app():
                 _notify_demo(app, req)
                 return redirect(url_for("demo_thanks"))
 
+        # Show only what's still free on the date in hand, so a re-render after
+        # an error can't offer a slot that was taken in the meantime. With no
+        # date chosen yet the full grid is listed and the JS narrows it as soon
+        # as one is picked (and without JS the checks above are the backstop).
+        chosen = None
+        if form.get("preferred_date"):
+            try:
+                chosen = datetime.strptime(form["preferred_date"], "%Y-%m-%d").date()
+            except ValueError:
+                chosen = None
         return render_template(
             "demo.html",
-            slots=slots,
+            slots=available_slots(cfg, chosen) if chosen else slots,
             form=form,
             min_date=today.isoformat(),
             max_date=max_date.isoformat(),
@@ -405,6 +445,23 @@ def create_app():
             demo_url=cfg["DEMO_CONTACT_URL"],
         )
 
+    @app.route("/demo/slots")
+    def demo_slots_api():
+        """Times still bookable on ?date=YYYY-MM-DD, for the form's time picker.
+        Public and read-only: it exposes which slots are free, which is exactly
+        what the form shows anyway, and nothing about who booked them."""
+        cfg = app.config
+        raw = request.args.get("date", "")
+        try:
+            day = datetime.strptime(raw, "%Y-%m-%d").date()
+        except ValueError:
+            return jsonify(ok=False, error="Invalid date."), 400
+
+        closed = demo_day_status(cfg, day)
+        if closed:
+            return jsonify(ok=True, date=raw, open=False, reason=closed, slots=[])
+        return jsonify(ok=True, date=raw, open=True, slots=available_slots(cfg, day))
+
     @app.route("/demo/thanks")
     def demo_thanks():
         return render_template("demo_thanks.html", demo_url=app.config["DEMO_CONTACT_URL"])