Event sign-up sheet RFC

[lewisbelcher]

Description

A user should be able to:

1. Select events in the calendar and click a button to create an event sign-up sheet that can be printed and distributed at physical meetings
2. Scan filled in sign-up sheets using desktop/mobile and have the relevant checked fields auto-filled in a page which can then be attributed with a user and the user will be enrolled in those events

Part 1 is useful as a standalone feature.

The intention for part 2 (scanning the sign-up sheets) is to encode selected event IDs in a QR code and include this in a corner of the sign-up sheet. This QR code can then be used to not only communicate which events are present on the page and in what order, but also to locate the document and, in turn, locate relevant checkboxes and identify whether they have been checked.

QR code creation

At the moment is assumed that only event IDs need to be encoded in the QR code, but this may be extended in the future.

What size QR code do we need?

• The maximum desired number of events per page is around 40.
• It's probably reasonable to assume that each ID can be contained within 3 bytes (up to an ID of 16,777,216).
• 40 such 3-byte IDs would require encoding 120 bytes in the QR code, plus some headroom for some potential metadata (~30 bytes for good measure).
• This means we'd need ~150 bytes in the QR code.
• The nearest QR code version to this size is version 7 (see here) with lowest error correction, which provides 154 bytes.
• We can probably do a lot better than this by compressing the data going into the QR code. This remains to be investigated.

Estimated issue size

I think this issue is large because it involves implementing new, non-trivial functionality (document creation, QR encoding, computer vision).

Prerequisites

All platform-related prerequisites are already met.

Requirements

• [ ] Create a print-friendly webpage containing basic header information (name, email address etc. to make the attendee identifiable)
• [ ] Pack and compress a list of event ID integers
• [ ] QR code creation
• [ ] QR code scanner
• [ ] CV magic to locate the document and relevant checkboxes
• [ ] Data ingestion into the system (as a first step we assume that the organiser can manually search for the attendee in the system)

Possible implementations

Entirely JS based

• QR scanner
• Investigate appropriate libraries for:
  • Data compression
  • QR generation
  • CV

Webassembly

Webassembly could be explored as an alternative to JS.

• Could allow for more custom image processing and CV functionality
• Could give significant speed benefits
• Almost certainly more complicated
• Almost certainly more fun

Design specifications

TODO

Open questions

• Are we safe to assume a maximum plausible ID can be contained within 3 bytes? If we use appropriate compression can we use 4 bytes anyway?
• Is there a relevant benefit for a Webassembly approach other than that Lewis would like to investigate it? Would it create too much complexity and make maintenance a pain?

[lewisbelcher]

Extra questions / things to consider:

• How do we deal with multi-day events? They have the same ID across multiple days. At the moment we'll need to just assume attendance to one day implies attendance to all days
• Event clusters in general and multi-shift events? How can we adjust for these?

[lewisbelcher]

After some exploration, here is a script that should produce a QR for a list of 30 Uint64 IDs:

const pako = require('pako');
const QRCode = require('qrcode');

// Some example IDs:
const arr = new BigUint64Array([1n, 2n, 3n, 4n, 5n, 6n, 7n, 8n, 9n, 10n, 11n, 12n, 13n, 14n, 15n, 16n, 17n, 18n, 19n, 20n, 21n, 22n, 23n, 83383n, 123n, 9999n, 18446744073709551613n, 111n, 123n, 678n]);

// Compress these IDs using pako:
const compressed = pako.deflate(arr.buffer);

// Test decompressing to check that the ouput is the same:
const uncompressed = pako.inflate(compressed);
const uncompressed_arr = new BigUint64Array(uncompressed.buffer);

// Create a QR code:
QRCode.toFile(
  'qr-code.png',
  [{data: compressed.buffer, mode: 'byte' }],
  { version: 7 },
  function (err, url) {
    console.log(url)
})

[lewisbelcher]

Extra questions / things to consider:

* How do we deal with multi-day events? They have the same ID across multiple days. At the moment we'll need to just assume attendance to one day implies attendance to all days

* Event clusters in general and multi-shift events? How can we adjust for these?

• We're safe to assume that attendance is all or nothing for multi-day events.
• No special treatment needed for other event clusters (maybe in the future group them together on the resulting form, but for now just ordered by date and time is fine).

[johanbook]

Example of QR code generated in Zetkin calendar