wen?

A Discord bot that tells you when stuff is.

/wen f1 → next F1 race
/wen f1 sprint → next sprint
That's it. That's the bot.

_{Works as a user install or server bot · Written in Java because why not · build status}

Usage

/wen f1              → next F1 event
/wen f1 sprint       → named filter
/wen f1 monaco       → free-text search across event fields
/wen help            → list available calendars and filters

What it does

Fetches iCal (.ics) feeds in the background
Responds to Discord slash commands with upcoming events
Keyword lookup, named filters, free-text search, autocomplete
Prefilters for noisy calendars (e.g., only "Grand Prix" events from a full F1 feed)

How it works

Discord Gateway (WebSocket)
  → GatewayEventParser (dsl-json)
    → Processor (query parse, calendar lookup, filter)
      → CalendarFeed.query() (pre-sorted events, predicate match)
        → DiscordHttpClient.respond() (rate-limited HTTP)

Calendar feeds refresh on configurable intervals via virtual threads. Each feed runs its own
background loop with jitter to avoid thundering herd. A semaphore limits concurrent refreshes to 3.
GC telemetry via JFR streams — pause stats, allocation stalls, and heap usage logged every 60s.

What it runs on

256MB RAM. Shared CPU. One Fly.io machine.

Component	Details
Runtime	Java 25, JLink-stripped to only the modules the app needs
GC	ZGC, 40MB soft max, compact object headers
Concurrency	Virtual threads — gateway, calendar refresh, HTTP, health
HTTP	`java.net.http` — HttpClient + WebSocket, no frameworks
Parsing	`biweekly` (iCal), `tomlj` (config), `dsl-json` (JSON)
Container	Multi-stage Docker, `alpine:3` runtime
Deploy	Fly.io, `shared-cpu-1x`, 256MB, single machine

In production: ~1% CPU, <200MB RSS, GC pauses under 100µs, 4 dependencies.

Discord setup

1. Create application

Go to Discord Developer Portal
New Application → name it
Note the Application ID

2. Create bot

Bot tab → Add Bot
Reset Token → copy it (this is your DISCORD_TOKEN)

3. Bot settings

Setting	Value	Why
Public Bot	Your call	Whether others can invite it
Presence Intent	Off	Don't need it
Server Members Intent	Off	Don't need it
Message Content Intent	Off	Slash commands only

4. Invite

OAuth2 → URL Generator
Scopes: bot, applications.commands
Bot permissions: none
Open the URL to invite

5. Environment variables

Variable	Required	Description
`DISCORD_TOKEN`	Yes	Bot token from Discord Developer Portal
`DISCORD_APPLICATION_ID`	Yes	Application ID from Discord Developer Portal
`WEN_CONFIG_B64`	Production	Base64-encoded `config.toml` (required in Docker/Fly.io)
`HEALTH_PORT`	No	Health check HTTP port (default: `8080`)
`UNHEALTHY_THRESHOLD_MS`	No	Watchdog exit threshold in milliseconds (default: `600000` = 10 minutes)

Configuration

Create a config.toml:

[[calendars]]
name = "Formula 1"
url = "https://example.com/f1-calendar.ics"
keywords = ["f1", "formula1"]
refreshInterval = "PT1H"  # ISO-8601 duration
fallback = false

[calendars.prefilter]
field = "summary"
contains = "Grand Prix"

[calendars.filters.sprint]
field = "summary"
contains = "Sprint"

Calendar fields

Field	Required	Description
`name`	✅	Display name
`url`	✅	iCal feed URL
`keywords`	✅	Trigger words (e.g., `["f1", "formula1"]`)
`refreshInterval`		How often to refresh (default: `PT6H`)
`fallback`		Use when no keyword matches (default: `false`)
`prefilter`		Filter applied to all events from this calendar
`filters.<name>`		Named filters users can specify

Filter fields

Field	Required	Description
`contains`	✅	Substring to match (case-insensitive)
`field`		`summary`, `description`, `location`, or `categories` (default: `summary`)

Building & Running

Local development

mvn clean package
DISCORD_TOKEN="..." DISCORD_APPLICATION_ID="..." \
  java -Dconfig=config.toml -jar target/wen.jar

Pass config via -Dconfig system property.

Docker

docker build -t wen .
docker run \
  -e DISCORD_TOKEN="..." \
  -e DISCORD_APPLICATION_ID="..." \
  -e WEN_CONFIG_B64="$(base64 -w0 config.toml)" \
  wen

Config must be base64-encoded as WEN_CONFIG_B64.

Fly.io

fly apps create wen
fly secrets set \
  DISCORD_TOKEN="..." \
  DISCORD_APPLICATION_ID="..." \
  WEN_CONFIG_B64="$(base64 -w0 config.toml)"
fly deploy

Subsequent deploys: fly deploy

Built for the "wen race" crowd 🏁

License

MIT

anirbanmu/wen