#!/bin/bash
# 03-slack-webhook.sh — post a message to a Slack channel on each HearthGate event.
#
# Why you might want this:
#   You share the Mac with a small team — maybe a home lab, maybe an oncall
#   rotation. Everyone in #infra-alerts sees in Slack the moment someone
#   SSHes in, and they see when the session ends. No one has to ask "are
#   you on the box right now?".
#
# Setup once (5 minutes):
#   1. Go to https://api.slack.com/messaging/webhooks
#   2. Create a Slack app, enable "Incoming Webhooks"
#   3. "Add New Webhook to Workspace" → pick the channel → copy the URL
#   4. Export the URL as SLACK_WEBHOOK_URL, or paste it into the value below
#      only on a machine you control. Treat webhook URLs like secrets.
#
# Setup:
#   Make the script executable, then add it from HearthGate's Hooks tab.
#   Full guide: https://codnamacs.com/hearthgate/help/features/hooks
#
# Customise the message:
#   The two `payload=` lines below build a Slack-formatted JSON; tweak the
#   emoji, the channel hostname display, whatever you like.
#
# Environment HearthGate provides:
#   HEARTHGATE_EVENT
#   HEARTHGATE_SESSION_DURATION_SEC (disconnect only)
#
# Test it:
#   SLACK_WEBHOOK_URL="https://hooks.slack.com/services/..." \
#     HEARTHGATE_EVENT=on-connect ./03-slack-webhook.sh

set -euo pipefail

# Prefer exporting SLACK_WEBHOOK_URL outside this file. Hard-coding also works,
# but only do that on a private machine/repo because webhook URLs are secrets.
SLACK_WEBHOOK_URL="${SLACK_WEBHOOK_URL:-}"

if [ -z "$SLACK_WEBHOOK_URL" ]; then
    echo "slack-webhook: SLACK_WEBHOOK_URL is not set, skipping." >&2
    # Exit 0 — the user hasn't configured the webhook yet and we should not
    # mark the hook as failed for that.
    exit 0
fi

EVENT="${HEARTHGATE_EVENT:-${1:-unknown}}"
DURATION_SEC="${HEARTHGATE_SESSION_DURATION_SEC:-}"
HOST="$(hostname -s)"

build_payload() {
    local emoji="$1"
    local text="$2"
    cat <<EOF
{"text":"${emoji} *HearthGate on ${HOST}*: ${text}"}
EOF
}

case "$EVENT" in
    on-connect|after-connect)
        payload="$(build_payload "🟢" "remote session started")"
        ;;
    on-disconnect|after-disconnect)
        if [ -n "$DURATION_SEC" ]; then
            payload="$(build_payload "🔴" "session ended after ${DURATION_SEC}s")"
        else
            payload="$(build_payload "🔴" "session ended")"
        fi
        ;;
    *)
        echo "slack-webhook: unrecognised event '$EVENT'" >&2
        exit 0
        ;;
esac

# --max-time so a slow Slack never holds the hook open longer than the
# HearthGate timeout. --silent because hook stdout shows up in the UI; we
# only care about errors here.
curl --silent --show-error --fail \
     --max-time 10 \
     -X POST -H 'Content-Type: application/json' \
     --data "$payload" \
     "$SLACK_WEBHOOK_URL" > /dev/null