#!/usr/bin/env bash
# infra/bin/wait-for-x DISPLAY TIMEOUT_SECONDS
#
# Poll until Xvfb on DISPLAY (e.g. ":99") accepts connections, or exit 1
# after TIMEOUT_SECONDS. Used as flystage's ExecStartPre
# (docs/design/infra.md section 3).
set -euo pipefail

usage() { echo "usage: $0 DISPLAY TIMEOUT_SECONDS" >&2; exit 2; }

[ $# -eq 2 ] || usage
display="$1"
timeout="$2"

case "$timeout" in
    ''|*[!0-9]*) usage ;;
esac

deadline=$(( $(date +%s) + timeout ))
while true; do
    if DISPLAY="$display" xdpyinfo >/dev/null 2>&1; then
        exit 0
    fi
    if [ "$(date +%s)" -ge "$deadline" ]; then
        echo "wait-for-x: $display not ready after ${timeout}s" >&2
        exit 1
    fi
    sleep 0.5
done