showmd

#!/bin/bash
# I'm lazy today and just using Bash for SRANDOM O:-)

set -eu

pandoc_header_include=$(
	cat <<-EOT
		<script>
			async function reloadIfChanged() {
				const resp = await fetch(location + ".stamp.txt");
				if (!resp.ok) {
					return;
				}

				const stamp = parseFloat(await resp.text());
				const oldStamp = history.state ?? 0.0;
				if (stamp > oldStamp) {
					history.replaceState(stamp, "");
					location.reload();
				}
			}

			setInterval(reloadIfChanged, 1000);
		</script>
	EOT
)

cleanup()
{
	rm -fr -- "$tmpdir"
	[ -z "${pid-}" ] || kill "$pid" 2>/dev/null || :
}

if command -v pandoc >/dev/null; then
	md2html()
	{
		if pandoc -H<(printf '%s' "$pandoc_header_include") -o"$2" -s --quiet "$1"; then
			date '+%s.%N' >"${2}.stamp.txt"
		fi
	}
elif command -v markdown >/dev/null; then
	md2html()
	{
		markdown "$1" > "$2" || :
	}
else
	# shellcheck disable=SC2016
	printf 'Missing any of `markdown` or `pandoc`\n' >&2
	exit 2
fi

: "${bind_address:=127.0.0.1}"
: "${port:=$(( SRANDOM % (65535 - 1024 + 1) + 1024 ))}"

if [ $# -ne 1 ]; then
	printf "Missing Markdown file\n" >&2
	exit 2
fi

md_file="$1"

tmpdir=$(mktemp -d) || exit 1
trap cleanup EXIT HUP INT TERM
html_file="${tmpdir}/${md_file##*/}.html"

md2html "$md_file" "$html_file"
python3 -m http.server -b "$bind_address" -d "$tmpdir" -- "$port" 2>/dev/null &
pid=$!
open "http://${bind_address}:${port}/${html_file##*/}"

if command -v inotifywait >/dev/null; then
	printf "Watching for changes ...\n"
	while inotifywait -qq "$md_file"; do
		md2html "$md_file" "$html_file"
	done
else
	printf "Missing inotifywait, not watching for changes\n" >&2
	wait "$pid"
fi