#!/bin/sh


print_usage() {
	echo "USAGE: docker-version [n]"
	echo
	echo "Prints out the currently stable Docker versions in descending order (latest first)."
	echo "If used with a numerical argument, you can get the latest (1) or second latest (2)."
	echo
	echo "Arguments"
	echo "    1        Print only latest version"
	echo "    2        Print only second latest version"
	echo "    3        Print only third latest version"
	echo "    n        Print only x-th latest version"
}

if [ "${#}" -eq "1" ]; then
	if [ "${1}" = "-h" ] || [ "${1}" = "--version" ]; then
		print_usage
		exit 0
	fi
	if ! echo "${1}" | grep -qE '^[0-9]+$'; then
		>&2 echo "Error, supplied argument must be an integer."
		exit 1
	fi
fi

if ! command -v curl >/dev/null 2>&1; then
	>&2 echo "Error, 'curl' binary is required but not found in path."
	exit 1
fi
if ! command -v jq >/dev/null 2>&1; then
	>&2 echo "Error, 'jq' binary is required but not found in path."
	exit 1
fi

i=0; max=100;
while [ $i -lt $max ]; do
	if VERSIONS="$(curl -sS https://api.github.com/repos/docker/docker-ce/releases \
		| jq '.[].tag_name' \
		| grep -E '"v[.0-9]+(-ce)?"' \
		| sed 's/"//g' \
		| sed 's/v//g' \
		| sort -ur )"; then
		if [ -z "${VERSIONS}" ]; then
			>&2 echo "Got rempty result. Trying again."
			i=$((i+1))
			sleep 1
		else
			break;
		fi
	else
		>&2 echo "Failed to fetch API. trying again."
		i=$((i+1))
		sleep 1
	fi
done


if [ "${#}" -eq "1" ]; then
	echo "${VERSIONS}" | head -${1} | tail -1
else
	echo "${VERSIONS}"
fi