#!/usr/bin/env sh

: ${PREFER_BUILDCTL=}
: ${PREFER_LEGACY=}

newerEqualThan() { # $1=minimum wanted version $2=actual-version
  [ "$1" = "$(printf "$1\n$2" | sort -V | head -n 1)" ]
}

buildmode="legacy"
if [ "$PREFER_BUILDCTL" = "1" ]; then
  buildmode="buildkit";
else
  serverVersion=$(docker info --format '{{.ServerVersion}}')
  experimental=$(docker info --format '{{.ExperimentalBuild}}')
  if [ "$PREFER_LEGACY" != "1" ] && ( newerEqualThan "18.09" $serverVersion || \
    ( newerEqualThan "18.06" $serverVersion && [ "true" = "$experimental" ] ) || \
    [ "$DOCKER_BUILDKIT" = "1" ]); then
    buildmode="docker-buildkit";
  fi
fi