#!/bin/bash

set -e
errx() { echo "error: $1">&2; exit 1; }
[[ $(id -u) -ne 0 ]] && errx "this script must be run as root"

install_dir="/usr/local"
go_dir="${install_dir}/go"
url="https://github.com/golang/go/archive"

v14="go1.4.3"
v14_sum="65e8d2ea08447f02f8b6ab63778e4d98586ac4fd676401dae0eda494c7829965"
bootstrap="${install_dir}/bootstrap-${v14}"
tgz14="${v14}.tar.gz"
path_v14="${install_dir}/${tgz14}"

v="${1-1.18.2}"
case "${v}" in
  1.16.7) new_sum="07502f16366fbc697b1b09b842d29116e6d6607c9dc42b1d7c54b96f528c7952";;
  1.17.1) new_sum="670ce36e100669f9be572a1603858ce4a64eb4b21a31fa5cdefb778609c40337";;
  1.17.2) new_sum="022fe1f533432a305db705448f50f9a3ea369586dc32d07219b1bc7db1e01577";;
  1.17.4) new_sum="91736588a47917aaa424dfdf482d8efcb44403a768e7a947c272a98881053386";;
  1.17.6) new_sum="de00bf818cda9e4712e9b3438c9c3d4f8318beb598d11abb0ba9d515883f6320";;
  1.18)   new_sum="63e5cab48f97c63dc2737eb35582316acf77084d109ac0571651cedaf40987c0";;
  1.18.2) new_sum="b76e590857060fdc575a37d4204c15df33de6d23e49d5cf9bdce93083e4dcddb";;
  *) errx "no hash found for version ${v}";;
esac

new="go${v}"
new_dir="${install_dir}/go-${new}"
tgznew="${new}.tar.gz"
path_new="${install_dir}/${tgznew}"

rm -f ${go_dir}

if [[ ! -d "${bootstrap}" ]]; then
  curl -sSL "${url}/${tgz14}" >${path_v14}
  [[ "$(sha256sum ${path_v14}|cut -d" " -f1)" != "${v14_sum}" ]] && errx "wrong checksum: ${path_v14}"
  tar xfz ${path_v14} -C ${install_dir}
  mv ${install_dir}/go-${v14} ${bootstrap}
fi

if [[ ! -d "${new_dir}" ]]; then
  curl -sSL "${url}/${tgznew}" >${path_new}
  [[ -z "${new_sum}" ]] && { sha256sum ${path_new}|cut -d" " -f1; exit 0; }
  [[ "$(sha256sum ${path_new}|cut -d" " -f1)" != "${new_sum}" ]] && errx "wrong checksum: ${path_new}"
  tar xfz ${path_new} -C ${install_dir}
fi

export CGO_ENABLED=0

if [[ ! -x "${bootstrap}/bin/go" ]]; then
  cd ${bootstrap}/src
  ./make.bash
fi

if [[ ! -x "${new_dir}/bin/go" ]]; then
  export GOROOT_BOOTSTRAP=${bootstrap}
  [[ "$(uname -m)" == "x86_64" ]] && export GOARCH=amd64 || export GOARCH=386
  cd ${new_dir}/src
  ./make.bash
fi

ln -s ${new_dir} ${go_dir}

export GOROOT=${go_dir}
export PATH=${PATH}:${GOROOT}/bin:~/go/bin

cat <<EOF
add this to your .bashrc/.profile:

export CGO_ENABLED=${CGO_ENABLED}
export GOPATH=~/go
export GOROOT=${GOROOT}
export GO111MODULE=on
export PATH=\${PATH}:\${GOROOT}/bin:~/go/bin

EOF

go version