#!/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"
v14_bootstrap="${install_dir}/bootstrap-${v14}"
tgz14="${v14}.tar.gz"
path_v14="${install_dir}/${tgz14}"
v19="go1.19.7"
v19_sum="1fe106fce9342c2a7ceeb04477341457cc9f0a3c07b9f2a993af09d654307f56"
v19_bootstrap="${install_dir}/bootstrap-${v19}"
tgz19="${v19}.tar.gz"
path_v19="${install_dir}/${tgz19}"

v="${1-1.21.0}"
case "${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";;
  1.18.3) new_sum="cc0e73239f5bc1521de9ddc54f46eb0e69cc41faabe3f468865483bb0f844b68";;
  1.18.4) new_sum="283442519c28f5c24dd8c849ebe0570a3ad92cd94610378b33b2053f60391fdf";;
  1.18.5) new_sum="30c07c08c9b9a79d652272ac3298c249a810a4c908e8937cf5e58d2414af1cc3";;
  1.19)   new_sum="6ac64f39e3f477ac793896437237e84b06d67c7657fbb34abcdbf73c77f6b7a3";;
  1.19.1) new_sum="884439c3de751c705e47a120af6b92b65770a952a7b8788244bc6d73b2548c3e";;
  1.19.5) new_sum="1c24a6a2bf71d64d0ca8e228028d6108521f06b6edc7bf6b34ed6d767a795809";;
  1.19.6) new_sum="0c7f4e6d2de3ae07d60377754955842ad357b0366df01116554fc619b1e99672";;
  1.19.7) new_sum="1fe106fce9342c2a7ceeb04477341457cc9f0a3c07b9f2a993af09d654307f56";;
  1.20.1) new_sum="5db737840a740457c1b4b73b90dad6daa57af0da420f3ea51c39a1a81abbcc41";;
  1.20.2) new_sum="176969bb14216dd45121e46d5d0f63d339edb9042d1389d485fb6b21ee172388";;
  1.21.0) new_sum="cf1d9b0504983c1a4c044856c389555070fbc58c3ce1703193a2c3ffe877a8b9";;
  *) errx "no hash found for version ${v}";;
esac
[[ "${v}" =~ 1\.2* ]] && v1_20=1 || v1_20=0

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

rm -f ${go_dir}

if [[ ! -d "${v14_bootstrap}" ]]; then
  curl -sSL "${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} ${v14_bootstrap}
fi

if [[ "${v1_20}" -eq 1 ]] && [[ ! -d "${v19_bootstrap}" ]]; then
  curl -sSL "${url}/${tgz19}" >${path_v19}
  [[ "$(sha256sum ${path_v19}|cut -d" " -f1)" != "${v19_sum}" ]] && errx "wrong checksum: ${path_v19}"
  tar xfz ${path_v19} -C ${install_dir}
  mv ${install_dir}/go-${v19} ${v19_bootstrap}
fi

if [[ ! -d "${new_dir}" ]]; then
  curl -sSL "${url}/${tgznew}" >${path_new}
  [[ -z "${new_sum}" ]] && { echo "hashsum for version ${new}:"; 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 "${v14_bootstrap}/bin/go" ]]; then
  cd ${v14_bootstrap}/src
  ./make.bash
fi

if [[ "${v1_20}" -eq 1 ]] && [[ ! -x "${v19_bootstrap}/bin/go" ]]; then
  export GOROOT_BOOTSTRAP=${v14_bootstrap}
  cd ${v19_bootstrap}/src
  ./make.bash
fi

if [[ ! -x "${new_dir}/bin/go" ]]; then
  [[ "${v1_20}" -eq 1 ]] && bootstrap=${v19_bootstrap} || bootstrap=${v14_bootstrap}
  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