#!/usr/bin/env bash
set -eo pipefail

declare -r GO_VERSION=1.18.3

# Hashes are from the table at https://golang.org/dl/
function go_hash () {
  case $1 in
    linux_amd64)
      echo 956f8507b302ab0bb747613695cdae10af99bbd39a90cae522b7c0302cc27245
      ;;
    linux_arm64)
      echo beacbe1441bee4d7978b900136d1d6a71d150f0a9bb77e9d50c822065623a35a
      ;;
    mac)
      echo a23a24c5528671d444328a36a98056902f699a5a211b6ad5db29ca0c012e0085
      ;;
    windows)
      echo 9c46023f3ad0300fcfd1e62f2b6c2dfd9667b1f2f5c7a720b14b792af831f071
      ;;
  esac
}

function install_go_linux () {
    local -r arch=$(dpkg --print-architecture)
    ARCHIVE=go${GO_VERSION}.linux-${arch}.tar.gz
    wget https://golang.org/dl/${ARCHIVE}
    echo "$(go_hash linux_${arch})  ${ARCHIVE}" | sha256sum --check --
    tar -C $1 -xzf ${ARCHIVE}
    rm ${ARCHIVE}
}

function install_go_mac () {
    ARCHIVE=go${GO_VERSION}.darwin-amd64.tar.gz
    wget https://golang.org/dl/${ARCHIVE}
    echo "$(go_hash mac)  ${ARCHIVE}" | shasum -a 256 --check -
    tar -C $1 -xzf ${ARCHIVE}
    rm ${ARCHIVE}
}

function install_go_windows () {
    ARCHIVE=go${GO_VERSION}.windows-amd64.zip
    wget https://golang.org/dl/${ARCHIVE}
    echo "$(go_hash windows)  ${ARCHIVE}" | sha256sum --check --
    unzip -qq -d $1 ${ARCHIVE}
    rm ${ARCHIVE}
}

function main () {
    if [[ $# != 1 ]]; then
        >&2 echo Usage: $0 '<install-dir>'
        exit 1
    fi
    local -r install_dir=$1

    rm -rf "$install_dir"
    mkdir -p "$install_dir"
    case $(uname) in
        Linux)
            install_go_linux "$install_dir"
            ;;
        Darwin)
            install_go_mac "$install_dir"
            ;;
        MSYS_NT*)
            install_go_windows "$install_dir"
            ;;
        *)
            >&2 echo Error: unknown OS $(uname)
            exit 1
            ;;
    esac

    "${install_dir}/go/bin/go" version
}

main ${@}