#!/usr/bin/sh

# goupgrade
# You need go installed and GOBIN needs to be in PATH.

set -eu

goup_local () {
  local go_cmd bin_dir sdk_dir installed latest current
  go_cmd="${1-go}"

  bin_dir="$($go_cmd env GOBIN)"
  bin_dir="${bin_dir:-"$($go_cmd env GOPATH)/bin"}"

  sdk_dir=~/sdk

  installed="$(echo "$bin_dir"/go1.* | xargs basename -a | sort -Vr)"
  latest="$(echo "$installed" | head -n1)"

  current="$(readlink "$(command -v go)")"

  env -i GOUP_LINK_NAME="$go_cmd" \
      GOUP_INSTALLED="'$installed'" \
      GOUP_LATEST="$latest" \
      GOUP_CURRENT="$current" \
      GOUP_BIN_DIR="$bin_dir" \
      GOUP_SDK_DIR="$sdk_dir"
}

goup_latest_avail () {
  local cmd
  if command -v curl >/dev/null
  then
    cmd='curl -s'
  elif command -v wget >/dev/null
  then
    cmd='wget -q -O -'
  else
    echo 'curl or wget is not installed!' >&2
    exit 1
  fi
  $cmd 'https://go.dev/VERSION?m=text' | head -n1
}

goup_install () {
  local version="$1"
  go install golang.org/dl/"$version"@latest
  "$GOUP_BIN_DIR/$version" download
}

goup_uninstall () {
  local version="$1"
  if [ "$GOUP_CURRENT" = "$version" ]
  then echo "can't unistall current version" && exit 1
  fi
  rm -rf "${GOUP_SDK_DIR:?}/$version"
  rm "$GOUP_BIN_DIR/$version"
}

goup_set () {
  local version="$1"

  if ! echo "$GOUP_INSTALLED" | grep -Fq "$version"
  then echo "$version not installed"; exit 1
  fi

  if [ "$GOUP_CURRENT" = "$version" ]
  then exit
  fi

  read -p "set $GOUP_LINK_NAME to version $version? [y/N] " -r bool

  if [ "$bool" != y ]
  then exit 1
  fi

  ln -fs "$version" "$GOUP_BIN_DIR/$GOUP_LINK_NAME"
  "$GOUP_LINK_NAME" download
  ln -fs "$("$GOUP_LINK_NAME" env GOROOT)/bin/gofmt" "$GOUP_BIN_DIR/gofmt"
}

linkname=go

while getopts l: arg
do case $arg in
  (l) linkname="$OPTARG";;
  (?) exit 2;;
esac
done
shift $((OPTIND - 1))

case ${1-} in
  (g|get)     eval "$(goup_local "$linkname")"; echo "$GOUP_CURRENT";;
  (c|check)   eval "$(goup_local "$linkname")"; [ "$(goup_latest_avail)" = "$GOUP_LATEST" ]; exit $?;;
  (l|list)    eval "$(goup_local "$linkname")"; echo "$GOUP_INSTALLED";;
  (s|set)     eval "$(goup_local "$linkname")"; : "${2:?You need to set a version!}";
              if [ "$2" = latest ]; then goup_set "$GOUP_LATEST"; else goup_set "$2"; fi;;
  (i|install) eval "$(goup_local "$linkname")"; goup_install "${2:?You need to set a version!}";;
  (d|delete)  eval "$(goup_local "$linkname")"; goup_uninstall "${2:?You need to set a version!}";;
  (u|upgrade) latest="$(goup_latest_avail)"; $0 -l "$linkname" i "$latest" && $0 s "$latest";;
  (h|help) cat <<END;;
usage of $0:
  $0 [options...] MODE [args...]

modes:
  [c]heck             check if latest version is installed (exit code)
  [d]elete   VERSION  delete a specific version
  [g]et               reads the link destination
  [h]elp              show help text
  [i]nstall  VERSION  install a specified version
  [l]ist              show all installed versions
  [s]et      VERSION  set the link to the chosen version (use 'latest' as pseudo version)
  [u]pgrade           install latest available version and set it

options:
  -l  linkname (defaults to \`go\`)
END
  (*) if [ -n "${1-}" ]
      then echo "unknown command '${1-}'!"
      else echo "missing command!"
      fi
      echo "try '$0 help' for help"
      exit 2;;
esac