_go-installed() {
  which go > /dev/null 2>&1
}

_within-go-project() {
  local check_dir=$PWD
  local next_check_dir=${check_dir%/*}

  while [ "$next_check_dir" != "" ]; do
    if [ -d "$check_dir/.gopath" ]; then
        echo "$check_dir/.gopath"
        return
    elif [ -f "$check_dir/.gopath" ]; then
        local gopath="$(cat "$check_dir/.gopath")"
        if [ -z "$gopath" ]; then
            echo "$check_dir"
        else
            echo "$gopath"
        fi
        return
    fi

    check_dir="$next_check_dir"
    next_check_dir=${check_dir%/*}
  done

  false
}

_append-go-path() {
  local bin_path="$*/bin"

  [[ $PATH == *:"$*"* ]] || export PATH="$PATH:$bin_path"
}

_strip-go-path() {
  local bin_path="$*/bin"

  [[ $PATH == *":$bin_path"* ]] && export PATH=$(
    echo -n "$PATH" |
    awk -v RS=: -v ORS=: '$0=="'"$bin_path"'" {next} {print}' |
    sed 's/:$//'
  )
}

_set-gopath() {
  export GOPATH="$*"
}

_unset-gopath() {
  unset GOPATH
}

_gopath() {
  local go_path
  if _go-installed && go_path=$(_within-go-project); then
    _set-gopath "$go_path"
    _append-go-path "$GOPATH"
  elif [[ -n $GOPATH ]]; then
    _strip-go-path "$GOPATH"
    _unset-gopath
  fi
}

# vim: ft=sh