#!/usr/bin/env bash

# Copyright 2021 The Kubernetes Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

set -o errexit
set -o nounset
set -o pipefail

[[ -n ${DEBUG:-} ]] && set -o xtrace

# Ensure the go tool exists and is a viable version.
verify_go_version() {
  if [[ -z "$(command -v go)" ]]; then
    if [[ "${INSTALL_GO:-"true"}" == "true" ]]; then
      curl -sSL https://golang.org/dl/go${GO_VERSION:-"1.16.3"}.linux-amd64.tar.gz | tar -C /usr/local -xzf -
      export PATH=/usr/local/go/bin:$PATH
      export PATH=$(go env GOPATH)/bin:$PATH
    else
      cat <<EOF
Can't find 'go' in PATH, please fix and retry.
See http://golang.org/doc/install for installation instructions.
EOF
      return 2
    fi
  fi

  local go_version
  IFS=" " read -ra go_version <<< "$(go version)"
  local minimum_go_version
  minimum_go_version=1.16.0
  if [[ "${minimum_go_version}" != $(echo -e "${minimum_go_version}\n${go_version[2]}" | sort -s -t. -k 1,1 -k 2,2n -k 3,3n | head -n1) && "${go_version[2]}" != "devel" ]]; then
    cat <<EOF
Detected go version: ${go_version[*]}.
Kubernetes requires ${minimum_go_version} or greater.
Please install ${minimum_go_version} or later.
EOF
    return 2
  fi
}

echo "Checking if go is available"
verify_go_version

go version

# Explicitly opt into go modules, even though we're inside a GOPATH directory
export GO111MODULE=on