#!/usr/bin/env bash

#
# Go Version Switcher/Downloader
# THIS SCRIPT SHOULD BE SOURCED UNLESS YOU WANT TO KEEP A STATIC GOROOT OF: /opt/goroot/go
# example usage: source ./go_version_switcher.sh 1.11.5
#

# Some defaults
GO_ROOT_PATH=/opt/goroot

# required binaries
BINS_REQ=(uname curl tar basename)

# validate args
if [ "$#" -ne 1 ]; then

    echo "Usage: $(basename "$0") <list,latest,go_version>"
    echo " --> list installed versions: $(basename "$0") list"
    echo " --> install and switch to latest version: $(basename "$0") latest"
    echo " --> install and switch to custom version: $(basename "$0") 1.13.1"
    exit 1
fi

# set vars
GO_VERSION="${1}"


# Functions --------------------------------------------------------------------

# check for Required program(s)
CHECK_REQUIREMENTS() {
  for p in ${BINS_REQ[@]}; do
    hash "$p" 2>&- || \
    { echo >&2 " Required program \"$p\" not installed."; exit 1; }
  done
}

# return GO OS if supported
VALIDATE_OS() {
  case "${OSTYPE}" in
    linux-gnu*) echo "linux"
                ;;
    darwin*)    echo "darwin"
                ;;
    *)          echo " !! error unsupported OS: $OSTYPE"
                exit 1
                ;;
  esac
}

# return GO ARCH if supported
VALIDATE_ARCH() {
  case "$(uname -m)" in
    x86_64) echo "amd64"
            ;;
    i386)   echo "386"
            ;;
    i686)   echo "386"
            ;;
    s390x)  echo "s390x"
            ;;
    *)      echo " !! error unsupported arch: $(uname -m)"
            exit 1
            ;;
    esac
}

# go install logic
INSTALL_GO() {
  if [ ! -d "${GO_ROOT_PATH}" ]; then
    echo ">> CREATING GO_ROOT_PATH DIR: ${GO_ROOT_PATH}"
    mkdir -p "${GO_ROOT_PATH}"
  fi

  if [ ! -d "${GO_ROOT_PATH}/go${GO_VERSION}/go" ]; then
    echo ">> ${GO_VERSION} not found. Attempting download and install..."
    CHECK_GO_URL
    echo ">> downloading ${GO_URL}"
    curl -L -o ${GO_ROOT_PATH}/go.tgz ${GO_URL}
    if [ $? -ne 0 ] ; then
      echo " !! error downloading go version: ${GO_VERSION}"
      exit 1
    fi
    mkdir ${GO_ROOT_PATH}/go${GO_VERSION} && \
    tar -xf ${GO_ROOT_PATH}/go.tgz -C ${GO_ROOT_PATH}/go${GO_VERSION} && rm -rf ${GO_ROOT_PATH}/go.tgz
    if [ $? -ne 0 ] ; then
      echo " !! error extracting tar: ${GO_ROOT_PATH}/go.tgz"
      exit 1
    fi
  else
    echo ">> ${GO_VERSION} already installed"
  fi

  echo "setting GOROOT=${GO_ROOT_PATH}/go${GO_VERSION}/go"
  export GOROOT=${GO_ROOT_PATH}/go${GO_VERSION}/go
  # TODO perhaps symlink go bin to an existing path instead of adding it...
  export PATH=${PATH}:${GOROOT}/bin

  # rewrite default link, in case you dont want to source this script
  echo "re-linking default GOROOT path"
  ln -sTvf ${GO_ROOT_PATH}/go${GO_VERSION}/go ${GO_ROOT_PATH}/go
}

# check if this version of go is valid/available
CHECK_GO_URL() {
  RES_CODE=$(curl -w "%{http_code}" -s -I --output /dev/null ${GO_URL})
  if [ ${RES_CODE} -ne 200 ] ; then
    echo " !! error downloading go version (http status: ${RES_CODE})"
    exit 1
  fi
}

# list previously installed versions
LIST_INSTALLED_VERSIONS() {
  echo ">> INSTALLED GO VERSIONS:"
  for v in $(ls -d ${GO_ROOT_PATH}/go1*); do
    basename "${v}"
  done
}

# displays the current latest version of go from official url
GET_LATEST_VERSION() {
  echo -n ">> LATEST RELEASED VERSION:"
  curl -s https://golang.org/VERSION?m=text
}

# MAIN -------------------------------------------------------------------------
CHECK_REQUIREMENTS


case "${GO_VERSION}" in
  list*)      LIST_INSTALLED_VERSIONS
              exit 0
              ;;
  latest*)    GET_LATEST_VERSION
              GO_VERSION=$(curl -s https://golang.org/VERSION?m=text | sed 's/[^0-9\.]*//g')
              ;;
esac

GO_OS=$(VALIDATE_OS)
GO_ARCH=$(VALIDATE_ARCH)
GO_URL="https://storage.googleapis.com/golang/go${GO_VERSION}.${GO_OS}-${GO_ARCH}.tar.gz"
INSTALL_GO