#!/usr/bin/env ruby

require 'open-uri'
require 'zlib'

if ARGV == []
  puts <<-'EOM'

go-install - download and extract golang official binary to /usr/local/go

Usage: go-install version

Examples
$ sudo go-install latest
$ sudo go-install 1.23.4
$ sudo go-install 1.22.10

PATH setting
export PATH=$PATH:/usr/local/go/bin
export PATH=$PATH:$HOME/go/bin

  EOM
  exit 1
end

if Process.uid != 0
  puts 'go-install requires privilege.'
  exit 1
end

versions = URI.open('https://golang.org/dl/').read.scan(/go(\d+\.\d+\.\d+)/).flatten.uniq
latest = versions.first

if ARGV[0] == 'latest'
  version = latest
elsif versions.include?(ARGV[0])
  version = ARGV[0]
else
  puts "version #{ARGV[0]} is not available."
  exit 1
end

uname = `uname -a` rescue ''
unless uname.include?('Linux')
  puts 'go-install supports only Linux.'
  exit 1
end

arch = uname.match(/x86_64|i.86/).to_s
if arch == ''
  puts 'go-install supports only x86_64 and x86.'
  exit 1
elsif arch == 'x86_64'
  arch = 'amd64'
else
  arch = '386'
end

verfile = '/usr/local/go/VERSION'
if FileTest.exist?(verfile)
  current_ver = open(verfile).read.split("\n").first.delete('go')
  if current_ver == version
    puts "version #{version} is already installed."
    exit 1
  end

  if FileTest.exist?("/usr/local/go#{current_ver}")
    suffix = Time.now.strftime('%Y%m%d.%H%M%S')
    backup_dir = "/usr/local/go#{current_ver}.#{suffix}"
  else
    backup_dir = "/usr/local/go#{current_ver}"
  end
  puts "Backup current version /usr/local/go --> #{backup_dir}"
  FileUtils.mv('/usr/local/go', backup_dir)
end

os = 'linux'
uri = "https://dl.google.com/go/go#{version}.#{os}-#{arch}.tar.gz"
cmd = 'tar -C /usr/local -xzf -'

puts "Download from #{uri}"
puts cmd

open("|#{cmd}", 'r+') { |io|
  io.write URI.open(uri).read
}

puts <<EOM

go#{version} is installed in /usr/local/go .

Add following lines to .profile or .bash_profile
export PATH=$PATH:/usr/local/go/bin
export PATH=$PATH:$HOME/go/bin

EOM