#!/usr/bin/env ruby
# Runs the wrapped command with envronment variables taken from etcd.

require 'json'
require 'net/http'

def usage
  puts "Usage: #{$PROGRAM_NAME} <etcd key> [ <etcd key> ... ] -- <command>"
end

def env_vars(keys)
  var = Array.new
  keys.each do |key|
    response = fetch "http://#{etcd_host}:#{etcd_port}/v2/keys#{key}"
    var << (JSON.parse(response)['node']['nodes'] || [])
      .map { |var| [var['key'].split('/').last, var['value']] }
      .to_h
  end
  var
end

def etcd_host
  host = (ENV['ETCD_HOST'] || `ip route | awk '/default/ { print $3 }'`).strip rescue ''
  raise 'etcd host not found' if host.empty?
  fetch "http://#{host}:#{etcd_port}/v2/keys/"
  host
end

def etcd_port
  ENV['ETCD_PORT'] || 4001
end

def fetch(uri_str, limit = 10)
  raise 'Too many HTTP redirects' if limit == 0
  response = Net::HTTP.get_response(URI(uri_str))
  case response
  when Net::HTTPSuccess then
    response.body
  when Net::HTTPRedirection then
    fetch(response['location'], limit - 1)
  else
    response.value
  end
end

if __FILE__ == $PROGRAM_NAME
  key_str, *commands = ARGV.join(" ").split(" -- ")
  keys = key_str.split(" ")
  if commands.empty?
    usage
    exit 1
  end
  exec env_vars(keys).reduce({}, :merge), *commands
end