#!/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)
  result = keys.reduce({}) do |memo, key|
    response = fetch "http://#{etcd_host}:#{etcd_port}/v2/keys#{key}"
    vars = (JSON.parse(response)['node']['nodes'] || [])
      .map { |var| [var['key'].split('/').last, var['value']] }
      .to_h
    memo.merge(vars)
  end
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

sep = ARGV.index '--'
if sep
  keys = ARGV[0...sep]
  commands = ARGV[(sep + 1)..-1]
else
  keys = ARGV.take(1)
  commands = ARGV.drop(1)
end
if commands.empty?
  usage
  exit 1
end
exec env_vars(keys), *commands