// Example app.js:

const CtrlEnv = require('ctrl-env')

const ctrlEnv = new CtrlEnv([
  ['SECRET']
, ['PORT', {required: false}]
], {
  prefix: 'TWITTER_FEED'
})

ctrlEnv.assert()

// Some Twitter Feed and Server pseudo code:

http.on('/feed', (request, response) => {
  Twitter.getFeed({
    handle: '_experiments'
  , secret: ctrlEnv.SECRET
  }, (error, feed) => {
    if (error) {
      throw error
    }

    response.send(feed)
  })
})

http.listen(ctrlEnv.PORT)

const exampleEnvVars = [
  // Variable is required and can be any value:
  ['REQUIRED_VARIABLE']

  // Variable is optional and can be any value:
, ['OPTIONAL_VARIABLE', {required: false}]

  // Variable is required and can only be yes or no:
, ['LIMITED_VARIABLE', {values: ['yes', 'no']}]

  // Variable is required and can only be an integer:
, ['TYPED_VARIABLE', {type: 'integer'}]

  // Variable is optional and can only be yes or no:
, ['OPTIONAL_LIMITED_VARIABLE', {required: false, values: ['yes', 'no']}]

  // Variable is required but is not prefixed:
, ['NODE_ENV', {prefixed: false}]
]

const ctrlEnv = new CtrlEnv(exampleEnvVars)

// Variables must be labeled TEST_(VARIABLENAME):
new CtrlEnv(..., {prefix: 'TEST'})

// Variables must be labeled TEST___(VARIABLENAME)
new CtrlEnv(..., {prefix: 'TEST', separator: '___'})