var validateMessage = function()

in scripts/validate-commit-msg.js [41:141]
69 lines of code
23 McCabe index (conditional complexity)

var validateMessage = function (raw) {
  var types = (config.types = config.types || 'conventional-commit-types')

  // resolve types from a module
  if (typeof types === 'string' && types !== '*') {
    types = Object.keys(require(types).types)
  }

  var messageWithBody = (raw || '')
    .split('\n')
    .filter(function (str) {
      return str.indexOf('#') !== 0
    })
    .join('\n')

  var message = messageWithBody.split('\n').shift()

  if (message === '') {
    console.log('Aborting commit due to empty commit message.')
    return false
  }

  var isValid = true

  if (MERGE_COMMIT_PATTERN.test(message)) {
    console.log('Merge commit detected.')
    return true
  }

  if (IGNORED.test(message)) {
    console.log('Commit message validation ignored.')
    return true
  }

  var match = PATTERN.exec(message)

  if (!match) {
    error('does not match "<type>(<scope>): <subject>" !')
    isValid = false
  } else {
    var firstLine = match[1]
    var squashing = !!match[2]
    var type = match[3]
    // var scope = match[4]
    var subject = match[5]

    var SUBJECT_PATTERN = new RegExp(config.subjectPattern || '.+')
    var SUBJECT_PATTERN_ERROR_MSG =
      config.subjectPatternErrorMsg || 'subject does not match subject pattern!'

    if (firstLine.length > MAX_LENGTH && !squashing) {
      error('is longer than %d characters !', MAX_LENGTH)
      isValid = false
    }

    if (types !== '*' && types.indexOf(type) === -1) {
      error(
        '"%s" is not allowed type ! Valid types are: %s',
        type,
        types.join(', ')
      )
      isValid = false
    }

    if (!SUBJECT_PATTERN.exec(subject)) {
      error(SUBJECT_PATTERN_ERROR_MSG)
      isValid = false
    }
  }

  // Some more ideas, do want anything like this ?
  // - Validate the rest of the message (body, footer, BREAKING CHANGE annotations)
  // - allow only specific scopes (eg. fix(docs) should not be allowed ?
  // - auto correct the type to lower case ?
  // - auto correct first letter of the subject to lower case ?
  // - auto add empty line after subject ?
  // - auto remove empty () ?
  // - auto correct typos in type ?
  // - store incorrect messages, so that we can learn

  isValid = isValid || config.warnOnFail

  if (isValid) {
    // exit early and skip messaging logics
    return true
  }

  var argInHelp = config.helpMessage && config.helpMessage.indexOf('%s') !== -1

  if (argInHelp) {
    console.log(config.helpMessage, messageWithBody)
  } else if (message) {
    console.log(message)
  }

  if (!argInHelp && config.helpMessage) {
    console.log(config.helpMessage)
  }

  return false
}