var trim = require('string.prototype.trim')
  , forEach = require('for-each')
  , isArray = function(arg) {
      return Object.prototype.toString.call(arg) === '[object Array]';
    }

module.exports = function (headers) {
  if (!headers)
    return {}

  var result = {}

  forEach(
      trim(headers).split('\n')
    , function (row) {
        var index = row.indexOf(':')
          , key = trim(row.slice(0, index)).toLowerCase()
          , value = trim(row.slice(index + 1))

        if (typeof(result[key]) === 'undefined') {
          result[key] = value
        } else if (isArray(result[key])) {
          result[key].push(value)
        } else {
          result[key] = [ result[key], value ]
        }
      }
  )

  return result
}