index.js

module.exports = function detectCSV (chunk, opts) {
  opts = opts || {}
  if (Buffer.isBuffer(chunk)) chunk = chunk + ''
  var delimiters = opts.delimiters || [',', ';', '\t', '|']
  var newlines = opts.newlines || ['\n', '\r']

  var lines = chunk.split(/[\n\r]+/g)

  var delimiter = determineMost(lines[0], delimiters)
  var newline = determineMost(chunk, newlines)

  if (!delimiter) {
    if (isQuoted(lines[0])) return { newline: newline }
    return null
  }

  return {
    delimiter: delimiter,
    newline: newline
  }
}

function determineMost (chunk, items) {
  var ignoreString = false
  var itemCount = {}
  var maxValue = 0
  var maxChar
  var currValue
  items.forEach(function (item) {
    itemCount[item] = 0
  })
  for (var i = 0; i < chunk.length; i++) {
    if (chunk[i] === '"') ignoreString = !ignoreString
    else if (!ignoreString && chunk[i] in itemCount) {
      currValue = ++itemCount[chunk[i]]
      if (currValue > maxValue) {
        maxValue = currValue
        maxChar = chunk[i]
      }
    }
  }
  return maxChar
}

function isQuoted (chunk) {
  // is correctly quoted
  var nextQuote = false
  if (chunk[0] !== '"') return false
  if (chunk[chunk.length - 1] !== '"') return false
  for (var i = 1; i < chunk.length - 1; i++) {
    if (chunk[i] === '"') nextQuote = !nextQuote
    else if (nextQuote) return false
  }
  return !nextQuote
}