index.js

function isObject (obj) {
  return typeof obj === 'object' && obj !== null
}

function forEach (obj, cb) {
  if (Array.isArray(obj)) {
    obj.forEach(cb)
  } else if (isObject(obj)) {
    Object.keys(obj).forEach(function (key) {
      var val = obj[key]
      cb(val, key)
    })
  }
}

function getTreeDepth (obj) {
  var depth = 0

  if (Array.isArray(obj) || isObject(obj)) {
    forEach(obj, function (val) {
      if (Array.isArray(val) || isObject(val)) {
        var tmpDepth = getTreeDepth(val)
        if (tmpDepth > depth) {
          depth = tmpDepth
        }
      }
    })

    return depth + 1
  }

  return depth
}

function stringify (obj, options) {
  options = options || {}
  var indent = JSON.stringify([1], null, get(options, 'indent', 2)).slice(2, -3)
  var addMargin = get(options, 'margins', false)
  var addArrayMargin = get(options, 'arrayMargins', false)
  var addObjectMargin = get(options, 'objectMargins', false)
  var maxLength = (indent === '' ? Infinity : get(options, 'maxLength', 80))
  var maxNesting = get(options, 'maxNesting', Infinity)

  return (function _stringify (obj, currentIndent, reserved) {
    if (obj && typeof obj.toJSON === 'function') {
      obj = obj.toJSON()
    }

    var string = JSON.stringify(obj)

    if (string === undefined) {
      return string
    }

    var length = maxLength - currentIndent.length - reserved

    var treeDepth = getTreeDepth(obj)
    if (treeDepth <= maxNesting && string.length <= length) {
      var prettified = prettify(string, {
        addMargin: addMargin,
        addArrayMargin: addArrayMargin,
        addObjectMargin: addObjectMargin
      })
      if (prettified.length <= length) {
        return prettified
      }
    }

    if (isObject(obj)) {
      var nextIndent = currentIndent + indent
      var items = []
      var delimiters
      var comma = function (array, index) {
        return (index === array.length - 1 ? 0 : 1)
      }

      if (Array.isArray(obj)) {
        for (var index = 0; index < obj.length; index++) {
          items.push(
            _stringify(obj[index], nextIndent, comma(obj, index)) || 'null'
          )
        }
        delimiters = '[]'
      } else {
        Object.keys(obj).forEach(function (key, index, array) {
          var keyPart = JSON.stringify(key) + ': '
          var value = _stringify(obj[key], nextIndent,
                                 keyPart.length + comma(array, index))
          if (value !== undefined) {
            items.push(keyPart + value)
          }
        })
        delimiters = '{}'
      }

      if (items.length > 0) {
        return [
          delimiters[0],
          indent + items.join(',\n' + nextIndent),
          delimiters[1]
        ].join('\n' + currentIndent)
      }
    }

    return string
  }(obj, '', 0))
}

// Note: This regex matches even invalid JSON strings, but since we’re
// working on the output of `JSON.stringify` we know that only valid strings
// are present (unless the user supplied a weird `options.indent` but in
// that case we don’t care since the output would be invalid anyway).
var stringOrChar = /("(?:[^\\"]|\\.)*")|[:,\][}{]/g

function prettify (string, options) {
  options = options || {}

  var tokens = {
    '{': '{',
    '}': '}',
    '[': '[',
    ']': ']',
    ',': ', ',
    ':': ': '
  }

  if (options.addMargin || options.addObjectMargin) {
    tokens['{'] = '{ '
    tokens['}'] = ' }'
  }

  if (options.addMargin || options.addArrayMargin) {
    tokens['['] = '[ '
    tokens[']'] = ' ]'
  }

  return string.replace(stringOrChar, function (match, string) {
    return string ? match : tokens[match]
  })
}

function get (options, name, defaultValue) {
  return (name in options ? options[name] : defaultValue)
}

module.exports = stringify