'use strict';

/**
 * Utility functions
 */

function typeOf(obj) {
  return Object.prototype.toString.call(obj);
}

function isString(obj) {
  return typeOf(obj) === '[object String]';
}

var hasOwn = Object.prototype.hasOwnProperty;

function has(object, key) {
  return object
    ? hasOwn.call(object, key)
    : false;
}

// Extend objects
//
function assign(obj /*from1, from2, from3, ...*/) {
  var sources = [].slice.call(arguments, 1);

  sources.forEach(function (source) {
    if (!source) { return; }

    if (typeof source !== 'object') {
      throw new TypeError(source + 'must be object');
    }

    Object.keys(source).forEach(function (key) {
      obj[key] = source[key];
    });
  });

  return obj;
}

////////////////////////////////////////////////////////////////////////////////

var UNESCAPE_MD_RE = /\\([\\!"#$%&'()*+,.\/:;<=>?@[\]^_`{|}~-])/g;

function unescapeMd(str) {
  if (str.indexOf('\\') < 0) { return str; }
  return str.replace(UNESCAPE_MD_RE, '$1');
}

////////////////////////////////////////////////////////////////////////////////

function isValidEntityCode(c) {
  /*eslint no-bitwise:0*/
  // broken sequence
  if (c >= 0xD800 && c <= 0xDFFF) { return false; }
  // never used
  if (c >= 0xFDD0 && c <= 0xFDEF) { return false; }
  if ((c & 0xFFFF) === 0xFFFF || (c & 0xFFFF) === 0xFFFE) { return false; }
  // control codes
  if (c >= 0x00 && c <= 0x08) { return false; }
  if (c === 0x0B) { return false; }
  if (c >= 0x0E && c <= 0x1F) { return false; }
  if (c >= 0x7F && c <= 0x9F) { return false; }
  // out of range
  if (c > 0x10FFFF) { return false; }
  return true;
}

function fromCodePoint(c) {
  /*eslint no-bitwise:0*/
  if (c > 0xffff) {
    c -= 0x10000;
    var surrogate1 = 0xd800 + (c >> 10),
        surrogate2 = 0xdc00 + (c & 0x3ff);

    return String.fromCharCode(surrogate1, surrogate2);
  }
  return String.fromCharCode(c);
}

var NAMED_ENTITY_RE   = /&([a-z#][a-z0-9]{1,31});/gi;
var DIGITAL_ENTITY_TEST_RE = /^#((?:x[a-f0-9]{1,8}|[0-9]{1,8}))/i;
var entities = require('./entities');

function replaceEntityPattern(match, name) {
  var code = 0;

  if (has(entities, name)) {
    return entities[name];
  } else if (name.charCodeAt(0) === 0x23/* # */ && DIGITAL_ENTITY_TEST_RE.test(name)) {
    code = name[1].toLowerCase() === 'x' ?
      parseInt(name.slice(2), 16)
    :
      parseInt(name.slice(1), 10);
    if (isValidEntityCode(code)) {
      return fromCodePoint(code);
    }
  }
  return match;
}

function replaceEntities(str) {
  if (str.indexOf('&') < 0) { return str; }

  return str.replace(NAMED_ENTITY_RE, replaceEntityPattern);
}

////////////////////////////////////////////////////////////////////////////////

var HTML_ESCAPE_TEST_RE = /[&<>"]/;
var HTML_ESCAPE_REPLACE_RE = /[&<>"]/g;
var HTML_REPLACEMENTS = {
  '&': '&amp;',
  '<': '&lt;',
  '>': '&gt;',
  '"': '&quot;'
};

function replaceUnsafeChar(ch) {
  return HTML_REPLACEMENTS[ch];
}

function escapeHtml(str) {
  if (HTML_ESCAPE_TEST_RE.test(str)) {
    return str.replace(HTML_ESCAPE_REPLACE_RE, replaceUnsafeChar);
  }
  return str;
}

////////////////////////////////////////////////////////////////////////////////

exports.assign            = assign;
exports.isString          = isString;
exports.has               = has;
exports.unescapeMd        = unescapeMd;
exports.isValidEntityCode = isValidEntityCode;
exports.fromCodePoint     = fromCodePoint;
exports.replaceEntities   = replaceEntities;
exports.escapeHtml        = escapeHtml;