/* eslint-env amd, node */

// https://github.com/umdjs/umd/blob/master/templates/returnExports.js
(function (root, factory) {
  'use strict';

  if (typeof define === 'function' && define.amd) {
    // AMD. Register as an anonymous module.
    define([], factory);
  } else if (typeof module === 'object' && module.exports) {
    // Node. Does not work with strict CommonJS, but
    // only CommonJS-like environments that support module.exports,
    // like Node.
    module.exports = factory();
  } else {
    // Browser globals (root is window)
    root.AnchorJS = factory();
    root.anchors = new root.AnchorJS();
  }
}(this, function () {
  'use strict';

  function AnchorJS(options) {
    this.options = options || {};
    this.elements = [];

    /**
     * Assigns options to the internal options object, and provides defaults.
     * @param {Object} opts - Options object
     */
    function _applyRemainingDefaultOptions(opts) {
      opts.icon = opts.hasOwnProperty('icon') ? opts.icon : '\ue9cb'; // Accepts characters (and also URLs?), like  '#', '¶', '❡', or '§'.
      opts.visible = opts.hasOwnProperty('visible') ? opts.visible : 'hover'; // Also accepts 'always' & 'touch'
      opts.placement = opts.hasOwnProperty('placement') ? opts.placement : 'right'; // Also accepts 'left'
      opts.class = opts.hasOwnProperty('class') ? opts.class : ''; // Accepts any class name.
      // Using Math.floor here will ensure the value is Number-cast and an integer.
      opts.truncate = opts.hasOwnProperty('truncate') ? Math.floor(opts.truncate) : 64; // Accepts any value that can be typecast to a number.
    }

    _applyRemainingDefaultOptions(this.options);

    /**
     * Checks to see if this device supports touch. Uses criteria pulled from Modernizr:
     * https://github.com/Modernizr/Modernizr/blob/da22eb27631fc4957f67607fe6042e85c0a84656/feature-detects/touchevents.js#L40
     * @return {Boolean} - true if the current device supports touch.
     */
    this.isTouchDevice = function() {
      return !!(('ontouchstart' in window) || window.DocumentTouch && document instanceof DocumentTouch);
    };

    /**
     * Add anchor links to page elements.
     * @param  {String|Array|Nodelist} selector - A CSS selector for targeting the elements you wish to add anchor links
     *                                            to. Also accepts an array or nodeList containing the relavant elements.
     * @return {this}                           - The AnchorJS object
     */
    this.add = function(selector) {
      var elements,
          elsWithIds,
          idList,
          elementID,
          i,
          index,
          count,
          tidyText,
          newTidyText,
          readableID,
          anchor,
          visibleOptionToUse,
          indexesToDrop = [];

      // We reapply options here because somebody may have overwritten the default options object when setting options.
      // For example, this overwrites all options but visible:
      //
      // anchors.options = { visible: 'always'; }
      _applyRemainingDefaultOptions(this.options);

      visibleOptionToUse = this.options.visible;
      if (visibleOptionToUse === 'touch') {
        visibleOptionToUse = this.isTouchDevice() ? 'always' : 'hover';
      }

      // Provide a sensible default selector, if none is given.
      if (!selector) {
        selector = 'h2, h3, h4, h5, h6';
      }

      elements = _getElements(selector);

      if (elements.length === 0) {
        return this;
      }

      _addBaselineStyles();

      // We produce a list of existing IDs so we don't generate a duplicate.
      elsWithIds = document.querySelectorAll('[id]');
      idList = [].map.call(elsWithIds, function assign(el) {
        return el.id;
      });

      for (i = 0; i < elements.length; i++) {
        if (this.hasAnchorJSLink(elements[i])) {
          indexesToDrop.push(i);
          continue;
        }

        if (elements[i].hasAttribute('id')) {
          elementID = elements[i].getAttribute('id');
        } else if (elements[i].hasAttribute('data-anchor-id')) {
          elementID = elements[i].getAttribute('data-anchor-id');
        } else {
          tidyText = this.urlify(elements[i].textContent);

          // Compare our generated ID to existing IDs (and increment it if needed)
          // before we add it to the page.
          newTidyText = tidyText;
          count = 0;
          do {
            if (index !== undefined) {
              newTidyText = tidyText + '-' + count;
            }

            index = idList.indexOf(newTidyText);
            count += 1;
          } while (index !== -1);
          index = undefined;
          idList.push(newTidyText);

          elements[i].setAttribute('id', newTidyText);
          elementID = newTidyText;
        }

        readableID = elementID.replace(/-/g, ' ');

        // The following code builds the following DOM structure in a more effiecient (albeit opaque) way.
        // '<a class="anchorjs-link ' + this.options.class + '" href="#' + elementID + '" aria-label="Anchor link for: ' + readableID + '" data-anchorjs-icon="' + this.options.icon + '"></a>';
        anchor = document.createElement('a');
        anchor.className = 'anchorjs-link ' + this.options.class;
        anchor.href = '#' + elementID;
        anchor.setAttribute('aria-label', 'Anchor link for: ' + readableID);
        anchor.setAttribute('data-anchorjs-icon', this.options.icon);

        if (visibleOptionToUse === 'always') {
          anchor.style.opacity = '1';
        }

        if (this.options.icon === '\ue9cb') {
          anchor.style.font = '1em/1 anchorjs-icons';

          // We set lineHeight = 1 here because the `anchorjs-icons` font family could otherwise affect the
          // height of the heading. This isn't the case for icons with `placement: left`, so we restore
          // line-height: inherit in that case, ensuring they remain positioned correctly. For more info,
          // see https://github.com/bryanbraun/anchorjs/issues/39.
          if (this.options.placement === 'left') {
            anchor.style.lineHeight = 'inherit';
          }
        }

        if (this.options.placement === 'left') {
          anchor.style.position = 'absolute';
          anchor.style.marginLeft = '-1em';
          anchor.style.paddingRight = '0.5em';
          elements[i].insertBefore(anchor, elements[i].firstChild);
        } else { // if the option provided is `right` (or anything else).
          anchor.style.paddingLeft = '0.375em';
          elements[i].appendChild(anchor);
        }
      }

      for (i = 0; i < indexesToDrop.length; i++) {
        elements.splice(indexesToDrop[i] - i, 1);
      }
      this.elements = this.elements.concat(elements);

      return this;
    };

    /**
     * Removes all anchorjs-links from elements targed by the selector.
     * @param  {String|Array|Nodelist} selector - A CSS selector string targeting elements with anchor links,
     *                                            OR a nodeList / array containing the DOM elements.
     * @return {this}                           - The AnchorJS object
     */
    this.remove = function(selector) {
      var index,
          domAnchor,
          elements = _getElements(selector);

      for (var i = 0; i < elements.length; i++) {
        domAnchor = elements[i].querySelector('.anchorjs-link');
        if (domAnchor) {
          // Drop the element from our main list, if it's in there.
          index = this.elements.indexOf(elements[i]);
          if (index !== -1) {
            this.elements.splice(index, 1);
          }
          // Remove the anchor from the DOM.
          elements[i].removeChild(domAnchor);
        }
      }
      return this;
    };

    /**
     * Removes all anchorjs links. Mostly used for tests.
     */
    this.removeAll = function() {
      this.remove(this.elements);
    };

    /**
     * Urlify - Refine text so it makes a good ID.
     *
     * To do this, we remove apostrophes, replace nonsafe characters with hyphens,
     * remove extra hyphens, truncate, trim hyphens, and make lowercase.
     *
     * @param  {String} text - Any text. Usually pulled from the webpage element we are linking to.
     * @return {String}      - hyphen-delimited text for use in IDs and URLs.
     */
    this.urlify = function(text) {
      // Regex for finding the nonsafe URL characters (many need escaping): & +$,:;=?@"#{}|^~[`%!'<>]./()*\
      var nonsafeChars = /[& +$,:;=?@"#{}|^~[`%!'<>\]\.\/\(\)\*\\]/g,
          urlText;

      // The reason we include this _applyRemainingDefaultOptions is so urlify can be called independently,
      // even after setting options. This can be useful for tests or other applications.
      if (!this.options.truncate) {
        _applyRemainingDefaultOptions(this.options);
      }

      // Note: we trim hyphens after truncating because truncating can cause dangling hyphens.
      // Example string:                                  // " ⚡⚡ Don't forget: URL fragments should be i18n-friendly, hyphenated, short, and clean."
      urlText = text.trim()                               // "⚡⚡ Don't forget: URL fragments should be i18n-friendly, hyphenated, short, and clean."
                    .replace(/\'/gi, '')                  // "⚡⚡ Dont forget: URL fragments should be i18n-friendly, hyphenated, short, and clean."
                    .replace(nonsafeChars, '-')           // "⚡⚡-Dont-forget--URL-fragments-should-be-i18n-friendly--hyphenated--short--and-clean-"
                    .replace(/-{2,}/g, '-')               // "⚡⚡-Dont-forget-URL-fragments-should-be-i18n-friendly-hyphenated-short-and-clean-"
                    .substring(0, this.options.truncate)  // "⚡⚡-Dont-forget-URL-fragments-should-be-i18n-friendly-hyphenated-"
                    .replace(/^-+|-+$/gm, '')             // "⚡⚡-Dont-forget-URL-fragments-should-be-i18n-friendly-hyphenated"
                    .toLowerCase();                       // "⚡⚡-dont-forget-url-fragments-should-be-i18n-friendly-hyphenated"

      return urlText;
    };

    /**
     * Determines if this element already has an AnchorJS link on it.
     * Uses this technique: http://stackoverflow.com/a/5898748/1154642
     * @param    {HTMLElemnt}  el - a DOM node
     * @return   {Boolean}     true/false
     */
    this.hasAnchorJSLink = function(el) {
      var hasLeftAnchor = el.firstChild && ((' ' + el.firstChild.className + ' ').indexOf(' anchorjs-link ') > -1),
          hasRightAnchor = el.lastChild && ((' ' + el.lastChild.className + ' ').indexOf(' anchorjs-link ') > -1);

      return hasLeftAnchor || hasRightAnchor || false;
    };

    /**
     * Turns a selector, nodeList, or array of elements into an array of elements (so we can use array methods).
     * It also throws errors on any other inputs. Used to handle inputs to .add and .remove.
     * @param  {String|Array|Nodelist} input - A CSS selector string targeting elements with anchor links,
     *                                         OR a nodeList / array containing the DOM elements.
     * @return {Array} - An array containing the elements we want.
     */
    function _getElements(input) {
      var elements;
      if (typeof input === 'string' || input instanceof String) {
        // See https://davidwalsh.name/nodelist-array for the technique transforming nodeList -> Array.
        elements = [].slice.call(document.querySelectorAll(input));
      // I checked the 'input instanceof NodeList' test in IE9 and modern browsers and it worked for me.
      } else if (Array.isArray(input) || input instanceof NodeList) {
        elements = [].slice.call(input);
      } else {
        throw new Error('The selector provided to AnchorJS was invalid.');
      }
      return elements;
    }

    /**
     * _addBaselineStyles
     * Adds baseline styles to the page, used by all AnchorJS links irregardless of configuration.
     */
    function _addBaselineStyles() {
      // We don't want to add global baseline styles if they've been added before.
      if (document.head.querySelector('style.anchorjs') !== null) {
        return;
      }

      var style = document.createElement('style'),
          linkRule =
          ' .anchorjs-link {'                       +
          '   opacity: 0;'                          +
          '   text-decoration: none;'               +
          '   -webkit-font-smoothing: antialiased;' +
          '   -moz-osx-font-smoothing: grayscale;'  +
          ' }',
          hoverRule =
          ' *:hover > .anchorjs-link,'              +
          ' .anchorjs-link:focus  {'                +
          '   opacity: 1;'                          +
          ' }',
          anchorjsLinkFontFace =
          ' @font-face {'                           +
          '   font-family: "anchorjs-icons";'       + // Icon from icomoon; 10px wide & 10px tall; 2 empty below & 4 above
          '   src: url(data:n/a;base64,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) format("truetype");' +
          ' }',
          pseudoElContent =
          ' [data-anchorjs-icon]::after {'          +
          '   content: attr(data-anchorjs-icon);'   +
          ' }',
          firstStyleEl;

      style.className = 'anchorjs';
      style.appendChild(document.createTextNode('')); // Necessary for Webkit.

      // We place it in the head with the other style tags, if possible, so as to
      // not look out of place. We insert before the others so these styles can be
      // overridden if necessary.
      firstStyleEl = document.head.querySelector('[rel="stylesheet"], style');
      if (firstStyleEl === undefined) {
        document.head.appendChild(style);
      } else {
        document.head.insertBefore(style, firstStyleEl);
      }

      style.sheet.insertRule(linkRule, style.sheet.cssRules.length);
      style.sheet.insertRule(hoverRule, style.sheet.cssRules.length);
      style.sheet.insertRule(pseudoElContent, style.sheet.cssRules.length);
      style.sheet.insertRule(anchorjsLinkFontFace, style.sheet.cssRules.length);
    }
  }

  return AnchorJS;
}));