Sort a list of comments in date and reply order

commentsToTree.js

/**
 * Given a list of random comments, having dates and parentIds, this code
 * sorts the list following parent-child relationships and dates.
 *
 * Notation:
 *   C1R2 stands for 'Second reply to first comment'
 *   C2R2R1R1 stands for '1st Reply to the 1st Reply to the
 *                       2nd Reply of the 2nd Comment'
 *
 * Input:
 *
 * C1
 * C2
 * C2R1
 * C3
 * C2R1R1
 * C2R2
 * C4
 * C2R2R1
 * C2R2R2
 * C3R1
 * C2R2R1R1
 * C2R2R3
 * C4R1
 * C4R2
 *
 * Output:
 *
 * C4
 *   C4R1
 *   C4R2
 * C3
 *   C3R1
 * C2
 *   C2R1
 *     C2R1R1
 *   C2R2
 *     C2R2R1
 *       C2R2R1R1
 *     C2R2R2
 *     C2R2R3
 * C1
 *
 */

var comment = function(id, date, parentId, text) {
  this.id = id;
  this.date = date;
  this.parentId = parentId;
  this.text = text;
}

var comments = [];

/**
 * Users enter comments.

 * C1R2 stands for 'Second reply to first comment'
 */
comments.push(new comment(1, 2001, null, 'C1'));
comments.push(new comment(2, 2002, null, 'C2'));
comments.push(new comment(3, 2003, 2, 'C2R1'));
comments.push(new comment(4, 2004, null, 'C3'));
comments.push(new comment(5, 2005, 3, 'C2R1R1'));
comments.push(new comment(6, 2006, 2, 'C2R2'));
comments.push(new comment(7, 2007, null, 'C4'));
comments.push(new comment(8, 2008, 6, 'C2R2R1'));
comments.push(new comment(9, 2009, 6, 'C2R2R2'));
comments.push(new comment(10, 2010, 4, 'C3R1'));
comments.push(new comment(11, 2011, 8, 'C2R2R1R1'));
comments.push(new comment(12, 2012, 6, 'C2R2R3'));
comments.push(new comment(13, 2013, 7, 'C4R1'));
comments.push(new comment(14, 2014, 7, 'C4R2'));

// Sort the comments in descending date order
sortCommentsByDate(comments, true);

// Generate a tree structure
var commentsInTreeForm = buildTree(comments, null);

// Remove replies from first level of comments
commentsInTreeForm = removeRepliesFromFirstLevel(commentsInTreeForm);

// Transform the tree structure to a list
var commentArray = getArrayFromCommentTree(commentsInTreeForm);

// Output the result
console.log(commentArray);

/**
 * Implementation
 */
function buildTree(comments, parentId) {
  var output = [];

  for (var i = 0; i < comments.length; i++) {
    var comment = comments[i];

    if (comment.parentId === parentId) {
      comment.children = buildTree(comments, comment.id);
      output.push(comment);
    }
  }

  if (parentId) {
    // First level of comments are in desc date order, replies in asc date
    sortCommentsByDate(output, false);
  }

  return output;
}

function sortCommentsByDate(comments, desc) {
    comments.sort(function (first, second) {
      if (desc) {
          return second.date - first.date;
      } else {
          return first.date - second.date;
      }
    });
}

function removeRepliesFromFirstLevel(comments) {
  var newComments = [];

  for (var i = 0; i < comments.length; i++) {
    var comment = comments[i];

    if (!comment.parentId) {
      newComments.push(comment);
    }
  }

  return newComments;
}

function getArrayFromCommentTree(comments, commentArray) {
  if (!commentArray) {
    commentArray = [];
  }

  for (var i = 0; i < comments.length; i++) {
    var comment = comments[i];

    commentArray.push(comment);

    if (comment.children.length !== 0) {
      getArrayFromCommentTree(comment.children, commentArray);
    }
  }

  return commentArray;
}