Requirements

Your task will be to build a simplified version of the Reddit feed API that powers http://old.reddit.com. Please use Go as the programming language. This will be a REST API that allows users to do the following:

Create new posts. Posts should be validated for correctness. They should have the following fields:

1. Title
2. Author: This should be a random 8 character string prefixed with t2_. The 8 character string should only contain lowercase letters and numbers. For example, my user ID is t2_11qnzrqv.
3. Link: This should be a valid URL. It's ok if your validation is not perfect.
4. Subreddit: The subreddit associated with this post.
5. Content: In the case of a text-only post. A post cannot have both a link and content populated.
6. Score: The total score associated with the upvotes and downvotes of a post.
7. Promoted: A boolean field indicating whether or not the post is an ad or not.
8. NSFW: Not safe for work. A boolean that indicates whether or not the post is safe for work

Generate a feed of posts. This feed should have the following characteristics:

1. It should be ranked by score, and the post with the highest score should show up first.
2. It should be paginated, and each page should have at most 27 posts. Your API should support fetching a specific page in the feed.
3. If a page has 3 posts or greater, the second post should always be a promoted post if a promoted post is available, regardless of the score.
4. If a page has greater than 16 posts, the 16th post should always be a promoted post if a promoted post is available, regardless of the score.
5. As an exception to rules 3 and 4, a promoted post should never be shown adjacent to an NSFW post. You can ignore rules 3 and 4 in this case.