require "http/client"
require "json" 

class RedditWrapper(T)
  JSON.mapping(
    kind: String,
    data: T)
end

class RedditChild
  JSON.mapping(
    url: String,
    name: String,
    title: String)
end

class RedditResponse
  JSON.mapping(
    modhash: String,
    dist: Int32,
    children: Array(RedditWrapper(RedditChild)))

  def self.from_subreddits(subreddits : Array(String))
    request_url = "https://www.reddit.com/r/#{subreddits.join "+" }/hot.json?limit=30"
    response = HTTP::Client.get(request_url, headers: HTTP::Headers {
      "User-agent" => "Joann-Pupper-Bot"
    })

    return nil unless body = response.body?

    begin
      RedditWrapper(RedditResponse).from_json body
    rescue
      nil
    end
  end

  def self.from_subreddit(subreddit)
    from_subreddits [subreddit]
  end

  def posts_matching(&block)
    children
      .map(&.data)
      .select { |it| yield it }
  end
end

def filter_reddit_json(json, completed, extensions = ["png", "json"])
  json.data.posts_matching do |post|
    extensions.any? { |it| post.url.ends_with? it } && !completed.includes? post.url
  end
end

def get_reddit_post(subreddit, completed)
    json = RedditResponse.from_subreddit subreddit
    post = json.try { |json| filter_reddit_json(json, completed).first? }
    post.try { |post| completed.push(post.name); { post.url, post.title } }
end