Refactor some reddit polling code

src/joann-pupper-bot/reddit.cr

@@ -1,27 +1,59 @@
 require "http/client"
 require "json" 
 
-def get_reddit_json(subreddit)
-    request_url = "https://www.reddit.com/r/#{subreddit}/hot.json?limit=30"
-    response = HTTP::Client.get(request_url, headers: HTTP::Headers {
-        "User-agent" => "Joann-Pupper-Bot"
-    })
-    response.body?.try { |body| JSON.parse(body) }
+class RedditWrapper(T)
+  JSON.mapping(
+    kind: String,
+    data: T)
 end
 
-def filter_reddit_json(json, completed)
-    json["data"]["children"]
-        .as_a
-        .map(&.["data"])
-        .select do |it| 
-            url = it["url"].as_s
-            name = it["name"].as_s
-            !completed.includes?(name) && (url.ends_with?(".png") || url.ends_with?(".jpg"))
-        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 = get_reddit_json(subreddit)
+    json = RedditResponse.from_subreddit subreddit
     post = json.try { |json| filter_reddit_json(json, completed).first? }
-    post.try { |post| completed.push(post["name"].as_s); { post["url"].as_s, post["title"].as_s } }
+    post.try { |post| completed.push(post.name); { post.url, post.title } }
 end