Add get_longest_chain function and comments.

update_chain.php

@@ -7,6 +7,7 @@ if ($conn->connect_error) {
     die("Connection failed: " . $conn->connect_error);
 }
 
+# Sends the given text wrapped in triple backticks as Markdown.
 function send_code($post_message) {
   global $bot_api;
   global $chat_id;
@@ -23,6 +24,8 @@ function send_code($post_message) {
   $result = file_get_contents($url, false, $context);
 }
 
+# Takes a user array as input. Checks who follows him/her and adds
+# him/her to $output array. Exits when a user is followed by no one.
 function get_chain_from_user($user) {
   global $conn;
   $output = array($user);
@@ -43,5 +46,29 @@ function get_chain_from_user($user) {
   return $output;
 }
 
+# First generates a list of people not following anyone (end_points)
+# Then runs get_chain_from_user on all of them and stores them in
+# $chains array. Then compares the arrays inside $chains array and
+# returns the longest one.
+function get_longest_chain() {
+  global $conn;
+  $query = "SELECT user_id, username FROM users WHERE follows = -1;";
+  $end_points = $conn->query($query);
+  if ($end_points->num_rows == 0) {
+    return array();
+  }
+  $chains = array();
+  while ($end_point = $end_points->fetch_assoc()){
+    $chain = get_chain_from_user($end_points);
+    array_push($chains, $chain);
+  }
+  $longest_chain_index = 0;
+  for ($i = 0; $i < count($chains); $i++){
+    if (count($chains[$i]) > count($chains[$longest_chain_index])) {
+      $longest_chain_index = $i;
+    }
+  }
+  return $chains[$longest_chain_index];
+}
 $conn->close();
 ?>