alias SigProc = Proc(Array(String), Int32, Array(String)) def fetch_decrypt_function(id = "CvFH_6DNRCY") document = YT_POOL.client &.get("/watch?v=#{id}&gl=US&hl=en").body url = document.match(/src="(?\/yts\/jsbin\/player_ias-[^\/]+\/en_US\/base.js)"/).not_nil!["url"] player = YT_POOL.client &.get(url).body function_name = player.match(/^(?[^=]+)=function\(\w\){\w=\w\.split\(""\);[^\. ]+\.[^( ]+/m).not_nil!["name"] function_body = player.match(/^#{Regex.escape(function_name)}=function\(\w\){(?[^}]+)}/m).not_nil!["body"] function_body = function_body.split(";")[1..-2] var_name = function_body[0][0, 2] var_body = player.delete("\n").match(/var #{Regex.escape(var_name)}={(?(.*?))};/).not_nil!["body"] operations = {} of String => SigProc var_body.split("},").each do |operation| op_name = operation.match(/^[^:]+/).not_nil![0] op_body = operation.match(/\{[^}]+/).not_nil![0] case op_body when "{a.reverse()" operations[op_name] = ->(a : Array(String), b : Int32) { a.reverse } when "{a.splice(0,b)" operations[op_name] = ->(a : Array(String), b : Int32) { a.delete_at(0..(b - 1)); a } else operations[op_name] = ->(a : Array(String), b : Int32) { c = a[0]; a[0] = a[b % a.size]; a[b % a.size] = c; a } end end decrypt_function = [] of {SigProc, Int32} function_body.each do |function| function = function.lchop(var_name).delete("[].") op_name = function.match(/[^\(]+/).not_nil![0] value = function.match(/\(\w,(?[\d]+)\)/).not_nil!["value"].to_i decrypt_function << {operations[op_name], value} end return decrypt_function end def decrypt_signature(fmt : Hash(String, JSON::Any)) return "" if !fmt["s"]? || !fmt["sp"]? sp = fmt["sp"].as_s sig = fmt["s"].as_s.split("") DECRYPT_FUNCTION.each do |proc, value| sig = proc.call(sig, value) end return "&#{sp}=#{sig.join("")}" end