#!/usr/bin/env lua

--Copyright (c) 2015 Igor Bogomazov <ygrex@ygrex.ru>

--Permission is hereby granted, free of charge, to any person obtaining a copy
--of this software and associated documentation files (the "Software"), to deal
--in the Software without restriction, including without limitation the rights
--to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
--copies of the Software, and to permit persons to whom the Software is
--furnished to do so, subject to the following conditions:

--The above copyright notice and this permission notice shall be included in
--all copies or substantial portions of the Software.

--THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
--IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
--FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
--AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
--LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
--OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
--SOFTWARE.

-- 2015051100 edition
-- Info: gopher://ygrex.ru/1/debian/parse-youtube/

local curl = assert(require "curl");
local rex = assert(require "rex_gnu");

-- curl callback
local function http_recv(dest, input)
	dest[#dest + 1] = input;
	return #input;
end;

-- download a page specified by URL
local function getpage(url)
	local c = assert(curl.easy_init());
	local head, body = {}, {};
	c:setopt(curl.OPT_FOLLOWLOCATION, 1);
	c:setopt(curl.OPT_URL, url);
	c:setopt(
		curl.OPT_HEADERFUNCTION,
		function(...) return http_recv(head, ...) end
	);
	c:setopt(
		curl.OPT_WRITEFUNCTION,
		function(...) return http_recv(body, ...) end
	);
	assert(c:perform());
	head = table.concat(head);
	body = table.concat(body);
	if not rex.find(head, [[^HTTP/[0-9]\.[0-9] 200 ]]) then
		io.stderr:write(
			("HTTP 200 expected, received:\n%s\n"):format(head)
		);
		os.exit(1);
	end;
	return body;
end;

-- split a string
local function split(str, sep)
	local r = {};
	local idx, a, b;
	repeat
		idx = (b or 0) + 1;
		a, b = str:find(sep, idx, true);
		if b then
			r[#r + 1] = str:sub(idx, b - #sep);
		else
			r[#r + 1] = str:sub(idx);
		end;
	until a == nil;
	return r;
end;

-- convert array of "key=value" to associative array pairs
local function assoc(array)
	local r = {};
	for i = 1, #array do
		local key, value = array[i]:match "^([^=]+)=(.*)$";
		if key then
			r[key] = value;
		else
			io.stderr:write(("k=v parse failure: %s.\n"):format(
				array[i]
			));
		end;
	end;
	return r;
end;

-- extract a stream map data
local function parse_page(body)
	local pattern = [["url_encoded_fmt_stream_map"[ \t]*:[ \t]*"([^"]+)"]]
	local raw = rex.match(body, pattern);
	if not raw then
		io.stderr:write(
			("Pattern not found on the page: %s.\n"):format(
				pattern
			)
		);
		os.exit(1);
	end;
	local map = split(raw, ",");
	for imap = 1, #map do
		map[imap] = assoc(split(curl.unescape(map[imap]), [[\u0026]]));
	end;
	return map;
end;

-- show parsed stream map data
local function show(map)
	for ivar = 1, #map do
		local var = map[ivar];
		print("  type:", var["type"]);
		print("  qlty:", var["quality"]);
		print("  conn:", var["conn"]);
		print("stream:", var["stream"]);
		print("   url:", var["url"]);
		print();
	end;
end;

-- entry point
local function main(...)
	local url = ...;
	show(parse_page(getpage(url)));
end;

return main(...);