join_captcha.lua
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join_captcha.lua
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	--[[
	mattata v2.0 - Join Captcha Plugin
	Handles captcha verification for new members joining the group.
	]]

	local plugin = {}
	plugin.name = 'join_captcha'
	plugin.category = 'admin'
	plugin.description = 'Captcha challenge for new members'
	plugin.commands = {}
	plugin.help = ''
	plugin.group_only = true
	plugin.admin_only = false

	local json = require('dkjson')

	-- Generate a simple math captcha
	local function generate_captcha()
	math.randomseed(os.time())
	local a = math.random(1, 20)
	local b = math.random(1, 20)
	local operators = { '+', '-' }
	local op = operators[math.random(1, 2)]
	local answer
	if op == '+' then
	answer = a + b
	else
	-- Ensure non-negative result
	if a < b then a, b = b, a end
	answer = a - b
	end
	return string.format('%d %s %d', a, op, b), tostring(answer)
	end

	-- Generate wrong answers for the keyboard
	local function generate_options(correct_answer)
	local options = { correct_answer }
	local correct_num = tonumber(correct_answer)
	while #options < 4 do
	local wrong = correct_num + math.random(-5, 5)
	if wrong ~= correct_num and wrong >= 0 then
	local str = tostring(wrong)
	local duplicate = false
	for _, v in ipairs(options) do
	if v == str then duplicate = true; break end
	end
	if not duplicate then
	table.insert(options, str)
	end
	end
	end
	-- Shuffle
	for i = #options, 2, -1 do
	local j = math.random(1, i)
	options[i], options[j] = options[j], options[i]
	end
	return options
	end

	function plugin.on_member_join(api, message, ctx)
	if not ctx.is_group then return end

	-- Check if captcha is enabled
	local enabled = ctx.db.execute(
	"SELECT value FROM chat_settings WHERE chat_id = $1 AND key = 'captcha_enabled'",
	{ message.chat.id }
	)
	if not enabled or #enabled == 0 or enabled[1].value ~= 'true' then
	return
	end

	if not require('src.core.permissions').can_restrict(api, message.chat.id) then return end

	local timeout_result = ctx.db.execute(
	"SELECT value FROM chat_settings WHERE chat_id = $1 AND key = 'captcha_timeout'",
	{ message.chat.id }
	)
	local timeout = (timeout_result and #timeout_result > 0) and tonumber(timeout_result[1].value) or 300

	for _, new_member in ipairs(message.new_chat_members) do
	if new_member.is_bot then goto continue end

	-- Restrict the new member
	api.restrict_chat_member(message.chat.id, new_member.id, {
	can_send_messages = false,
	can_send_audios = false,
	can_send_documents = false,
	can_send_photos = false,
	can_send_videos = false,
	can_send_video_notes = false,
	can_send_voice_notes = false,
	can_send_polls = false,
	can_send_other_messages = false,
	can_add_web_page_previews = false
	}, { until_date = os.time() + timeout })

	-- Generate captcha
	local question, answer = generate_captcha()
	local options = generate_options(answer)

	-- Build keyboard
	local keyboard = { inline_keyboard = { {} } }
	for _, opt in ipairs(options) do
	table.insert(keyboard.inline_keyboard[1], {
	text = opt,
	callback_data = string.format('join_captcha:%s:%s:%s', message.chat.id, new_member.id, opt)
	})
	end

	local tools = require('telegram-bot-lua.tools')
	local text = string.format(
	'Welcome, <a href="tg://user?id=%d">%s</a>! Please solve this to verify you\'re human:\n\n<b>What is %s?</b>\n\nYou have %d seconds.',
	new_member.id,
	tools.escape_html(new_member.first_name),
	question,
	timeout
	)

	local sent = api.send_message(message.chat.id, text, 'html', false, false, nil, json.encode(keyboard))

	-- Store captcha state
	if sent and sent.result then
	ctx.session.set_captcha(message.chat.id, new_member.id, answer, sent.result.message_id, timeout)
	end

	::continue::
	end
	end

	function plugin.on_callback_query(api, callback_query, message, ctx)
	local data = callback_query.data
	if not data then return end

	local chat_id, user_id, selected = data:match('^(%-?%d+):(%d+):(.+)$')
	if not chat_id then return end

	chat_id = tonumber(chat_id)
	user_id = tonumber(user_id)

	-- Only the joining user can answer
	if callback_query.from.id ~= user_id then
	return api.answer_callback_query(callback_query.id, 'This captcha is not for you.')
	end

	local captcha = ctx.session.get_captcha(chat_id, user_id)
	if not captcha then
	return api.answer_callback_query(callback_query.id, 'This captcha has expired.')
	end

	if selected == captcha.text then
	-- Correct answer - unrestrict user
	api.restrict_chat_member(chat_id, user_id, {
	can_send_messages = true,
	can_send_audios = true,
	can_send_documents = true,
	can_send_photos = true,
	can_send_videos = true,
	can_send_video_notes = true,
	can_send_voice_notes = true,
	can_send_polls = true,
	can_send_other_messages = true,
	can_add_web_page_previews = true
	})
	ctx.session.clear_captcha(chat_id, user_id)

	local tools = require('telegram-bot-lua.tools')
	api.edit_message_text(message.chat.id, message.message_id, string.format(
	'<a href="tg://user?id=%d">%s</a> has been verified. Welcome!',
	user_id, tools.escape_html(callback_query.from.first_name)
	), 'html')
	api.answer_callback_query(callback_query.id, 'Correct! Welcome to the group.')
	else
	-- Wrong answer
	api.answer_callback_query(callback_query.id, 'Wrong answer. Try again!')
	end
	end

	return plugin

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