Modification of https://github.com/TingPing/plugins/blob/master/HexChat/playback.lua to store state locally

my_playback.lua

local lgi = require('lgi')
local GLib = lgi.require('GLib')

hexchat.register('Playback', '1', "Integration with ZNC's Playback module")

--[[
 This should behave like this:
  
   On connect (end of MOTD):
       if new server, play all
       if old server, play all after latest timestamp
   On close query:
       clear all
   On new message:
       update latest timestamp
]]

local CAP_NAME = 'znc.in/playback'
local servers = hexchat.pluginprefs -- Table of id to timestamp

-- Request capability
hexchat.hook_print('Capability List', function (args)
	if args[2]:find(CAP_NAME) then
		hexchat.command('quote CAP REQ :' .. CAP_NAME)

		local ctx = hexchat.props.context

		hexchat.hook_timer(1, function ()
			-- Emit this event right after the current one
			if ctx:set() then
				hexchat.emit_print('Capability Request', CAP_NAME)
			end
		end)
	end
end)

-- Capability supported
hexchat.hook_print('Capability Acknowledgement', function (args)
	local server_id = hexchat.props.context:get_info('host')
	
	hexchat.emit_print('Capability Request', CAP_NAME)

	if args[2]:find(CAP_NAME) and not servers[server_id] then
		servers[server_id] = 0 -- New server
	end
end)

function connect_hook(word, word_eol)
	local server_id = hexchat.props.context:get_info('host')
	local timestamp = servers[server_id]

	if timestamp then
		hexchat.command('quote PRIVMSG *playback :play * ' .. tostring(timestamp))
	end
end

-- On successful connection play history
hexchat.hook_server('376', connect_hook)
hexchat.hook_server('422', connect_hook)

-- Store the timestamp of the latest message on the server
hexchat.hook_server_attrs('PRIVMSG', function (word, word_eol, attrs)
	local server_id = hexchat.props.context:get_info('host')
	if servers[server_id] then
		timestamp = GLib.get_real_time() / 1000000 -- epoch in seconds with milisecond precision UTC
		servers[server_id] = timestamp
	end
end, hexchat.PRI_LOWEST)