E-mail validator | Lua 5.1+, LuaJit

--[[
    ####--------------------------------####
    #--# Author:   by uriid1            #--#
    #--# License:  GNU GPLv3            #--#
    #--# Telegram: @main_moderator      #--#
    #--# E-mail:   [email protected]   #--#
    ####--------------------------------####
--]]

local function email_validator(str)
    if type(str) ~= 'string' then
        return false, 'E-mail is not a string'
    end

    -- Capture
    str = str:lower()
    local re_local_part = '([a-z0-9%.!#%$%%&\'%*%+%-/=%?^_`{|}~%(%) "]+)'
    local re_domain = '([a-z0-9%(%)%-%.:%[%]]+)'
    local local_part, domain = str:match('^'..re_local_part..'@'..re_domain..'$')

    -- Check exists local-part and domain
    if not local_part or not domain then
        return false, 'Invalid local-part or domain name'
    end

    -- Check length
    if #local_part > 64 then
        return false, 'Local-part over 64 symbol'
    elseif #domain > 255 then
        return false, 'Domain over 255 symbol'
    end

    -- Check local-part in quotes
    local text_in_quotes = local_part:match('^"(.+)"$')
    if text_in_quotes then
        if text_in_quotes:match('[^a-z0-9!#$%%&\'%*%+%-/=%?^_ `{|}~%.]') then
           return false, 'Invalid characters in quotes local_part'
        end
    else
        if local_part:find('"') then
            return false, 'Invalid character " in local-part'
        end
    end

    -- Check comment
    local comment_in_local_part = local_part:match('(%(.+%))')
    if comment_in_local_part then
        local some_text, count_char = comment_in_local_part:gsub('[()]', '')
        if count_char > 2 then
            return false, 'Multiple comment in local-part are not allowed'
        end
        local_part = local_part:gsub('%('..some_text..'%)', '')
    end

    local comment_in_domain = domain:match('(%(.+%))')
    if comment_in_domain then
        local some_text, count_char = comment_in_domain:gsub('[()]', '')
        if count_char > 2 then
            return false, 'Multiple comment in domain are not allowed'
        end
        domain = domain:gsub('%('..some_text..'%)', '')
    end

    -- Check [] characters in local-part
    if local_part:match('%[.+%]') then
        return false, 'Invalid local-part, characters []'
    end

    -- Check correct local-part
    if local_part:find("%.%.") or
       local_part:find("%-%-") or
       local_part:find("%+%+") then
        return false, 'Too many periods in local-part'
    end

    -- Dot pos check in local-part
    if local_part:sub(1, 1) == '.' then
        return false, 'Dot cannot be the first character'
    elseif local_part:sub(-1) == '.' then
        return false, 'Dot cannot be the last character'
    end

    -- DNS domain check
    local hostname = domain:match('^[%d%a%-%.]+$')
    if hostname then
        if domain:sub(0, 1) == '.' or
           domain:sub(-1) == '.'   or
           domain:find('%.%.')
        then
            return false, 'Invalid domain name'
        end
    end

    -- IpV4
    local ipv4 = domain:match('^%[(.+)%]$')
    if ipv4 then
        local a, b, c, d = domain:match('(%d+)%.(%d+)%.(%d+)%.(%d+)')
        if a and b and c and d then
            if not ((tonumber(a) < 256) and
                    (tonumber(b) < 256) and
                    (tonumber(c) < 256) and
                    (tonumber(d) < 256))
            then
                return false, 'Invalid ipV4 domain'
            end
        end
    end

    -- ipV6
    local ipv6 = domain:match('^%[ipv6:(.-)%]$')
    if ipv6 then
        if not ipv6:find('^[a-f0-9]+'..(':[a-f0-9]+'):rep(7)..'$') then
            return false, 'Invalid IPv6 domain'
        end
    end

    return true
end


-- Test
print('[-- Valid --]')
local valid = {
    '[email protected]';
    '[email protected]';
    '[email protected]';
    'simple@[127.128.0.255]';
    'postmaster@[IPv6:2001:0db8:85a3:0000:0000:8a2e:0370:7334]';
    'postmaster(coment)@domain.lol';
    'postmaster@(comment)domain.lol';
}

for i = 1, #valid do
    local res, err = email_validator(valid[i])
    if res then
        print('Test:', i, res)
    else
        print('Test:', i, res, valid[i], err)
    end
end


print('\n[-- Invalid --]')
local invalid = {
    'blablabla';
    '   [email protected] ';
    '[email protected]';
    '[email protected]';
    'Abc.example.com';
    'A@b@[email protected]';
    'a"b(c)d,e:f;g<h>i[j\\k][email protected]';
    'just"not"[email protected]';
    'this is"not\a[email protected]';
    'this\\ still\\"not\\[email protected]';
    '1234567890123456789012345678901234567890123456789012345678901234+x@example.com';
    'i_like_underscore@but_its_not_allowed_in_this_part.example.com';
    'QA[icon]CHOCOLATE[icon]@test.com';
    '[]!@#$%^&@gmail.com';
}

for i = 1, #invalid do
    local res, err = email_validator(invalid[i])
    if not res then
        print('Test:', i, res)
    else
        print('Test:', i, res, invalid[i], err)
    end
end