local tickets_key = KEYS[1]
local worker_index_key = KEYS[2]
local owners_key = KEYS[3]

local worker_id = ARGV[1]
local limit = tonumber(ARGV[2])

local function reply(status, tickets)
    return cjson.encode({status = status, tickets = tickets or {}})
end

local function decode_table(raw)
    if not raw then
        return nil
    end
    local ok, value = pcall(cjson.decode, raw)
    if not ok or type(value) ~= 'table' then
        return nil
    end
    return value
end

local function valid_ticket(ticket, proxy_id)
    return ticket and ticket.version == 1 and ticket.proxyId == proxy_id and
        ticket.workerId == worker_id and type(ticket.workerIndexKey) == 'string' and
        ticket.workerIndexKey == worker_index_key and tonumber(ticket.assignmentEpoch) and
        tonumber(ticket.assignmentEpoch) > 0 and tonumber(ticket.requiredSnapshotEpoch) and
        tonumber(ticket.requiredSnapshotEpoch) > tonumber(ticket.assignmentEpoch)
end

local function valid_assignment(assignment, ticket)
    return assignment and assignment.version == 1 and assignment.draining == true and
        assignment.proxyId == ticket.proxyId and assignment.workerId == ticket.workerId and
        tonumber(assignment.epoch) == tonumber(ticket.assignmentEpoch)
end

if type(worker_id) ~= 'string' or worker_id == '' or not limit or limit <= 0 then
    return reply('invalid')
end

local scan_limit = limit * 4
local ids = redis.call('ZRANGE', worker_index_key, 0, scan_limit - 1)
local tickets = {}
for _, proxy_id in ipairs(ids) do
    local raw = redis.call('HGET', tickets_key, proxy_id)
    local ticket = decode_table(raw)
    local assignment = decode_table(redis.call('HGET', owners_key, proxy_id))
    if valid_ticket(ticket, proxy_id) and valid_assignment(assignment, ticket) and #tickets < limit then
        tickets[#tickets + 1] = raw
    else
        redis.call('HDEL', tickets_key, proxy_id)
        redis.call('ZREM', worker_index_key, proxy_id)
    end
end
return reply('ok', tickets)