local poolkey = KEYS[1]
local qkey = KEYS[2]
local activekey = KEYS[3]

local checkin_item = ARGV[1]

if redis.call('EXISTS', poolkey) == 0 then
    return { -1, {} } -- pool doesn't exist
end

if checkin_item ~= "" then
    redis.call("HDEL", activekey, checkin_item)
    redis.call("HINCRBY", poolkey, "complete_count", 1)
end

local pool_type = redis.call('HGET', poolkey, "order")
local allotment = tonumber(redis.call("HGET", poolkey, "concurrency"))
local active = redis.call("HLEN", activekey) + (redis.call("HGET", poolkey, "_active_count") or 0)

local pop_count = allotment - active

local popped_items = {}

if pop_count > 0 then
    if pool_type == "fifo" then
        popped_items = redis.call("LPOP", qkey, pop_count) or {}
    elseif pool_type == "lifo" then
        popped_items = redis.call("RPOP", qkey, pop_count) or {}
    elseif pool_type == "random" then
        popped_items = redis.call("SPOP", qkey, pop_count) or {}
    elseif pool_type == "priority" then
        local temp_items = redis.call("ZPOPMAX", qkey, pop_count) or {}
        for i,v in ipairs(temp_items) do
            if i % 2 == 1 then
                table.insert(popped_items, v)
            end
        end
    end
end

-- Reserve slots for these jobs while we return to Ruby and deserialize them
--  This could also be inlined by just storing a key in the queue and storing parameters
--  in a Hash, but this seems more efficient.
redis.call('HINCRBY', poolkey, "_active_count", #popped_items)

return { active, popped_items }