local MultiQueue = {}
do
    local multi_queue = {}
    multi_queue.__index = multi_queue

    function multi_queue:__tostring()
        local str = "MultiQueue"
        for i=1,#self.Tags do
            str = str.."\n"..self.Tags[i].." = ["..self.Queues[ self.Tags[i] ].Count.."]{"..table.concat(self.Queues[ self.Tags[i] ].Items, ", ").."}"
        end
        return str
    end

    function multi_queue:Insert(tag, obj)
        local q = self.Queues[tag]
        if not q then error("Invalid tag") end

        q.Count = q.Count + 1
        q.Items[q.Count] = obj
    end

    function multi_queue:Remove(tag, obj)
        local q = self.Queues[tag]
        if not q then error("Invalid tag") end
        if not obj then return end

        local shift = 0
        local i = 1
        local c = q.Count
        while i <= c do
            q.Items[i] = q.Items[i + shift]
            if q.Items[i] == obj then
                shift = shift + 1
                q.Count = q.Count - 1
            else
                i = i + 1
            end
        end
    end

    -- Terminates when f returns a truthy value
    function multi_queue:Iterate(tag, f)
        local q = self.Queues[tag]
        if not q then error("Invalid tag") end

        local items = q.Items
        for i=1,q.Count do
            local res = f(items[i])
            if res then return res end
        end
    end

    -- Terminates when f returns a truthy value
    function multi_queue:IterateAll(f)
        for i=1,#self.Tags do
            local q = self.Queues[ self.Tags[i] ]
            local items = q.Items
            for i=1,q.Count do
                local res = f(items[i])
                if res then return res end
            end
        end
    end

    local new = function(tags)
        local queues = {}

        for i=1,#tags do
            queues[ tags[i] ] = {
                Count = 0,
                Items = {}
            }
        end

        local t = setmetatable({
            Queues = queues,
            Tags = tags
        }, multi_queue)

        return t
    end

    MultiQueue = setmetatable({
        new = new
    }, {
        __call = function(_, ...) return new(...) end
    })
end

return MultiQueue