local _ODA = { group = 0, group_version = false, aid = 0, data = 0, handler = false }

function _ODA.new(group, group_version, aid, data, handler)
    local instance = { group = group or 0, group_version = group_version or false, aid = aid or 0, data = data or 0, handler = handler or false }
    setmetatable(instance, { __index = _ODA })
    return instance
end

local _RDS_ODAs = {}
local _RDS_ODA_pointer = 1

---Registers an ODA to be used in the O of the group sequence. ODAs are stored as state data, thus running reset_rds will clear it
---Groups 14, 15, 2, 0 cannot be registered either version, groups 10, 4, 1 can be only registered as B, any other is free to take
---Group 3A will mean that there will be no group handler for this ODA, meaning it can only be interacted with via the 3A AID group, handler set is not possible with such groups
---@param group integer
---@param group_version boolean
---@param aid integer
---@param data integer
---@return integer oda_id
function ext.register_oda(group, group_version, aid, data)
    if group == 14 or group == 15 or group == 2 or group == 0 then error("Group is incorrect", 2) end
    if (group == 10 or group == 4 or group == 1) and group_version then error("Group is incorrect", 2) end
    local oda = _ODA.new(group, group_version, aid, data, false)
    for i = 1, #_RDS_ODAs do
        if _RDS_ODAs[i] == false then
            _RDS_ODAs[i] = oda
            return i
        end
    end
    table.insert(_RDS_ODAs, oda)
    return #_RDS_ODAs
end

---Unregisters an ODA, this stops the handler or AID being called/sent
---@param oda_id integer
function ext.unregister_oda(oda_id)
    if oda_id < 1 or oda_id > #_RDS_ODAs or _RDS_ODAs[oda_id] == false then error("Invalid ODA ID: " .. tostring(oda_id), 2) end

    _RDS_ODAs[oda_id] = false

    if _RDS_ODA_pointer == oda_id then _RDS_ODA_pointer = (_RDS_ODA_pointer % #_RDS_ODAs) + 1 end
end


---Sets the id_data for a existing ODA group
---@param oda_id integer
---@param data integer
function ext.set_oda_id_data(oda_id, data)
    if oda_id < 1 or oda_id > #_RDS_ODAs or _RDS_ODAs[oda_id] == false then error("Invalid ODA ID: " .. tostring(oda_id), 2) end
    _RDS_ODAs[oda_id].data = data
end

---Sets a function to handle the ODA data generation. 
---The handler is called when the group sequence 'K' slot is processed.
---The function must return 3 integers representing RDS Blocks B, C, and D.
---Please note that you do not need to compute the block A to indentify the group and group version, that will be done for you and EVERY SINGLE group has PTY and TP inserted (and also PI if its a B)
---You are asked to set groups B last 5 bits, leave rest 0
---@param oda_id integer The ID returned by register_oda
---@param fun ODAHandler
function ext.set_oda_handler(oda_id, fun)
    if oda_id < 1 or oda_id > #_RDS_ODAs or _RDS_ODAs[oda_id] == false then error("Invalid ODA ID: " .. tostring(oda_id), 2) end
    if _RDS_ODAs[oda_id].group == 3 then error("3A ODAs cannot have handlers.", 2) end
    _RDS_ODAs[oda_id].handler = fun
end

local function get_aid()
    local checked = 0

    while checked < #_RDS_ODAs do
        local oda = _RDS_ODAs[_RDS_ODA_pointer]

        if oda ~= false then
            local b = 3 << 12 | oda.group << 1 | (oda.group_version and 1 or 0)
            local data, aid = oda.data, oda.aid

            _RDS_ODA_pointer = (_RDS_ODA_pointer % #_RDS_ODAs) + 1
            return true, b, data, aid
        end

        _RDS_ODA_pointer = (_RDS_ODA_pointer % #_RDS_ODAs) + 1
        checked = checked + 1
    end

    return false, 0, 0, 0
end


local function get_data()
    local checked_count = 0

    while checked_count < #_RDS_ODAs do
        local oda = _RDS_ODAs[_RDS_ODA_pointer]

        if oda ~= false and type(oda.handler) == "function" then
            local generated, b, c, d = oda.handler()
            if generated then
                _RDS_ODA_pointer = (_RDS_ODA_pointer % #_RDS_ODAs) + 1
                b = b | oda.group << 12
                b = b | (oda.group_version and 1 or 0) << 11
                return generated, b, c, d
            end
        end

        _RDS_ODA_pointer = (_RDS_ODA_pointer % #_RDS_ODAs) + 1
        checked_count = checked_count + 1
    end

    return false, 0, 0, 0
end

function group(group_type)
    if group_type == "O" or group_type == "K" then
        if #_RDS_ODAs == 0 then return false, 0, 0, 0 end
        if _RDS_ODA_pointer > #_RDS_ODAs or _RDS_ODA_pointer < 1 then _RDS_ODA_pointer = 1 end

        if group_type == "O" then return get_aid()
        elseif group_type == "K" then return get_data() end
    end
    return false, 0, 0, 0
end

table.insert(on_states, function ()
    _RDS_ODAs = {}
    _RDS_ODA_pointer = 1
end)