local rds2_oda = {}

local _RDS2_ODA = { aid = 0, data = 0, handler = false, file_related = false, channel = 0 }
local _RDS2_next_channel = { normal = 16, file = 0 }

function _RDS2_ODA.new(aid, data, handler, file_related, channel)
    local instance = { aid = aid or 0, data = data or 0, handler = handler or false, file_related = file_related or false, channel = channel or 0 }
    setmetatable(instance, { __index = _RDS2_ODA })
    return instance
end

local _RDS2_ODAs = {}
local _RDS2_ODA_aid = 0
local _RDS2_ODA_pointer = 1

---@param aid integer
---@param data integer
---@param file_related boolean
---@return integer oda_id
function rds2_oda.register_oda_rds2(aid, data, file_related)
    local channel
    if file_related then
        channel = _RDS2_next_channel.file
        _RDS2_next_channel.file = _RDS2_next_channel.file + 1
    else
        channel = _RDS2_next_channel.normal
        _RDS2_next_channel.normal = _RDS2_next_channel.normal + 1
    end

    local oda = _RDS2_ODA.new(aid, data, false, file_related, channel)
    for i = 1, #_RDS2_ODAs do
        if _RDS2_ODAs[i] == false then
            _RDS2_ODAs[i] = oda
            return i
        end
    end
    table.insert(_RDS2_ODAs, oda)
    return #_RDS2_ODAs
end

---Unregisters an RDS 2 ODA, this stops the handler or AID being called/sent
---@param oda_id integer
function rds2_oda.unregister_oda_rds2(oda_id)
    if oda_id < 1 or oda_id > #_RDS2_ODAs or _RDS2_ODAs[oda_id] == false then error("Invalid ODA ID: " .. tostring(oda_id), 2) end

    _RDS2_ODAs[oda_id] = false

    if _RDS2_ODA_pointer == oda_id then _RDS2_ODA_pointer = _RDS2_ODA_pointer + 1 end
end


---@param oda_id integer
---@param data integer
function rds2_oda.set_oda_id_data_rds2(oda_id, data)
    if oda_id < 1 or oda_id > #_RDS2_ODAs or _RDS2_ODAs[oda_id] == false then error("Invalid ODA ID: " .. tostring(oda_id), 2) end
    _RDS2_ODAs[oda_id].data = data
end

---The callback function for an ODA handler
---@alias RDS2_ODAHandler fun(integer): (boolean, integer, integer, integer, integer)

---You are asked to not fill in the channel id in block A, however you are asked to fill in the function number (if you do not know what is that, just OR block A with (1 << 14))
---@param oda_id integer
---@param func RDS2_ODAHandler
function rds2_oda.set_oda_handler_rds2(oda_id, func)
    if oda_id < 1 or oda_id > #_RDS2_ODAs or _RDS2_ODAs[oda_id] == false then error("Invalid ODA ID: " .. tostring(oda_id), 2) end
    _RDS2_ODAs[oda_id].handler = func
end

function rds2_oda.rds2_group(stream)
    if #_RDS2_ODAs == 0 then return false, 0, 0, 0, 0 end

    if _RDS2_ODA_pointer > #_RDS2_ODAs then _RDS2_ODA_pointer = 1 end
    local checked = 0
    while checked < #_RDS2_ODAs and _RDS2_ODAs[_RDS2_ODA_pointer] == false do
        _RDS2_ODA_pointer = _RDS2_ODA_pointer + 1
        if _RDS2_ODA_pointer > #_RDS2_ODAs then _RDS2_ODA_pointer = 1 end
        checked = checked + 1
    end
    if checked == #_RDS2_ODAs then return false, 0, 0, 0, 0 end

    local oda = _RDS2_ODAs[_RDS2_ODA_pointer]
    local channel = oda.channel
    if oda.file_related then channel = channel & 0xF end

    _RDS2_ODA_pointer = _RDS2_ODA_pointer + 1

    local next_oda = nil
    if _RDS2_ODA_pointer <= #_RDS2_ODAs then next_oda = _RDS2_ODAs[_RDS2_ODA_pointer] end

    if _RDS2_ODA_aid == 0 and stream == 1 then
        _RDS2_ODA_aid = 1
        local block1_base = (2 << 14) | channel

        if next_oda and oda.data > 0 and oda.data <= 0xFFFF and next_oda.data == 0 then
            _RDS2_ODA_pointer = _RDS2_ODA_pointer + 1
            return true, block1_base | (1 << 6), oda.aid, oda.data, next_oda.aid
        elseif next_oda and oda.data == 0 and next_oda.data > 0 and next_oda.data <= 0xFFFF then
            _RDS2_ODA_pointer = _RDS2_ODA_pointer + 1
            return true, block1_base | (2 << 6), oda.aid, next_oda.aid, next_oda.data
        elseif next_oda ~= nil and oda.data == 0 and next_oda.data == 0 then
            _RDS2_ODA_pointer = _RDS2_ODA_pointer + 1
            if _RDS2_ODA_pointer <= #_RDS2_ODAs then
                local third_oda = _RDS2_ODAs[_RDS2_ODA_pointer]
                _RDS2_ODA_pointer = _RDS2_ODA_pointer + 1
                return true, block1_base | (3 << 6), oda.aid, next_oda.aid, third_oda.aid
            else return true, block1_base, oda.aid, (oda.data >> 16) & 0xffff, oda.data & 0xffff end
        end

        return true, block1_base, oda.aid, (oda.data >> 16) & 0xffff, oda.data & 0xffff
    else
        _RDS2_ODA_aid = _RDS2_ODA_aid + 1
        if _RDS2_ODA_aid > 8 then _RDS2_ODA_aid = 0 end
        if oda.handler then
            local generated = false
            checked = 0
            while generated == false and checked < #_RDS2_ODAs do
                local ok, a, b, c, d
                ok, generated, a, b, c, d = pcall(oda.handler, stream)
                if not (generated and ok) then
                    _RDS2_ODA_pointer = _RDS2_ODA_pointer + 1
                    if _RDS2_ODA_pointer > #_RDS2_ODAs then _RDS2_ODA_pointer = 1 end
                    oda = _RDS2_ODAs[_RDS2_ODA_pointer]
                    checked = checked + 1
                else
                    local channel_bitshift = 8
                    local fid = (a & 0xC000) >> 14
                    local fn_msb = (a >> 13) & 1
                    if fid == 0 and fn_msb == 0 then return true, 0, b, c, d -- Tunnel, not sure why but sure
                    -- FID == 0 and FN_MSB = 1 means RFT data, file data
                    -- FID == 1 is the standard ODA group
                    -- FID == 2 is AID
                    -- FID == 3 is reserved
                    elseif fid == 2 and fn_msb == 0 then channel_bitshift = 0 end -- This is AID
                    return generated, (channel << channel_bitshift) | a, b, c, d
                end
            end
            if checked == #_RDS2_ODAs then return false, 0, 0, 0, 0 end
        end
        return true, (2 << 14) | channel, oda.aid, (oda.data >> 16) & 0xffff, oda.data & 0xffff
    end
end

table.insert(hooks.on_state, function ()
    _RDS2_ODAs = {}
    _RDS2_ODA_aid = 0
    _RDS2_ODA_pointer = 1
end)

return rds2_oda