function on_open()
    refresh()
end

-- // FIXME: dependency checks
add_packs = {}
rem_packs = {}

function apply()
    core.reconfig_packs(add_packs, rem_packs)
end

function refresh_changes()
    document.apply_btn.enabled = (#add_packs>0) or (#rem_packs>0)
end

function move_pack(id)
    -- cancel pack addition
    if table.has(add_packs, id) then
        document["pack_"..id]:move_into(document.packs_add)
        table.remove_value(add_packs, id)
    -- cancel pack removal
    elseif table.has(rem_packs, id) then
        document["pack_"..id]:move_into(document.packs_cur)
        table.remove_value(rem_packs, id)
    -- add pack
    elseif table.has(packs_installed, id) then
        document["pack_"..id]:move_into(document.packs_add)
        table.insert(rem_packs, id)
    -- remove pack
    else
        document["pack_"..id]:move_into(document.packs_cur)
        table.insert(add_packs, id)
    end
    refresh_changes()
end

function place_pack(panel, packid, packinfo, callback)
    packinfo.id = packid
    callback = callback or ""
    if packinfo.has_indices then
        packid = packid.."*"
    end
    packinfo.id_verbose = packid
    packinfo.callback = callback
    panel:add(gui.template("pack", packinfo))
end

function refresh()
    packs_installed = pack.get_installed()
    packs_available = pack.get_available()
    
    local packs_cur = document.packs_cur
    local packs_add = document.packs_add

    packs_cur:clear()
    packs_add:clear()
    refresh_changes()

    for i,id in ipairs(packs_installed) do
        local packinfo = pack.get_info(id)
        packinfo.index = i
        callback = id ~= "base" and string.format('move_pack("%s")', id) or nil
        place_pack(packs_cur, id, packinfo, callback)
    end

    for i,id in ipairs(packs_available) do
        local packinfo = pack.get_info(id)
        packinfo.index = i
        callback = string.format('move_pack("%s")', id)
        place_pack(packs_add, id, packinfo, callback)
    end

    -- apply packs movements
    for i,id in ipairs(packs_installed) do
        if table.has(rem_packs, id) then
            document["pack_"..id]:move_into(packs_add)
        end
    end
    for i,id in ipairs(packs_available) do
        if table.has(add_packs, id) then
            document["pack_"..id]:move_into(packs_cur)
        end
    end
end