local parent = term.current()
local tabCount = 0
local allTabs = {}
local tabOrder = {}
local currentTab = nil

local function setTerm(new_term)
    parent = new_term
end

local function addTab(tab, order_idx)
    assert(tab.name, "tab needs a unique name")
    local isCurrentTab = currentTab == nil
    if isCurrentTab then
        currentTab = tab
    end
    local tw, th = parent.getSize()
    tab.window = window.create(parent, 1, 1, tw, th, isCurrentTab)
    tab.scrollPos = 1
    tab.pageDown = function ()
        local tw, th = tab.window.getSize()
        tab.scrollPos = tab.scrollPos + th
    end
    tab.pageUp = function ()
        local tw, th = tab.window.getSize()
        tab.scrollPos = math.max(1, tab.scrollPos-th)
    end
    allTabs[tab.name] = tab
    tabOrder[order_idx] = tab.name
    tabCount = tabCount + 1
    return tab
end

local function showTab(name)
    if currentTab ~= nil then
        currentTab.window.setVisible(false)
    end
    currentTab = allTabs[name]
    if currentTab == nil then
        -- backwards compatible idx lookup
        currentTab = allTabs[tabOrder[name]]
    end
    assert(currentTab ~= nil, "tab name '" .. name .. "' was not registered")
    currentTab.window.setVisible(true)
end

local function switchTab()
    assert(tabCount > 0, "tabs need to be registered in order to switch tabs")
    local idx = 0
    if currentTab ~= nil then
        currentTab.window.setVisible(false)
        for i, name in pairs(tabOrder) do
            if name == currentTab.name then
                idx = i
                break
            end
        end
    end
    idx = idx + 1
    if idx > tabCount then
        idx = 1
    end
    currentTab = allTabs[tabOrder[idx]]
    currentTab.window.setVisible(true)
end

local function getCurrentTab()
    return currentTab
end

local function getAllTabs()
    return allTabs
end

local function updateSize()
    local tw, th = parent.getSize()
    for name, tab in pairs(allTabs) do
        tab.window.reposition(1, 1, tw, th)
    end
end

local function onTouch(touch_x, touch_y)
    if currentTab ~= nil then
        currentTab.onTouch(currentTab, touch_x, touch_y)
    end
end


return {
    setTerm=setTerm,
    addTab=addTab,
    showTab=showTab,
    switchTab=switchTab,
    updateSize=updateSize,
    onTouch=onTouch,
    currentTab=getCurrentTab,
    allTabs=getAllTabs,
}