local backingList = {}
local length = 0
local paginationOffset = 1
local frame = term.current()
local drawLine = nil

local function setTerm(termlike)
    frame = termlike
end

local function setDrawLineFunc(drawLineFunc)
    drawLine = drawLineFunc
end

local function redrawLine(idx)
    if drawLine then
        local tw, th = frame.getSize()
        if idx >= paginationOffset and idx-paginationOffset <= th then
            frame.setCursorPos(1,idx-paginationOffset+1)
            drawLine(frame, backingList[idx])
        end
    end
end

local function itemAt(idx)
    return backingList[idx]
end

local function updateItemAt(idx, item)
    backingList[idx] = item
    if idx > length then
        length = idx
    end
    redrawLine(idx)
end

local function clearAfter(idx)
    local tw, th = frame.getSize()
    for j = length, idx+1, -1 do
        backingList[j] = nil
    end
    length = idx
    for y = paginationOffset-idx+2, th, 1 do
        frame.setCursorPos(1, y)
        frame.clearLine()
    end
end

local function redraw()
    if drawLine then
        local tw, th = frame.getSize()
        local backingIdx = paginationOffset
        for idx = 1, th, 1 do
            if backingList[backingIdx] ~= nil then
                frame.setCursorPos(idx)
                drawLine(frame, backingList[backingIdx])
            end
        end
    end
end

local function updatePage(newOffset)
    if newOffset ~= paginationOffset then
        paginationOffset = newOffset
        redraw()
    end
end


return {
    setTerm=setTerm,
    setDrawLineFunc=setDrawLineFunc,
    itemAt=itemAt,
    updateItemAt=updateItemAt,
    clearAfter=clearAfter,
    redraw=redraw,
    updatePage=updatePage,
}