local backingList = {}
local length = 0
local paginationPos = 1
local frame = term.current()
local drawEntry = nil

local function setTerm(termlike)
    frame = termlike
end

local function setDrawEntryFunc(drawLineFunc)
    drawEntry = drawLineFunc
end

local function redrawEntry(idx)
    local tw, th = frame.getSize()
    if idx >= paginationPos and idx-paginationPos <= th then
        frame.setCursorPos(1, idx-paginationPos+1)
        if drawEntry then
            drawEntry(frame, backingList[idx])
        else
            frame.setBackgroundColor(colors.red)
            frame.clearLine()
            frame.setBackgroundColor(colors.black)
        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
    redrawEntry(idx)
end

local function getLength()
    return length
end

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

local function redraw()
    if drawEntry then
        local tw, th = frame.getSize()
        local backingIdx = paginationPos
        for idx = 1, th, 1 do
            frame.setCursorPos(1, idx)
            if backingList[backingIdx] == nil then
                frame.clearLine()
            else
                drawEntry(frame, backingList[backingIdx])
            end
            backingIdx = backingIdx + 1
        end
    else
        frame.setBackgroundColor(colors.red)
        frame.clear()
        frame.setBackgroundColor(colors.black)
    end
end

local function updatePage(scrollPos)
    if scrollPos ~= paginationPos then
        paginationPos = scrollPos
        redraw()
    end
end

local function updatePartial(filter)
    if drawEntry then
        local tw, th = frame.getSize()
        local backingIdx = paginationPos
        for idx = 1, th, 1 do
            frame.setCursorPos(1, idx)
            if backingList[backingIdx] ~= nil and filter(backingList[backingIdx]) then
                drawEntry(frame, backingList[backingIdx])
            end
            backingIdx = backingIdx + 1
        end
    end
end


return {
    setTerm=setTerm,
    setDrawEntryFunc=setDrawEntryFunc,
    itemAt=itemAt,
    updateItemAt=updateItemAt,
    length=getLength,
    clearFrom=clearFrom,
    redraw=redraw,
    updatePage=updatePage,
    updatePartial=updatePartial,
}