DDR Demo thing

local w,h = term.getSize()

local running

local notes = {}
local receptor = {
    x = 3,
    y = 2,
    blink = 4
}

local keymap = {
    left=1,
    down=2,
    up=3,
    right=4
}
local notemap = {'<', 'V', '^', '>'}

local utime = 0.1
local utimer

local judgement
local judgetime = 0

local score = 0
local bgcolor = colors.black

local function doJudge(num)
    judgement = num
    judgetime = 0.5 + utime
end

local function update(dt)
    for i=#notes, 1, -1 do
        local note = notes[i]
        if note.y > -receptor.y then
            note.y = note.y - 1
        else
            table.remove(notes, i)
            doJudge(0)
            score = score - 5
        end
    end

    if receptor.blink > 0 then
        receptor.blink = receptor.blink - 1
    else
        receptor.blink = 4

        -- for testing
        table.insert(notes, {
            col = math.random(4);
            y = 19;
        })
    end

    judgetime = judgetime - dt

    if utime == 0 then
        bgcolor = 2^math.random(15)
    end
end

local function keypressed(k)
    if keymap[k] then
        for i,note in pairs(notes) do
            if note.col == keymap[k] then
                local dist = math.abs(note.y)
                if dist == 0 then
                    doJudge(1) -- marvelous
                    score = score + 10
                elseif dist <= 1 then
                    doJudge(2) -- perfect
                    score = score + 5
                elseif dist <= 2 then
                    doJudge(3) -- great
                    score = score + 1
                end

                if dist <= 2 then
                    table.remove(notes, i)
                end
                break
            end
        end
    end

    if k == 'backspace' then
        running = false
    end
end

local function draw()
    local t = term
    local w,h = term.getSize()

    t.setBackgroundColor(bgcolor)
    t.clear()


    -- draw the receptor
    t.setTextColor(
        receptor.blink == 0 and
        colors.white or
        colors.lightGray
    )
    t.setCursorPos(receptor.x, receptor.y)
    t.write('>    <')

    -- draw the notes
    local notecolors = {
        colors.red,
        colors.yellow,
        colors.lime,
        colors.lightBlue
    }

    for _, note in pairs(notes) do
        t.setCursorPos(note.col + receptor.x, note.y + receptor.y)
        t.setTextColor(notecolors[note.col])
        t.write(notemap[note.col])
    end

    -- judgement
    local words = {
        [0] = {'miss', colors.red};
        {'Amazing!', colors.lightBlue};
        {'Perfect!', colors.yellow};
        {'Nice!', colors.lime};
    }

    if judgement and judgetime > 0 then
        local item = words[judgement]
        local word, color = item[math.random(#item - 1)], item[#item]

        t.setCursorPos(receptor.x + 8, receptor.y)
        t.setTextColor(judgetime >= 0.5 and colors.white or color)
        t.write(word)
    end

    -- score
    local scorestr = ('0'):rep(4 - #tostring(score)) ..score
    t.setCursorPos(receptor.x + 8, receptor.y + 2)
    t.setTextColor(colors.yellow)
    t.write(scorestr)
end

local function selectMode()
    local modes = {'Easy','Normal','Hard','Satan',"You're high."}
    local times = {0.2, 0.15, 0.1, 0.05, 0}
    local selection = 1

    local t = term


    while true do
        t.setTextColor(colors.white)
        t.setBackgroundColor(colors.black)
        t.clear()

        t.setCursorPos(3, 2)
        t.write 'Select Difficulty'
        for i,v in pairs(modes) do
            t.setTextColor(colors.white)
            if selection == i then
                t.setTextColor(colors.lime)
                t.setCursorPos(2, i + 3)
                t.write '>'
            end
            t.setCursorPos(3, i + 3)
            t.write(v)
        end

        local _, k = os.pullEvent('key')
        if k == keys.up then
            selection =
                selection > 1 and
                selection - 1 or
            #modes
        elseif k == keys.down then
            selection =
                selection < #modes and
                selection + 1 or
            1
        elseif k == keys.enter then
            return times[selection]
        end
    end
end

term.setBackgroundColor(colors.black)
term.clear()

utime = selectMode()
utimer = os.startTimer(utime)

running = true
while running do
    draw()

    local ev, p1 = os.pullEvent()

    if ev == 'timer' and p1 == utimer then
        update(utime)
        utimer = os.startTimer(utime)
    elseif ev == 'key' then
        keypressed(keys.getName(p1))
    end
end

term.setBackgroundColor(colors.black)
term.clear()
term.setCursorPos(1,1)