taken from https://github.com/blunty666/CC-Programs-and-APIs/blob/master/games/WhereIsDan/WhereIsDan.lua

local BOX = {
    WIDTH = 20,
    HEIGHT = 9,
}

local BUTTON = {
    WIDTH = 18,
}

local TIMEOUT = 300 -- cache quotes for 5 minutes

local URL = "https://raw.githubusercontent.com/blunty666/CC-Programs-and-APIs/master/games/WhereIsDan/quotes.lua"

local WIDTH, HEIGHT = term.getSize()
local CENTER_X, CENTER_Y = math.ceil(WIDTH/2), math.ceil(HEIGHT/2)

do
    local DELTA_X, DELTA_Y = math.floor(BOX.WIDTH/2), math.floor(BOX.HEIGHT/2)

    BOX.X_MIN = CENTER_X - DELTA_X
    BOX.X_MAX = BOX.X_MIN + BOX.WIDTH - 1

    BOX.Y_MIN = CENTER_Y - DELTA_Y
    BOX.Y_MAX = BOX.Y_MIN + BOX.HEIGHT - 1

    BOX.BUTTON_TEXT = {
        X = CENTER_X,
        Y = BOX.Y_MIN + 2,
    }

    BOX.BUTTON = {
        X_MIN = CENTER_X - math.floor(BUTTON.WIDTH/2),
        X_MAX = CENTER_X - math.floor(BUTTON.WIDTH/2) + BUTTON.WIDTH - 1,

        Y_MIN = BOX.Y_MIN + 1,
        Y_MAX = BOX.Y_MIN + 3,
    }

    BOX.TEXT = {
        X = CENTER_X,
        Y = BOX.Y_MIN + 5,
    }
end

local CHANGE_PROBABILITY = 0.15

local particles = {}

local function randomColour()
    return 2^(math.random(0, 14))
end

local directions = {
    [0] = vector.new(0, -1, 0),
    [1] = vector.new(1, 0, 0),
    [2] = vector.new(0, 1, 0),
    [3] = vector.new(-1, 0, 0),
}

local function newParticle(x, y, colour, directionIndex)
    return {
        position = vector.new(x, y, 0),
        colour = colour,
        directionIndex = directionIndex,
        direction = directions[directionIndex],
        distanceTravelled = 0,
    }
end

local function isInTerm(x, y)
    return 1 <= x and x <= WIDTH and 1 <= y and y <= HEIGHT
end

local function shouldChangeDirection(particle)
    return math.random() < CHANGE_PROBABILITY
end

local function shouldDraw(particle)
    local x, y = particle.position.x, particle.position.y
    return not (BOX.X_MIN <= x and x <= BOX.X_MAX and BOX.Y_MIN <= y and y <= BOX.Y_MAX)
end

local function draw(particle)
    term.setCursorPos(particle.position.x, particle.position.y)
    term.setBackgroundColour(particle.colour)
    term.write(" ")
end

local function updateParticles()
    while true do
        for _, particle in ipairs(particles) do
            local nextPosition = particle.position + particle.direction
            if not isInTerm(nextPosition.x, nextPosition.y) or shouldChangeDirection(particle) then

                local directionDelta = (math.random() > 0.5 and 1) or -1
                local newDirectionIndex, newDirection = particle.directionIndex, nil
                repeat
                    newDirectionIndex = (newDirectionIndex + directionDelta) % 4
                    newDirection = directions[newDirectionIndex]
                    nextPosition = particle.position + newDirection
                until isInTerm(nextPosition.x, nextPosition.y)

                -- update direction
                particle.directionIndex = newDirectionIndex
                particle.direction = newDirection

                -- reset distanceTravelled
                particle.distanceTravelled = 0
            end

            -- move particle
            particle.position = nextPosition

            -- increase distanceTravelled
            particle.distanceTravelled = particle.distanceTravelled + 1

            -- check if should draw particle and draw
            if shouldDraw(particle) then
                draw(particle)
            end
        end
        sleep(0.05)
    end
end

local function writeText(xPos, yPos, text, bgCol, textCol)
    if bgCol then term.setBackgroundColour(bgCol) end
    if textCol then term.setTextColour(textCol) end
    term.setCursorPos(xPos, yPos)
    term.write(text)
end

local function writeTextAligned(text, xPos, yPos, bgCol, textCol)
    local startX = xPos - math.ceil(#text/2)
    writeText(startX, yPos, text, bgCol, textCol)
end

local function drawButton(colour)
    paintutils.drawFilledBox(BOX.BUTTON.X_MIN, BOX.BUTTON.Y_MIN, BOX.BUTTON.X_MAX, BOX.BUTTON.Y_MAX, colour)
    writeTextAligned("WHERE IS DAN?", BOX.BUTTON_TEXT.X, BOX.BUTTON_TEXT.Y, colour, colours.white)
end

local function searchBarTimer()
    return math.random() / 4
end

local function handleEvents()
    local quotes = {
        "<INSERT TEXT HERE>",
    }
    local requested = false
    local cachedTime = -(math.huge)

    local clicked = false

    local updateTimer = false
    local counter = 1

    local event = {os.pullEventRaw()}
    while true do
        if event[1] == "terminate" or (event[1] == "char" and string.lower(event[2]) == "q") then
            break
        elseif event[1] == "mouse_click" then
            if event[2] == 1 and (BOX.BUTTON.X_MIN <= event[3] and event[3] <= BOX.BUTTON.X_MAX) and (BOX.BUTTON.Y_MIN <= event[4] and event[4] <= BOX.BUTTON.Y_MAX) then
                clicked = true
                drawButton(colours.red)
            end
        elseif event[1] == "mouse_up" then
            if clicked then
                drawButton(colours.green)
                if os.clock() - cachedTime > TIMEOUT then
                    if not requested then
                        http.request(URL)
                        requested = true
                    end
                end
                if not updateTimer then
                    updateTimer = os.startTimer(searchBarTimer())
                    writeText(BOX.X_MIN, BOX.TEXT.Y, string.rep(" ", BOX.WIDTH), colours.black)
                    writeTextAligned("Searching for Dan...", BOX.TEXT.X, BOX.TEXT.Y + 1, colours.black, colours.white)
                end
                clicked = false
            end
        elseif event[1] == "http_success" and event[2] == URL then

            quotes = textutils.unserialise(event[3].readAll())
            requested = false
            cachedTime = os.clock()

        elseif event[1] == "timer" then
            if event[2] == updateTimer then
                if counter <= BOX.WIDTH - 2 then
                    writeText(BOX.X_MIN + 1, BOX.TEXT.Y, string.rep(" ", counter), colours.cyan)
                    updateTimer = os.startTimer(searchBarTimer())
                    counter = counter + 1
                else
                    writeText(BOX.X_MIN, BOX.TEXT.Y, string.rep(" ", BOX.WIDTH), colours.black)
                    writeText(BOX.X_MIN, BOX.TEXT.Y + 1, string.rep(" ", BOX.WIDTH), colours.black)
                    writeTextAligned(quotes[math.random(1, #quotes)], BOX.TEXT.X, BOX.TEXT.Y, colours.black, colours.white)
                    updateTimer = false
                    counter = 1
                end
            end
        end
        event = {os.pullEventRaw()}
    end
end

term.setBackgroundColour(colours.black)
term.clear()

drawButton(colours.green)
writeTextAligned("Press 'q' to Quit", BOX.TEXT.X, BOX.TEXT.Y + 3, colours.black, colours.white)

for i = 1, 25 do
    local x = math.random(1, WIDTH)
    local y = math.random(1, HEIGHT)
    local colour = randomColour()
    local directionIndex = math.random(0, 3)
    table.insert(particles, newParticle(x, y, colour, directionIndex))
end

parallel.waitForAny(handleEvents, updateParticles)

term.setBackgroundColour(colours.black)
term.setTextColour(colours.white)
term.setCursorPos(1, 1)
term.clear()