-- Constants
local WIDTH = 51
local HEIGHT = 10
local SCROLL_STEP = 1
local SCROLL_UP_KEY = keys.up
local SCROLL_DOWN_KEY = keys.down

-- Function to draw a filled rectangle
function drawRect(x, y, width, height, color)
    term.setBackgroundColor(color)
    term.setCursorPos(x, y)
    term.clearLine()
    for i = 1, height do
        term.setCursorPos(x, y + i - 1)
        term.write(string.rep(" ", width))
    end
end

-- Function to draw text
function drawText(x, y, text, color)
    term.setTextColor(color)
    term.setCursorPos(x, y)
    term.write(text)
end

-- Function to create a button
function drawButton(x, y, width, text, bgColor, textColor)
    drawRect(x, y, width, 3, bgColor)
    drawText(x + 1, y + 1, text, textColor)
end

-- Function to draw the navigation bar
function drawNavBar()
    drawRect(1, 6, WIDTH, 3, colors.gray)
    drawButton(2, 7, 10, "Home", colors.lightGray, colors.black)
    drawButton(13, 7, 15, "Features", colors.lightGray, colors.black)
    drawButton(30, 7, 12, "About", colors.lightGray, colors.black)
    drawButton(44, 7, 8, "Help", colors.lightGray, colors.black)
end

-- Function to render content with scrolling
function drawScrollableContent(content, scrollOffset, pageHeight)
    -- Calculate the start and end of the visible content
    local startLine = scrollOffset + 1
    local endLine = math.min(scrollOffset + pageHeight, #content)

    -- Draw visible content
    for i = startLine, endLine do
        drawText(2, i - scrollOffset + 10, content[i], colors.white)
    end
end

-- Function to draw the main screen
function drawMainScreen(scrollOffset)
    term.clear()
    term.setBackgroundColor(colors.black)
    term.setTextColor(colors.white)

    -- Draw header
    drawRect(1, 1, WIDTH, 5, colors.blue)
    drawText(2, 2, "Doggy OS", colors.white)

    -- Draw navigation bar
    drawNavBar()

    -- Draw content area
    drawRect(1, 10, WIDTH, HEIGHT, colors.black)
    local content = {
        "Welcome to Doggy OS!",
        "A user-friendly and secure operating system.",
        "Designed with both novice and advanced users in mind.",
        "Explore our features and learn more about security and privacy.",
        "Navigate using function keys: F1, F4, F5, F6.",
        "Press F1 for Home, F4 for Features, F5 for About, and F6 for Help."
    }
    drawScrollableContent(content, scrollOffset, HEIGHT)
end

-- Function to draw the features page
function drawFeaturesPage(scrollOffset)
    term.clear()
    term.setBackgroundColor(colors.black)
    term.setTextColor(colors.white)

    -- Draw header
    drawRect(1, 1, WIDTH, 5, colors.blue)
    drawText(2, 2, "Doggy OS - Features", colors.white)

    -- Draw navigation bar
    drawNavBar()

    -- Draw content area
    drawRect(1, 10, WIDTH, HEIGHT, colors.black)
    local content = {
        "Features of Doggy OS:",
        "- User-friendly Interface",
        "- Customizable Settings",
        "- Fun and Interactive",
        "- Advanced Security Features",
        "- Privacy Controls",
        "- Regular Updates",
        "Discover more and customize to fit your needs.",
        "Explore these features to enhance your experience."
    }
    drawScrollableContent(content, scrollOffset, HEIGHT)
end

-- Function to draw the about page
function drawAboutPage(scrollOffset)
    term.clear()
    term.setBackgroundColor(colors.black)
    term.setTextColor(colors.white)

    -- Draw header
    drawRect(1, 1, WIDTH, 5, colors.blue)
    drawText(2, 2, "Doggy OS - About", colors.white)

    -- Draw navigation bar
    drawNavBar()

    -- Draw content area
    drawRect(1, 10, WIDTH, HEIGHT, colors.black)
    local content = {
        "Security & Privacy:",
        "Doggy OS prioritizes your security and privacy.",
        "Key features include:",
        "- Encrypted User Data",
        "- Regular Security Updates",
        "- Privacy-focused Design",
        "Choose between Advanced or Simple modes.",
        "Tailored to meet both casual and power users' needs."
    }
    drawScrollableContent(content, scrollOffset, HEIGHT)
end

-- Function to draw the help page
function drawHelpPage(scrollOffset)
    term.clear()
    term.setBackgroundColor(colors.black)
    term.setTextColor(colors.white)

    -- Draw header
    drawRect(1, 1, WIDTH, 5, colors.blue)
    drawText(2, 2, "Doggy OS - Help", colors.white)

    -- Draw navigation bar
    drawNavBar()

    -- Draw content area
    drawRect(1, 10, WIDTH, HEIGHT, colors.black)
    local content = {
        "Help & Instructions:",
        "Use the function keys to navigate:",
        "- F1: Home",
        "- F4: Features",
        "- F5: About",
        "- F6: Help",
        "Follow on-screen instructions for more details.",
        "For additional support, refer to the official documentation.",
        "Contact support if you need further assistance."
    }
    drawScrollableContent(content, scrollOffset, HEIGHT)
end

-- Function to handle user input
function handleInput()
    local scrollOffset = 0
    local maxScroll = 10 -- Maximum number of lines that can be scrolled

    while true do
        local event, key = os.pullEvent("key")
        if key == keys.f1 then
            drawMainScreen(scrollOffset)
        elseif key == keys.f4 then
            drawFeaturesPage(scrollOffset)
        elseif key == keys.f5 then
            drawAboutPage(scrollOffset)
        elseif key == keys.f6 then
            drawHelpPage(scrollOffset)
        elseif key == SCROLL_UP_KEY then
            if scrollOffset > 0 then
                scrollOffset = scrollOffset - SCROLL_STEP
                drawFeaturesPage(scrollOffset) -- or drawAboutPage(scrollOffset), etc.
            end
        elseif key == SCROLL_DOWN_KEY then
            if scrollOffset < maxScroll then
                scrollOffset = scrollOffset + SCROLL_STEP
                drawFeaturesPage(scrollOffset) -- or drawAboutPage(scrollOffset), etc.
            end
        elseif key == keys.q then
            break
        end
    end
end

-- Main Program
drawMainScreen(0)
handleInput()