DOGGY BOOTLOADER V2

local function main()
    local ci = component.invoke
    local computer = computer or require("computer")

    local function invoke(component, method, ...)
        local result = table.pack(pcall(component[method], ...))
        if not result[1] then return nil, result[2] else return table.unpack(result, 2, result.n) end
    end

    local function tryLoad(address)
        local handle, err = invoke(component.proxy(address), "open", "/init.lua")
        if not handle then return nil, "Failed to open /init.lua: " .. tostring(err) end
        local buffer = ""
        repeat
            local data, err = invoke(component.proxy(address), "read", handle, math.maxinteger or math.huge)
            if not data and err then
                invoke(component.proxy(address), "close", handle)
                return nil, "Failed to read /init.lua: " .. tostring(err)
            end
            buffer = buffer .. (data or "")
        until not data
        invoke(component.proxy(address), "close", handle)
        local fn, err = load(buffer, "=init")
        if not fn then return nil, "Failed to load /init.lua: " .. tostring(err) end
        return fn
    end

    local function displayError(errorMessage)
        local gpu = component.list("gpu")()
        local w, h = invoke(component.proxy(gpu), "getResolution")
        local boxWidth, boxHeight = 80, 6
        local boxX, boxY = math.floor((w - boxWidth) / 2), math.floor((h - boxHeight) / 2)
        invoke(component.proxy(gpu), "setBackground", 0x001f3f)
        invoke(component.proxy(gpu), "fill", boxX, boxY, boxWidth, boxHeight, " ")
        invoke(component.proxy(gpu), "setForeground", 0xFF4500)
        invoke(component.proxy(gpu), "setBackground", 0x001f3f)
        local textX = math.floor((boxWidth - #errorMessage) / 2) + boxX
        local textY = math.floor((boxHeight - 1) / 2) + boxY
        invoke(component.proxy(gpu), "set", textX, textY, errorMessage)
        computer.beep(800, 1)
        while true do
            local event = {computer.pullSignal()}
            if event[1] == "key_down" then
                computer.shutdown(true)
                break
            end
        end
    end

    local function displayMenu(selectedIndex)
        local gpu = component.list("gpu")()
        local w, h = invoke(component.proxy(gpu), "getResolution")
        local boxWidth, boxHeight = 60, 4 + #l
        local boxX, boxY = math.floor((w - boxWidth) / 2), math.floor((h - boxHeight) / 2)
        local drives = {}
        for address, label in component.list("filesystem") do
            if label ~= "tmpfs" then
                table.insert(drives, {address = address, label = label})
            end
        end
        if #drives == 0 then
            displayError("ERROR: No bootable medium found! Insert a bootable device.")
            return
        end
        invoke(component.proxy(gpu), "setBackground", 0x001f3f)
        invoke(component.proxy(gpu), "fill", boxX, boxY, boxWidth, boxHeight, " ")
        invoke(component.proxy(gpu), "setForeground", 0xFFFFFF)
        invoke(component.proxy(gpu), "setBackground", 0x001f3f)
        invoke(component.proxy(gpu), "set", boxX + 2, boxY + 1, "Select OS to boot:")
        for i, drive in ipairs(drives) do
            local lineY = boxY + i + 2
            local textColor = i == selectedIndex and 0xFFD700 or 0xFFFFFF
            invoke(component.proxy(gpu), "setForeground", textColor)
            invoke(component.proxy(gpu), "set", boxX + 2, lineY, drive.label .. " (" .. drive.address .. ")")
        end
        computer.beep(800, 0.1)
    end

    local selectedIndex = math.ceil(#l / 2)
    displayMenu(selectedIndex)

    while true do
        local event = {computer.pullSignal()}
        if event[1] == "key_down" then
            if event[4] == 200 and selectedIndex > 1 then
                selectedIndex = selectedIndex - 1
                displayMenu(selectedIndex)
            elseif event[4] == 208 and selectedIndex < #l then
                selectedIndex = selectedIndex + 1
                displayMenu(selectedIndex)
            elseif event[4] == 28 then
                local selectedDrive = component.list("filesystem")()
                local initFn, err = tryLoad(selectedDrive)
                if initFn then
                    computer.setBootAddress(selectedDrive)
                    computer.beep(800, 0.2)
                    computer.beep(800, 0.6)
                    computer.beep(800, 0.2)
                    return initFn()
                else
                    displayError("ERROR: Unable to boot from " .. (l[selectedIndex] and l[selectedIndex].label or "selected device") .. ". Check the device and try again.")
                    computer.beep(800, 0.1)
                    computer.beep(800, 0.1)
                    computer.beep(800, 0.1)
                end
            end
        end
    end
end

main()