less for computercraft (more/cat)

-- Less-like program to view a file in pages
local function less(filename)
    -- Try to open the file
    local file = fs.open(filename, "r")
    if not file then
        error("File not found: " .. filename, 0)
        return
    end

    -- Constants for display
    local width, height = term.getSize()
    local lines = {}
    local scrollPosition = 1

    -- Read the file content into lines
    local line = file.readLine()
    while line do
        table.insert(lines, line)
        line = file.readLine()
    end
    file.close()

    -- Function to display a portion of the file
    local function display()
        term.clear()
        term.setCursorPos(1, 1)
        for i = scrollPosition, math.min(scrollPosition + height - 1, #lines) do
            print(lines[i])
        end
    end

    -- Main loop to handle scrolling
    while true do
        display()
        local event, key = os.pullEvent("key")

        -- Scrolling down
        if key == keys.down or key == keys.pageDown then
            if scrollPosition + height - 1 < #lines then
                scrollPosition = scrollPosition + 1
            end
        -- Scrolling up
        elseif key == keys.up or key == keys.pageUp then
            if scrollPosition > 1 then
                scrollPosition = scrollPosition - 1
            end
        -- Exit on "q" key
        elseif key == keys.q then
            break
        end
    end
end

-- Main program execution
local tArgs = { ... }

if #tArgs > 0 then
    -- If a filename is passed, try to open the file
    local filename = tArgs[1]
    less(filename)
else
    -- Ask the user for a filename if no argument is passed
    print("Enter filename: ")
    local filename = read()
    less(filename)
end