Basic Button Implementation

--- Used to store all registered buttons
local buttons = {}

--- Creates a new button object, with position {x,y}, size {width,height}, text "text", and the given colors.
--- The callback value is a function that you pass to this function, and it will be called when the button is pressed.
local function newButton(x, y, width, height, text, textColor, bgColor, callback)
  --- Our button object. This stores all the relevant data about the button.
  local button = {
    x = x,
    y = y,
    width = width,
    height = height,
    text = text,
    textColor = textColor,
    bgColor = bgColor,
    callback = callback
  }

  table.insert(buttons, button) -- insert our new button into the list

  return button -- So we can edit the button later, if needed.
end

--- Draws all buttons.
local function drawButtons(_term)
  -- Either use the inputted terminal object, or just draw directly to the terminal if not provided.
  local term = _term or term

  for _, button in ipairs(buttons) do -- For each button ...
    --- Used to draw the background of the button.
    local blank_space = (' '):rep(button.width)

    -- Set the relevant colors for the button.
    term.setBackgroundColor(button.bgColor)
    term.setTextColor(button.textColor)

    for y = button.y, button.y + button.height - 1 do -- For each y position on the button
      term.setCursorPos(button.x, y) -- Set the cursor at the 'start' of each line on the button
      term.write(blank_space) -- draw the background of the button
    end

    -- Write the text onto the button. For this, we will center the text.

    -- Note for the x_middle, we also subtract half of the length of the text. This centers the text horizontally, since we start writing 'at the left'.
    -- For y, we just center it once.
    local x_middle = math.ceil((button.x + button.width / 2) - (#button.text / 2))
    local y_middle = math.ceil(button.y + button.height / 2)
    term.setCursorPos(x_middle, y_middle)
    term.write(button.text)
  end
end

--- Checks whether the given input click (x, y) is within the bounds of (x1, y1) and (x2, y2)
---@return boolean inBounds Whether the value is within bounds.
local function withinBounds(x1, y1, x2, y2, x, y)
  return x >= x1 and x <= x2
     and y >= y1 and y <= y2
end

--- Test which button was clicked given an x,y position. Returns the first in the list, make sure your buttons don't overlap!
local function testButtons(x, y)
  for _, button in ipairs(buttons) do -- for each button ...
    -- If the click is within the bounds set by the button...
    if withinBounds(button.x, button.y, button.x + button.width - 1, button.y + button.height - 1, x, y) then
      return button -- Return the button!
    end
  end

  -- If we make it here, no button was clicked! Nothing is returned.
end

--- Checks if a button was pressed given an x,y click position, then runs the button that was pressed.
local function runButton(x, y)
  local buttonPressed = testButtons(x, y) -- determine which button was clicked

  if buttonPressed then -- If a button was clicked
    buttonPressed.callback(buttonPressed) -- Call the callback of the button, passing itself as a parameter.
  end
end