ComputerCraft - Read, but only a number

--- read_number, by fatboychummy
--- You have full permission to use this in any way you see fit, as long as you don't claim it as your own.
--- Do note this comes without liability, and I am not responsible for any damages caused by this code.


--- This is a function that allows the user to input a number, and enforces that the input is a number.
--- It also allows you to specify a minimum and maximum value for the number.
--- Usage is at the bottom of the file.

--- Please note that this function has some slight amount of jank to it, and it's not perfect.
--- In order to enter a negative value, for example, it is recommended you type
--- in the positive version of the number you wish to enter *then* hit the negative sign.
--- This is because the negative sign is used to negate the current number, and
--- if you try to enter a negative sign before any numbers, it will drop in -0.
--- If you try to get rid of the 0, it will also remove the negative sign.

-- ########################################################################
-- # IF YOU WANT TO USE THIS FUNCTION IN YOUR OWN PROGRAM, COPY FROM HERE #
-- ########################################################################

--- Like read(), but this will only allow the user to input an integer.
---@param min integer? The minimum value allowed.
---@param max integer? The maximum value allowed.
---@return integer value The number the user entered.
local function read_number(min, max)
  local input = {}
  local len = 0
  local position = 0

  min = min or -math.huge
  max = max or math.huge
  local function clamp(val)
    if val > max then return max end
    if val < min then return min end
    return val
  end
  local function get_number()
    return tonumber(table.concat(input)) or 0
  end

  local x, y = term.getCursorPos()
  local last_len = #input

  --- Redraw the input line.
  local function redraw()
    term.setCursorPos(x, y) -- move the cursor to the start of the line.
    term.write((' '):rep(last_len)) -- clear the line
    term.setCursorPos(x, y) -- move the cursor back to the start of the line.
    term.write(table.concat(input) or "") -- write the input string.
    term.setCursorPos(x + position, y) -- move the cursor to the correct position.
  end

  -- Enable blinking to show the cursor to the user.
  term.setCursorBlink(true)

  while true do
    redraw()
    last_len = #input
    local event, key_char = os.pullEvent()
    if event == "key" then
      -- Handle backspace, enter, arrow keys.
      if key_char == keys.backspace then
        -- Remove the current character - 1 from the input string
        if position > 0 then
          table.remove(input, position) -- we use table.remove here so the table is compacted.
          position = position - 1
          if len > 0 then len = len - 1 end
          if position < 0 then position = 0 end

          -- if backspace removed the negative sign, then we need to negate the number.
          if input[1] == '-' then
            local clipped = clamp(get_number())
            input = {}
            for char in tostring(clipped):gmatch(".") do
              table.insert(input, char)
            end
            len = #input
            position = 0
          end
        end
      elseif key_char == keys.delete then
        -- Remove the current character + 1 from the input string
        if position < len then
          table.remove(input, position + 1)
          if len > 0 then len = len - 1 end
          if position > len then position = len end
        end
      elseif key_char == keys.left then
        -- Move the cursor left
        position = position - 1
        if position < 0 then position = 0 end
      elseif key_char == keys.right then
        -- Move the cursor right
        position = position + 1
        if position > len then position = len end
      elseif key_char == keys.enter then
        -- due to the fact that we enforce numbers only, we can assume that the input is always valid.
        -- however, we should enforce it being in range.
        local n = get_number()
        if n < min or n > max then
          -- if the number is out of range, then we should redraw the input line with the number in red.
          local old = term.getTextColor()
          term.setTextColor(colors.red)
          redraw()
          term.setTextColor(old)
          sleep(0.25)
        else
          -- if the number is in range, then we can return it.
          term.setCursorBlink(false)
          print()
          return n
        end
      end
    elseif event == "char" then
      -- Handle actual numbers, 0-9 (and the minus sign if min < 0)
      if key_char:match("%d") then
        -- Insert the number at the current position
        local _position = position
        if input[position + 1] == '-' then
          -- handle attempting to insert in front of the negative sign.
          _position = position + 1
        end
        table.insert(input, _position + 1, key_char)
        position = _position + 1
        len = len + 1
      elseif key_char == '-' then
        if min < 0 then
          -- Negate the current number, clipping the value to the "maximum" for whatever side of the number line we're on.

          -- 1. Negate
          if input[1] == '-' then
            table.remove(input, 1)
          else
            table.insert(input, 1, '-')
          end

          -- 2. Clip
          local clipped = clamp(get_number())
          input = {}
          for char in tostring(clipped):gmatch(".") do
            table.insert(input, char)
          end
          len = #input
          position = len
        end
      end
    elseif event == "paste" then
      -- Handle pasted text, we need to enforce that this is a valid number.

      -- Use a very basic pattern to check if the pasted text is a valid number.
      if key_char:match("^%-?%d+$") then
        -- Clear the input and insert the pasted text.
        input = {}
        for char in key_char:gmatch(".") do
          table.insert(input, char)
        end
        len = #input
        position = len
      end
    end
  end
end

-- ######################################################################
-- # IF YOU WANT TO USE THIS FUNCTION IN YOUR OWN PROGRAM, COPY TO HERE #
-- ######################################################################

-- tests

write("Read number, no min/max: ")
print(read_number())

write("Read number, min 0: ")
print(read_number(0))

write("Read number, min 0, max 10: ")
print(read_number(0, 10))

write("Read number, min -10, max 10: ")
print(read_number(-10, 10))

write("Read number, min -10, max -5: ")
print(read_number(-10, -5))

write("Read number, no min, max -5: ")
print(read_number(nil, -5))