Calculator OOP

w, h = term.getSize()
local stringW = ""
for i = 1, w - 2 do
  stringW = stringW .. " "
end
function initializeCalc()
  term.setBackgroundColor(colors.green)
  term.clear()
  term.setCursorPos(w / 2 - 4, 1)
  term.write("Calculator")
  term.setCursorPos(w / 2 - 9, 2)
  term.write("+  -  *  /  **  ^  %")
  term.setCursorPos(2, 4)
  term.setBackgroundColor(colors.lime)
  term.write(stringW)
  term.setCursorPos(1, h)
  term.setBackgroundColor(colors.blue)
  term.write("Graph")
  term.setCursorPos(w - 3, h)
  term.setBackgroundColor(colors.red)
  term.write("Back")
end

local emphasis = {}
  emphasis["+"] = true
  emphasis["-"] = true
  emphasis["/"] = true
  emphasis["*"] = true
  emphasis["^"] = true
  emphasis["%"] = true
  emphasis["("] = true
  emphasis[")"] = true
  emphasis["="] = true
  emphasis["<"] = true
  emphasis[">"] = true
  emphasis["!"] = true

local letters = {}
  letters["a"] = true
  letters["b"] = true
  letters["c"] = true
  letters["d"] = true
  letters["e"] = true
  letters["f"] = true
  letters["g"] = true
  letters["h"] = true
  letters["i"] = true
  letters["j"] = true
  letters["k"] = true
  letters["l"] = true
  letters["m"] = true
  letters["n"] = true
  letters["o"] = true
  letters["p"] = true
  letters["q"] = true
  letters["r"] = true
  letters["s"] = true
  letters["t"] = true
  letters["u"] = true
  letters["v"] = true
  letters["w"] = true
  letters["x"] = true
  letters["y"] = true
  letters["z"] = true

local dontuse = {}
  dontuse["~"] = true
  dontuse["@"] = true
  dontuse["`"] = true
  dontuse["$"] = true
  dontuse["#"] = true
  dontuse["&"] = true
  dontuse[";"] = true
  dontuse[":"] = true
  dontuse["\""] = true
  dontuse["'"] = true
  dontuse["_"] = true
  dontuse["?"] = true
  dontuse[","] = true
  dontuse["|"] = true
  dontuse["\\"] = true
  dontuse["["] = true
  dontuse["]"] = true
  dontuse["{"] = true
  dontuse["}"] = true

local printtype = nil
local globalvars = {}
local calcdone = false
while not calcdone do
  local gInput = nil
  local fInput = nil
  local calculate = nil
  initializeCalc()
  local currentY = 1
  local input = {}
  input[1] = ""
  local inputDone = false
  while not inputDone do
    pressed = nil
    term.setCursorPos(2, #input + 4)
    term.setBackgroundColor(colors.green)
    term.write(stringW)
    term.setBackgroundColor(colors.lime)
    for i = 1, #input do
      term.setCursorPos(2, i + 3)
      term.write(stringW)
      term.setCursorPos(2, i + 3)
      for n = 1, #input[i] do
        letter = string.sub(input[i], n, n)
        if emphasis[letter] == true then
          term.setTextColor(colors.yellow)
        elseif letters[letter] == true then
          term.setTextColor(colors.pink)
        else
          term.setTextColor(colors.white)
        end
        term.write(letter)
      end
    end
    pressed = {os.pullEvent()}   -----------------------start---V
    if pressed[1] == "mouse_click" and pressed[2] == 1 and pressed[3] >= w - 3 and pressed[3] <= w and pressed[4] == h then
      calcdone = true
      break
    elseif pressed[1] == "mouse_click" and pressed[2] == 1 and pressed[3] >= 1 and pressed[3] <= 5 and pressed[4] == h then
      while true do
        local graphPosX = 0
        local graphPosY = 0
        w, h = term.getSize()
        term.setBackgroundColor(colors.blue)
        term.clear()
        term.setCursorPos(w/2 - 4, 1)
        term.write("Grapher")
        term.setCursorPos(1, 3)
        term.write("y=")
        term.setCursorPos(w - 3, h)
        term.setBackgroundColor(colors.blue)
        term.write("Back")
        pressed = {os.pullEvent()} -------start graph --v
        gInput = nil
        if pressed[1] == "mouse_click" and pressed[2] == 1 and pressed[4] == 3 then
          term.setCursorPos(3, 3)
          gInput = read()
        elseif pressed[1] == "mouse_click" and pressed[2] == 1 and pressed[3] >= w - 3 and pressed[3] <= w and pressed[4] == h then
          initializeCalc()
          break
        end
        if gInput then
          oTemp = fs.open("_runGraph", "w")
          oTemp.writeLine("graphtab = {}")
          oTemp.writeLine("for x = -100, 100 do")
          oTemp.writeLine("  graphtab[x] = " .. tostring(gInput))
          oTemp.writeLine("end")
          oTemp.flush()
          oTemp.close()
          os.loadAPI("_runGraph")
          local donegraphing = false
          while not donegraphing do
            term.setBackgroundColor(colors.black)
            term.clear()
            for i = graphPosX, w - graphPosX do
              paintutils.drawLine(i - graphPosX, h - _runGraph.graphtab[i] + 1 + graphPosY, i + 1 - graphPosX, h - _runGraph.graphtab[i + 1] + 1 + graphPosY, colors.green)
              term.setCursorPos(1, 1)
            end
            --[[for i, v in pairs(_runGraph.graphtab) do
              paintutils.drawPixel(i, h - v + 1, colors.blue)
              term.setCursorPos(1, 1)
            end]]--
            shell.run("delete _runGraph")
            pressed = {os.pullEvent()}
            if pressed[1] == "key" then
              if pressed[2] == 200 then  --up
                graphPosY = graphPosY - 1
              elseif pressed[2] == 208 then  --down
                graphPosY = graphPosY + 1
              elseif pressed[2] == 203 then  --left
                graphPosX = graphPosX + 1
              elseif pressed[2] == 205 then --right
                graphPosX = graphPosX - 1
              end
            end
          end
        end
      end
    end
    if #input[currentY] == w - 2 then
      currentY = currentY + 1
      input[currentY] = ""
    end
    if pressed[1] == "char" and not dontuse[pressed[2]] then
      input[currentY] = input[currentY] .. pressed[2]
    elseif pressed[1] == "key" then
      if pressed[2] == 14 then --delete
        if input[currentY] == "" and #input ~= 1 then
          input[currentY] = nil
          currentY = currentY - 1
        end
        input[currentY] = string.sub(input[currentY], 0, #input[currentY] - 1)
      elseif pressed[2] == 28 then --enter
        inputDone = true
      end
    end
  end
  if calcdone then break end
  local fInput = ""
  for i = 1, #input do
    fInput = fInput .. input[i]
  end
  local var = nil
  local varnum = nil
  var = string.find(fInput, "=")
  if var then
    printtype = "var"
    var = nil
    varnum = 0
    for i, v in pairs(letters) do
      local stringstart = 0
      while string.find(fInput, i, stringstart) do
        var = string.find(fInput, i, stringstart)
        if var then
          stringstart = var + 1
          varnum = varnum + 1
        end
      end
    end
    for i = 1, #tostring(fInput) do
      for k, e in pairs(letters) do
        if string.sub(fInput, i, i) == k then
          var = i
          break
        end
      end
      if var then
        break
      end
    end
    varnum = string.sub(fInput, var - 1, varnum)
    --term.setBackgroundColor(colors.blue)
    --print(varnum)
    globalvars[#globalvars + 1] = varnum
    --fInput = string.sub(#tostring(fInput), 1, var - 1) .. " local " .. string.sub(tostring(fInput), var, #tostring(fInput))
  else
    fInput = "answer = " .. tostring(fInput)
    printtype = "math"
  end
  answer = nil
  calculate = nil
  calculate = loadstring(fInput)
  calculate()
  term.setBackgroundColor(colors.black)
  term.setTextColor(colors.white)
  if printtype == "math" then
    term.setCursorPos(w / 2 - #tostring(answer) / 2, h - 1)
    term.write(answer)
  elseif printtype == "var" then
    term.setCursorPos(w / 2 - #tostring(varnum) / 2, h - 1)
    term.write(fInput)
  end
  sleep(2)
end

local vnil = nil
for i, v in pairs(globalvars) do
  --print(v .. " = nil")
  vnil = loadstring(v .. " = nil")
  vnil()
end