bgColor = -1 -- white
fontW, fontH = 16, 16
displayCols, displayRows = 40, 10
displayW, displayH = fontW*displayCols, fontH*displayRows
width, height = displayW, displayH
cursorBlinkRate = 500
--eventRate = 50
eventRate = 20 -- high speed!
eventsPerCursorBlink = cursorBlinkRate/eventRate
needsRepaint = false
repaintTriggeringVars = {"curX", "curY", "cursorVisible", "scrollX", "scrollY"}
fatCursor = true

-- volatile data
if not inited then
  scrollX, scrollY = 0, 0
  curX, curY = 0, 0
  lines = {"hello", "world"}
  needsRepaint = true
  inited = true
end

local min, max = math.min, math.max

get("#109") -- copyRect

fontRendererEnv = newCleanEnv()
fontRenderer = get("#178", fontRendererEnv)

grab("#175") -- tableToString

function renderText(x, y, s)
  --print("renderText", x, y, s)
  fontRendererEnv.render(s)
  --print("fontWidth="..tostring(fontRendererEnv.fontWidth))
  copyRect(fontRendererEnv, _G, 0, 0, fontRendererEnv.width, fontRendererEnv.height, x, y)
  --[[for y=0, 1 do
    for x=0, 15 do
      print(fontRendererEnv.pixels[x+y*fontRendererEnv.width+1])
    end
  end]]
end

function setPixel(x, y, col)
  if x >= 0 and y >= 0 and x < displayW and y < displayH then
    pixels[x+y*width+1] = col
  end
end

function invertPixel(x, y)
  if x >= 0 and y >= 0 and x < displayW and y < displayH then
    local ofs = x+y*width+1
    pixels[ofs] = pixels[ofs] and -1-pixels[ofs] or -1
  end
end

function stepCursor()
  if lastCurX ~= curX or lastCurY ~= curY then
    cursorCount = -1
  end
  lastCurX = curX
  lastCurY = curY
  cursorCount = (cursorCount+1) % (eventsPerCursorBlink*2)
  cursorVisible = cursorCount < eventsPerCursorBlink
end

function renderCursor()
  if cursorVisible then
    for x=0, fatCursor and fontW-1 or 0 do
      for y=0, fontH-1 do
        invertPixel((curX-scrollX)*fontW+x, (curY-scrollY)*fontH+y)
      end
    end
  end
end

function cursorLeft()
  if curX > 0 then
    curX=curX-1
  elseif curY > 0 then
    curY=curY-1
  end
end

function cursorRight()
  curX=curX+1
end

function cursorUp()
  if curY > 0 then
    curY=curY-1
  end
end

function cursorDown()
  if curY < #lines-1 then
    curY=curY+1
  end
end

function saveVars()
  savedVars = {}
  for _, var in ipairs(repaintTriggeringVars) do
    savedVars[var] = _G[var]
  end
end

function compareVars()
  for _, var in ipairs(repaintTriggeringVars) do
    if savedVars[var] ~= _G[var] then
      needsRepaint = true
      return
    end
  end
end

function moveCursorToSpot(x, y)
  local col = math.floor((x+scrollX)/fontW)
  local row = math.floor((y+scrollY)/fontH)
  row = max(0, min(row, #lines-1))
  col = max(0, col)
  curX, curY = col, row
end

function processEvents()
  saveVars()
  
  if inputEvents then
    for _, e in ipairs(inputEvents) do
      --print("event:", tableToString(e))
      if e[1] == 'keyPressed' then
        if e.keyCode == 39 then
          cursorRight()
        elseif e.keyCode == 37 then
          cursorLeft()
        elseif e.keyCode == 40 then
          cursorDown()
        elseif e.keyCode == 38 then
          cursorUp()
        end
      elseif e[1] == 'mousePressed' then
        moveCursorToSpot(e.x, e.y)
      end
    end
  end
  
  stepCursor()
  
  compareVars()
end

function render()
  if needsRepaint then
    pixels = {}
    for i = 1, width*height do pixels[i] = bgColor end

    for l = 1, min(#lines-scrollY, displayRows) do
      renderText(0, (l-1)*fontH, lines[l+scrollY]:sub(scrollX+1, scrollX+1+displayCols))
    end
    
    renderCursor()
    needsRepaint = false
  end
end

function step()
  pixels = nil
  processEvents()
  render()
end

step()
animateAgainIn = {eventRate, step}