vars /allvars
  U[64] buf         // A buffer that can store the current and next row
  U curr_gen = 0       // Swap these offsets back and forth per generation
  U next_gen = 32
  UU drawing_row_offset = 0  // Use this to track which row we're drawing
  U current_rule = 73

fn init_eca_state()
  // Scroll to attributes
  ppu_reset_addr($2000 + 960)
  // Set attributes for background
  for U i = 0; i < 64; i+= 1
    {PPUDATA}(%11111111)

  // Init the buffer to zero
  buf = U[64]()
  // Add an initial cell
  buf[16] = 1


fn assemble_code(U left, U middle, U right) U
  U out = %00000000
  out |= left << 2
  out |= middle << 1
  out |= right
  return out

fn calc_next_cell(U left, U middle, U right) U
  U code = assemble_code(left, middle, right)
  ct U mask7 = %10000000
  ct U mask6 = %01000000
  ct U mask5 = %00100000
  ct U mask4 = %00010000
  ct U mask3 = %00001000
  ct U mask2 = %00000100
  ct U mask1 = %00000010
  ct U mask0 = %00000001
  switch code
    case %00000111
      return (current_rule & mask7) >> 7
    case %00000110
      return (current_rule & mask6) >> 6
    case %00000101
      return (current_rule & mask5) >> 5
    case %00000100
      return (current_rule & mask4) >> 4
    case %00000011
      return (current_rule & mask3) >> 3
    case %00000010
      return (current_rule & mask2) >> 2
    case %00000001
      return (current_rule & mask1) >> 1
    case %00000000
      return (current_rule & mask0) >> 0

fn calc_and_advance_gen()
  // Calculate the next row's values
  U left_ind = 0
  U right_ind = 0
  U left_cell = 0
  U mid_cell = 0
  U right_cell = 0
  U next_cell = 0
  for U i = 0; i < 32; i += 1
    // Calculate indices for left and right of cell
    if i == 0
      left_ind = 31
    else
      left_ind = i - 1
    if i == 31
      right_ind = 0
    else
      right_ind = i + 1
    // Get left and right of cell
    left_cell = buf[curr_gen + left_ind]
    mid_cell = buf[curr_gen + i]
    right_cell = buf[curr_gen + right_ind]
    // Calc next cell
    next_cell = calc_next_cell(left_cell, mid_cell, right_cell)
    // Set next cell
    buf[next_gen + i] = next_cell

  // Advance next generation
  if curr_gen == 0
    curr_gen = 32
    next_gen = 0
  else
    curr_gen = 0
    next_gen = 32

  // advance drawing row offset, looping back to top
  drawing_row_offset += 1
  if drawing_row_offset == 30
    drawing_row_offset = 0

fn upload_curr_gen()
  // "scroll" to the row we're at
  UU row_start = $2000
  row_start += (drawing_row_offset * 32)
  ppu_reset_addr(row_start)
  for U i = 0; i < 32; i += 1 //32 columns
    //next_cell = 0 //get_next_gen(i)
    {PPUDATA}(buf[i+curr_gen])


nmi eca_nmi()
  // Turn on rendering sprites and bg
  {PPUMASK}(PPUMASK_ON | PPUMASK_NO_CLIP)

  upload_curr_gen()

  ppu_reset_scroll(0, 0)

// Main mode for running the ECA
mode eca_main()
: nmi eca_nmi
  // Initialize the screen
  init_eca_state()
  // Wait 10 frames
  nmi
  nmi
  nmi
  nmi
  nmi
  nmi
  nmi
  nmi
  nmi
  nmi
  // Loop forever:
  while true
    nmi
    calc_and_advance_gen()

charmap(".#-=n!@~E$%^S&*(C)_+A{}|12345678qwertyuiop<asd>")

data /titlescreen
    [] title
        ("................................"
         "................................"
         "................................"
         "................................"
         "..........############.........."
         ".........##############........."
         ".........##..........##........."
         ".........##..........##........."
         ".........##..n!E$S&..##........."
         ".........##..@~%^*(..##........."
         ".........##....C)....##........."
         ".........##...._+....##........."
         ".........##....A{....##........."
         ".........##....}|....##........."
         ".........##..........##........."
         ".........##..........##........."
         ".........##############........."
         "..........############.........."
         "................................"
         "................................"
         "...........###########.........."
         "..........#..........#.........."
         "..........#.12345678.#.........."
         "..........#...<...>..#.........."
         "..........#..........#.........."
         "..........###########..........."
         "................................"
         "................................"
         "................................"
         "................................"
         "................................")

vars /titlescreen
  UU wipeline = 0

// nmi for entrypoint for the program
nmi main_nmi()
  // Turn on rendering sprites and bg
  {PPUMASK}(PPUMASK_ON | PPUMASK_NO_CLIP)

  ppu_reset_scroll(0, 0)

  if wipeline
    UU row_start = $2000
    row_start += ((wipeline - 1) * 32)
    ppu_reset_addr(row_start)
    for U i = 0; i < 32; i += 1 //32 columns
      //next_cell = 0 //get_next_gen(i)
      {PPUDATA}(0)

// The main entry point for the program
mode main()
: nmi main_nmi
  // Set the palette:
  palette = example_palette
  ppu_upload_palette()

  ppu_reset_addr($2000)

  // Load the title screen
  CCC/titlescreen titlep = @title
  for UU i = 0; i < 960; i += 1
    {PPUDATA}(titlep{i})

  for UU i = 0; i < 64; i += 1
    {PPUDATA}(%00000000)
  
  // Turn rendering on
  {PPUMASK}(PPUMASK_BG_ON)

  // Turn the NMI on
  {PPUCTRL}(PPUCTRL_NMI_ON)

  // Display title screen for 120 frames
  for U i = 0; i < 120; i += 1
    nmi

  for U i = 1; i <= 30; i += 1 // use this to wipe the screen
    wipeline = i
    nmi

  // Go to the main eca mode
  goto mode eca_main()
  : preserves /allvars

// Define the tileset (commonly called CHR):
chrrom
  file(fmt, "spritesheet.chr")