-- Space Ace (ReadySoft 1989, WHDLoad v1.3): a demo player, not an arena bot.
--
-- Space Ace is a laserdisc game: every scene is a clip, and the game checks
-- for one move at fixed moments of it. The moves are in the game's own
-- table, so this bot reads the answer from RAM instead of carrying the
-- walkthrough. Found under playbooks/spaceace/spaceace.hdf (AROS ROM, 2 MB
-- chip, 8 MB fast so WHDLoad preloads the four disks):
--
--   $158.w   the stick as the game reads it each frame (JOY1DAT and fire)
--   $160.w   the moves pressed since the last check, OR-ed: fire 1, down 2,
--            right 4, up $200, left $400. A second press before the check
--            makes it $606, a wrong move. Cleared by every check.
--   $15a.l   frames since the last press; a right move scores only if
--            pressed fewer than 90 frames before its check
--   $326.w   the part of the game (1..4; 4 is Borf)
--   $267.b   the scene within the part
--   $269.b   the moment within the scene, one step about every 7 frames
--   $380e    per part, a word offset (from $380e) to the part's checks:
--            6-byte entries {scene, moment, move.w, outcome.b, pad.b}, ended
--            by scene 0. moment >= $80 means "this move at any moment is
--            fatal"; otherwise the move must be in $160 when $269 reaches
--            the moment, or the clip of outcome (a death) plays
--            (the check is at $18a8 in the game's code).
--
-- The bot presses each expected move LEAD moments before its check, once
-- per visit to the scene (a death replays it), for HOLD frames, so it is
-- one clean press.

local PART, SCENE, MOMENT, PENDING = 0x326, 0x267, 0x269, 0x160
local TABLE = 0x380e
local LEAD, HOLD = 1, 3

local BITS = { [0x1] = 16, [0x2] = 2, [0x4] = 8, [0x200] = 1, [0x400] = 4 }
-- what the bot says as it presses (say(): the watcher's panel)
local WORDS = { [16] = "fire!", [2] = "moving down", [8] = "moving right", [1] = "moving up", [4] = "moving left" }
local say = say or function() end

local checks = {}          -- per part: list of {scene, moment, move}
local function load_part(part)
  if checks[part] then return checks[part] end
  local off = ram.u16(TABLE + (part - 1) * 2)
  if not off then return nil end
  if off >= 0x8000 then off = off - 0x10000 end
  local a, list = TABLE + off, {}
  for k = 0, 63 do
    local scene = ram.u8(a + 6 * k)
    if scene == 0 then break end
    local moment = ram.u8(a + 6 * k + 1)
    local move = ram.u16(a + 6 * k + 2)
    if moment < 0x80 and BITS[move] then list[#list + 1] = { scene, moment, move } end
  end
  checks[part] = list
  return list
end

local done = {}            -- "part:scene:moment" pressed on this visit
local was_scene, was_moment, was_part
local press_left, press_bits = 0, 0
local stats = { presses = 0 }

function init(port, players)
  print(string.format("spaceace bot on port %d", port))
end

function frame(n)
  local part, scene, moment = ram.u16(PART), ram.u8(SCENE), ram.u8(MOMENT)
  if not part or part < 1 or part > 4 then return 0 end
  -- a new visit to a scene (or a replay after a death): forget its presses
  if scene ~= was_scene or part ~= was_part or (was_moment and moment < was_moment) then done = {} end
  was_scene, was_moment, was_part = scene, moment, part

  if press_left > 0 then
    press_left = press_left - 1
    return press_bits
  end

  local list = load_part(part)
  if not list then return 0 end
  -- the next check of this scene not yet passed
  local best
  for _, c in ipairs(list) do
    if c[1] == scene and c[2] >= moment and (not best or c[2] < best[2]) then
      local key = part .. ":" .. scene .. ":" .. c[2]
      if not done[key] then best = c end
    end
  end
  if best and best[2] - moment <= LEAD and ram.u16(PENDING) == 0 then
    done[part .. ":" .. scene .. ":" .. best[2]] = true
    press_bits, press_left = BITS[best[3]], HOLD - 1
    stats.presses = stats.presses + 1
    say(string.format("%s  (part %d, scene %d, move %d)", WORDS[press_bits], part, scene, stats.presses))
    return press_bits
  end
  return 0
end