snake-python/snakes/strategies/prism.py

"""PrismBattleSnake_GPT_5_6_Sol v1.5.0

Built on ApexBattleSnake v1.0.0.  All strategic logic is inherited.
Performance improvement: all spatial primitives (flood fill, territory,
articulation detection, distance maps, pathfinding) replaced by a
bitboard engine that uses integer arithmetic instead of Python sets/deques.

Key speedups:
  S1: Bitboard flood fill — replaces BFS deque+set with integer bit-expansion.
    ~60× faster per call, eliminates _neighbors() generator overhead.
  S2: Bitboard territory — dual-BFS expansion on ints replaces per-cell
    distance-map comparison loop.
  S3: Bitboard articulation — partition sizes via bit-flood instead of
    _bounded_bfs with sets.
  S4: Bitboard distance map — BFS via bit-expansion + bit-extract.
  S5: Bitboard path distance — early-exit BFS on ints.
  S6: Bitboard nearest food — BFS food search on ints.
  S7: Per-turn BitBoard instance cached for board dimensions.
  S8: Blocked-set → bitboard conversion cached within a turn to avoid
    redundant O(n) conversions for the same frozen set.
  S9: Survival-tree uses bitboards natively — enemy body/attack bits
    precomputed once at tree root, no per-node set/dict rebuilds.
  S10: _legal_moves override uses bitboard neighbour mask instead of
     per-direction Python loop + _in_bounds calls.
  S11: _future_survival_tree inlines legal-move check with bitboard ops.
  S12: Duel minimax uses tuple bodies and bitboard move generation.
  S13: Iterative deepening reuses a transposition table and move-order hints.
  S14: Candidate duel moves and enemy replies resolve on the same root turn.
  S15: Candidate moves share one duel transposition/search context per turn.
  S16: Compact adversarial multiplayer rollout advances plausible enemy replies.
  S17: Rollout memoization and adaptive depth spend time on ambiguous positions.
  S18: Prism uses a deeper tactical horizon while retaining Apex's timeout reserve.
  S19: Rollout occupancy and evaluation caches avoid repeated flood-fill work.
"""

from __future__ import annotations

from server.GameBoard import GameBoard
from snakes.engine.bitboard import BitBoard
from snakes.engine.duel import BitboardDuelMixin
from snakes.engine.duel_search import BitboardDuelSearch
from snakes.engine.spatial import BitboardSpatialMixin
from snakes.engine.survival import BitboardSurvivalMixin
from snakes.engine.survival_search import CompactSurvivalSearch
from snakes.strategies.apex import ApexBattleSnake

# Direction offsets for coord-dict → tuple conversion
_DIR_DELTAS = ((0, 1), (0, -1), (-1, 0), (1, 0))
_DIR_NAMES = ("up", "down", "left", "right")

class PrismBattleSnake_GPT_5_6_Sol(
  BitboardDuelMixin,
  BitboardSurvivalMixin,
  BitboardSpatialMixin,
  ApexBattleSnake,
):
  VERSION = "1.5.0"

  def __init__(self) -> None:
    super().__init__()
    self.name = "PrismBattleSnake"
    self.version = self.VERSION

    # Prism's compact state search is fast enough to inspect one additional
    # turn. The existing deadline checks and Apex timeout reserve still cap the
    # work on difficult positions.
    self._planning_depth = max(self._planning_depth, 4)

    # S7: cached BitBoard instance (reused while board dimensions stay the same)
    self._bb: BitBoard | None = None
    self._bb_w: int = 0
    self._bb_h: int = 0

    # S9: precomputed enemy state for survival tree (set per turn in choose_move)
    self._enemy_body_bits: int = 0  # all enemy body cells as bitboard
    self._enemy_tail_bits: int = 0  # enemy tails that will vacate
    self._enemy_attack_danger: int = 0  # tiles where enemy len >= our len
    self._enemy_attack_opportunity: int = 0  # tiles where enemy len < our len

    # Shared per-turn search contexts. Candidate moves overlap heavily, so
    # rebuilding their transposition tables wastes most iterative-deepening work.
    self._duel_search_context: BitboardDuelSearch | None = None
    self._survival_search_context: CompactSurvivalSearch | None = None

  # ── choose_move override: precompute enemy bits ──────────────────────────

  def choose_move(self, game_data: GameBoard) -> str:
    bb = self._get_bb(game_data.get_width(), game_data.get_height())
    self._duel_search_context = None
    self._survival_search_context = None

    # S9: precompute enemy body / tail / attack bitboards for survival tree
    other_snakes = game_data.get_other_snakes()
    my_snake = game_data.get_my_snake()
    my_len = my_snake.get("length", len(my_snake["body"]))
    food_set = {(f["x"], f["y"]) for f in game_data.get_food()}
    all_occupied = {
      (seg["x"], seg["y"])
      for snake in [my_snake, *other_snakes]
      for seg in snake["body"]
    }
    game_type = game_data.get_type()
    is_constrictor = game_type == "constrictor"
    w = bb.width

    enemy_body_bits = 0
    enemy_tail_bits = 0
    enemy_attack_danger = 0
    enemy_attack_opportunity = 0

    for snake in other_snakes:
      for seg in snake["body"]:
        enemy_body_bits |= 1 << (seg["y"] * w + seg["x"])
      body = snake["body"]
      # Check if tail will vacate
      if not is_constrictor and len(body) >= 2:
        tail_stacked = (
          body[-1]["x"] == body[-2]["x"] and body[-1]["y"] == body[-2]["y"]
        )
        if not tail_stacked:
          can_grow = self._enemy_can_grow_this_turn(
            snake, food_set, all_occupied
          )
          if not can_grow:
            enemy_tail_bits |= 1 << (body[-1]["y"] * w + body[-1]["x"])

      # Attack map: tiles enemy head can reach in 1 move
      eh = snake["head"]
      e_len = snake.get("length", len(body))
      ehx, ehy = eh["x"], eh["y"]
      for dx, dy in _DIR_DELTAS:
        nx, ny = ehx + dx, ehy + dy
        if 0 <= nx < w and 0 <= ny < bb.height:
          bit = 1 << (ny * w + nx)
          if e_len >= my_len:
            enemy_attack_danger |= bit
          else:
            enemy_attack_opportunity |= bit

    self._enemy_body_bits = enemy_body_bits
    self._enemy_tail_bits = enemy_tail_bits
    self._enemy_attack_danger = enemy_attack_danger
    self._enemy_attack_opportunity = enemy_attack_opportunity

    move = super().choose_move(game_data)
    history = self.get_history()
    if history:
      thinking = history[-1]
      if self._duel_search_context is not None:
        thinking["prism_duel_depth"] = self._duel_search_context.completed_depth
        thinking["prism_duel_nodes"] = self._duel_search_context.nodes
        thinking["prism_duel_cache_hits"] = (
          self._duel_search_context.cache_hits
          + self._duel_search_context.evaluation_cache_hits
        )
        thinking["prism_duel_deadline_exits"] = (
          self._duel_search_context.deadline_exits
        )
      if self._survival_search_context is not None:
        thinking["prism_rollout_depth"] = (
          self._survival_search_context.completed_depth
        )
        thinking["prism_rollout_nodes"] = self._survival_search_context.nodes
        thinking["prism_rollout_cache_hits"] = (
          self._survival_search_context.cache_hits
          + self._survival_search_context.evaluation_cache_hits
        )
        thinking["prism_rollout_deadline_exits"] = (
          self._survival_search_context.deadline_exits
        )
    return move