pf1e-simulator/src/pf1e_simulator/combat.py

"""Deterministic combat engine: attacks, crits, DR, hp states, initiative, rounds.

Phase 0 documented deviations from PF1e (conventions):
- One action per turn: move OR attack (no move+attack, no AoO, no flanking).
- Natural 1 always misses; natural 20 always hits and threatens a crit.
- A confirmed crit multiplies the total damage (dice + flat bonus) by crit_mult.
- DR applies once, after crit multiplication; any bypassing type defeats DR.
- Death when hp < min(-10, -CON); hp <= 0 cannot act.
- Initiative ties: higher initiative_mod first, then list order (no re-roll).
- Movement: one step per move action toward the nearest enemy, following the
  true shortest path (Dijkstra cost field from the target); ties keep delta order.
- Line of effect gates all attacks: a target fully behind blocking terrain
  cannot be attacked, and the policy moves to gain sight instead.
- Cover (corner rule) grants +4 AC on hit and crit-confirm rolls; melee and
  ranged reuse the same corner rule.
- Ranged: only the first range increment is enforced in Phase 0 (no distance
  penalty, no soft cover from creatures).
"""

from __future__ import annotations

from collections.abc import Callable
from dataclasses import asdict, dataclass
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from typing import Literal

    from pf1e_simulator.grid import Grid
    from pf1e_simulator.map import Pos
    from pf1e_simulator.models import AttackSpec, Combatant, DamageReduction
    from pf1e_simulator.rng import Rng

from pf1e_simulator.los import has_cover, has_line_of_effect

_SQUARE_FT = 5  # Phase 0 maps use 5-ft squares
_DEATH_FLOOR = -10  # PF1e: dead when hp < -10 or -CON, whichever is lower
_NATURAL_ONE = 1  # PF1e: natural 1 always misses
_NATURAL_TWENTY = 20  # PF1e: natural 20 always hits and threatens
_COVER_AC_BONUS = 4  # PF1e: partial cover grants +4 AC

_STEP_DELTAS: tuple[Pos, ...] = (
    (-1, -1),
    (-1, 0),
    (-1, 1),
    (0, -1),
    (0, 1),
    (1, -1),
    (1, 0),
    (1, 1),
)


@dataclass(frozen=True)
class CombatantStats:
    """Aggregated outcomes for one combatant over a battle."""

    hits: int = 0
    crits: int = 0
    damage_dealt: int = 0
    damage_taken: int = 0


@dataclass
class CombatantState:
    """Mutable runtime state of one combatant on the grid."""

    combatant: Combatant
    side: str
    pos: Pos
    hp: int

    @property
    def active(self) -> bool:
        return self.hp > 0

    @property
    def dead(self) -> bool:
        return self.hp < self.death_threshold

    @property
    def death_threshold(self) -> int:
        return min(_DEATH_FLOOR, -self.combatant.abilities.con_score)


@dataclass(frozen=True)
class AttackResult:
    """Outcome of one attack roll, including the raw rolls for the log."""

    hit: bool
    crit: bool
    damage: int
    roll: int
    total: int
    ac: int


@dataclass(frozen=True)
class Action:
    """What a policy wants a combatant to do this turn."""

    kind: Literal["attack", "move", "wait"]
    target_id: str | None = None


@dataclass(frozen=True)
class CombatResult:
    """Outcome of a full battle: winner, rounds, log, and per-combatant stats."""

    winner: str | None
    rounds: int
    transcript: tuple[str, ...]
    stats: dict[str, CombatantStats]


@dataclass
class _LiveStats:
    hits: int = 0
    crits: int = 0
    damage_dealt: int = 0
    damage_taken: int = 0


class CombatEngine:
    """Runs one battle to completion on a grid with a single RNG stream."""

    def __init__(
        self,
        rng: Rng,
        grid: Grid,
        states: list[CombatantState],
        *,
        round_cap: int = 100,
        policy: Policy | None = None,
    ) -> None:
        self._rng = rng
        self._grid = grid
        self._states = states
        self._round_cap = round_cap
        self._policy = policy if policy is not None else default_policy
        self._transcript: list[str] = []
        self._stats: dict[str, _LiveStats] = {s.combatant.id: _LiveStats() for s in states}

    def run(self) -> CombatResult:
        """Run the battle and return the final result and transcript."""
        order = self._roll_initiative()
        round_no = 1
        while round_no <= self._round_cap:
            for state in order:
                if not state.active:
                    continue
                action = self._policy(self, state)
                self._execute(state, action, round_no)
                if self._winner_side() is not None:
                    break
            if self._winner_side() is not None:
                break
            round_no += 1
        winner = self._winner_side()
        if winner is not None:
            self._log(f"battle over: {winner} win in {round_no} rounds")
        else:
            self._log(f"battle over: draw after {self._round_cap} rounds")
        stats = {cid: CombatantStats(**asdict(live)) for cid, live in self._stats.items()}
        return CombatResult(
            winner=winner,
            rounds=round_no if winner is not None else self._round_cap,
            transcript=tuple(self._transcript),
            stats=stats,
        )

    def nearest_enemy(self, state: CombatantState) -> CombatantState | None:
        """Closest active enemy by grid distance; ties keep list order."""
        enemies = [s for s in self._states if s.side != state.side and s.active]
        if not enemies:
            return None
        return min(
            enemies,
            key=lambda s: (self._grid.distance(state.pos, s.pos), self._states.index(s)),
        )

    def weapon_for(self, attacker: CombatantState, target: CombatantState) -> AttackSpec | None:
        """First weapon usable against the target at this range and with clear LoE."""
        if not has_line_of_effect(self._grid, attacker.pos, target.pos):
            return None
        dist_ft = self._grid.distance(attacker.pos, target.pos) * _SQUARE_FT
        for weapon in attacker.combatant.attacks:
            if weapon.kind in ("melee", "touch") and dist_ft <= weapon.reach_ft:
                return weapon
            if (
                weapon.kind == "ranged"
                and weapon.range_increment_ft is not None
                and dist_ft <= weapon.range_increment_ft
            ):
                return weapon
        return None

    def resolve_attack(
        self, attacker: CombatantState, target: CombatantState, weapon: AttackSpec
    ) -> AttackResult:
        """Roll one attack (with crit confirm and damage) and apply it."""
        roll = self._rng.d20()
        total = roll + weapon.attack_bonus
        ac = target.combatant.ac.total
        if has_cover(self._grid, attacker.pos, target.pos, ranged=weapon.kind == "ranged"):
            ac += _COVER_AC_BONUS
        hit = roll == _NATURAL_TWENTY or (roll != _NATURAL_ONE and total >= ac)
        crit = False
        damage = 0
        if hit:
            if roll != _NATURAL_ONE and roll >= weapon.crit_range:
                confirm = self._rng.d20()
                crit = confirm != _NATURAL_ONE and confirm + weapon.attack_bonus >= ac
            damage = sum(c.formula.roll(self._rng) for c in weapon.damage) + weapon.damage_bonus
            if crit:
                damage *= weapon.crit_mult
            damage = self._apply_dr(damage, weapon, target)
        target.hp -= damage
        return AttackResult(hit=hit, crit=crit, damage=damage, roll=roll, total=total, ac=ac)

    def _apply_dr(self, damage: int, weapon: AttackSpec, target: CombatantState) -> int:
        dr: DamageReduction | None = target.combatant.dr
        if dr is None:
            return damage
        types = {t for component in weapon.damage for t in component.types}
        if types & dr.bypass:
            return damage
        return max(0, damage - dr.amount)

    def _roll_initiative(self) -> list[CombatantState]:
        rolls: dict[str, tuple[int, int]] = {}
        for state in self._states:
            roll = self._rng.d20()
            rolls[state.combatant.id] = (roll, roll + state.combatant.initiative_mod)
        order = sorted(
            self._states,
            key=lambda s: (
                rolls[s.combatant.id][1],
                s.combatant.initiative_mod,
                self._states.index(s),
            ),
            reverse=True,
        )
        for state in order:
            roll, total = rolls[state.combatant.id]
            self._log(
                f"initiative: {state.combatant.id} "
                f"d20={roll}+{state.combatant.initiative_mod}={total}"
            )
        return order

    def _winner_side(self) -> str | None:
        active_sides = {s.side for s in self._states if s.active}
        if len(active_sides) == 1:
            return active_sides.pop()
        return None

    def _execute(self, state: CombatantState, action: Action, round_no: int) -> None:
        target = next((s for s in self._states if s.combatant.id == action.target_id), None)
        if action.kind == "attack":
            if target is None or not target.active:
                self._log(f"round {round_no} {state.combatant.id}: wait")
                return
            weapon = self.weapon_for(state, target)
            if weapon is None:
                self._log(f"round {round_no} {state.combatant.id}: wait")
                return
            self._attack(state, target, weapon, round_no)
        elif action.kind == "move":
            if target is None:
                self._log(f"round {round_no} {state.combatant.id}: wait")
                return
            self._move(state, target, round_no)
        else:
            self._log(f"round {round_no} {state.combatant.id}: wait")

    def _attack(
        self, attacker: CombatantState, target: CombatantState, weapon: AttackSpec, round_no: int
    ) -> None:
        hp_before = target.hp
        result = self.resolve_attack(attacker, target, weapon)
        live = self._stats[attacker.combatant.id]
        live.hits += int(result.hit)
        live.crits += int(result.crit)
        live.damage_dealt += result.damage
        self._stats[target.combatant.id].damage_taken += result.damage
        outcome = "CRIT" if result.crit else "HIT" if result.hit else "MISS"
        line = (
            f"round {round_no} {attacker.combatant.id}: {weapon.name} vs {target.combatant.id} "
            f"d20={result.roll}+{weapon.attack_bonus}={result.total} AC {result.ac} -> {outcome}"
        )
        if result.hit:
            line += f" {result.damage} damage ({hp_before}->{target.hp})"
        self._log(line)
        if target.dead:
            self._log(f"round {round_no} {attacker.combatant.id}: {target.combatant.id} dead")
        elif not target.active:
            self._log(f"round {round_no} {attacker.combatant.id}: {target.combatant.id} down")

    def _move(self, state: CombatantState, target: CombatantState, round_no: int) -> None:
        step = self._step_toward(state, target)
        if step is None:
            self._log(f"round {round_no} {state.combatant.id}: wait")
            return
        self._log(
            f"round {round_no} {state.combatant.id}: move "
            f"({state.pos[0]},{state.pos[1]})->({step[0]},{step[1]})"
        )
        state.pos = step

    def _step_toward(self, state: CombatantState, target: CombatantState) -> Pos | None:
        speed_cells = state.combatant.speed_land_ft // _SQUARE_FT
        if speed_cells <= 0:
            return None
        blocked = frozenset(s.pos for s in self._states if s is not state and s.active)
        to_target = self._grid.reachable(target.pos, None, blocked)
        if state.pos not in to_target:
            return None
        best: tuple[int, Pos] | None = None
        row, col = state.pos
        for d_row, d_col in _STEP_DELTAS:
            nxt = (row + d_row, col + d_col)
            cost = to_target.get(nxt)
            if cost is None:
                continue
            step = self._grid.step_cost(state.pos, nxt, 0)
            if step > speed_cells:
                continue
            score = step + cost
            if best is None or score < best[0]:
                best = (score, nxt)
        if best is None:
            return None
        return best[1]

    def _log(self, line: str) -> None:
        self._transcript.append(line)


Policy = Callable[[CombatEngine, CombatantState], Action]


def default_policy(engine: CombatEngine, state: CombatantState) -> Action:
    """Attack the nearest active enemy when a weapon is in range, else approach."""
    target = engine.nearest_enemy(state)
    if target is None:
        return Action(kind="wait")
    if engine.weapon_for(state, target) is not None:
        return Action(kind="attack", target_id=target.combatant.id)
    return Action(kind="move", target_id=target.combatant.id)