class_name SimWorld
extends RefCounted
## The whole game simulation for one instance (a lobby or one dungeon run).
##
## It is a plain RefCounted with no nodes, no physics server and no rendering,
## which buys three things: the dedicated server runs it headless at negligible
## cost, a unit test can drive a thousand ticks in milliseconds, and the client
## can run the exact same class in replica mode for prediction.
##
## Authority: [member authoritative] is true on the server only. In replica mode
## the world never runs AI, never fires emitters and never resolves a hit -- it
## only integrates bullets it was told about and holds actor state for drawing.
## That is the whole anti-cheat story: a client physically has no code path that
## can decide it dealt or avoided damage.

var tick: int = 0
var authoritative: bool = true
var pool := BulletPool.new()
var rng := RandomNumberGenerator.new()

var players: Dictionary[int, SimPlayer] = {}
var enemies: Dictionary[int, SimEnemy] = {}
var boss: SimBoss = null

## Drained by the owner every tick. See [SimEvent].
var events: Array[Dictionary] = []

## The world's static geometry. Never null: worlds without a generated map get
## a plain walled room, which keeps every caller free of null checks and lets a
## unit test build a world without thinking about terrain.
var map: MapGrid = null

## Set on a lobby world so the interact button can open a dungeon.
var portal_enabled: bool = false
## Where the hub's dungeon portal sits. Per-world now that maps vary in size.
var portal_pos := Vector2.ZERO
var spawn_point := Vector2(0.0, 240.0)
## Arrival protection granted to players entering this world. 0 in the hub,
## SimConfig.SPAWN_GRACE_TICKS in a dungeon.
var spawn_grace_ticks: int = 0

var _next_actor_id: int = 1
var _ctx := EmitContext.new()


func _init(seed_value: int = 0) -> void:
	rng.seed = seed_value
	_ctx.rng = rng
	set_map(_default_room())


## A walled box roughly the size of the old fixed arena, so a world built with
## no map behaves the way the game did before terrain existed.
static func _default_room() -> MapGrid:
	var g := MapGrid.new(42, 24, MapGrid.Kind.WALL)
	g.fill_rect(Rect2i(1, 1, 40, 22), MapGrid.Kind.FLOOR)
	g.centre_on_origin()
	return g


func set_map(new_map: MapGrid) -> void:
	map = new_map
	# The pool culls bullets against the same geometry, on both sides.
	pool.map = new_map


func next_actor_id() -> int:
	var id := _next_actor_id
	_next_actor_id += 1
	return id


# --- Population -------------------------------------------------------------

func add_player(peer_id: int, display_name: String) -> SimPlayer:
	var p := SimPlayer.new()
	p.peer_id = peer_id
	p.display_name = display_name
	p.reset_for_instance(spawn_point, spawn_grace_ticks)
	players[peer_id] = p
	return p


func remove_player(peer_id: int) -> void:
	players.erase(peer_id)


func spawn_enemy(def: EnemyDef, at: Vector2, phase_offset: int = 0) -> SimEnemy:
	var e := SimEnemy.new()
	e.id = next_actor_id()
	e.def = def
	e.pos = at
	e.home = at
	e.hp = def.max_hp
	e.phase_offset = phase_offset
	e.heading = Vector2.RIGHT.rotated(rng.randf() * TAU)
	enemies[e.id] = e
	return e


func spawn_boss(def: BossDef) -> SimBoss:
	var b := SimBoss.new()
	b.id = next_actor_id()
	b.def = def
	b.pos = def.spawn_pos
	b.hp = def.max_hp
	boss = b
	return b


func alive_player_count() -> int:
	var n := 0
	for p in players.values():
		if p.alive:
			n += 1
	return n


## Nearest living player to [param from]. Aimed emitters and chasing enemies use
## this; it is the only targeting primitive in the game.
func nearest_player(from: Vector2) -> SimPlayer:
	var best: SimPlayer = null
	var best_d := INF
	for p in players.values():
		if not p.alive:
			continue
		var d := from.distance_squared_to(p.pos)
		if d < best_d:
			best_d = d
			best = p
	return best


# --- Input ------------------------------------------------------------------

## Accept a batch of client inputs. Everything questionable is dropped here
## rather than deeper in, so there is a single place to audit.
func queue_input(peer_id: int, frames: Array[InputFrame]) -> void:
	var p: SimPlayer = players.get(peer_id)
	if p == null:
		return
	for f in frames:
		if f.tick <= p.last_input_tick:
			continue  # replay or out-of-order duplicate
		if f.tick < tick - SimConfig.INPUT_MAX_AGE:
			continue  # too old to matter
		if f.tick > tick + SimConfig.INPUT_MAX_LEAD:
			continue  # client claiming to be far in the future
		if p.input_queue.size() >= SimConfig.INPUT_MAX_AGE:
			p.input_queue.pop_front()  # flood guard
		p.input_queue.append(f)
	p.input_queue.sort_custom(func(a: InputFrame, b: InputFrame) -> bool: return a.tick < b.tick)


# --- Tick -------------------------------------------------------------------

func step() -> void:
	tick += 1
	if authoritative:
		pool.clear_spawn_log()
		_step_players()
		_step_enemies()
		_step_boss()
		pool.step()
		_resolve_bullet_hits()
		_emit_wall_kill_events()
		_emit_spawn_events()
	else:
		# Replica: bullets only. Actor state arrives in snapshots.
		pool.step()


func _step_players() -> void:
	for p in players.values():
		p.regenerate()
		if p.spawn_grace > 0:
			p.spawn_grace -= 1
		if p.fire_cooldown > 0:
			p.fire_cooldown -= 1

		var frame := _take_input(p)

		if not p.alive:
			if p.respawn_lockout > 0:
				p.respawn_lockout -= 1
			# No timed respawn: a downed player waits for the hub. Asking to go
			# is an input like any other, so a dead client cannot be revived by
			# anything except its own request reaching the server -- and not
			# before the lockout expires, however early its UI lets it ask.
			if p.can_request_respawn() and (frame.pressed(InputFrame.BTN_INTERACT) or p.linkdead):
				events.append({"t": SimEvent.Type.RESPAWN_REQUESTED, "peer": p.peer_id})
			continue

		p.aim = frame.aim
		p.pos = Movement.step_player(p.pos, frame.move, SimConfig.PLAYER_SPEED, map)

		if frame.pressed(InputFrame.BTN_FIRE) and p.can_fire():
			_fire_player_shot(p)

		_step_escape(p, frame)

		if portal_enabled and frame.pressed(InputFrame.BTN_INTERACT):
			if p.pos.distance_to(portal_pos) <= SimConfig.PORTAL_RADIUS:
				events.append({"t": SimEvent.Type.PORTAL_USED, "peer": p.peer_id})


## Pull the next input for this player, or coast on the last one. Coasting is
## capped so a client that stops sending cannot keep moving forever.
func _take_input(p: SimPlayer) -> InputFrame:
	if not p.input_queue.is_empty():
		var f: InputFrame = p.input_queue.pop_front()
		p.last_input_tick = f.tick
		p.held_input = f
		p.starved_ticks = 0
		return f
	p.starved_ticks += 1
	if p.starved_ticks > SimConfig.INPUT_MAX_AGE:
		var idle := InputFrame.new()
		idle.aim = p.held_input.aim
		p.held_input = idle
	return p.held_input


func _fire_player_shot(p: SimPlayer) -> void:
	p.fire_cooldown = SimConfig.PLAYER_FIRE_COOLDOWN
	events.append({"t": SimEvent.Type.PLAYER_FIRED, "peer": p.peer_id})
	var dir := Vector2.RIGHT.rotated(p.aim)
	pool.spawn(
		p.pos + dir * SimConfig.PLAYER_MUZZLE_OFFSET,
		dir * SimConfig.PLAYER_BULLET_SPEED,
		SimConfig.PLAYER_BULLET_RADIUS,
		SimConfig.PLAYER_BULLET_LIFETIME,
		SimConfig.PLAYER_BULLET_DAMAGE,
		SimConfig.TEAM_PLAYER,
		SimConfig.KIND_PLAYER_SHOT)


func _step_escape(p: SimPlayer, frame: InputFrame) -> void:
	# A dropped connection is treated as holding the button down. Pulling the
	# plug then costs exactly what pressing escape costs -- one second of
	# standing there, still killable -- instead of an instant, safe exit.
	if p.linkdead or frame.pressed(InputFrame.BTN_ESCAPE):
		if p.escape_ticks == 0:
			events.append({"t": SimEvent.Type.ESCAPE_STARTED, "peer": p.peer_id})
		p.escape_ticks += 1
		if p.escape_ticks >= SimConfig.ESCAPE_CHANNEL_TICKS:
			p.escape_ticks = 0
			events.append({"t": SimEvent.Type.ESCAPE_COMPLETED, "peer": p.peer_id})
	elif p.escape_ticks > 0:
		p.escape_ticks = 0
		events.append({"t": SimEvent.Type.ESCAPE_CANCELLED, "peer": p.peer_id})


func _step_enemies() -> void:
	for e in enemies.values():
		if not e.alive:
			continue
		# Aggro is re-evaluated every tick and gates both movement and fire, so
		# a dungeon full of enemies is quiet until you walk into it -- which is
		# what makes exploring a decision rather than a countdown.
		e.target = _aggro_target(e)
		_move_enemy(e)
		if e.target != null:
			_run_emitters(e.def.emitters, e.pos,
				posmod(e.local_tick + e.phase_offset, maxi(e.def.pattern_loop_ticks, 1)))
			e.local_tick += 1


## Nearest living player within aggro range and in line of sight. Sight matters
## as much as range: an enemy that shoots you through a wall makes cover
## meaningless, and one that never loses you makes retreating impossible.
func _aggro_target(e: SimEnemy) -> SimPlayer:
	var t := nearest_player(e.pos)
	if t == null:
		return null
	var range_sq: float = e.def.aggro_range * e.def.aggro_range
	if e.pos.distance_squared_to(t.pos) > range_sq:
		return null
	if not map.has_line_of_sight(e.pos, t.pos):
		return null
	return t


func _move_enemy(e: SimEnemy) -> void:
	var dt := SimConfig.TICK_DELTA
	var speed: float = e.def.speed
	match e.def.move:
		EnemyDef.Move.STATIC:
			pass
		EnemyDef.Move.DRIFT:
			# Drifters patrol whether or not they have seen anyone; everything
			# else only moves once aggroed.
			var delta := e.heading * speed * dt
			var next := map.slide_circle(e.pos, delta, e.def.radius)
			# Reflect on whichever axis the map refused. Works for the outer
			# wall and an interior pillar alike, with no special cases.
			if absf(next.x - e.pos.x) < absf(delta.x) - 0.001:
				e.heading.x = -e.heading.x
			if absf(next.y - e.pos.y) < absf(delta.y) - 0.001:
				e.heading.y = -e.heading.y
			e.pos = next
		EnemyDef.Move.ORBIT:
			var a := float(e.local_tick + e.phase_offset) * dt * (speed / maxf(e.def.move_param, 1.0))
			var want := e.home + Vector2.RIGHT.rotated(a) * e.def.move_param
			e.pos = map.slide_circle(e.pos, want - e.pos, e.def.radius)
		EnemyDef.Move.APPROACH:
			if e.target == null:
				return
			if e.local_tick % maxi(e.def.retarget_interval, 1) == 0:
				e.target_dir = (e.target.pos - e.pos).normalized()
			e.pos = map.slide_circle(e.pos, e.target_dir * speed * dt, e.def.radius)
		EnemyDef.Move.STRAFE:
			if e.target == null:
				return
			if e.local_tick % maxi(e.def.retarget_interval, 1) == 0:
				var to_player := e.target.pos - e.pos
				var d := to_player.length()
				var radial := 0.0
				if d > e.def.move_param + 20.0:
					radial = 1.0
				elif d < e.def.move_param - 20.0:
					radial = -1.0
				var toward := Vector2.ZERO if d < 0.001 else to_player / d
				e.target_dir = (toward * radial + toward.orthogonal() * 0.7).normalized()
			e.pos = map.slide_circle(e.pos, e.target_dir * speed * dt, e.def.radius)


func _step_boss() -> void:
	if boss == null or not boss.alive or boss.def == null:
		return
	var wanted := boss.def.phase_index_for(boss.hp_fraction())
	if wanted != boss.phase_index:
		boss.phase_index = wanted
		boss.phase_tick = 0
		events.append({"t": SimEvent.Type.BOSS_PHASE, "phase": wanted})
	var phase := boss.current_phase()
	if phase == null:
		return
	# A boss never leaves its arena. Enforced here rather than left to each
	# boss's movement code, because boss rooms deliberately do not lock: the
	# player can always walk out, and the fight only stays a fight if the boss
	# cannot follow. Currently a no-op (every boss is stationary), which is
	# exactly when an invariant is cheapest to establish.
	if boss.room.size != Vector2.ZERO:
		boss.pos = boss.room.position + Vector2(
			clampf(boss.pos.x - boss.room.position.x, 0.0, boss.room.size.x),
			clampf(boss.pos.y - boss.room.position.y, 0.0, boss.room.size.y))

	if boss.phase_tick >= phase.telegraph_ticks:
		var local := posmod(boss.phase_tick - phase.telegraph_ticks, maxi(phase.loop_ticks, 1))
		_run_emitters(phase.emitters, boss.pos, local, boss.room)
	boss.phase_tick += 1


## Shared emitter driver for enemies and bosses -- the reason a boss pattern can
## be dropped onto a trash mob and vice versa.
func _run_emitters(emitters: Array[BulletEmitter], origin: Vector2, local_tick: int,
		bounds: Rect2 = Rect2()) -> void:
	if emitters.is_empty():
		return
	var target := nearest_player(origin)
	_ctx.pool = pool
	_ctx.origin = origin
	# Curtain patterns span the room they are fired in. Without a room, fall
	# back to a box around the shooter rather than the whole map, or a trash
	# enemy would sweep bullets across the entire dungeon.
	_ctx.bounds = bounds if bounds.size != Vector2.ZERO \
		else Rect2(origin - Vector2(400.0, 300.0), Vector2(800.0, 600.0))
	_ctx.origin = origin
	_ctx.local_tick = local_tick
	_ctx.has_target = target != null
	_ctx.target = origin + Vector2.DOWN * 200.0 if target == null else target.pos
	for e in emitters:
		if e == null or not e.should_fire(local_tick):
			continue
		_ctx.shot_index = e.shot_index_at(local_tick)
		e.fire(_ctx)


# --- Hit resolution (server only) -------------------------------------------

func _resolve_bullet_hits() -> void:
	for i in pool.high_water:
		if pool.alive[i] == 0:
			continue
		var bp: Vector2 = pool.pos[i]
		var br: float = pool.radius[i]
		if pool.team[i] == SimConfig.TEAM_ENEMY:
			for p in players.values():
				# invulnerable() covers arrival grace as well as post-hit
				# i-frames -- a player who just walked into a live bullet field
				# must not be hit by what was already in the air.
				if not p.alive or p.invulnerable():
					continue
				if Movement.circles_overlap(bp, br, p.pos, SimConfig.PLAYER_RADIUS):
					_damage_player(p, pool.damage[i])
					_kill_bullet(i)
					break
		else:
			var consumed := false
			if boss != null and boss.alive \
					and Movement.circles_overlap(bp, br, boss.pos, boss.def.radius):
				_damage_boss(pool.damage[i])
				consumed = true
			if not consumed:
				for e in enemies.values():
					if not e.alive:
						continue
					if Movement.circles_overlap(bp, br, e.pos, e.def.radius):
						_damage_enemy(e, pool.damage[i])
						consumed = true
						break
			if consumed:
				_kill_bullet(i)


## Bullets removed early must be announced -- clients cannot derive a hit.
func _kill_bullet(slot: int) -> void:
	events.append({"t": SimEvent.Type.BULLET_DESPAWN, "uid": pool.uid[slot]})
	pool.despawn(slot)


## Damage deliberately does NOT interrupt an escape channel -- see the note on
## SimConfig.ESCAPE_CHANNEL_TICKS for why that would reward pulling the plug.
func _damage_player(p: SimPlayer, amount: int) -> void:
	p.hp = maxi(p.hp - amount, 0)
	events.append({"t": SimEvent.Type.PLAYER_HIT, "peer": p.peer_id, "dmg": amount, "hp": p.hp})
	if p.hp <= 0:
		p.alive = false
		p.escape_ticks = 0
		p.respawn_lockout = SimConfig.RESPAWN_LOCKOUT_TICKS
		events.append({"t": SimEvent.Type.PLAYER_DIED, "peer": p.peer_id})


func _damage_enemy(e: SimEnemy, amount: int) -> void:
	e.hp = maxi(e.hp - amount, 0)
	events.append({"t": SimEvent.Type.ENEMY_HIT, "id": e.id, "dmg": amount, "hp": e.hp})
	if e.hp <= 0:
		e.alive = false
		# The def id rides along so the instance layer can score it without
		# looking up an actor that is about to stop existing.
		events.append({"t": SimEvent.Type.ENEMY_DIED, "id": e.id, "def": String(e.def.id)})


func _damage_boss(amount: int) -> void:
	var phase := boss.current_phase()
	var mult := 1.0 if phase == null else phase.damage_taken_mult
	var applied := maxi(1, roundi(float(amount) * mult))
	boss.hp = maxi(boss.hp - applied, 0)
	events.append({"t": SimEvent.Type.ENEMY_HIT, "id": boss.id, "dmg": applied, "hp": boss.hp})
	if boss.hp <= 0:
		boss.alive = false
		events.append({"t": SimEvent.Type.BOSS_DIED, "def": String(boss.def.id)})


## Bullets that died against geometry. A client is only streamed the map near
## itself, so it cannot be relied on to work these out for itself.
func _emit_wall_kill_events() -> void:
	for dead_uid in pool.wall_kill_log:
		events.append({"t": SimEvent.Type.BULLET_DESPAWN, "uid": dead_uid})


func _emit_spawn_events() -> void:
	for slot in pool.spawn_log:
		if pool.alive[slot] == 0:
			continue  # spawned and killed inside the same tick
		events.append({
			"t": SimEvent.Type.BULLET_SPAWN,
			"uid": pool.uid[slot],
			"pos": pool.pos[slot],
			"vel": pool.vel[slot],
			"r": pool.radius[slot],
			"life": pool.life[slot],
			"kind": pool.kind[slot],
			"team": pool.team[slot],
			"accel": pool.accel[slot],
			"turn": pool.turn[slot],
		})


func drain_events() -> Array[Dictionary]:
	var out := events
	events = []
	return out


# --- Replica side -----------------------------------------------------------

## Apply a server event to a non-authoritative world.
func apply_event(ev: Dictionary) -> void:
	match int(ev["t"]):
		SimEvent.Type.BULLET_SPAWN:
			pool.spawn(ev["pos"], ev["vel"], ev["r"], ev["life"], 0,
				ev["team"], ev["kind"], ev["accel"], ev["turn"], ev["uid"])
		SimEvent.Type.BULLET_DESPAWN:
			var slot := pool.find_by_uid(int(ev["uid"]))
			if slot >= 0:
				pool.despawn(slot)
		_:
			pass