class_name NetCodec
extends RefCounted
## Binary encoders for the two server -> client streams.
##
## Snapshots are lossy and unreliable: only what is needed to draw and predict.
## Events are exact and reliable: things a client can never re-derive, above all
## bullet spawns and the despawns caused by a hit.

# --- Snapshot ---------------------------------------------------------------

## [param cleared_countdown] is whole seconds until a cleared dungeon returns
## its party, or Protocol.COUNTDOWN_NONE when that does not apply.
static func encode_snapshot(world: SimWorld,
		cleared_countdown: int = Protocol.COUNTDOWN_NONE) -> PackedByteArray:
	var b := StreamPeerBuffer.new()
	b.big_endian = false
	b.put_u32(world.tick)
	b.put_u8(clampi(cleared_countdown, 0, Protocol.COUNTDOWN_NONE))

	b.put_u8(mini(world.players.size(), 255))
	for p in world.players.values():
		b.put_u32(p.peer_id)
		b.put_float(p.pos.x)
		b.put_float(p.pos.y)
		b.put_u16(wrapi(roundi(p.aim / TAU * 65536.0), 0, 65536))
		b.put_u16(clampi(p.hp, 0, 65535))
		var flags := 0
		if p.alive:
			flags |= Protocol.F_ALIVE
		if p.iframes > 0:
			flags |= Protocol.F_INVULN
		if p.escape_ticks > 0:
			flags |= Protocol.F_ESCAPING
		if p.spawn_grace > 0:
			flags |= Protocol.F_SPAWN_GRACE
		if p.linkdead:
			flags |= Protocol.F_LINKDEAD
		b.put_u8(flags)
		b.put_u8(clampi(roundi(p.escape_progress() * 255.0), 0, 255))
		# Echoed so the owning client knows how far to rewind when reconciling.
		b.put_u32(p.last_input_tick)

	var live_enemies: Array[SimEnemy] = []
	for e in world.enemies.values():
		if e.alive:
			live_enemies.append(e)
	b.put_u16(mini(live_enemies.size(), 65535))
	for e in live_enemies:
		b.put_u32(e.id)
		b.put_float(e.pos.x)
		b.put_float(e.pos.y)
		b.put_u16(clampi(e.hp, 0, 65535))
		# Radius and visual travel with the snapshot so a client that joins
		# mid-fight can draw an enemy without any extra handshake.
		b.put_u8(clampi(roundi(e.def.radius * 2.0), 0, 255))
		b.put_u8(clampi(e.def.visual, 0, 255))

	var has_boss := world.boss != null and world.boss.alive
	b.put_u8(1 if has_boss else 0)
	if has_boss:
		b.put_u32(world.boss.id)
		b.put_float(world.boss.pos.x)
		b.put_float(world.boss.pos.y)
		b.put_u32(maxi(world.boss.hp, 0))
		b.put_u8(clampi(world.boss.phase_index, 0, 255))
	return b.data_array


static func decode_snapshot(data: PackedByteArray) -> Dictionary:
	var b := StreamPeerBuffer.new()
	b.big_endian = false
	b.data_array = data
	var snap := {
		"tick": b.get_u32(),
		"cleared_countdown": b.get_u8(),
		"players": [], "enemies": [], "boss": null,
	}

	var pcount := b.get_u8()
	for _i in pcount:
		snap["players"].append({
			"peer": b.get_u32(),
			"pos": Vector2(b.get_float(), b.get_float()),
			"aim": float(b.get_u16()) / 65536.0 * TAU,
			"hp": b.get_u16(),
			"flags": b.get_u8(),
			"escape": float(b.get_u8()) / 255.0,
			"last_input_tick": b.get_u32(),
		})

	var ecount := b.get_u16()
	for _i in ecount:
		snap["enemies"].append({
			"id": b.get_u32(),
			"pos": Vector2(b.get_float(), b.get_float()),
			"hp": b.get_u16(),
			"radius": float(b.get_u8()) * 0.5,
			"visual": b.get_u8(),
		})

	if b.get_u8() == 1:
		snap["boss"] = {
			"id": b.get_u32(),
			"pos": Vector2(b.get_float(), b.get_float()),
			"hp": b.get_u32(),
			"phase": b.get_u8(),
		}
	return snap


# --- Events -----------------------------------------------------------------

## Events the client never sees; the instance layer consumes them server-side.
## These describe a decision the server is about to act on, not an outcome --
## leaking them would tell a client about a message it might try to forge.
const SERVER_ONLY := [
	SimEvent.Type.PORTAL_USED,
	SimEvent.Type.ESCAPE_COMPLETED,
	SimEvent.Type.RESPAWN_REQUESTED,
]


## [param server_tick] rides along so the client can fast-forward a bullet by
## however many ticks the packet spent in flight, instead of popping it in at
## the muzzle a round-trip late.
static func encode_events(server_tick: int, events: Array[Dictionary]) -> PackedByteArray:
	var b := StreamPeerBuffer.new()
	b.big_endian = false
	b.put_u32(server_tick)
	var count := 0
	var body := StreamPeerBuffer.new()
	body.big_endian = false
	for ev in events:
		var t := int(ev["t"])
		if SERVER_ONLY.has(t):
			continue
		body.put_u8(t)
		match t:
			SimEvent.Type.BULLET_SPAWN:
				body.put_u32(ev["uid"])
				body.put_float(ev["pos"].x)
				body.put_float(ev["pos"].y)
				body.put_float(ev["vel"].x)
				body.put_float(ev["vel"].y)
				body.put_float(ev["r"])
				body.put_u16(clampi(int(ev["life"]), 0, 65535))
				body.put_u8(int(ev["kind"]))
				body.put_u8(int(ev["team"]))
				body.put_float(ev["accel"])
				body.put_float(ev["turn"])
			SimEvent.Type.BULLET_DESPAWN:
				body.put_u32(ev["uid"])
			SimEvent.Type.PLAYER_HIT:
				body.put_u32(ev["peer"])
				body.put_u16(clampi(int(ev["dmg"]), 0, 65535))
				body.put_u16(clampi(int(ev["hp"]), 0, 65535))
			SimEvent.Type.PLAYER_DIED, SimEvent.Type.ESCAPE_STARTED, \
			SimEvent.Type.ESCAPE_CANCELLED:
				body.put_u32(ev["peer"])
			SimEvent.Type.PLAYER_RESPAWNED:
				body.put_u32(ev["peer"])
				body.put_float(ev["pos"].x)
				body.put_float(ev["pos"].y)
			SimEvent.Type.ENEMY_HIT:
				body.put_u32(ev["id"])
				body.put_u16(clampi(int(ev["dmg"]), 0, 65535))
				body.put_u32(maxi(int(ev["hp"]), 0))
			SimEvent.Type.ENEMY_DIED:
				body.put_u32(ev["id"])
			SimEvent.Type.BOSS_PHASE:
				body.put_u8(clampi(int(ev["phase"]), 0, 255))
			SimEvent.Type.BOSS_DIED:
				pass
		count += 1
	b.put_u16(count)
	b.put_data(body.data_array)
	return b.data_array


## Returns { "tick": int, "events": Array[Dictionary] }.
static func decode_events(data: PackedByteArray) -> Dictionary:
	var out: Array[Dictionary] = []
	var b := StreamPeerBuffer.new()
	b.big_endian = false
	b.data_array = data
	var server_tick := b.get_u32()
	var count := b.get_u16()
	for _i in count:
		var t := b.get_u8()
		var ev := {"t": t}
		match t:
			SimEvent.Type.BULLET_SPAWN:
				ev["uid"] = b.get_u32()
				ev["pos"] = Vector2(b.get_float(), b.get_float())
				ev["vel"] = Vector2(b.get_float(), b.get_float())
				ev["r"] = b.get_float()
				ev["life"] = b.get_u16()
				ev["kind"] = b.get_u8()
				ev["team"] = b.get_u8()
				ev["accel"] = b.get_float()
				ev["turn"] = b.get_float()
			SimEvent.Type.BULLET_DESPAWN:
				ev["uid"] = b.get_u32()
			SimEvent.Type.PLAYER_HIT:
				ev["peer"] = b.get_u32()
				ev["dmg"] = b.get_u16()
				ev["hp"] = b.get_u16()
			SimEvent.Type.PLAYER_DIED, SimEvent.Type.ESCAPE_STARTED, \
			SimEvent.Type.ESCAPE_CANCELLED:
				ev["peer"] = b.get_u32()
			SimEvent.Type.PLAYER_RESPAWNED:
				ev["peer"] = b.get_u32()
				ev["pos"] = Vector2(b.get_float(), b.get_float())
			SimEvent.Type.ENEMY_HIT:
				ev["id"] = b.get_u32()
				ev["dmg"] = b.get_u16()
				ev["hp"] = b.get_u32()
			SimEvent.Type.ENEMY_DIED:
				ev["id"] = b.get_u32()
			SimEvent.Type.BOSS_PHASE:
				ev["phase"] = b.get_u8()
			SimEvent.Type.BOSS_DIED:
				pass
		out.append(ev)
	return {"tick": server_tick, "events": out}


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

static func encode_inputs(frames: Array[InputFrame]) -> PackedByteArray:
	var b := StreamPeerBuffer.new()
	b.big_endian = false
	b.put_u8(mini(frames.size(), 255))
	for f in frames:
		f.write(b)
	return b.data_array


static func decode_inputs(data: PackedByteArray) -> Array[InputFrame]:
	var out: Array[InputFrame] = []
	if data.size() < 1:
		return out
	var b := StreamPeerBuffer.new()
	b.big_endian = false
	b.data_array = data
	var count := b.get_u8()
	# A malformed or hostile packet must not make the server read past the end.
	if data.size() < 1 + count * InputFrame.SIZE:
		return out
	for _i in count:
		out.append(InputFrame.read(b))
	return out


# --- Roster -----------------------------------------------------------------
# Who is online and where. Low frequency (membership changes only), so it is
# the one message that carries strings; everything hot stays fixed-width.

static func encode_roster(entries: Array[Dictionary]) -> PackedByteArray:
	var b := StreamPeerBuffer.new()
	b.big_endian = false
	b.put_u8(mini(entries.size(), 255))
	for e in entries:
		b.put_u32(int(e["peer"]))
		b.put_utf8_string(String(e["name"]))
		b.put_u8(int(e["kind"]))
		b.put_u32(int(e["instance"]))
		b.put_u8(1 if e["alive"] else 0)
	return b.data_array


static func decode_roster(data: PackedByteArray) -> Array[Dictionary]:
	var out: Array[Dictionary] = []
	if data.size() < 1:
		return out
	var b := StreamPeerBuffer.new()
	b.big_endian = false
	b.data_array = data
	var count := b.get_u8()
	for _i in count:
		# get_utf8_string reads its own length prefix, so a truncated packet
		# yields empty strings rather than reading off the end.
		out.append({
			"peer": b.get_u32(),
			"name": b.get_utf8_string(),
			"kind": b.get_u8(),
			"instance": b.get_u32(),
			"alive": b.get_u8() == 1,
		})
	return out