SteamWar/LobbySystem/src/de/steamwar/lobby/particle/BodyMotion.java

/*
 *   This file is a part of the SteamWar software.
 *
 *   Copyright (C) 2026 SteamWar.de-Serverteam
 *
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU Affero General Public License as published by
 *   the Free Software Foundation, either version 3 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 *   GNU Affero General Public License for more details.
 *
 *   You should have received a copy of the GNU Affero General Public License
 *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

package de.steamwar.lobby.particle;

import lombok.experimental.UtilityClass;
import org.bukkit.Location;
import org.bukkit.entity.Player;

import java.util.Map;
import java.util.WeakHashMap;

// How a player's body moves: the direction it faces, worked out the way the Minecraft client turns the body, because
// the server's own body rotation for players does not follow what other players see, and how fast it moves.
// Walking turns the body towards the walking direction; standing still it only turns once the head looks more than
// 50 degrees to the side. It also notices jumps, landings and starting to sneak, which reward touches react to.
@UtilityClass
public class BodyMotion {

    private final float MAX_HEAD_TURN = 50;
    private final double MOVING = 0.0025;

    private final Map<Player, State> states = new WeakHashMap<>();
    // Counts server ticks, so events can be matched to the tick they happened in
    private long tick;

    private static class State {
        private float body;
        private double x;
        private double y;
        private double z;
        // Blocks per tick, smoothed so single steps do not jerk the wings
        private double speed;
        private boolean onGround = true;
        private boolean sneaking;
        // Highest point of the current time in the air
        private double peakY;
        private long jumpTick = Long.MIN_VALUE;
        private long landTick = Long.MIN_VALUE;
        private double landFall;
        private long sneakTick = Long.MIN_VALUE;
    }

    // Called once per server tick before the players are updated
    public void nextTick() {
        tick++;
    }

    // Called once per server tick for every online player
    @SuppressWarnings("deprecation")
    public void tick(Player player) {
        Location location = player.getLocation();
        State state = states.get(player);
        if (state == null) {
            state = new State();
            state.body = location.getYaw();
            state.x = location.getX();
            state.y = location.getY();
            state.z = location.getZ();
            states.put(player, state);
            return;
        }

        float head = location.getYaw();
        double dx = location.getX() - state.x;
        double dy = location.getY() - state.y;
        double dz = location.getZ() - state.z;
        state.x = location.getX();
        state.y = location.getY();
        state.z = location.getZ();
        state.speed = state.speed * 0.8 + Math.sqrt(dx * dx + dy * dy + dz * dz) * 0.2;

        boolean onGround = player.isOnGround();
        if (state.onGround && !onGround && dy > 0) {
            state.jumpTick = tick;
        }
        if (!onGround) {
            state.peakY = state.onGround ? location.getY() : Math.max(state.peakY, location.getY());
        } else if (!state.onGround) {
            state.landTick = tick;
            state.landFall = state.peakY - location.getY();
        }
        state.onGround = onGround;
        if (player.isSneaking() && !state.sneaking) {
            state.sneakTick = tick;
        }
        state.sneaking = player.isSneaking();

        float target = state.body;
        if (dx * dx + dz * dz > MOVING) {
            target = (float) Math.toDegrees(Math.atan2(dz, dx)) - 90;
            // Walking backwards keeps the body facing forwards
            float away = Math.abs(wrap(head) - target);
            if (away > 95 && away < 265) {
                target -= 180;
            }
        }
        state.body += wrap(target - state.body) * 0.3f;
        float headTurn = wrap(head - state.body);
        if (Math.abs(headTurn) > MAX_HEAD_TURN) {
            state.body += headTurn - Math.signum(headTurn) * MAX_HEAD_TURN;
        }
    }

    // The tracked body direction in degrees, or the head direction for players not tracked yet
    public float yaw(Player player) {
        State state = states.get(player);
        return state == null ? player.getLocation().getYaw() : state.body;
    }

    // Smoothed speed in blocks per tick; sprinting is about 0.28, fast elytra flight well above 1
    public double speed(Player player) {
        State state = states.get(player);
        return state == null ? 0 : state.speed;
    }

    public long currentTick() {
        return tick;
    }

    public boolean jumped(Player player) {
        State state = states.get(player);
        return state != null && state.jumpTick == tick;
    }

    // Ticks since the last jump, or a large number if there was none
    public long ticksSinceJump(Player player) {
        State state = states.get(player);
        return state == null || state.jumpTick == Long.MIN_VALUE ? Long.MAX_VALUE : tick - state.jumpTick;
    }

    // How far the player fell if they landed this tick, otherwise -1
    public double landed(Player player) {
        State state = states.get(player);
        return state != null && state.landTick == tick ? state.landFall : -1;
    }

    public boolean startedSneaking(Player player) {
        State state = states.get(player);
        return state != null && state.sneakTick == tick;
    }

    private float wrap(float degrees) {
        float wrapped = degrees % 360;
        if (wrapped >= 180) wrapped -= 360;
        if (wrapped < -180) wrapped += 360;
        return wrapped;
    }
}