ProjectAres/PGM/src/main/java/tc/oc/pgm/tracker/trackers/CombatLogTracker.java

package tc.oc.pgm.tracker.trackers;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import javax.annotation.Nullable;
import javax.inject.Inject;

import net.md_5.bungee.api.chat.TranslatableComponent;
import org.bukkit.GameMode;
import org.bukkit.Location;
import org.bukkit.Material;
import org.bukkit.block.Block;
import org.bukkit.entity.LivingEntity;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.EventPriority;
import org.bukkit.event.Listener;
import org.bukkit.event.entity.EntityDamageByBlockEvent;
import org.bukkit.event.entity.EntityDamageEvent;
import org.bukkit.event.entity.PlayerDeathEvent;
import org.bukkit.event.player.PlayerQuitEvent;
import org.bukkit.inventory.ItemStack;
import org.bukkit.potion.PotionEffect;
import org.bukkit.potion.PotionEffectType;
import java.time.Duration;
import java.time.Instant;
import tc.oc.commons.bukkit.util.Materials;
import tc.oc.pgm.events.ListenerScope;
import tc.oc.pgm.events.PlayerParticipationStopEvent;
import tc.oc.pgm.match.Match;
import tc.oc.pgm.match.MatchPlayer;
import tc.oc.pgm.match.MatchScope;
import tc.oc.pgm.match.Matches;

/**
 * Predicts the death of players who disconnect while participating, and simulates the
 * damage and death events that would have been fired if they had stayed in the game.
 *
 * Also prevents team switching while in imminent danger..
 */
@ListenerScope(MatchScope.RUNNING)
public class CombatLogTracker implements Listener {
    // Logout within this time since last damage is considered combat log
    private static final Duration RECENT_DAMAGE_THRESHOLD = Duration.ofSeconds(3);

    // Maximum height player can fall without taking damage
    private static final double SAFE_FALL_DISTANCE = 2;

    // Minimum water required to stop the player's fall
    private static final int BREAK_FALL_WATER_DEPTH = 3;

    private final Match match;

    private static class Damage {
        public final Instant time;
        public final EntityDamageEvent event;

        private Damage(Instant time, EntityDamageEvent event) {
            this.time = time;
            this.event = event;
        }
    }

    private static class ImminentDeath {
        public final EntityDamageEvent.DamageCause cause; // what will cause the death
        public final Location deathLocation;
        public final Block blockDamager;
        public final boolean alreadyDamaged;              // if the player has already been damaged by this cause

        private ImminentDeath(EntityDamageEvent.DamageCause cause, Location deathLocation, @Nullable Block blockDamager, boolean damaged) {
            this.cause = cause;
            this.deathLocation = deathLocation;
            this.blockDamager = blockDamager;
            this.alreadyDamaged = damaged;
        }
    }

    private Map<Player, Damage> recentDamage = new HashMap<>();

    @Inject CombatLogTracker(Match match) {
        this.match = match;
    }

    private static boolean hasFireResistance(LivingEntity entity) {
        for(PotionEffect effect : entity.getActivePotionEffects()) {
            if(PotionEffectType.FIRE_RESISTANCE.equals(effect.getType())) return true;
        }
        return false;
    }

    private static double getResistanceFactor(LivingEntity entity) {
        int amplifier = 0;
        for(PotionEffect effect : entity.getActivePotionEffects()) {
            if(PotionEffectType.DAMAGE_RESISTANCE.equals(effect.getType()) && effect.getAmplifier() > amplifier) {
                amplifier = effect.getAmplifier();
            }
        }
        return 1d - (amplifier / 5d);
    }

    @EventHandler(priority = EventPriority.HIGH, ignoreCancelled = true)
    public void onPlayerDamage(EntityDamageEvent event) {
        if(event.getDamage() <= 0) return;

        if(!(event.getEntity() instanceof Player)) return;
        Player player = (Player) event.getEntity();

        if(player.getGameMode() == GameMode.CREATIVE) return;

        if(player.isDead()) return;

        if(player.getNoDamageTicks() > 0) return;

        if(getResistanceFactor(player) <= 0) return;

        switch(event.getCause()) {
            case ENTITY_EXPLOSION:
            case BLOCK_EXPLOSION:
            case CUSTOM:
            case FALL:
            case FALLING_BLOCK:
            case LIGHTNING:
            case MELTING:
            case SUICIDE:
            case THORNS:
                return; // Skip damage causes that are not particularly likely to be followed by more damage

            case FIRE:
            case FIRE_TICK:
            case LAVA:
                if(hasFireResistance(player)) return;
                break;
        }

        // Record the player's damage with a timestamp
        this.recentDamage.put(player, new Damage(Instant.now(), event));
    }

    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
    public void onPlayerDeath(PlayerDeathEvent event) {
        // Clear last damage when a player dies
        this.recentDamage.remove(event.getEntity());
    }

    // This must be called BEFORE the listener that removes the player from the match
    @EventHandler(priority = EventPriority.LOWEST, ignoreCancelled = true)
    public void onQuit(PlayerQuitEvent event) {
        Match match = Matches.get(event.getWorld());
        if(match == null || !match.isRunning()) return;

        MatchPlayer player = match.getPlayer(event.getPlayer());
        if(player == null || !player.isParticipating()) return;

        ImminentDeath imminentDeath = this.getImminentDeath(player.getBukkit());
        if(imminentDeath == null) return;

        if(!imminentDeath.alreadyDamaged) {
            // Simulate the damage event that would have killed them,
            // allowing the tracker to figure out the cause of death
            EntityDamageEvent damageEvent;
            if(imminentDeath.blockDamager != null) {
                damageEvent = new EntityDamageByBlockEvent(imminentDeath.blockDamager, player.getBukkit(), imminentDeath.cause, player.getBukkit().getHealth());
            } else {
                damageEvent = new EntityDamageEvent(player.getBukkit(), imminentDeath.cause, player.getBukkit().getHealth());
            }
            match.callEvent(damageEvent);

            // If the damage event was cancelled, don't simulate the kill
            if(damageEvent.isCancelled()) return;

            player.getBukkit().setLastDamageCause(damageEvent);
        }

        // Simulate the player's death. The tracker will assume the death was caused by the
        // last damage event, which was either a real one or the fake one we generated above.
        ArrayList<ItemStack> drops = new ArrayList<>();
        for(ItemStack stack : player.getInventory().contents()) {
            if(stack != null && stack.getType() != Material.AIR) drops.add(stack);
        }

        try {
            currentDeathEvent = new PlayerDeathEvent(player.getBukkit(), drops, 0, player.getDisplayName() + " logged out to avoid death");
            match.callEvent(currentDeathEvent);
        } finally {
            currentDeathEvent = null;
        }
    }

    // A simple way to tag an event as a combat log, hacky but it works
    private static @Nullable PlayerDeathEvent currentDeathEvent;
    public static boolean isCombatLog(PlayerDeathEvent event) {
        return event == currentDeathEvent;
    }

    @EventHandler(priority = EventPriority.LOWEST, ignoreCancelled = true)
    public void onParticipationStop(PlayerParticipationStopEvent event) {
        if(event.getMatch().isRunning() && this.getImminentDeath(event.getPlayer().getBukkit()) != null) {
            event.setCancelled(true);
            event.getPlayer().sendWarning(new TranslatableComponent("match.noCombatLog"), true);
        }
    }

    /**
     * Get the cause of the player's imminent death, or null if they are not about to die
     * NOTE: not idempotent, has the side effect of clearing the recentDamage cache
     */
    public @Nullable ImminentDeath getImminentDeath(Player player) {
        // If the player is already dead or in creative mode, we don't care
        if(player.isDead() || player.getGameMode() == GameMode.CREATIVE) return null;

        // If the player was on the ground, or is flying, or is able to fly, they are fine
        if(!(player.isOnGround() || player.isFlying() || player.getAllowFlight())) {
            // If the player is falling, detect an imminent falling death
            double fallDistance = player.getFallDistance();
            Block landingBlock = null;
            int waterDepth = 0;
            Location location = player.getLocation();

            if(location.getY() > 256) {
                // If player is above Y 256, assume they fell at least to there
                fallDistance += location.getY() - 256;
                location.setY(256);
            }

            // Search the blocks directly beneath the player until we find what they would have landed on
            Block block = null;
            for(; location.getY() >= 0; location.add(0, -1, 0)) {
                block = location.getBlock();
                if(block != null) {
                    landingBlock = block;

                    if(Materials.isWater(landingBlock.getType())) {
                        // If the player falls through water, reset fall distance and inc the water depth
                        fallDistance = -1;
                        waterDepth += 1;

                        // Break if they have fallen through enough water to stop falling
                        if(waterDepth >= BREAK_FALL_WATER_DEPTH) break;
                    } else {
                        // If the block is not water, reset the water depth
                        waterDepth = 0;

                        if(Materials.isColliding(landingBlock.getType()) || Materials.isLava(landingBlock.getType())) {
                            // Break if the player hits a solid block or lava
                            break;
                        } else if(landingBlock.getType() == Material.WEB) {
                            // If they hit web, reset their fall distance, but assume they keep falling
                            fallDistance = -1;
                        }
                    }
                }

                fallDistance += 1;
            }

            double resistanceFactor = getResistanceFactor(player);
            boolean fireResistance = hasFireResistance(player);

            // Now decide if the landing would have killed them
            if(location.getBlockY() < 0) {
                // The player would have fallen into the void
                return new ImminentDeath(EntityDamageEvent.DamageCause.VOID, location, null, false);
            } else if(landingBlock != null) {
                if(Materials.isColliding(landingBlock.getType()) && player.getHealth() <= resistanceFactor * (fallDistance - SAFE_FALL_DISTANCE)) {
                    // The player would have landed on a solid block and taken enough fall damage to kill them
                    return new ImminentDeath(EntityDamageEvent.DamageCause.FALL, landingBlock.getLocation().add(0, 0.5, 0), null, false);
                } else if (Materials.isLava(landingBlock.getType()) && resistanceFactor > 0 && !fireResistance) {
                    // The player would have landed in lava, and we give the lava the benefit of the doubt
                    return new ImminentDeath(EntityDamageEvent.DamageCause.LAVA, landingBlock.getLocation(), landingBlock, false);
                }
            }
        }

        // If we didn't predict a falling death, detect combat log due to recent damage
        Damage damage = this.recentDamage.remove(player);
        if(damage != null && damage.time.plus(RECENT_DAMAGE_THRESHOLD).isAfter(Instant.now())) {
            // Player logged out too soon after taking damage
            return new ImminentDeath(damage.event.getCause(), player.getLocation(), null, true);
        }

        return null;
    }
}