MinimumCostFlowCalculator.php

<?php
 
/*
 *
 *  ____            _        _   __  __ _                  __  __ ____
 * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
 * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
 * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
 * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * @author PocketMine Team
 * @link http://www.pocketmine.net/
 *
 *
 */
 
declare(strict_types=1);
 
namespace pocketmine\block\utils;
 
use pocketmine\block\Block;
use pocketmine\math\Facing;
use pocketmine\world\World;
use function array_fill_keys;
use function array_map;
use function intdiv;
use function min;
 
final class MinimumCostFlowCalculator{
 
    private const CAN_FLOW_DOWN = 1;
    private const CAN_FLOW = 0;
    private const BLOCKED = -1;
 
    private array $flowCostVisited = [];
 
    public function __construct(
        private World $world,
        private int $flowDecayPerBlock,
        private \Closure $canFlowInto
    ){}
 
    private function calculateFlowCost(int $blockX, int $blockY, int $blockZ, int $accumulatedCost, int $maxCost, Facing $originOpposite, Facing $lastOpposite) : int{
        $cost = 1000;
 
        foreach(Facing::HORIZONTAL as $j){
            if($j === $originOpposite || $j === $lastOpposite){
                continue;
            }
            [$dx, $dy, $dz] = Facing::OFFSET[$j->value];
            $x = $blockX + $dx;
            $y = $blockY + $dy;
            $z = $blockZ + $dz;
 
            if(!isset($this->flowCostVisited[$hash = World::blockHash($x, $y, $z)])){
                if(!$this->world->isInWorld($x, $y, $z) || !$this->canFlowInto($this->world->getBlockAt($x, $y, $z))){
                    $this->flowCostVisited[$hash] = self::BLOCKED;
                }elseif($this->world->getBlockAt($x, $y - 1, $z)->canBeFlowedInto()){
                    $this->flowCostVisited[$hash] = self::CAN_FLOW_DOWN;
                }else{
                    $this->flowCostVisited[$hash] = self::CAN_FLOW;
                }
            }
 
            $status = $this->flowCostVisited[$hash];
 
            if($status === self::BLOCKED){
                continue;
            }elseif($status === self::CAN_FLOW_DOWN){
                return $accumulatedCost;
            }
 
            if($accumulatedCost >= $maxCost){
                continue;
            }
 
            $realCost = $this->calculateFlowCost($x, $y, $z, $accumulatedCost + 1, $maxCost, $originOpposite, Facing::opposite($j));
 
            if($realCost < $cost){
                $cost = $realCost;
            }
        }
 
        return $cost;
    }
 
    public function getOptimalFlowDirections(int $originX, int $originY, int $originZ) : array{
        $flowCost = array_fill_keys(array_map(fn(Facing $f) => $f->value, Facing::HORIZONTAL), 1000);
        $maxCost = intdiv(4, $this->flowDecayPerBlock);
        foreach(Facing::HORIZONTAL as $j){
            [$dx, $dy, $dz] = Facing::OFFSET[$j->value];
            $x = $originX + $dx;
            $y = $originY + $dy;
            $z = $originZ + $dz;
 
            if(!$this->world->isInWorld($x, $y, $z) || !$this->canFlowInto($this->world->getBlockAt($x, $y, $z))){
                $this->flowCostVisited[World::blockHash($x, $y, $z)] = self::BLOCKED;
            }elseif($this->world->getBlockAt($x, $y - 1, $z)->canBeFlowedInto()){
                $this->flowCostVisited[World::blockHash($x, $y, $z)] = self::CAN_FLOW_DOWN;
                $flowCost[$j->value] = $maxCost = 0;
            }elseif($maxCost > 0){
                $this->flowCostVisited[World::blockHash($x, $y, $z)] = self::CAN_FLOW;
                $opposite = Facing::opposite($j);
                $flowCost[$j->value] = $this->calculateFlowCost($x, $y, $z, 1, $maxCost, $opposite, $opposite);
                $maxCost = min($maxCost, $flowCost[$j->value]);
            }
        }
 
        $this->flowCostVisited = [];
 
        $minCost = min($flowCost);
 
        $isOptimalFlowDirection = [];
 
        foreach($flowCost as $facing => $cost){
            if($cost === $minCost){
                $isOptimalFlowDirection[] = $facing;
            }
        }
 
        return $isOptimalFlowDirection;
    }
 
    private function canFlowInto(Block $block) : bool{
        return ($this->canFlowInto)($block);
    }
}