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====== Design pattern Builder ======

Giả sử chúng ta có một đối tượng có rất nhiều trường cần khởi tạo, khi đó class cần khởi tạo sẽ chứa rất nhiều tham số. Như thế sẽ làm code không được đẹp và khó nâng cấp về sau.

Mẫu Builder trích xuất mã xây dựng đối tượng ra khỏi lớp của chính nó và di chuyển nó sang các đối tượng riêng biệt. Mẫu tổ chức xây dựng đối tượng thành một tập hợp các bước (buildWalls, buildDoor, v.v.). Để tạo một đối tượng, thực hiện một loạt các bước này trên một đối tượng xây dựng. Phần quan trọng là không cần phải gọi tất cả các bước. Chúng ta chỉ có thể gọi những bước cần thiết để tạo cấu hình cụ thể của một đối tượng.

<file php>
<?php

namespace RefactoringGuru\Builder\Conceptual;

/**
 * The Builder interface specifies methods for creating the different parts of
 * the Product objects.
 */
interface Builder
{
    public function producePartA(): void;

public function producePartB(): void;

public function producePartC(): void;
}

/**
 * The Concrete Builder classes follow the Builder interface and provide
 * specific implementations of the building steps. Your program may have several
 * variations of Builders, implemented differently.
 */
class ConcreteBuilder1 implements Builder
{
    private $product;

/**
     * A fresh builder instance should contain a blank product object, which is
     * used in further assembly.
     */
    public function __construct()
    {
        $this->reset();
    }

public function reset(): void
    {
        $this->product = new Product1();
    }

/**
     * All production steps work with the same product instance.
     */
    public function producePartA(): void
    {
        $this->product->parts[] = "PartA1";
    }

public function producePartB(): void
    {
        $this->product->parts[] = "PartB1";
    }

public function producePartC(): void
    {
        $this->product->parts[] = "PartC1";
    }

/**
     * Concrete Builders are supposed to provide their own methods for
     * retrieving results. That's because various types of builders may create
     * entirely different products that don't follow the same interface.
     * Therefore, such methods cannot be declared in the base Builder interface
     * (at least in a statically typed programming language). Note that PHP is a
     * dynamically typed language and this method CAN be in the base interface.
     * However, we won't declare it there for the sake of clarity.
     *
     * Usually, after returning the end result to the client, a builder instance
     * is expected to be ready to start producing another product. That's why
     * it's a usual practice to call the reset method at the end of the
     * `getProduct` method body. However, this behavior is not mandatory, and
     * you can make your builders wait for an explicit reset call from the
     * client code before disposing of the previous result.
     */
    public function getProduct(): Product1
    {
        $result = $this->product;
        $this->reset();

return $result;
    }
}

/**
 * It makes sense to use the Builder pattern only when your products are quite
 * complex and require extensive configuration.
 *
 * Unlike in other creational patterns, different concrete builders can produce
 * unrelated products. In other words, results of various builders may not
 * always follow the same interface.
 */
class Product1
{
    public $parts = [];

public function listParts(): void
    {
        echo "Product parts: " . implode(', ', $this->parts) . "\n\n";
    }
}

/**
 * The Director is only responsible for executing the building steps in a
 * particular sequence. It is helpful when producing products according to a
 * specific order or configuration. Strictly speaking, the Director class is
 * optional, since the client can control builders directly.
 */
class Director
{
    /**
     * @var Builder
     */
    private $builder;

/**
     * The Director works with any builder instance that the client code passes
     * to it. This way, the client code may alter the final type of the newly
     * assembled product.
     */
    public function setBuilder(Builder $builder): void
    {
        $this->builder = $builder;
    }

/**
     * The Director can construct several product variations using the same
     * building steps.
     */
    public function buildMinimalViableProduct(): void
    {
        $this->builder->producePartA();
    }

public function buildFullFeaturedProduct(): void
    {
        $this->builder->producePartA();
        $this->builder->producePartB();
        $this->builder->producePartC();
    }
}

/**
 * The client code creates a builder object, passes it to the director and then
 * initiates the construction process. The end result is retrieved from the
 * builder object.
 */
function clientCode(Director $director)
{
    $builder = new ConcreteBuilder1();
    $director->setBuilder($builder);

echo "Standard basic product:\n";
    $director->buildMinimalViableProduct();
    $builder->getProduct()->listParts();

echo "Standard full featured product:\n";
    $director->buildFullFeaturedProduct();
    $builder->getProduct()->listParts();

// Remember, the Builder pattern can be used without a Director class.
    echo "Custom product:\n";
    $builder->producePartA();
    $builder->producePartC();
    $builder->getProduct()->listParts();
}

$director = new Director();
clientCode($director);
</file>

**Ví dụ:**

<file php SQLQueryBuilder.php>
<?php

namespace OneSite\DesignPattern\Builder;

/**
 * The Builder interface declares a set of methods to assemble an SQL query.
 *
 * All of the construction steps are returning the current builder object to
 * allow chaining: $builder->select(...)->where(...)
 */
interface SQLQueryBuilder
{
    public function select(string $table, array $fields): SQLQueryBuilder;

public function where(string $field, string $value, string $operator = '='): SQLQueryBuilder;

public function limit(int $start, int $offset): SQLQueryBuilder;

// +100 other SQL syntax methods...

public function getSQL(): string;
}
</file>

<file php MysqlQueryBuilder.php>
<?php

namespace OneSite\DesignPattern\Builder;

/**
 * Each Concrete Builder corresponds to a specific SQL dialect and may implement
 * the builder steps a little bit differently from the others.
 *
 * This Concrete Builder can build SQL queries compatible with MySQL.
 */
class MysqlQueryBuilder implements SQLQueryBuilder
{
    protected $query;

protected function reset(): void
    {
        $this->query = new \stdClass;
    }

/**
     * Build a base SELECT query.
     */
    public function select(string $table, array $fields): SQLQueryBuilder
    {
        $this->reset();
        
        $this->query->base = "SELECT " . implode(", ", $fields) . " FROM " . $table;
        $this->query->type = 'select';

return $this;
    }

/**
     * Add a WHERE condition.
     */
    public function where(string $field, string $value, string $operator = '='): SQLQueryBuilder
    {
        if (!in_array($this->query->type, ['select', 'update', 'delete'])) {
            throw new \Exception("WHERE can only be added to SELECT, UPDATE OR DELETE");
        }
        $this->query->where[] = "$field $operator '$value'";

return $this;
    }

/**
     * Add a LIMIT constraint.
     */
    public function limit(int $start, int $offset): SQLQueryBuilder
    {
        if (!in_array($this->query->type, ['select'])) {
            throw new \Exception("LIMIT can only be added to SELECT");
        }
        $this->query->limit = " LIMIT " . $start . ", " . $offset;

return $this;
    }

/**
     * Get the final query string.
     */
    public function getSQL(): string
    {
        $query = $this->query;
        $sql = $query->base;
        if (!empty($query->where)) {
            $sql .= " WHERE " . implode(' AND ', $query->where);
        }
        if (isset($query->limit)) {
            $sql .= $query->limit;
        }
        $sql .= ";";
        return $sql;
    }

}
</file>

<file php SQLQueryBuilder.php>
<?php

namespace OneSite\DesignPattern\Builder;

/**
 * This Concrete Builder is compatible with PostgreSQL. While Postgres is very
 * similar to Mysql, it still has several differences. To reuse the common code,
 * we extend it from the MySQL builder, while overriding some of the building
 * steps.
 */
class PostgresQueryBuilder extends MysqlQueryBuilder
{
    /**
     * Among other things, PostgreSQL has slightly different LIMIT syntax.
     */
    public function limit(int $start, int $offset): SQLQueryBuilder
    {
        parent::limit($start, $offset);

$this->query->limit = " LIMIT " . $start . " OFFSET " . $offset;

return $this;
    }

// + tons of other overrides...
}

</file>

<file php BuilderTest.php>
<?php

namespace OneSite\DesignPattern\Tests;

use OneSite\DesignPattern\Builder\MysqlQueryBuilder;
use OneSite\DesignPattern\Builder\PostgresQueryBuilder;
use OneSite\DesignPattern\Builder\SQLQueryBuilder;
use PHPUnit\Framework\TestCase;

/**
 * Class BuilderTest
 * @package OneSite\DesignPattern\Tests
 */
class BuilderTest extends TestCase
{
    /**
     *
     */
    public function testBuilderPattern()
    {
        $this->clientCode(new MysqlQueryBuilder());

$this->clientCode(new PostgresQueryBuilder());

return $this->assertTrue(true);
    }

/**
     * @param SQLQueryBuilder $queryBuilder
     */
    private function clientCode(SQLQueryBuilder $queryBuilder)
    {
        $query = $queryBuilder
            ->select("users", ["name", "email", "password"])
            ->where("age", 18, ">")
            ->where("age", 30, "<")
            ->limit(10, 20)
            ->getSQL();

echo $query;
    }
}
</file>

===== Tham khảo =====

* https://refactoring.guru/design-patterns/builder

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