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THE SOFTWARE.

Operation.php

<?php
/**
 * (c) PSP UK Group Ltd. <hello@psp-group.co.uk>
 *
 * For the full copyright and license information,
 * please view the LICENSE file that was distributed with this source code.
 */

namespace Psp\Fluent;

/**
 * A fluent operation interface.
 *
 * Acts much like a promise by performing an operation and executing configured callables.
 *
 * @see http://en.wikipedia.org/wiki/Fluent_interface
 */
final class Operation
{
    /**
     * @var array
     */
    private $parts = array();

    /**
     * Prevent new instances created outside of the class itself.
     *
     * @param callable $when
     */
    private function __construct(callable $when)
    {
        $this->addPart('when', $when);
    }

    /**
     * Create a new Operation instance.
     *
     * @param callable $when The callable to invoke as part of the operation.
     *
     * @return static
     */
    public static function when(callable $when)
    {
        return new static($when);
    }

    /**
     * Add a callable to the internal collection.
     *
     * @param string $partName
     * @param callable $callable
     *
     * @return void
     */
    private function addPart($partName, callable $callable)
    {
        $this->parts[$partName][] = $callable;
    }

    /**
     * Invoke configured callables.
     *
     * @param string $partName
     *
     * @return mixed The result of the last callable.
     */
    private function invokePart($partName)
    {
        if (( ! isset ($this->parts[$partName]))) {
            return null;
        }

        $lastResult = null;
        foreach ($this->parts[$partName] as $callable) {
            $lastResult = call_user_func($callable);
        }

        return $lastResult;
    }

    /**
     * Add a callable to be invoked immediately before the operation.
     *
     * @param callable $before
     *
     * @return $this
     */
    public function before(callable $before)
    {
        $this->addPart('before', $before);

        return $this;
    }

    /**
     * Add a callable to be invoked if the operation succeeds.
     *
     * @param callable $then
     *
     * @return $this
     */
    public function then(callable $then)
    {
        $this->addPart('then', $then);

        return $this;
    }

    /**
     * Add a callable to be invoked if the operation fails.
     *
     * @param callable $otherwise
     *
     * @return $this
     */
    public function otherwise(callable $otherwise)
    {
        $this->addPart('otherwise', $otherwise);

        return $this;
    }

    /**
     * Run the operation and any configured callables.
     *
     * @return mixed The result of the operation.
     */
    public function complete()
    {
        $this->invokePart('before');

        try {
            $result = $this->invokePart('when');

            $this->invokePart('then');

            return $result;

        } catch (\Exception $exception) {
            try {
                $this->invokePart('otherwise');
            } catch (\Exception $ignore) {
            }

            throw $exception;
        }
    }
}

usage.php

<?php

Fluent\Operation::when(
    function () {
        // do work...
    }
)->before(
    function ()  {
        // start a transaction
    }
)->then(
    function () {
        // commit the transaction
    }
)->otherwise(
    function () {
        // rollback the transaction
    }
)->complete();