Example of adding Twig support to the composer-dist-installer package

.env.local.php.dist

<?php
/*----------------------------------------------------*/
// Local environment vars
/*----------------------------------------------------*/
{% set db_name = '{!Database name?[]?|wordpress!}' %}
{% set db_user = '{!Database user []?|=ENV[USER]!}' %}
{% set db_password = '{!Database password?!}' %}
{% set db_host = '{!Database host []?|localhost!}' %}
{% set db_home = '{!Wordpress home url []?|http://mysite.dev/!}' %}
{% set db_siteurl = '{!Wordpress site url []?|http://mysite.dev/cms/!}' %}

return array(
    'DB_NAME'       => '{{ db_name }}',
    'DB_USER'       => '{{ db_user }}',
    'DB_PASSWORD'   => '{{ db_password }}',
    'DB_HOST'       => '{{ db_host }}',
    'WP_HOME'       => '{{ db_home }}',
    'WP_SITEURL'    => '{{ db_siteurl }}',
);

composer.json

"dist-installer-params": [
  {
    "type": "Cube\\ComposerDistInstaller\\Processor\\TwigProcessor",
    "file": ".env.local.php"
  }
}

TwigProcessor.php

<?php
/**
 * Copyright (c) 2015 Cu.be Solutions
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

namespace Cube\ComposerDistInstaller\Processor;

use Composer\IO\IOInterface;
use Twig_Environment;
use Twig_Loader_Array;

/**
 * The Twig processor
 *
 * @package Cube\ComposerDistInstaller
 */
class TwigProcessor implements ProcessorInterface
{

    protected $io;
    protected $config;

    public function __construct(IOInterface $io)
    {
        $this->setIO($io);
    }

    public function process(array $config)
    {
        $this->setConfig($config);
        $config = $this->getConfig();

        $realFile = $config['file'];

        $exists = is_file($realFile);

        $action = $exists ? 'Rewriting' : 'Creating';

        if ($exists) {
            if ($this->getIO()->askConfirmation('Destination file "' . $realFile .'" already exists, overwrite (y/n)? ')) {
                $this->getIO()->write(sprintf('<info>%s the "%s" file</info>', $action, $realFile));
                $oldFile = $realFile . '.old';
                copy($realFile, $oldFile);
                $this->getIO()->write(sprintf('A copy of the old configuration file was saved to %s', $oldFile));
            } else {
                return false;
            }
        } else {
            if (!is_dir($dir = dirname($realFile))) {
                mkdir($dir, 0755, true);
            }
        }

        $template = file_get_contents($config['dist-file']);

        $templateContents = preg_replace_callback('/\{\!(.*)\!\}/', array($this, '_templateReplace'), $template);

        $twig = new Twig_Environment(new Twig_Loader_Array([]));
        $template = $twig->createTemplate($templateContents);
        $renderedContents = $template->render([]);

        print_r($renderedContents);
        file_put_contents($realFile, $renderedContents);

        return true;
    }

    /**
     * @return IOInterface
     */
    public function getIO()
    {
        return $this->io;
    }

    /**
     * @param IOInterface $io
     */
    public function setIO(IOInterface $io)
    {
        $this->io = $io;
    }

    /**
     * @return mixed
     */
    public function getConfig()
    {
        return $this->config;
    }

    /**
     * @param mixed $config
     */
    public function setConfig($config)
    {
        if (empty($config['file'])) {
            throw new \InvalidArgumentException('The extra.dist-installer-params.file setting is required.');
        }

        if (empty($config['dist-file'])) {
            $config['dist-file'] = $config['file'].'.dist';
        }

        if (!is_file($config['dist-file'])) {
            throw new \InvalidArgumentException(sprintf('The dist file "%s" does not exist. Check your dist-file config or create it.', $config['dist-file']));
        }
        $this->config = $config;
    }

    /**
     * @return array
     */
    protected function _getEnvValue($variable)
    {
        if (isset($this->config['env-map'])) {
            $envMap = $this->config['env-map'];
            if (isset($envMap[$variable])) {
                $variable = $envMap[$variable];
            }
        }
        return getenv($variable);
    }

    /**
     * @param array $matches
     * @return string
     */
    protected function _templateReplace(array $matches)
    {
        $result = $matches[0];
        if (count($matches) > 1) {
            $explode = explode('|', $matches[1]);
            $question = $explode[0];
            $index = 0;
            do {
                $default = @$explode[++$index] ?: null;
                // if default syntax is =ENV[VARIABLE_NAME] then extract VARIABLE_NAME from the environment as default value
                if (strpos($default, '=ENV[') === 0) {
                    $envMatch = [];
                    preg_match('/^\=ENV\[(.*)\]$/', $default, $envMatch);
                    if (isset($envMatch[1])) {
                        $default = $this->_getEnvValue($envMatch[1]);
                    }
                }
            } while( empty($default) && $index < count($explode) );
            $question = str_replace('[]', "[$default]", $question);
            $result = $this->getIO()->ask(rtrim($question) . ' ', $default);
        }
        return $result;
    }
}

This looks great! Haven't tested it though, I'll do that with the PR.

One question: instead of _templateReplace: can we inject environment variables into a variable called something like installer.env or maybe just env?

I think you can do that in the ->render([]) call using $_ENV. Something like that would allow for a 100% Twig-only processor, which would be cleaner IMO.

Oh wow, thats a good idea.

Using https://github.com/Incenteev/ParameterHandler first for generating the installer.env file using your console and then using installer.env for populating the twig templates.

We could also make two twig flavours: one which uses the themplateReplace and one which I just described.

What do you think?