<?php

namespace App;

/**
 * This is a PSR-4 autoloader based on the example implementation by the PHP-FIG
 * at https://www.php-fig.org/psr/psr-4/. It includes an optional functionality
 * of allowing multiple base directories for a single namespace prefix. A
 * separate implementation besides the Composer's autoloader is done for cases
 * when Composer is not available on the server environment such as production.
 * It also provides loading non-PSR-4 compliant classes.
 *
 * Given a foo-bar package of classes in the file system at the following
 * paths ...
 *
 *     /path/to/packages/foo-bar/
 *         src/
 *             Baz.php             # Foo\Bar\Baz
 *             Qux/
 *                 Quux.php        # Foo\Bar\Qux\Quux
 *         tests/
 *             BazTest.php         # Foo\Bar\BazTest
 *             Qux/
 *                 QuuxTest.php    # Foo\Bar\Qux\QuuxTest
 *
 * ... add the path to the class files for the \Foo\Bar\ namespace prefix
 * as follows:
 *
 *      <?php
 *      // Instantiate the loader to registers the SPL autoload
 *      $loader = new App\Autoloader;
 *
 *      // Register the base directories for the namespace prefix
 *      $loader->addNamespace('Foo\Bar', '/path/to/packages/foo-bar/src');
 *      $loader->addNamespace('Foo\Bar', '/path/to/packages/foo-bar/tests');
 *
 * The following line would cause the autoloader to attempt to load the
 * \Foo\Bar\Qux\Quux class from /path/to/packages/foo-bar/src/Qux/Quux.php:
 *
 *      <?php
 *      new \Foo\Bar\Qux\Quux;
 *
 * The following line would cause the autoloader to attempt to load the
 * \Foo\Bar\Qux\QuuxTest class from /path/to/packages/foo-bar/tests/Qux/QuuxTest.php:
 *
 *      <?php
 *      new \Foo\Bar\Qux\QuuxTest;
 */
class Autoloader
{
    /**
     * An associative array with namespace prefixes as keys and values of arrays
     * of base directories for classes in that namespace.
     */
    protected $prefixes = [];

    /**
     * An associative array of classes as keys and their paths as values.
     */
    protected $classmap = [];

    /**
     * Class constructor that registers loader with a SPL autoloader stack.
     */
    public function __construct()
    {
        spl_autoload_register([$this, 'load']);
    }

    /**
     * Adds a base directory for a namespace prefix.
     *
     * @param string $prefix The namespace prefix.
     * @param string $baseDir A base directory for class files in the
     * namespace.
     * @param bool $prepend If true, prepend the base directory to the stack
     * instead of appending it; this causes it to be searched first rather
     * than last.
     */
    public function addNamespace($prefix, $baseDir, $prepend = false)
    {
        // normalize namespace prefix
        $prefix = trim($prefix, '\\') . '\\';

        // normalize the base directory with a trailing separator
        $baseDir = rtrim($baseDir, '\\/') . '/';

        // initialize the namespace prefix array
        if (isset($this->prefixes[$prefix]) === false) {
            $this->prefixes[$prefix] = [];
        }

        // retain the base directory for the namespace prefix
        if ($prepend) {
            array_unshift($this->prefixes[$prefix], $baseDir);
        } else {
            array_push($this->prefixes[$prefix], $baseDir);
        }
    }

    /**
     * Add a classmap. Classmap is a simplistic imitation of the Composer's
     * classmap autoloading.
     */
    public function addClassmap($class, $path)
    {
        $this->classmap[$class] = $path;
    }

    /**
     * Loads the class file for a given class name.
     *
     * @param string $class The fully-qualified class name.
     * @return mixed The mapped file name on success, or boolean false on
     * failure.
     */
    public function load($class)
    {
        // the current namespace prefix
        $prefix = $class;

        // Work backwards through the namespace names of the fully-qualified
        // class name to find a mapped file name
        while (false !== $pos = strrpos($prefix, '\\')) {

            // retain the trailing namespace separator in the prefix
            $prefix = substr($class, 0, $pos + 1);

            // the rest is the relative class name
            $relativeClass = substr($class, $pos + 1);

            // try to load a mapped file for the prefix and relative class
            $mappedFile = $this->loadMappedFile($prefix, $relativeClass);
            if ($mappedFile) {
                return $mappedFile;
            }

            // Remove the trailing namespace separator for the next iteration
            // of strrpos()
            $prefix = rtrim($prefix, '\\');
        }

        // Check if file is maybe in classmap
        if (!empty($this->classmap[$class])) {
            return $this->requireFile($this->classmap[$class]) ? $this->classmap[$class] : false;
        }

        // Mapped file not found
        return false;
    }

    /**
     * Load the mapped file for a namespace prefix and relative class.
     *
     * @param string $prefix The namespace prefix.
     * @param string $relativeClass The relative class name.
     * @return mixed Boolean false if no mapped file can be loaded, or the
     * name of the mapped file that was loaded.
     */
    protected function loadMappedFile($prefix, $relativeClass)
    {
        // are there any base directories for this namespace prefix?
        if (isset($this->prefixes[$prefix]) === false) {
            return false;
        }

        // Look through base directories for this namespace prefix
        foreach ($this->prefixes[$prefix] as $baseDir) {
            // replace the namespace prefix with the base directory,
            // replace namespace separators with directory separators
            // in the relative class name, append with .php
            $file = $baseDir
                  . str_replace('\\', '/', $relativeClass)
                  . '.php';

            // If the mapped file exists, require it
            if ($this->requireFile($file)) {
                return $file;
            }
        }

        // Mapped file not found
        return false;
    }

    /**
     * If a file exists, require it from the file system.
     *
     * @param string $file The file to require.
     * @return bool True if the file exists, false if not.
     */
    protected function requireFile($file)
    {
        if (file_exists($file)) {
            require_once $file;
            return true;
        }

        return false;
    }
}