<?php

namespace EventEspresso\core;

/**
 * Class Psr4Autoloader
 * A general-purpose autoloader implementation that includes the optional
 * functionality of allowing multiple base directories for a single namespace
 * prefix.
 * 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
 *      $loader = new \Example\Psr4Autoloader;
 *      // register the autoloader
 *      $loader->register();
 *      // 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;
 *
 * @package                Event Espresso
 * @subpackage             core
 * @author                 php-fig.org
 * @see                    http://www.php-fig.org/psr/psr-4/examples/
 */
class Psr4Autoloader
{
    /**
     * namespace separator
     */
    public const NS = '\\';

    /**
     * An associative array where the key is a namespace prefix and the value
     * is an array of base directories for classes in that namespace.
     *
     * @var array
     */
    protected array $prefixes = [];


    /**
     * returns an array of registered namespace prefixes
     *
     * @param string $prefix
     * @return array
     */
    public function prefixes(string $prefix = ''): array
    {
        if (! empty($prefix)) {
            // are there any base directories for this namespace prefix?
            return $this->prefixes[ $prefix ] ?? [];
        }
        return $this->prefixes;
    }


    /**
     * Register loader with SPL autoloader stack.
     *
     * @return void
     */
    public function register()
    {
        spl_autoload_register([$this, 'loadClass']);
    }


    /**
     * Adds a base directory for a namespace prefix.
     *
     * @param string $prefix    The namespace prefix.
     * @param string $base_dir  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.
     * @return bool             returns TRUE if the namespace was successfully added
     */
    public function addNamespace(string $prefix, string $base_dir, bool $prepend = false): bool
    {
        // normalize namespace prefix
        $prefix = trim($prefix, Psr4Autoloader::NS) . Psr4Autoloader::NS;
        // normalize the base directory with a trailing separator
        $base_dir = str_replace(['\\', '/'], '/', $base_dir);
        $base_dir = rtrim($base_dir, '/\\') . '/';
        // initialize the namespace prefix array
        if (! isset($this->prefixes[ $prefix ])) {
            $this->prefixes[ $prefix ] = [];
        }
        // retain the base directory for the namespace prefix
        if ($prepend) {
            array_unshift($this->prefixes[ $prefix ], $base_dir);
        } else {
            $this->prefixes[ $prefix ][] = $base_dir;
        }
        return isset($this->prefixes[ $prefix ]);
    }


    /**
     * Loads the class file for a given class name.
     *
     * @param string $class The fully-qualified class name.
     * @return string The mapped file name on success or boolean false on failure.
     */
    public function loadClass(string $class): string
    {
        // 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, Psr4Autoloader::NS)) {
            // retain the trailing namespace separator in the prefix
            $prefix = substr($class, 0, $pos + 1);
            // the rest is the relative class name
            $relative_class = substr($class, $pos + 1);
            // try to load a mapped file for the prefix and relative class
            $mapped_file = $this->loadMappedFile($prefix, $relative_class);
            if ($mapped_file) {
                return $mapped_file;
            }
            // remove the trailing namespace separator for the next iteration of strrpos()
            $prefix = rtrim($prefix, Psr4Autoloader::NS);
        }
        // never found a mapped file
        return '';
    }


    /**
     * Load the mapped file for a namespace prefix and relative class.
     *
     * @param string $prefix         The namespace prefix.
     * @param string $relative_class The relative class name.
     * @return string                empty string if no mapped file can be loaded,
     *                               or the name of the mapped file that was loaded.
     */
    protected function loadMappedFile(string $prefix, string $relative_class): string
    {
        // look through base directories for this namespace prefix
        foreach ($this->prefixes($prefix) as $base_dir) {
            // replace the namespace prefix with the base directory,
            // replace namespace separators with directory separators
            // in the relative class name, append with .php
            $file = $base_dir
                    . str_replace(Psr4Autoloader::NS, '/', $relative_class)
                    . '.php';
            // if the mapped file exists, require it
            if ($this->requireFile($file)) {
                // yes, we're done
                return $file;
            }
        }
        // never found it
        return '';
    }


    /**
     * 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(string $file): bool
    {
        if (file_exists($file)) {
            require $file;
            return true;
        }
        return false;
    }
}
