<?php
/**
 * File-based courseware: one .pptx file per lesson in the repo-root courseware/ directory.
 */

if (!function_exists('courseware_root')) {
    function courseware_root() {
        if (isset($GLOBALS['_courseware_root']) && $GLOBALS['_courseware_root'] !== '') {
            $resolved = realpath($GLOBALS['_courseware_root']);
            return $resolved === false ? '' : $resolved;
        }
        $resolved = realpath(__DIR__ . '/../../courseware');
        return $resolved === false ? '' : $resolved;
    }
}

if (!function_exists('courseware_is_slug')) {
    function courseware_is_slug($slug) {
        if (!is_string($slug) || $slug === '' || $slug === '.' || $slug === '..') {
            return false;
        }
        if (strpos($slug, "\0") !== false) {
            return false;
        }
        if (strpos($slug, '/') !== false || strpos($slug, '\\') !== false) {
            return false;
        }
        return true;
    }
}

if (!function_exists('courseware_is_pptx_name')) {
    function courseware_is_pptx_name($name) {
        if (!is_string($name) || strlen($name) < 6) {
            return false;
        }
        if (strpos($name, "\0") !== false || strpos($name, '/') !== false || strpos($name, '\\') !== false) {
            return false;
        }
        return strtolower(substr($name, -5)) === '.pptx';
    }
}

if (!function_exists('courseware_inside_root')) {
    function courseware_inside_root($path, $root) {
        $root_norm = rtrim(str_replace('\\', '/', $root), '/');
        $path_norm = rtrim(str_replace('\\', '/', $path), '/');
        if ($root_norm === '' || $path_norm === '') {
            return false;
        }
        $insensitive = (DIRECTORY_SEPARATOR === '\\');
        if ($insensitive) {
            if (strcasecmp($path_norm, $root_norm) === 0) {
                return true;
            }
            $prefix = $root_norm . '/';
            return strncasecmp($path_norm, $prefix, strlen($prefix)) === 0;
        }
        return $path_norm === $root_norm || strpos($path_norm, $root_norm . '/') === 0;
    }
}

if (!function_exists('courseware_is_absolute_path')) {
    function courseware_is_absolute_path($path) {
        if (!is_string($path) || $path === '') {
            return false;
        }
        if ($path[0] === '/' || $path[0] === '\\') {
            return true;
        }
        return (bool) preg_match('#^[A-Za-z]:[\\\\/]#', $path);
    }
}

if (!function_exists('courseware_scan_pptx_entries')) {
    function courseware_scan_pptx_entries() {
        $root = courseware_root();
        $found = array();
        if ($root === '' || !is_dir($root)) {
            return $found;
        }
        $entries = @scandir($root);
        if ($entries === false) {
            return $found;
        }
        foreach ($entries as $name) {
            if ($name === '.' || $name === '..') {
                continue;
            }
            if (!courseware_is_pptx_name($name)) {
                continue;
            }
            $slug = substr($name, 0, -5);
            if (!courseware_is_slug($slug)) {
                continue;
            }
            if (!isset($found[$slug])) {
                $found[$slug] = $name;
            }
        }
        return $found;
    }
}

if (!function_exists('courseware_link_stays_inside')) {
    function courseware_link_stays_inside($raw, $root) {
        if (!is_link($raw)) {
            return true;
        }
        $link = @readlink($raw);
        if ($link === false || strpos($link, "\0") !== false) {
            return false;
        }
        $target = courseware_is_absolute_path($link)
            ? $link
            : (dirname($raw) . DIRECTORY_SEPARATOR . $link);
        $resolved_link = realpath($target);
        if ($resolved_link === false || !courseware_inside_root($resolved_link, $root)) {
            return false;
        }
        return true;
    }
}

if (!function_exists('courseware_resolve_pptx')) {
    function courseware_resolve_pptx($slug) {
        if (!courseware_is_slug($slug)) {
            return null;
        }
        $root = courseware_root();
        if ($root === '') {
            return null;
        }
        $entries = courseware_scan_pptx_entries();
        if (!isset($entries[$slug])) {
            return null;
        }
        $name = $entries[$slug];
        $raw = $root . DIRECTORY_SEPARATOR . $name;
        if (!courseware_link_stays_inside($raw, $root)) {
            return null;
        }
        $resolved = realpath($raw);
        if ($resolved === false || !is_file($resolved)) {
            return null;
        }
        if (!courseware_inside_root($resolved, $root)) {
            return null;
        }
        if (!courseware_is_pptx_name(basename($resolved)) && !courseware_is_pptx_name($name)) {
            return null;
        }
        return array(
            'slug' => $slug,
            'title' => $slug,
            'filename' => $name,
            'path' => $resolved,
        );
    }
}

if (!function_exists('courseware_build_deck')) {
    function courseware_build_deck($slug) {
        $found = courseware_resolve_pptx($slug);
        if ($found === null) {
            return null;
        }
        return array(
            'slug' => $found['slug'],
            'title' => $found['title'],
            'filename' => $found['filename'],
            'url' => 'courseware-file.php?deck=' . rawurlencode($found['slug']),
        );
    }
}

if (!function_exists('courseware_list_decks')) {
    function courseware_list_decks() {
        $decks = array();
        $seen = array();
        foreach (courseware_scan_pptx_entries() as $slug => $name) {
            unset($name);
            if (isset($seen[$slug])) {
                continue;
            }
            $deck = courseware_build_deck($slug);
            if ($deck !== null) {
                $seen[$slug] = true;
                $decks[] = $deck;
            }
        }
        usort($decks, function ($a, $b) {
            return strnatcasecmp($a['title'], $b['title']);
        });
        return $decks;
    }
}

if (!function_exists('courseware_clamp_page')) {
    function courseware_clamp_page($deck, $page) {
        $page = intval($page);
        if ($page < 1) {
            return 1;
        }
        $count = (is_array($deck) && isset($deck['page_count'])) ? intval($deck['page_count']) : 0;
        if ($count < 1) {
            return $page;
        }
        if ($page > $count) {
            return $count;
        }
        return $page;
    }
}

if (!function_exists('courseware_content_disposition')) {
    function courseware_content_disposition($filename) {
        $safe = str_replace(array("\r", "\n", '"', '\\'), '_', strval($filename));
        $ascii = preg_replace('/[^\x20-\x7E]/', '_', $safe);
        if ($ascii === '' || $ascii === '_' || $ascii === '.pptx') {
            $ascii = 'courseware.pptx';
        }
        return 'inline; filename="' . $ascii . '"; filename*=UTF-8\'\'' . rawurlencode($filename);
    }
}