<?php
require_once __DIR__ . '/db.php';

function h(?string $s): string
{
    return htmlspecialchars($s ?? '', ENT_QUOTES, 'UTF-8');
}

/* ---------------------------------------------------------------------------
 * Library scanner
 * Walks VIDEOS_ROOT recursively, upserts every directory into `folders` and
 * every *.mp4 into `videos` (keyed by relative path so IDs stay stable across
 * rescans), then flags rows whose files disappeared as is_missing.
 * ------------------------------------------------------------------------- */
function scanLibrary(): array
{
    $root = rtrim(VIDEOS_ROOT, '/');
    if (!is_dir($root)) {
        throw new RuntimeException("VIDEOS_ROOT does not exist: $root");
    }

    $db = db();
    $stats = ['folders' => 0, 'videos' => 0, 'missing_folders' => 0, 'missing_videos' => 0];
    $seenFolderIds = [];
    $seenVideoIds  = [];

    $upsertFolder = $db->prepare(
        'INSERT INTO folders (parent_id, name, path, depth, sort_order, is_missing)
         VALUES (?, ?, ?, ?, ?, 0)
         ON DUPLICATE KEY UPDATE parent_id = VALUES(parent_id), name = VALUES(name),
             depth = VALUES(depth), sort_order = VALUES(sort_order), is_missing = 0,
             id = LAST_INSERT_ID(id)'
    );
    $upsertVideo = $db->prepare(
        'INSERT INTO videos (folder_id, name, filename, path, size_bytes, sort_order, is_missing)
         VALUES (?, ?, ?, ?, ?, ?, 0)
         ON DUPLICATE KEY UPDATE folder_id = VALUES(folder_id), name = VALUES(name),
             filename = VALUES(filename), size_bytes = VALUES(size_bytes),
             sort_order = VALUES(sort_order), is_missing = 0,
             id = LAST_INSERT_ID(id)'
    );

    $walk = function (string $dir, ?int $parentId, string $relBase, int $depth)
        use (&$walk, $db, $upsertFolder, $upsertVideo, &$stats, &$seenFolderIds, &$seenVideoIds): void {

        $entries = scandir($dir) ?: [];
        $entries = array_values(array_filter($entries, fn($e) => $e[0] !== '.'));
        usort($entries, 'strnatcasecmp'); // "Video2" before "Video10"

        $folderSort = 0;
        $videoSort  = 0;
        foreach ($entries as $entry) {
            $full = $dir . '/' . $entry;
            $rel  = $relBase === '' ? $entry : $relBase . '/' . $entry;

            if (is_dir($full)) {
                $upsertFolder->execute([$parentId, $entry, $rel, $depth, $folderSort++]);
                $folderId = (int)$db->lastInsertId();
                $seenFolderIds[] = $folderId;
                $stats['folders']++;
                $walk($full, $folderId, $rel, $depth + 1);
            } elseif (is_file($full) && strtolower(pathinfo($entry, PATHINFO_EXTENSION)) === 'mp4') {
                if ($parentId === null) {
                    continue; // mp4 directly in the root is skipped; use course folders
                }
                $name = pathinfo($entry, PATHINFO_FILENAME);
                $upsertVideo->execute([$parentId, $name, $entry, $rel, filesize($full) ?: 0, $videoSort++]);
                $seenVideoIds[] = (int)$db->lastInsertId();
                $stats['videos']++;
            }
        }
    };

    $db->beginTransaction();
    try {
        $walk($root, null, '', 0);

        // Anything not seen this pass no longer exists on disk.
        $flagMissing = function (string $table, array $seenIds) use ($db): int {
            if ($seenIds) {
                $in = implode(',', array_map('intval', $seenIds));
                $sql = "UPDATE $table SET is_missing = 1 WHERE is_missing = 0 AND id NOT IN ($in)";
            } else {
                $sql = "UPDATE $table SET is_missing = 1 WHERE is_missing = 0";
            }
            return $db->exec($sql);
        };
        $stats['missing_folders'] = $flagMissing('folders', $seenFolderIds);
        $stats['missing_videos']  = $flagMissing('videos', $seenVideoIds);

        $db->commit();
    } catch (Throwable $e) {
        $db->rollBack();
        throw $e;
    }
    return $stats;
}

/* ---------------------------------------------------------------------------
 * Progress helpers
 * ------------------------------------------------------------------------- */

/**
 * Progress for one folder's whole subtree, matched by path prefix.
 * Returns ['total' => n, 'completed' => n, 'percent' => 0-100].
 * Percent gives partial credit for videos that are started but not finished.
 */
function folderProgress(int $userId, string $folderPath): array
{
    $stmt = db()->prepare(
        "SELECT COUNT(*) AS total,
                COALESCE(SUM(vp.completed), 0) AS completed,
                COALESCE(SUM(
                    CASE
                        WHEN vp.completed = 1 THEN 1
                        WHEN vp.duration_seconds > 0
                             THEN LEAST(vp.position_seconds / vp.duration_seconds, 1)
                        ELSE 0
                    END
                ), 0) AS credit
         FROM videos v
         JOIN folders f ON f.id = v.folder_id
         LEFT JOIN video_progress vp ON vp.video_id = v.id AND vp.user_id = ?
         WHERE v.is_missing = 0 AND f.is_missing = 0
           AND (f.path = ? OR f.path LIKE ?)"
    );
    $stmt->execute([$userId, $folderPath, likePrefix($folderPath) . '/%']);
    $row = $stmt->fetch();
    $total = (int)$row['total'];
    return [
        'total'     => $total,
        'completed' => (int)$row['completed'],
        'percent'   => $total > 0 ? (int)round(100 * $row['credit'] / $total) : 0,
    ];
}

/** Escape LIKE wildcards in a path used as a prefix. */
function likePrefix(string $path): string
{
    return str_replace(['\\', '%', '_'], ['\\\\', '\\%', '\\_'], $path);
}

function getFolder(int $id): ?array
{
    $stmt = db()->prepare('SELECT * FROM folders WHERE id = ? AND is_missing = 0');
    $stmt->execute([$id]);
    return $stmt->fetch() ?: null;
}

function getVideo(int $id): ?array
{
    $stmt = db()->prepare(
        'SELECT v.*, f.path AS folder_path, f.name AS folder_name
         FROM videos v JOIN folders f ON f.id = v.folder_id
         WHERE v.id = ? AND v.is_missing = 0'
    );
    $stmt->execute([$id]);
    return $stmt->fetch() ?: null;
}

function childFolders(?int $parentId): array
{
    $sql = 'SELECT * FROM folders WHERE is_missing = 0 AND parent_id '
         . ($parentId === null ? 'IS NULL' : '= ?')
         . ' ORDER BY sort_order, name';
    $stmt = db()->prepare($sql);
    $stmt->execute($parentId === null ? [] : [$parentId]);
    return $stmt->fetchAll();
}

/** Videos in a folder, joined with the user's progress. */
function folderVideos(int $folderId, int $userId): array
{
    $stmt = db()->prepare(
        'SELECT v.*, vp.position_seconds, vp.duration_seconds AS watched_duration, vp.completed
         FROM videos v
         LEFT JOIN video_progress vp ON vp.video_id = v.id AND vp.user_id = ?
         WHERE v.folder_id = ? AND v.is_missing = 0
         ORDER BY v.sort_order, v.name'
    );
    $stmt->execute([$userId, $folderId]);
    return $stmt->fetchAll();
}

/** Breadcrumb chain root -> ... -> folder. */
function folderBreadcrumbs(array $folder): array
{
    $crumbs = [$folder];
    while ($folder['parent_id'] !== null) {
        $folder = getFolder((int)$folder['parent_id']);
        if (!$folder) break;
        array_unshift($crumbs, $folder);
    }
    return $crumbs;
}

/** Most recently watched, unfinished videos for the "Continue watching" strip. */
function continueWatching(int $userId, int $limit = 6): array
{
    $stmt = db()->prepare(
        'SELECT v.id, v.name, f.path AS folder_path,
                vp.position_seconds, vp.duration_seconds, vp.updated_at
         FROM video_progress vp
         JOIN videos v  ON v.id = vp.video_id AND v.is_missing = 0
         JOIN folders f ON f.id = v.folder_id
         WHERE vp.user_id = ? AND vp.completed = 0 AND vp.position_seconds > 5
         ORDER BY vp.updated_at DESC
         LIMIT ' . (int)$limit
    );
    $stmt->execute([$userId]);
    return $stmt->fetchAll();
}

function formatDuration(?float $seconds): string
{
    if ($seconds === null || $seconds <= 0) return '';
    $s = (int)round($seconds);
    return $s >= 3600
        ? sprintf('%d:%02d:%02d', intdiv($s, 3600), intdiv($s % 3600, 60), $s % 60)
        : sprintf('%d:%02d', intdiv($s, 60), $s % 60);
}