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

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

/* ---------------------------------------------------------------------------
 * Video duration probing (used by the scanner so listings can show durations
 * before anyone plays the video). Pure-PHP mp4 parse first, ffprobe fallback.
 * ------------------------------------------------------------------------- */
function probeDuration(string $file): ?float
{
    $d = mp4Duration($file);
    if ($d !== null && $d > 0) return $d;

    if (function_exists('shell_exec')) {
        $out = @shell_exec('ffprobe -v error -show_entries format=duration -of csv=p=0 '
                           . escapeshellarg($file) . ' 2>/dev/null');
        if ($out !== null && is_numeric(trim($out))) {
            return (float)trim($out);
        }
    }
    return null;
}

/** Read the duration from an mp4's moov/mvhd box. Returns seconds or null. */
function mp4Duration(string $path): ?float
{
    $fp = @fopen($path, 'rb');
    if (!$fp) return null;
    $fileSize = filesize($path) ?: 0;
    $duration = null;

    $readBox = function (int $pos) use ($fp): ?array {
        fseek($fp, $pos);
        $hdr = fread($fp, 8);
        if (strlen($hdr) < 8) return null;
        $size   = unpack('N', substr($hdr, 0, 4))[1];
        $type   = substr($hdr, 4, 4);
        $hdrLen = 8;
        if ($size === 1) {                    // 64-bit box size
            $ext = fread($fp, 8);
            if (strlen($ext) < 8) return null;
            $size   = unpack('J', $ext)[1];
            $hdrLen = 16;
        }
        return ($size >= $hdrLen) ? [$size, $type, $hdrLen] : null;
    };

    // Walk top-level boxes to find moov, then its mvhd child.
    for ($pos = 0; $pos < $fileSize;) {
        $box = $readBox($pos);
        if (!$box) break;
        [$size, $type, $hdrLen] = $box;
        if ($size === 0) $size = $fileSize - $pos;   // box extends to EOF

        if ($type === 'moov') {
            for ($p = $pos + $hdrLen, $end = $pos + $size; $p < $end;) {
                $child = $readBox($p);
                if (!$child) break;
                [$cSize, $cType, $cHdrLen] = $child;
                if ($cType === 'mvhd') {
                    fseek($fp, $p + $cHdrLen);
                    $body = fread($fp, 32);
                    if (strlen($body) >= 20) {
                        if (ord($body[0]) === 1 && strlen($body) >= 32) {   // version 1
                            $timescale = unpack('N', substr($body, 20, 4))[1];
                            $dur       = unpack('J', substr($body, 24, 8))[1];
                        } else {                                            // version 0
                            $timescale = unpack('N', substr($body, 12, 4))[1];
                            $dur       = unpack('N', substr($body, 16, 4))[1];
                        }
                        if ($timescale > 0) $duration = $dur / $timescale;
                    }
                    break 2;
                }
                $p += $cSize;
            }
            break;
        }
        $pos += $size;
    }
    fclose($fp);
    return $duration;
}

/* ---------------------------------------------------------------------------
 * Quiz file parser
 * Format ("*_quiz_solved.txt"):
 *   [&] Question text (Select two)
 *   - wrong option
 *   - right option -- Correct
 * Returns [['text', 'options' => [...], 'correct' => [optIndex,...], 'multi'], ...]
 * ------------------------------------------------------------------------- */
function parseQuizFile(string $absPath): array
{
    $raw = @file_get_contents($absPath);
    if ($raw === false) return [];

    $questions = [];
    $cur = null;
    foreach (preg_split('/\r\n|\r|\n/', $raw) as $line) {
        $line = trim($line);
        if ($line === '') continue;

        if (str_starts_with($line, '[&]')) {
            if ($cur && $cur['options']) $questions[] = $cur;
            $cur = ['text' => trim(substr($line, 3)), 'options' => [], 'correct' => []];
        } elseif (str_starts_with($line, '-') && $cur !== null) {
            $opt = trim(substr($line, 1));
            if (preg_match('/\s*--\s*correct\s*$/i', $opt)) {
                $opt = trim(preg_replace('/\s*--\s*correct\s*$/i', '', $opt));
                $cur['correct'][] = count($cur['options']);
            }
            $cur['options'][] = $opt;
        } elseif ($cur !== null && !$cur['options']) {
            $cur['text'] .= ' ' . $line;   // wrapped question text
        }
    }
    if ($cur && $cur['options']) $questions[] = $cur;

    foreach ($questions as &$q) {
        $q['multi'] = count($q['correct']) > 1;
    }
    return $questions;
}

/* ---------------------------------------------------------------------------
 * Library scanner
 * Walks VIDEOS_ROOT recursively, upserts every directory into `folders`,
 * every *.mp4 into `videos`, and every *_quiz_solved.txt into `quizzes`
 * (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, 'quizzes' => 0,
              'missing_folders' => 0, 'missing_videos' => 0, 'missing_quizzes' => 0];
    $seenFolderIds = [];
    $seenVideoIds  = [];
    $seenQuizIds   = [];

    $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)'
    );
    $upsertQuiz = $db->prepare(
        'INSERT INTO quizzes (folder_id, name, filename, path, num_questions, sort_order, is_missing)
         VALUES (?, ?, ?, ?, ?, ?, 0)
         ON DUPLICATE KEY UPDATE folder_id = VALUES(folder_id), name = VALUES(name),
             filename = VALUES(filename), num_questions = VALUES(num_questions),
             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, $upsertQuiz,
            &$stats, &$seenFolderIds, &$seenVideoIds, &$seenQuizIds): void {

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

        $folderSort = 0;
        $videoSort  = 0;
        $quizSort   = 0;
        foreach ($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();
                $stats['videos']++;
            } elseif (is_file($full) && preg_match('/_quiz_solved\.txt$/i', $entry)) {
                if ($parentId === null) {
                    continue;
                }
                $numQuestions = count(parseQuizFile($full));
                if ($numQuestions === 0) {
                    continue; // unparseable file — don't index an empty quiz
                }
                $name = trim(preg_replace('/_quiz_solved\.txt$/i', '', $entry));
                $upsertQuiz->execute([$parentId, $name, $entry, $rel, $numQuestions, $quizSort++]);
                $seenQuizIds[] = (int)$db->lastInsertId();
                $stats['quizzes']++;
            }
        }
    };

    $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);
        $stats['missing_quizzes'] = $flagMissing('quizzes', $seenQuizIds);

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

    // Fill in durations for videos that don't have one yet (new files, or
    // indexed before duration probing existed). Only missing ones are probed,
    // so rescans stay fast.
    $stats['durations_probed'] = 0;
    $rows = $db->query(
        'SELECT id, path FROM videos WHERE duration_seconds IS NULL AND is_missing = 0'
    )->fetchAll();
    $upd = $db->prepare('UPDATE videos SET duration_seconds = ? WHERE id = ?');
    foreach ($rows as $r) {
        $d = probeDuration($root . '/' . $r['path']);
        if ($d !== null && $d > 0) {
            $upd->execute([$d, (int)$r['id']]);
            $stats['durations_probed']++;
        }
    }

    return $stats;
}

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

/**
 * Progress for one folder's whole subtree (videos + quizzes), matched by
 * path prefix. Returns ['total' => n, 'completed' => n, 'percent' => 0-100].
 * Percent gives partial credit for half-watched videos and partial scores.
 */
function folderProgress(int $userId, string $folderPath): array
{
    $args = [$userId, $folderPath, likePrefix($folderPath) . '/%'];

    $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 ?)"
    );
    $stmt->execute($args);
    $videos = $stmt->fetch();

    $stmt = db()->prepare(
        "SELECT COUNT(*) AS total,
                COALESCE(SUM(qp.completed), 0) AS completed,
                COALESCE(SUM(
                    CASE
                        WHEN qp.completed = 1 THEN 1
                        WHEN q.num_questions > 0
                             THEN LEAST(COALESCE(qp.best_score, 0) / q.num_questions, 1)
                        ELSE 0
                    END
                ), 0) AS credit
         FROM quizzes q
         JOIN folders f ON f.id = q.folder_id
         LEFT JOIN quiz_progress qp ON qp.quiz_id = q.id AND qp.user_id = ?
         WHERE q.is_missing = 0 AND f.is_missing = 0
           AND (f.path = ? OR f.path LIKE ?)"
    );
    $stmt->execute($args);
    $quizzes = $stmt->fetch();

    $total  = (int)$videos['total'] + (int)$quizzes['total'];
    $credit = $videos['credit'] + $quizzes['credit'];
    return [
        'total'     => $total,
        'completed' => (int)$videos['completed'] + (int)$quizzes['completed'],
        'percent'   => $total > 0 ? (int)round(100 * $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();
}

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

/** Quizzes in a folder, joined with the user's results. */
function folderQuizzes(int $folderId, int $userId): array
{
    $stmt = db()->prepare(
        'SELECT q.*, qp.best_score, qp.last_score, qp.attempts, qp.completed
         FROM quizzes q
         LEFT JOIN quiz_progress qp ON qp.quiz_id = q.id AND qp.user_id = ?
         WHERE q.folder_id = ? AND q.is_missing = 0
         ORDER BY q.sort_order, q.name'
    );
    $stmt->execute([$userId, $folderId]);
    return $stmt->fetchAll();
}

/** Absolute, containment-checked path of a quiz file (null if gone). */
function quizFilePath(array $quiz): ?string
{
    $file = realpath(rtrim(VIDEOS_ROOT, '/') . '/' . $quiz['path']);
    $root = realpath(VIDEOS_ROOT);
    if ($file === false || $root === false
        || !str_starts_with($file, $root . DIRECTORY_SEPARATOR) || !is_file($file)) {
        return null;
    }
    return $file;
}

/** 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);
}