Add auto-thumbnails, library-wide remaining time, backup restore

Auto-generated course thumbnails: find_course_thumbnail() falls back to
grabbing a frame from a course's first video via ffmpeg when there's no
manual cover image, cached to .offlineu_thumbnail.jpg so it only ever
runs once. Folded into the "Precompute" prewarm button, now "Precompute
Lengths & Cover Art".

Library-wide "Remaining" stat: sums every course's already-cached
duration (no ffprobe, just a JSON read) into the dashboard's Library
Stats card, alongside the existing "Watched" figure.

Backup restore: new /api/backup/restore endpoint and a "Choose Backup
File..." control in Settings, with zip-slip and missing-course guards.
Also fixed a gap in the export itself - next_up.json and
outline_config.json weren't being backed up before, so restore wouldn't
have been a true round trip.

Move Surprise Me from a full-width button above the course list to a
dice-icon button in the dashboard header, swapping with the course-name
badge depending on whether a course is loaded.

Update README to cover all of the above.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -85,17 +85,21 @@ silently stay blank instead of erroring.
   opt-in transcript search across subtitle files
 - Course cards show media file count, total video/audio runtime, and
   completion % at a glance
+- Cover art: uses a manually-placed `cover`/`folder`/`thumbnail`/`thumb`/
+  `poster` image if a course has one, otherwise auto-generates one via
+  `ffmpeg` from a frame of the course's first video
 - Hide courses/folders from the browser without touching anything on disk;
   bulk-select to hide or queue several at once
 - Bulk rename across course/folder names (find & replace)
 
 **Dashboard**
-- Library-wide stats (courses, lessons completed, time watched, day streak)
+- Library-wide stats (courses, lessons completed, time watched, time
-  and a 90-day activity heatmap
+  remaining, day streak) and a 90-day activity heatmap
 - Next Up queue (manually curated, reorderable)
 - Pick Back Up (courses with progress that have gone stale)
 - Recently Added / Recently Viewed
-- Surprise Me — random pick, weighted toward incomplete courses
+- Surprise Me — dice icon in the header, random pick weighted toward
+  incomplete courses
 
 **Playback & progress**
 - Video/audio player with resize, playback-speed presets, and resume-from-
@@ -103,9 +107,11 @@ silently stay blank instead of erroring.
 - Auto-tracks watch progress and completion per lesson
 - Video/audio durations read via `ffprobe` and cached persistently per
   course (`.offlineu_duration_cache.json`), so total runtime and per-lesson
-  length show up before you've ever pressed play — not just after
+  length show up before you've ever pressed play — not just after; the
-- Settings → "Precompute Video Lengths" walks the whole library in the
+  same cache backs the library-wide "time remaining" stat
-  background to populate that cache up front, with live progress
+- Settings → "Precompute Lengths & Cover Art" walks the whole library in
+  the background to populate durations and thumbnails up front, with live
+  progress
 
 **Notes**
 - Timestamped notes per lesson, capturable via a keyboard shortcut without
@@ -120,9 +126,12 @@ silently stay blank instead of erroring.
   5-minute filesystem-scan cache)
 
 **Backup & integrations**
-- One-click backup export: settings, hidden-path choices, recent-view
+- One-click backup export and restore: settings, hidden-path choices, the
-  history, and every course's progress/notes as a zip (not the course files
+  Next Up queue, recent-view history, Outline config, and every course's
-  themselves)
+  progress/notes as a zip (not the course files themselves). Restore
+  overwrites current data and needs a matching course folder to already
+  exist for each course's progress to land - it's a "put my data back"
+  action, not a merge
 - Optional [Outline](https://www.getoutline.com/) integration — push a
   lesson's notes to an Outline document/collection
 
@@ -142,10 +151,11 @@ Everything under `OFFLINEU_DATA_DIR` (app-wide, not tied to a course):
 
 Per-course, written inside the course's own folder on the library volume:
 
-| File                              | Contents                                          |
+| File                              | Contents                                              |
-| ----------------------------------- | ---------------------------------------------------- |
+| ----------------------------------- | -------------------------------------------------------- |
-| `.offlineu_progress.json`           | Per-lesson completed/progress/duration/notes         |
+| `.offlineu_progress.json`           | Per-lesson completed/progress/duration/notes             |
-| `.offlineu_duration_cache.json`     | ffprobe duration cache, keyed by (path, size, mtime) |
+| `.offlineu_duration_cache.json`     | ffprobe duration cache, keyed by (path, size, mtime)     |
+| `.offlineu_thumbnail.jpg`           | Auto-generated cover art (only if no manual cover exists) |
 
 ---
 
@@ -162,7 +172,8 @@ MyCourse/
 │   └── resources/
 │       └── extras.md
 ├── .offlineu_progress.json        ← created automatically
-└── .offlineu_duration_cache.json  ← created automatically
+├── .offlineu_duration_cache.json  ← created automatically
+└── .offlineu_thumbnail.jpg        ← created automatically, only if no manual cover exists
 ```
 
 No metadata files needed — course/section/lesson names come straight from

offlineu_core.py

@@ -36,6 +36,7 @@ TEXT_EXTENSIONS = {'.txt', '.md', '.html', '.htm', '.pdf', '.docx', '.doc', '.rt
 QUIZ_INDICATORS = {'quiz', 'exam', 'test', 'assessment', 'exercise', 'assignment', 'homework'}
 IMAGE_EXTENSIONS = {'.jpg', '.jpeg', '.png', '.webp'}
 THUMBNAIL_BASENAMES = ('cover', 'folder', 'thumbnail', 'thumb', 'poster')
+AUTO_THUMBNAIL_FILENAME = '.offlineu_thumbnail.jpg'
 
 # Base directory the "Library" browser scans for courses, so users don't have
 # to type a full filesystem path. Matches the ./courses volume mount in
@@ -560,20 +561,73 @@ def _has_direct_media(directory: Path) -> bool:
 
 def find_course_thumbnail(course_path: str) -> Optional[str]:
     """
-    Look for a cover image directly inside a course folder (not recursive -
+    A course's cover image: a manually-placed one directly inside the
-    this only needs to catch the common 'cover.jpg next to the sections'
+    folder (cover/folder/thumbnail/thumb/poster.*, checked non-recursively
-    layout, not go hunting through every subfolder).
+    - just the common 'cover.jpg next to the sections' layout, not every
+    subfolder) if there is one, otherwise an auto-generated frame grabbed
+    from the course's first video. Almost none of this library's courses
+    ship with real cover art, so without the fallback the grid view would
+    be mostly bare initials.
     """
+    course_dir = Path(course_path)
     try:
-        names = {f.name.lower(): f for f in Path(course_path).iterdir() if f.is_file()}
+        names = {f.name.lower(): f for f in course_dir.iterdir() if f.is_file()}
     except (PermissionError, OSError):
         return None
+
     for base in THUMBNAIL_BASENAMES:
         for ext in IMAGE_EXTENSIONS:
             match = names.get(f'{base}{ext}')
             if match:
                 return str(match)
-    return None
+
+    auto_thumb = names.get(AUTO_THUMBNAIL_FILENAME)
+    if auto_thumb:
+        return str(auto_thumb)
+
+    # Generating (or determining there's nothing to generate from) is the
+    # one part of this that isn't a cheap directory listing - cache the
+    # outcome briefly so repeat image requests for a doc-only course don't
+    # re-walk its files on every load.
+    return cache_get_or_compute(
+        f'auto_thumbnail:{course_dir}',
+        lambda: _generate_course_thumbnail(course_dir)
+    )
+
+
+def _generate_course_thumbnail(course_dir: Path) -> Optional[str]:
+    """
+    Grab a single frame from the course's first video as stand-in cover
+    art, via ffmpeg, cached to .offlineu_thumbnail.jpg so this only ever
+    runs once per course - the next call finds that file directly through
+    the fast path above instead of hitting this function again. Returns
+    None (nothing cached to disk) if the course has no video at all, so a
+    video added later is still picked up on the next request past the
+    short in-memory cache above.
+    """
+    video_files = sorted(
+        f for f in course_dir.rglob('*')
+        if f.is_file() and f.suffix.lower() in VIDEO_EXTENSIONS
+    )
+    if not video_files:
+        return None
+    source = video_files[0]
+
+    duration = _probe_media_duration_seconds(source) or 0
+    offset = min(30.0, duration * 0.1) if duration else 5.0
+
+    output_path = course_dir / AUTO_THUMBNAIL_FILENAME
+    try:
+        result = subprocess.run(
+            ['ffmpeg', '-y', '-ss', str(offset), '-i', str(source),
+             '-frames:v', '1', '-vf', 'scale=480:-1', '-q:v', '3', str(output_path)],
+            capture_output=True, timeout=20
+        )
+    except (OSError, subprocess.SubprocessError):
+        return None
+    if result.returncode != 0 or not output_path.exists():
+        return None
+    return str(output_path)
 
 
 _SECTION_NAME_RE = re.compile(
@@ -985,6 +1039,24 @@ def _course_total_duration_seconds(course_dir: Path, media_files: List[Path]) ->
     return total if have_any else None
 
 
+def _cached_course_duration_seconds(course_dir: Path) -> float:
+    """
+    Sum of whatever's already in a course's persistent duration cache file,
+    without walking its files or ever touching ffprobe - for the
+    library-wide "time remaining" stat, which needs to stay cheap enough to
+    compute on every dashboard load (it runs inside the same per-course
+    loop as _scan_library_activity). A course that's never been viewed,
+    searched, or prewarmed yet just contributes 0 here; run "Precompute
+    Lengths & Cover Art" in Settings for a complete total.
+    """
+    try:
+        with open(course_dir / DURATION_CACHE_FILENAME, 'r') as f:
+            cache = json.load(f)
+    except (FileNotFoundError, json.JSONDecodeError, OSError):
+        return 0.0
+    return sum(entry.get('duration_seconds') or 0 for entry in cache.values())
+
+
 def _course_summary(course_dir: Path) -> Dict[str, Any]:
     """Build the {type, name, path, media_files, hidden, has_thumbnail,
     duration_display} shape shared by the Library browser, search results,
@@ -1185,6 +1257,7 @@ def _scan_library_activity() -> Dict[str, Any]:
     lessons_tracked = 0
     completed_lessons = 0
     watched_seconds = 0
+    total_duration_seconds = 0.0
     active_dates = set()
     activity_by_date: Dict[str, int] = {}
     courses: List[Dict[str, Any]] = []
@@ -1192,6 +1265,7 @@ def _scan_library_activity() -> Dict[str, Any]:
 
     for course_dir in get_all_course_dirs():
         total_courses += 1
+        total_duration_seconds += _cached_course_duration_seconds(course_dir)
         try:
             with open(course_dir / '.offlineu_progress.json', 'r') as f:
                 progress = json.load(f)
@@ -1248,6 +1322,7 @@ def _scan_library_activity() -> Dict[str, Any]:
         'lessons_tracked': lessons_tracked,
         'completed_lessons': completed_lessons,
         'watched_seconds': watched_seconds,
+        'total_duration_seconds': total_duration_seconds,
         'streak_days': streak_days,
         'activity_by_date': activity_by_date,
         'courses': courses,
@@ -1269,11 +1344,17 @@ def get_random_incomplete_course() -> Optional[Path]:
 
 def format_library_stats(scan: Dict[str, Any]) -> Dict[str, Any]:
     """Library-wide overview for the dashboard's stats card, from a _scan_library_activity() result."""
+    remaining_seconds = max(0, scan['total_duration_seconds'] - scan['watched_seconds'])
     return {
         'total_courses': scan['total_courses'],
         'lessons_tracked': scan['lessons_tracked'],
         'completed_lessons': scan['completed_lessons'],
         'watched_display': format_duration(scan['watched_seconds']),
+        # None until at least some course's duration cache has been
+        # populated (via viewing/searching the library or running
+        # "Precompute Lengths & Cover Art") - a remaining estimate from a
+        # library that's mostly uncached would just be misleadingly low.
+        'remaining_display': format_duration(remaining_seconds) if scan['total_duration_seconds'] else None,
         'streak_days': scan['streak_days']
     }
 
@@ -2180,9 +2261,10 @@ _duration_prewarm_state: Dict[str, Any] = {
 def _run_duration_prewarm():
     """
     Walk every course in the library and populate its persistent duration
-    cache (see _course_total_duration_seconds) up front, so opening a
+    cache (see _course_total_duration_seconds) and cover-art thumbnail
-    course for the first time doesn't pay the ffprobe cost right then -
+    (see _generate_course_thumbnail) up front, so opening a course or
-    it was already paid here, once, in the background.
+    browsing the library for the first time doesn't pay either cost right
+    then - both were already paid here, once, in the background.
     """
     global _duration_prewarm_state
     course_dirs = get_all_course_dirs()
@@ -2196,6 +2278,7 @@ def _run_duration_prewarm():
                 if f.is_file() and f.suffix.lower() in VIDEO_EXTENSIONS | AUDIO_EXTENSIONS
             ]
             _course_total_duration_seconds(course_dir, media_files)
+            find_course_thumbnail(str(course_dir))
             _duration_prewarm_state['done'] += 1
     except Exception as e:
         _duration_prewarm_state['error'] = str(e)
@@ -2210,7 +2293,7 @@ def _run_duration_prewarm():
 
 @app.route('/api/library/prewarm-durations', methods=['POST'])
 def prewarm_durations_api():
-    """Kick off (or report on an already-running) background scan of every course's video/audio duration."""
+    """Kick off (or report on an already-running) background scan of every course's video/audio duration and cover art."""
     if not _duration_prewarm_state['running']:
         threading.Thread(target=_run_duration_prewarm, daemon=True).start()
     return jsonify(_duration_prewarm_state)
@@ -2489,21 +2572,30 @@ def reset_settings_api():
     })
 
 
+# Shared between download_backup and restore_backup so the two can never
+# drift out of sync with each other about what belongs at the archive root.
+BACKUP_ROOT_FILES = {
+    'settings.json': SETTINGS_FILE,
+    'hidden_paths.json': HIDDEN_PATHS_FILE,
+    'next_up.json': NEXT_UP_FILE,
+    'recent_views.json': RECENT_VIEWS_FILE,
+    'outline_config.json': OUTLINE_CONFIG_FILE,
+}
+
+
 @app.route('/api/backup')
 def download_backup():
     """
     Bundle everything that isn't recoverable from the course files
-    themselves - settings, hidden-path curation, recently-viewed history,
+    themselves - settings, hidden-path curation, the Next Up queue,
-    and every course's progress/notes file - into a single downloadable
+    recently-viewed history, Outline config, and every course's
-    zip. Cheap insurance before a NAS migration or a docker volume mistake.
+    progress/notes file - into a single downloadable zip. Cheap insurance
+    before a NAS migration or a docker volume mistake; see restore_backup
+    for the other half of this round trip.
     """
     buffer = io.BytesIO()
     with zipfile.ZipFile(buffer, 'w', zipfile.ZIP_DEFLATED) as zf:
-        for name, path in (
+        for name, path in BACKUP_ROOT_FILES.items():
-            ('settings.json', SETTINGS_FILE),
-            ('hidden_paths.json', HIDDEN_PATHS_FILE),
-            ('recent_views.json', RECENT_VIEWS_FILE),
-        ):
             if os.path.exists(path):
                 zf.write(path, name)
 
@@ -2519,6 +2611,59 @@ def download_backup():
     return send_file(buffer, mimetype='application/zip', as_attachment=True, download_name=filename)
 
 
+@app.route('/api/backup/restore', methods=['POST'])
+def restore_backup():
+    """
+    Restore a zip produced by download_backup: the root-level app files in
+    BACKUP_ROOT_FILES, plus each course's progress file from
+    progress/<relative-course-path>/.offlineu_progress.json. Overwrites
+    whatever's currently there - this is a deliberate "put my data back"
+    action, not a merge.
+    """
+    uploaded = request.files.get('backup')
+    if not uploaded or not uploaded.filename:
+        return jsonify({'success': False, 'error': 'No backup file selected'}), 400
+
+    try:
+        zf = zipfile.ZipFile(io.BytesIO(uploaded.read()))
+    except zipfile.BadZipFile:
+        return jsonify({'success': False, 'error': 'That file is not a valid zip archive'}), 400
+
+    os.makedirs(DATA_DIR, exist_ok=True)
+    names = set(zf.namelist())
+    restored = []
+    skipped = []
+
+    for archive_name, dest_path in BACKUP_ROOT_FILES.items():
+        if archive_name not in names:
+            continue
+        with zf.open(archive_name) as src, open(dest_path, 'wb') as dst:
+            dst.write(src.read())
+        restored.append(archive_name)
+
+    library_root = os.path.abspath(get_library_root())
+    for name in names:
+        if not (name.startswith('progress/') and name.endswith('/.offlineu_progress.json')):
+            continue
+        relative = name[len('progress/'):-len('/.offlineu_progress.json')]
+        dest_dir = os.path.abspath(os.path.join(library_root, relative))
+        # Guard against a zip entry trying to write outside the library
+        # root (zip-slip) - restore is a trusted, deliberate admin action,
+        # but the archive's paths themselves shouldn't be trusted blindly.
+        if not (dest_dir == library_root or dest_dir.startswith(library_root + os.sep)):
+            skipped.append(relative)
+            continue
+        if not os.path.isdir(dest_dir):
+            skipped.append(relative)
+            continue
+        with zf.open(name) as src, open(os.path.join(dest_dir, '.offlineu_progress.json'), 'wb') as dst:
+            dst.write(src.read())
+        restored.append(name)
+
+    invalidate_cache()
+    return jsonify({'success': True, 'restored': len(restored), 'skipped': skipped})
+
+
 @app.route('/load_course', methods=['POST'])
 def load_course():
     """Load course from selected directory"""

templates/course_dashboard.html

@@ -136,6 +136,25 @@
             white-space: nowrap;
         }
 
+        .header-icon-btn {
+            display: flex;
+            align-items: center;
+            justify-content: center;
+            width: 44px;
+            height: 44px;
+            flex-shrink: 0;
+            border-radius: 50%;
+            background: var(--bg-primary);
+            border: 1px solid var(--accent);
+            color: var(--accent);
+            text-decoration: none;
+            transition: background 0.2s, color 0.2s;
+        }
+        .header-icon-btn:hover {
+            background: var(--accent);
+            color: white;
+        }
+
         .course-name-heading {
             /* course.name is the raw folder name, unlike lesson titles
                (cleaned up via _clean_lesson_name) - real course folders are
@@ -288,14 +307,6 @@
             box-sizing: border-box;
         }
 
-        .surprise-me-btn {
-            display: block;
-            width: 100%;
-            text-align: center;
-            font-size: 1.05em;
-            font-weight: 600;
-            box-sizing: border-box;
-        }
 
         .progress-bar {
             background: #444;
@@ -982,6 +993,8 @@
             </a>
             {% if course %}
             <div class="header-course-badge">{{ course.name }}</div>
+            {% elif library_stats and library_stats.total_courses %}
+            <a href="/random-pick" class="header-icon-btn" title="Surprise Me - random incomplete course">{{ icons.icon('dice', 20) }}</a>
             {% endif %}
         </div>
     </div>
@@ -1153,12 +1166,6 @@
         </div>
         {% endmacro %}
 
-        {% if library_stats and library_stats.total_courses %}
-        <div class="container">
-            <a class="btn surprise-me-btn" href="/random-pick">{{ icons.icon('dice', 16) }} Surprise Me</a>
-        </div>
-        {% endif %}
-
         <div class="container">
             <div class="card" id="library-card">
                 <h2><span class="card-header-label">{{ icons.icon('grid') }}Your Courses</span></h2>
@@ -1212,6 +1219,12 @@
                             <div class="stats-tile-value">{{ library_stats.watched_display }}</div>
                             <div class="stats-tile-label">Watched</div>
                         </div>
+                        {% if library_stats.remaining_display %}
+                        <div class="stats-tile">
+                            <div class="stats-tile-value">{{ library_stats.remaining_display }}</div>
+                            <div class="stats-tile-label">Remaining</div>
+                        </div>
+                        {% endif %}
                         <div class="stats-tile">
                             <div class="stats-tile-value">{{ library_stats.streak_days }}</div>
                             <div class="stats-tile-label">Day streak</div>

templates/help.html

@@ -163,7 +163,7 @@
                 <li><strong>Browse your library</strong> from the main page, or enter a path manually in Settings</li>
                 <li><strong>Click a course</strong> to load it - folders drill down, courses open directly</li>
                 <li><strong>Start learning!</strong> Progress, notes, and completion are all saved automatically</li>
-                <li>Not sure what to watch? <strong>{{ icons.icon('dice', 14) }} Surprise Me</strong> at the top of the dashboard picks a random course you haven't finished</li>
+                <li>Not sure what to watch? The dice icon {{ icons.icon('dice', 14) }} in the top-right of the dashboard header picks a random course you haven't finished</li>
             </ul>
         </div>
 

templates/settings.html

@@ -451,10 +451,10 @@
                 <span class="setting-desc">Courses are cached briefly for speed - use this after adding or removing files directly on disk if you don't want to wait a few minutes for it to notice.</span>
 
                 <div style="display: flex; align-items: center; gap: 10px; margin-top: 10px;">
-                    <button class="btn btn-secondary btn-sm" id="prewarm-durations-btn" onclick="startDurationPrewarm()">{{ icons.icon('refresh', 14) }} Precompute Video Lengths</button>
+                    <button class="btn btn-secondary btn-sm" id="prewarm-durations-btn" onclick="startDurationPrewarm()">{{ icons.icon('refresh', 14) }} Precompute Lengths &amp; Cover Art</button>
                     <span id="prewarm-durations-status" style="font-size: 0.85em; color: var(--text-muted);"></span>
                 </div>
-                <span class="setting-desc">Reads every video/audio file's length up front and caches it, so course cards in the Library show their total runtime immediately instead of computing it the first time each course is viewed.</span>
+                <span class="setting-desc">Reads every video/audio file's length and generates cover art for any course without one, up front - so course cards in the Library show their runtime and artwork immediately instead of computing it the first time each course is viewed.</span>
             </div>
         </div>
 
@@ -540,10 +540,18 @@
             <h2>Backup &amp; Export</h2>
             <div class="setting-row">
                 <label>Download a backup
-                    <span class="setting-desc">Settings, hidden-path curation, recently-viewed history, and every course's progress/notes - not the course files themselves.</span>
+                    <span class="setting-desc">Settings, hidden-path curation, the Next Up queue, recently-viewed history, Outline config, and every course's progress/notes - not the course files themselves.</span>
                 </label>
                 <a class="btn" href="/api/backup">Download Backup</a>
             </div>
+            <div class="setting-row">
+                <label for="restore-backup-input">Restore from a backup
+                    <span class="setting-desc">Overwrites current settings and progress with what's in the zip. Course files on disk aren't touched.</span>
+                </label>
+                <input type="file" id="restore-backup-input" accept=".zip" style="display: none;" onchange="handleRestoreFileChosen(this)">
+                <button class="btn btn-secondary" onclick="document.getElementById('restore-backup-input').click()">Choose Backup File…</button>
+            </div>
+            <span id="restore-backup-status" style="font-size: 0.85em; min-height: 1.2em; display: block;"></span>
         </div>
 
         <div class="card">
@@ -1068,6 +1076,41 @@
                 .catch(() => {});
         })();
 
+        function handleRestoreFileChosen(input) {
+            const file = input.files && input.files[0];
+            input.value = '';  // allow re-choosing the same file later
+            if (!file) return;
+
+            if (!confirm(`Restore from "${file.name}"? This overwrites your current settings and every course's progress/notes with what's in the backup.`)) {
+                return;
+            }
+
+            const status = document.getElementById('restore-backup-status');
+            status.style.color = 'var(--text-muted)';
+            status.textContent = 'Restoring…';
+
+            const formData = new FormData();
+            formData.append('backup', file);
+            fetch('/api/backup/restore', { method: 'POST', body: formData })
+                .then(r => r.json())
+                .then(data => {
+                    if (data.success) {
+                        status.style.color = 'var(--success)';
+                        const skippedNote = data.skipped && data.skipped.length
+                            ? ` (${data.skipped.length} course${data.skipped.length === 1 ? '' : 's'} skipped - not found in the current library)`
+                            : '';
+                        status.innerHTML = `${ICON_SVGS.check} Restored ${data.restored} file${data.restored === 1 ? '' : 's'}${skippedNote} - reload to see it take effect`;
+                    } else {
+                        status.style.color = 'var(--error)';
+                        status.textContent = data.error || 'Restore failed';
+                    }
+                })
+                .catch(() => {
+                    status.style.color = 'var(--error)';
+                    status.textContent = 'Could not reach the server';
+                });
+        }
+
         function loadCourseFromPath() {
             const input = document.getElementById('manual-course-path');
             const status = document.getElementById('manual-course-status');