# Discovery & Personalization Engine

Covers the trending system, following feed, personalized homepage, similar artworks, unified activity feed, and all input signal collection that powers the ranking formula.

---

## Table of Contents

1. [Architecture Overview](#1-architecture-overview)
2. [Input Signal Collection](#2-input-signal-collection)
3. [Windowed Stats (views & downloads)](#3-windowed-stats-views--downloads)
4. [Trending Engine](#4-trending-engine)
5. [Discover Routes](#5-discover-routes)
6. [Following Feed](#6-following-feed)
7. [Personalized Homepage](#7-personalized-homepage)
8. [Similar Artworks API](#8-similar-artworks-api)
9. [Unified Activity Feed](#9-unified-activity-feed)
10. [Meilisearch Configuration](#10-meilisearch-configuration)
11. [Caching Strategy](#11-caching-strategy)
12. [Scheduled Jobs](#12-scheduled-jobs)
13. [Testing](#13-testing)
14. [Operational Runbook](#14-operational-runbook)

---

## 1. Architecture Overview

```
Browser
  │
  ├─ POST /api/art/{id}/view      → ArtworkViewController
  ├─ POST /api/art/{id}/download  → ArtworkDownloadController
  └─ POST /api/artworks/{id}/favorite / reactions / awards / comments
          │
          ▼
    ArtworkStatsService           UserStatsService
    artwork_stats (all-time +     user_statistics
    windowed counters)            └─ artwork_views_received_count
    artwork_downloads (log)           downloads_received_count
          │
          ▼
    skinbase:reset-windowed-stats   (nightly/weekly)
    └─ zeros views_24h / views_7d
    └─ recomputes downloads_24h / downloads_7d from log
          │
          ▼
    skinbase:recalculate-trending   (every 30 min)
    └─ bulk UPDATE artworks.trending_score_24h / _7d
    └─ dispatches IndexArtworkJob → Meilisearch
          │
          ▼
    Meilisearch index (artworks)
    └─ sortable: trending_score_7d, trending_score_24h, views, ...
    └─ filterable: author_id, tags, category, orientation, is_public, ...
          │
          ▼
    HomepageService / DiscoverController / SimilarArtworksController
    └─ Redis cache (5 min TTL)
          │
          ▼
    Inertia + React frontend
```

---

## 2. Input Signal Collection

### 2.1 View tracking — `POST /api/art/{id}/view`

**Controller:** `App\Http\Controllers\Api\ArtworkViewController`  
**Route name:** `api.art.view`  
**Throttle:** 5 requests per 10 minutes per IP  

**Deduplication (layered):**

| Layer | Mechanism | Scope |
|---|---|---|
| Client-side | `sessionStorage` key `sb_viewed_{id}` set before the request | Browser tab lifetime |
| Server-side | `$request->session()->put('art_viewed.{id}', true)` | Laravel session lifetime |
| Throttle | `throttle:5,10` route middleware | Per-IP per-artwork |

The React component `ArtworkActions.jsx` fires a `useEffect` on mount that checks `sessionStorage` first, then hits the endpoint. The response includes `counted: true|false` so callers can confirm whether the increment actually happened.

**What gets incremented:**

```
artwork_stats.views          +1  (all-time)
artwork_stats.views_24h      +1  (zeroed nightly)
artwork_stats.views_7d       +1  (zeroed weekly)
user_statistics.artwork_views_received_count  +1  (creator aggregate)
```

Via `ArtworkStatsService::incrementViews()` with `defer: true` (Redis when available, direct DB fallback).

---

### 2.2 Download tracking — `POST /api/art/{id}/download`

**Controller:** `App\Http\Controllers\Api\ArtworkDownloadController`  
**Route name:** `api.art.download`  
**Throttle:** 10 requests per minute per IP  

The endpoint:
1. Inserts a row in `artwork_downloads` (persistent event log with `created_at`)
2. Increments `artwork_stats.downloads`, `downloads_24h`, `downloads_7d`
3. Returns `{"ok": true, "url": "<highest-res thumbnail URL>"}` for the native browser download

The `<a download>` buttons in `ArtworkActions.jsx` call `trackDownload()` on click — a fire-and-forget `fetch()` POST. The actual browser download is triggered by the `href`/`download` attributes and is never blocked by the tracking request.

**What gets incremented:**

```
artwork_downloads             INSERT (event log, persisted forever)
artwork_stats.downloads       +1  (all-time)
artwork_stats.downloads_24h   +1  (recomputed from log nightly)
artwork_stats.downloads_7d    +1  (recomputed from log weekly)
user_statistics.downloads_received_count  +1  (creator aggregate)
```

Via `ArtworkStatsService::incrementDownloads()` with `defer: true`.

---

### 2.3 Other signals (already existed)

| Signal | Endpoint / Service | Written to |
|---|---|---|
| Favorite toggle | `POST /api/artworks/{id}/favorite` | `user_favorites`, `artwork_stats.favorites` |
| Reaction toggle | `POST /api/artworks/{id}/reactions` | `artwork_reactions` |
| Award | `ArtworkAwardController` | `artwork_award_stats.score_total` |
| Comment | `ArtworkCommentController` | `artwork_comments`, `activity_events` |
| Follow | `FollowService` | `user_followers`, `activity_events` |

---

### 2.4 ArtworkStatsService — Redis deferral

When Redis is available all increments are pushed to a list key `artwork_stats:deltas` as JSON payloads. A separate job/command (`processPendingFromRedis`) drains the queue and applies bulk `applyDelta()` calls. If Redis is unavailable the service falls back transparently to a direct DB increment.

```php
// Deferred (default for view/download controllers)
$svc->incrementViews($artworkId, 1, defer: true);

// Immediate (e.g. favorites toggle needs instant feedback)
$svc->incrementDownloads($artworkId, 1, defer: false);
```

---

## 3. Windowed Stats (views & downloads)

### 3.1 Why windowed columns?

The trending formula needs _recent_ activity, not all-time totals. `artwork_stats.views` is a monotonically increasing counter — using it for trending would permanently favour old popular artworks and new artworks could never compete.

The solution is four cached window columns refreshed on a schedule:

| Column | Meaning | Reset cadence |
|---|---|---|
| `views_24h` | Views since last midnight reset | Nightly at 03:30 |
| `views_7d` | Views since last Monday reset | Weekly (Mon) at 03:30 |
| `downloads_24h` | Downloads in last 24 h | Nightly at 03:30 (recomputed from log) |
| `downloads_7d` | Downloads in last 7 days | Weekly (Mon) at 03:30 (recomputed from log) |

### 3.2 How views windowing works

**No per-view event log exists** (storing millions of view rows would be expensive). Instead:

- Every view event increments `views_24h` and `views_7d` alongside `views`.
- The reset command **zeroes** both columns. Artworks re-accumulate from the reset time onward.
- Accuracy is "views since last reset", which is close enough for trending (error ≤ 1 day).

### 3.3 How downloads windowing works

**`artwork_downloads` is a full event log** with `created_at`. The reset command:

1. Queries `COUNT(*) FROM artwork_downloads WHERE artwork_id = ? AND created_at >= NOW() - {interval}` for each artwork in chunks of 1000.
2. Writes the exact count back to `downloads_24h` / `downloads_7d`.

This overwrites any drift from deferred Redis increments, making download windows always accurate at reset time.

### 3.4 Reset command

```bash
php artisan skinbase:reset-windowed-stats --period=24h
php artisan skinbase:reset-windowed-stats --period=7d
```

Uses chunked PHP loop (no `GREATEST()` / `INTERVAL` MySQL syntax) → works in both production MySQL and SQLite test DB.

---

## 4. Trending Engine

### 4.1 Formula

```
score = (award_score   × 5.0)
      + (favorites     × 3.0)
      + (reactions     × 2.0)
      + (downloads_Xd  × 1.0)   ← windowed: 24h or 7d
      + (views_Xd      × 2.0)   ← windowed: 24h or 7d
      - (hours_since_published × 0.1)

score = max(score, 0)   ← clamped via GREATEST()
```

Weights are constants in `TrendingService` (`W_AWARD`, `W_FAVORITE`, etc.) — adjust without a schema change.

### 4.2 Output columns

| Artworks column | Meaning |
|---|---|
| `trending_score_24h` | Score using `views_24h` + `downloads_24h`; targets artworks ≤ 7 days old |
| `trending_score_7d` | Score using `views_7d` + `downloads_7d`; targets artworks ≤ 30 days old |
| `last_trending_calculated_at` | Timestamp of last calculation |

### 4.3 Recalculation command

```bash
php artisan skinbase:recalculate-trending --period=24h
php artisan skinbase:recalculate-trending --period=7d
php artisan skinbase:recalculate-trending --period=all
php artisan skinbase:recalculate-trending --period=7d --skip-index  # skip Meilisearch jobs
php artisan skinbase:recalculate-trending --chunk=500               # smaller DB chunks
```

**Implementation:** `App\Services\TrendingService::recalculate()`

1. Chunks artworks published within the look-back window (`chunkById(1000, ...)`).
2. Issues one bulk MySQL `UPDATE ... WHERE id IN (...)` per chunk — no per-artwork queries in the hot path.
3. After each chunk, dispatches `IndexArtworkJob` per artwork to push updated scores to Meilisearch (skippable with `--skip-index`).

> **Note:** The raw SQL uses `GREATEST()` and `TIMESTAMPDIFF(HOUR, ...)` which are MySQL 8 only. The command is tested in production against MySQL; the 4 related Pest tests are skipped on SQLite with a clear skip message.

### 4.4 Meilisearch sync after calculation

`TrendingService::syncToSearchIndex()` dispatches `IndexArtworkJob` for every artwork in the trending window. The job calls `Artwork::searchable()` which triggers `toSearchableArray()`, which includes `trending_score_24h` and `trending_score_7d`.

---

## 5. Discover Routes

All routes under `/discover/*` are registered in `routes/web.php` and handled by `App\Http\Controllers\Web\DiscoverController`. All use **Meilisearch sorting** — no SQL `ORDER BY` in the hot path.

| Route | Name | Sort key | Auth |
|---|---|---|---|
| `/discover/trending` | `discover.trending` | `trending_score_7d:desc` | No |
| `/discover/fresh` | `discover.fresh` | `created_at:desc` | No |
| `/discover/top-rated` | `discover.top-rated` | `likes:desc` | No |
| `/discover/most-downloaded` | `discover.most-downloaded` | `downloads:desc` | No |
| `/discover/following` | `discover.following` | `created_at:desc` (DB) | Yes |

---

## 6. Following Feed

**Route:** `GET /discover/following` (auth required)  
**Controller:** `DiscoverController::following()`

### Logic

```
1. Get user's following IDs from user_followers
2. If empty    → show empty state (see below)
3. If present  → Artwork::whereIn('user_id', $followingIds)
                          ->orderByDesc('published_at')
                          ->paginate(24)
                 + cached 1 min per user per page
```

### Empty state

When the user follows nobody:

- `fallback_trending` — up to 12 trending artworks (Meilisearch, with DB fallback)
- `fallback_creators` — 8 most-followed verified users (ordered by `user_statistics.followers_count`)
- `empty: true` flag passed to the view
- The `discoverTrending()` call is wrapped in `try/catch` so a Meilisearch outage never breaks the empty state page

---

## 7. Personalized Homepage

**Controller:** `HomeController::index()`  
**Service:** `App\Services\HomepageService`

### Guest sections

```php
[
  'hero'     => first featured artwork,
  'trending' => 12 artworks sorted by trending_score_7d,
  'fresh'    => 12 newest artworks,
  'tags'     => 12 most-used tags,
  'creators' => creator spotlight,
  'news'     => latest news posts,
]
```

### Authenticated sections (personalized)

```php
[
  'hero'           => same as guest,
  'from_following' => artworks from followed creators (up to 12, cached 1 min),
  'trending'       => same as guest,
  'by_tags'        => artworks matching user's top 5 tags,
  'by_categories'  => fresh uploads in user's top 3 favourite categories,
  'tags'           => same as guest,
  'creators'       => same as guest,
  'news'           => same as guest,
  'preferences'    => { top_tags, top_categories },
]
```

### UserPreferenceService

`App\Services\UserPreferenceService::build(User $user)` — cached 5 min per user.

Computes preferences from the user's **favourited artworks**:

| Output key | Source |
|---|---|
| `top_tags` (up to 5) | Tags on artworks in `artwork_favourites` |
| `top_categories` (up to 3) | Categories on artworks in `artwork_favourites` |
| `followed_creators` | IDs from `user_followers` |

### getTrending() — Meilisearch-first

```php
Artwork::search('')
    ->options([
        'filter' => 'is_public = true AND is_approved = true',
        'sort'   => ['trending_score_7d:desc', 'trending_score_24h:desc', 'views:desc'],
    ])
    ->paginate($limit, 'page', 1);
```

Falls back to `getTrendingFromDb()` — `orderByDesc('trending_score_7d')` with no correlated subqueries — when Meilisearch is unavailable.

---

## 8. Similar Artworks API

**Route:** `GET /api/art/{id}/similar`  
**Controller:** `App\Http\Controllers\Api\SimilarArtworksController`  
**Route name:** `api.art.similar`  
**Throttle:** 60/min  
**Cache:** 5 min per artwork ID  
**Max results:** 12  

### Similarity algorithm

Meilisearch filters are built in priority order:

```
is_public = true
is_approved = true
id != {source_id}
author_id != {source_author_id}          ← same creator excluded
orientation = "{landscape|portrait}"     ← only for non-square (visual coherence)
(tags = "X" OR tags = "Y" OR ...)        ← tag overlap (primary signal)
  OR (if no tags)
(category = "X" OR ...)                  ← category fallback
```

Meilisearch's own ranking then sorts by relevance within those filters. Results are mapped to a slim JSON shape: `{id, title, slug, thumb, url, author_id}`.

---

## 9. Unified Activity Feed

**Route:** `GET /community/activity?type=global|following`  
**Controller:** `App\Http\Controllers\Web\CommunityActivityController`

### `activity_events` schema

| Column | Type | Notes |
|---|---|---|
| `id` | bigint PK | |
| `actor_id` | bigint FK users | Who did the action |
| `type` | varchar | `upload` `comment` `favorite` `award` `follow` |
| `target_type` | varchar | `artwork` `user` |
| `target_id` | bigint | ID of the target object |
| `meta` | json nullable | Extra data (e.g. award tier) |
| `created_at` | timestamp | No `updated_at` — immutable events |

### Where events are recorded

| Event type | Recording point |
|---|---|
| `upload` | `UploadController::finish()` on publish |
| `follow` | `FollowService::follow()` |
| `award` | `ArtworkAwardController::store()` |
| `favorite` | `ArtworkInteractionController::favorite()` |
| `comment` | `ArtworkCommentController::store()` |

All via `ActivityEvent::record($actorId, $type, $targetType, $targetId, $meta)`.

### Feed filters

- **Global** — all recent events, newest first, paginated 30/page
- **Following** — `WHERE actor_id IN (following_ids)` — only events from users you follow

The controller enriches each event batch with its target objects in a single query per target type (no N+1).

---

## 10. Meilisearch Configuration

Configured in `config/scout.php` under `meilisearch.index-settings`.

Push settings to a running instance:
```bash
php artisan scout:sync-index-settings
```

### Artworks index settings

**Searchable attributes** (ranked in order):
1. `title`
2. `tags`
3. `author_name`
4. `description`

**Filterable attributes:**
`tags`, `category`, `content_type`, `orientation`, `resolution`, `author_id`, `is_public`, `is_approved`

**Sortable attributes:**
`created_at`, `downloads`, `likes`, `views`, `trending_score_24h`, `trending_score_7d`, `favorites_count`, `awards_received_count`, `downloads_count`

### toSearchableArray() — fields indexed per artwork

```php
[
  'id', 'slug', 'title', 'description',
  'author_id', 'author_name',
  'category', 'content_type', 'tags',
  'resolution', 'orientation',
  'downloads', 'likes', 'views',
  'created_at', 'is_public', 'is_approved',
  'trending_score_24h', 'trending_score_7d',
  'favorites_count', 'awards_received_count', 'downloads_count',
  'awards' => { gold, silver, bronze, score },
]
```

---

## 11. Caching Strategy

| Data | Cache key | TTL | Driver |
|---|---|---|---|
| Homepage trending | `homepage.trending.{limit}` | 5 min | Redis/file |
| Homepage fresh | `homepage.fresh.{limit}` | 5 min | Redis/file |
| Homepage hero | `homepage.hero` | 5 min | Redis/file |
| Homepage tags | `homepage.tags.{limit}` | 5 min | Redis/file |
| User preferences | `user.prefs.{user_id}` | 5 min | Redis/file |
| Following feed | `discover.following.{user_id}.p{page}` | 1 min | Redis/file |
| Similar artworks | `api.similar.{artwork_id}` | 5 min | Redis/file |

**Rules:**
- Personalized data (`from_following`, `by_tags`, `by_categories`) is **not** independently cached — it falls inside `allForUser()` which is called fresh per request.
- Long-running cache busting: the trending command and reset command do not explicitly clear cache — the TTL is short enough that stale data self-expires within one trending cycle.

---

## 12. Scheduled Jobs

All registered in `routes/console.php` via `Schedule::command()`.

| Time | Command | Purpose |
|---|---|---|
| Every 30 min | `skinbase:recalculate-trending --period=24h` | Update `trending_score_24h` |
| Every 30 min | `skinbase:recalculate-trending --period=7d --skip-index` | Update `trending_score_7d` (background) |
| 03:00 daily | `uploads:cleanup` | Remove stale draft uploads |
| 03:10 daily | `analytics:aggregate-similar-artworks` | Offline similarity metrics |
| 03:20 daily | `analytics:aggregate-feed` | Feed evaluation metrics |
| 03:30 daily | `skinbase:reset-windowed-stats --period=24h` | Zero views_24h, recompute downloads_24h |
| Monday 03:30 | `skinbase:reset-windowed-stats --period=7d` | Zero views_7d, recompute downloads_7d |

**Reset runs at 03:30** so it fires after the other maintenance tasks (03:00–03:20). The next trending recalculation (every 30 min, including ~03:30 or ~04:00) picks up the freshly-zeroed windowed stats and writes accurate trending scores.

---

## 13. Testing

All tests live under `tests/Feature/Discovery/`.

| Test file | Coverage |
|---|---|
| `ActivityEventRecordingTest.php` | `ActivityEvent::record()`, all 5 types, actor relation, meta, route smoke tests for the activity feed |
| `FollowingFeedTest.php` | Auth redirect, empty state fallback, pagination, creator exclusion |
| `HomepagePersonalizationTest.php` | Guest vs auth homepage sections, preferences shape, 200 responses |
| `SimilarArtworksApiTest.php` | 404 cases, response shape, result count ≤ 12, creator exclusion |
| `SignalTrackingTest.php` | View endpoint (404s, first count, session dedup), download endpoint (404s, DB row, guest vs auth), route names |
| `TrendingServiceTest.php` | Zero artworks, skip outside window, skip private/unapproved — _recalculate() tests skipped on SQLite (MySQL-only SQL)_ |
| `WindowedStatsTest.php` | `incrementViews/Downloads` update all 3 columns, reset command zeros views, recomputes downloads from log, window boundary correctness |

Run all discovery tests:
```bash
php artisan test tests/Feature/Discovery/
```

Run specific suite:
```bash
php artisan test tests/Feature/Discovery/SignalTrackingTest.php
```

**SQLite vs MySQL note:** Four tests in `TrendingServiceTest` are marked `.skip()` with the message _"Requires MySQL: uses GREATEST() and TIMESTAMPDIFF()"_. Run them against a real MySQL instance in CI or staging to validate the bulk UPDATE formula.

---

## 14. Operational Runbook

### Trending scores are stuck / not updating

```bash
# Check last calculated timestamp
SELECT id, title, last_trending_calculated_at FROM artworks ORDER BY last_trending_calculated_at DESC LIMIT 5;

# Manually trigger recalculation
php artisan skinbase:recalculate-trending --period=all

# Re-push scores to Meilisearch
php artisan skinbase:recalculate-trending --period=7d
```

### Windowed counters look wrong after a deploy

```bash
# Force a reset and recompute
php artisan skinbase:reset-windowed-stats --period=24h
php artisan skinbase:reset-windowed-stats --period=7d

# Then recalculate trending with fresh numbers
php artisan skinbase:recalculate-trending --period=all
```

### Meilisearch out of sync with DB

```bash
# Re-push all artworks in the trending window
php artisan skinbase:recalculate-trending --period=all

# Or full re-index
php artisan scout:import "App\Models\Artwork"
```

### Push updated index settings (after changing config/scout.php)

```bash
php artisan scout:sync-index-settings
```

### Check what the trending formula is reading

```sql
SELECT
  a.id,
  a.title,
  a.published_at,
  s.views,
  s.views_24h,
  s.views_7d,
  s.downloads,
  s.downloads_24h,
  s.downloads_7d,
  s.favorites,
  a.trending_score_24h,
  a.trending_score_7d,
  a.last_trending_calculated_at
FROM artworks a
LEFT JOIN artwork_stats s ON s.artwork_id = a.id
WHERE a.is_public = 1 AND a.is_approved = 1
ORDER BY a.trending_score_7d DESC
LIMIT 20;
```

### Inspect the artwork_downloads log

```sql
-- Downloads in the last 24 hours per artwork
SELECT artwork_id, COUNT(*) as dl_24h
FROM artwork_downloads
WHERE created_at >= NOW() - INTERVAL 1 DAY
GROUP BY artwork_id
ORDER BY dl_24h DESC
LIMIT 20;
```