# Scoring Engine (AlertScoringService)

## Purpose

Produces a "fill up now or wait?" recommendation per user based on their local
station history. Output is one of: `fill_up`, `wait`, `no_signal`.
Never guess — stay silent (no_signal) when signals conflict or data is insufficient.

## The 4 signals (in priority order)

### Signal 1 — Local price trend (HIGHEST WEIGHT)
- Query `station_prices` for user's nearest 5 stations (within 5km of user lat/lng)
- Use last 14 days of history for `e10` (or user's preferred fuel type)
- Calculate 3-day rolling average vs 7-day rolling average
- **Falling**: 3-day avg < 7-day avg by ≥ 0.5p → positive wait signal
- **Rising**: 3-day avg > 7-day avg by ≥ 0.5p → fill_up signal
- **Flat**: difference < 0.5p → neutral, no signal
- Weight: 40 points max

### Signal 2 — Supermarket anchor effect (HIGH WEIGHT)
- Find nearest supermarket station (is_supermarket = 1) within 10km
- Check if supermarket cut price in last 48 hours (> 1p drop)
- Check if nearest non-supermarket stations have NOT yet followed
- If supermarket cut AND independents haven't moved → strong wait signal
- Weight: 35 points max

### Signal 3 — Day-of-week pattern (MEDIUM WEIGHT — needs 8+ weeks data)
- Per station: average price by day-of-week over last 90 days
- Only activate if station has 56+ days of history
- If today is statistically 1.5p+ cheaper than weekly average → mild fill_up
- If today is statistically 1.5p+ more expensive → mild wait
- Weight: 15 points max

### Signal 4 — Brent crude direction (LOW WEIGHT)
- Fetched daily from FRED API, stored in a simple `brent_prices` table
- 5-day trend: rising ≥ 3% → mild fill_up pressure; falling ≥ 3% → mild wait
- Weight: 10 points max

## Confidence thresholds

- Score 70–100: strong signal → fire recommendation + notification
- Score 40–69: weak signal → show in dashboard only, no push/SMS/WhatsApp
- Score 0–39: no_signal → stay silent entirely

**Only send notifications when confidence ≥ 70.** Never spam.

## Output (stored in scoring_results)

```php
[
    'recommendation' => 'wait',        // fill_up | wait | no_signal
    'confidence'     => 78,            // 0-100
    'signals'        => [
        'trend'       => ['direction' => 'falling', 'points' => 32],
        'supermarket' => ['triggered' => true, 'points' => 35],
        'day_pattern' => ['triggered' => false, 'points' => 0],
        'brent'       => ['direction' => 'flat', 'points' => 0],
    ],
    'local_avg_pence' => 14380,        // 143.80p
    'trend_delta'     => -2.3,         // pence change over 7 days
]
```

## Human-readable reason strings

Always generate a plain-English reason for the recommendation:
- "Prices near you have been falling for 6 days. Tesco {station} cut 3p yesterday — independents usually follow within 48 hours."
- "Prices are rising in your area — filling up today avoids paying more later."
- "No clear pattern this week — fill up at the cheapest station near you now."

Reason strings are stored in `scoring_results.signals` JSON and shown in the UI and notifications.

## Accuracy self-tracking

After 3 days, check if `wait` recommendation was correct (prices did fall further).
Store outcome in `scoring_results` for future display: "This signal has been right X% of the time in your area."