Preço dos Combustíveis

Portuguese drivers fill up 2-4 times a month, and prices can vary by €0.10/L on the same street. The official DGEG portal at `precoscombustiveis.dgeg.gov.pt` has every price, by law — every station must report changes within 24 hours under Decreto-Lei 117/2020. The portal works, technically. It just looks like 2009 and breaks on mobile.

Existing private aggregators are ad-heavy, slow, and miss the daily-utility features drivers actually want: distance sort from 'where I am', alerts when a station I care about drops below a price I picked, a clean mobile UI you can open in a car park at night.

The brief: ship a thin, fast, dark-by-default layer on top of the official data that makes the daily decision — 'where do I fill up' — answerable in five seconds.

The data pipeline matters more than the UI. A Railway-scheduled cron job hits the DGEG endpoints every four hours, normalises the response, diffs against the last known price per (station, fuel) and inserts only when something changed. That keeps the prices table small (price changes are rare per station per day), the materialised current-price view trivial to refresh, and the historical chart honest — every point is a real change, not a duplicate.

On the SEO side, the surface is built for the long-tail. Every distrito × concelho × fuel-type combination plus every station gets its own SSG'd page — ~3,800 indexable URLs — each targeting queries like 'preço gasóleo lisboa hoje' or 'gasolina 95 mais barata oeiras'. The internal-linking graph keeps every leaf within four clicks of the home.

The UI is utility-first: dark by default (it gets opened in cars at night), tabular monospace numerics aligned at the comma so prices stack visually, sparklines for the 30-day chart, MapLibre dark map for the geographic view. Generous touch targets. Postcode and 'use my location' on the hero. Geographic queries via Postgres `earthdistance` for sub-100ms 'stations within 15 km' lookups.

Stack: Next.js 15 + Postgres + Drizzle on Railway, with a separate cron service hitting DGEG every four hours and a separate hourly alert dispatcher. The materialised view `station_current` is refreshed concurrently after each scrape; reads against it are sub-millisecond.

Email alerts use double opt-in (magic-link confirmation), per-alert unsubscribe, and a hourly dispatcher that scans active subscriptions and triggers when the current price ≤ threshold. Anonymous — we keep an email and a threshold, nothing else. Resend handles delivery.

Public read-only JSON API at `/api/v1/precos` with CORS open and 60 req/min/IP rate limit, intended for journalism re-use. Open data should beget open data.

Each station page emits `GasStation` JSON-LD with priceRange, geo, openingHours; each district aggregator page emits `AggregateOffer`; every page emits `BreadcrumbList`. Per-station OG images generated dynamically via `next/og`.