server {
    listen 80;
    listen [::]:80;
    server_name _;

    root /usr/share/nginx/html;
    index index.html;

    # Reasonable hardening — TLS is terminated by an external reverse proxy
    # so we don't add HSTS here (let the edge own that header).
    add_header X-Content-Type-Options "nosniff" always;
    add_header X-Frame-Options "DENY" always;
    add_header Referrer-Policy "same-origin" always;

    # Internal liveness for the docker healthcheck.
    location = /healthz {
        access_log off;
        return 200 "ok\n";
        add_header Content-Type text/plain;
    }

    # Proxy API calls to the Flask service on the compose network.
    location /api/ {
        proxy_pass         http://api:8000;
        proxy_http_version 1.1;
        proxy_set_header   Host              $host;
        proxy_set_header   X-Real-IP         $remote_addr;
        proxy_set_header   X-Forwarded-For   $proxy_add_x_forwarded_for;
        proxy_set_header   X-Forwarded-Proto $scheme;
        proxy_read_timeout 60s;
        client_max_body_size 64m;
    }

    # SPA fallback — every unknown route returns index.html.
    location / {
        try_files $uri $uri/ /index.html;
    }

    # Long cache for hashed assets.
    location ~* \.(?:js|css|woff2?|svg|png|jpg|jpeg|webp|ico)$ {
        expires 30d;
        add_header Cache-Control "public, immutable";
        try_files $uri =404;
    }
}