gods-eye-view/server/providers/military-installations.js

import { makeRateLimiter, clientKey } from './common/rate-limit.js';
import {
  MILITARY_INSTALLATION_ELEMENT_CAP,
  MILITARY_INSTALLATION_MAX_RESPONSE_BYTES,
  MILITARY_INSTALLATION_DISK_TTL_MS,
  MILITARY_INSTALLATION_STALE_MS,
} from './military-installations/constants.js';
import {
  fetchOverpassPayload,
  overpassNotConfigured,
} from './overpass/transport.js';
import { resolveOverpassUpstreams } from './overpass/constants.js';
import {
  _militaryInstallationCache,
  trimMilitaryInstallationCache,
  writeMilitaryInstallationDisk,
  resolveMilitaryInstallationTier,
  readMilitaryInstallationDisk,
} from './military-installations/cache.js';
import {
  validMilitaryInstallationBox,
  quantizeMilitaryInstallationBox,
  militaryInstallationCacheKey,
  militaryInstallationFailureReason,
} from './military-installations/query.js';
import { coalesceProxyRequest } from './common/http.js';

const _militaryInstallationsRateLimiter = makeRateLimiter({
  windowMs: 60_000,
  max: 90,
  globalMax: 300,
});

const _militaryInstallationInFlight = new Map();

function militaryInstallationsProxy() {
  async function refresh(box, key) {
    const bbox = `${box.south},${box.west},${box.north},${box.east}`;
    const ql = `[out:json][timeout:20];(nwr["military"~"^(airfield|naval_base|range|barracks|base)$"](${bbox});nwr["landuse"="military"](${bbox}););out center tags geom ${MILITARY_INSTALLATION_ELEMENT_CAP};`;
    const upstream = await fetchOverpassPayload(
      `data=${encodeURIComponent(ql)}`,
      MILITARY_INSTALLATION_MAX_RESPONSE_BYTES,
    );
    if (
      upstream.status >= 400 ||
      upstream.rateLimited ||
      upstream.runtimeError
    ) {
      throw Object.assign(
        new Error('Mapped installation upstream unavailable'),
        {
          retryAfterMs: upstream.retryAfterMs,
          installationReason: upstream.rateLimited
            ? 'rate_limited'
            : upstream.status === 504
              ? 'timeout'
              : upstream.runtimeError
                ? 'query_failed'
                : 'unavailable',
        },
      );
    }
    const parsed = JSON.parse(upstream.body);
    const elements = Array.isArray(parsed?.elements)
      ? parsed.elements.slice(0, MILITARY_INSTALLATION_ELEMENT_CAP)
      : [];
    const payload = {
      elements,
      // Honest truncation flag — the client re-asks for its exact viewport so
      // off-view features can never starve in-view ones. The cap travels with
      // the payload so the client never has to hard-code it.
      saturated: elements.length >= MILITARY_INSTALLATION_ELEMENT_CAP,
      elementCap: MILITARY_INSTALLATION_ELEMENT_CAP,
      retrievedAt: new Date().toISOString(),
      status: 'ready',
    };
    const entry = { payload, cachedAt: Date.now() };
    _militaryInstallationCache.set(key, entry);
    trimMilitaryInstallationCache();
    writeMilitaryInstallationDisk(key, entry);
    return payload;
  }

  function install(middlewares) {
    middlewares.use('/api/military-installations', async (req, res) => {
      if (req.method !== 'GET') {
        res.writeHead(405, { 'Content-Type': 'application/json' });
        res.end(JSON.stringify({ error: 'Method Not Allowed' }));
        return;
      }
      const url = new URL(req.url, 'http://localhost');
      const requested = validMilitaryInstallationBox(url.searchParams);
      if (!requested) {
        res.writeHead(400, { 'Content-Type': 'application/json' });
        res.end(
          JSON.stringify({
            error: 'A non-dateline bbox no larger than 10 degrees is required',
          }),
        );
        return;
      }
      // Query the SNAPPED box, not the raw viewport: neighbouring views then
      // share one cache entry, and an outward snap always covers what was asked.
      // `exact=1` opts out — the client sends it after a SATURATED snapped
      // response, so a truncated tile can never starve the actual viewport. It
      // is keyed separately so exact and snapped answers never collide.
      const exact = url.searchParams.get('exact') === '1';
      const box = exact
        ? requested
        : quantizeMilitaryInstallationBox(requested);
      // Key at the precision the query actually uses (see militaryInstallationCacheKey).
      const key = exact
        ? `exact:${militaryInstallationCacheKey(box, 5)}`
        : militaryInstallationCacheKey(box);
      const now = Date.now();
      const cached = _militaryInstallationCache.get(key);
      if (!resolveOverpassUpstreams().length) {
        const stale =
          cached || (await readMilitaryInstallationDisk(key, Infinity));
        const disabled = overpassNotConfigured();
        res.writeHead(200, {
          'Content-Type': 'application/json',
          'Cache-Control': 'no-store',
          'X-Military-Installations': stale ? 'STALE' : 'DISABLED',
        });
        res.end(
          stale
            ? JSON.stringify({
                ...stale.payload,
                status: 'stale',
                retrievedAt:
                  stale.payload.retrievedAt ||
                  new Date(stale.cachedAt).toISOString(),
              })
            : disabled.body,
        );
        return;
      }
      if (!_militaryInstallationsRateLimiter(clientKey(req))) {
        res.writeHead(429, {
          'Content-Type': 'application/json',
          'Retry-After': '5',
        });
        res.end(JSON.stringify({ error: 'Rate limit exceeded' }));
        return;
      }
      const preflight = await resolveMilitaryInstallationTier({
        cacheKey: key,
        memoryCache: _militaryInstallationCache,
        inFlight: _militaryInstallationInFlight,
        readDisk: () =>
          readMilitaryInstallationDisk(key, MILITARY_INSTALLATION_DISK_TTL_MS),
        now,
      });
      if (preflight.source !== 'UPSTREAM') {
        if (preflight.source === 'DISK') {
          _militaryInstallationCache.set(key, preflight.entry);
          trimMilitaryInstallationCache();
        }
        res.writeHead(200, {
          'Content-Type': 'application/json',
          'Cache-Control': 'public, max-age=60',
          'X-Military-Installations': preflight.source,
        });
        res.end(
          JSON.stringify({ ...preflight.entry.payload, status: 'cached' }),
        );
        return;
      }
      const request = coalesceProxyRequest(
        _militaryInstallationInFlight,
        key,
        () => refresh(box, key),
      );
      try {
        const payload = await request.promise;
        res.writeHead(200, {
          'Content-Type': 'application/json',
          'Cache-Control': 'public, max-age=60',
          'X-Military-Installations': request.shared ? 'INFLIGHT' : 'MISS',
        });
        res.end(JSON.stringify(payload));
      } catch (error) {
        if (cached && now - cached.cachedAt <= MILITARY_INSTALLATION_STALE_MS) {
          res.writeHead(200, {
            'Content-Type': 'application/json',
            'Cache-Control': 'no-store',
            'X-Military-Installations': 'STALE',
          });
          res.end(JSON.stringify({ ...cached.payload, status: 'stale' }));
          return;
        }
        // Overpass is down: last-good mapped context at ANY age beats an empty
        // layer (the same serve-stale rule the Overpass proxy applies).
        const stale = await readMilitaryInstallationDisk(key, Infinity);
        if (stale) {
          res.writeHead(200, {
            'Content-Type': 'application/json',
            'Cache-Control': 'no-store',
            'X-Military-Installations': 'STALE-DISK',
          });
          res.end(JSON.stringify({ ...stale.payload, status: 'stale' }));
          return;
        }
        res.writeHead(503, {
          ...(error?.retryAfterMs
            ? { 'Retry-After': String(Math.ceil(error.retryAfterMs / 1000)) }
            : {}),
          'Content-Type': 'application/json',
          'Cache-Control': 'no-store',
        });
        res.end(
          JSON.stringify({
            error: 'Mapped installation context is temporarily unavailable',
            reason: militaryInstallationFailureReason(error),
            retryAfterMs: error?.retryAfterMs,
          }),
        );
      }
    });
  }

  return {
    name: 'military-installations-proxy',
    configureServer(server) {
      install(server.middlewares);
    },
    configurePreviewServer(server) {
      install(server.middlewares);
    },
  };
}

export { militaryInstallationsProxy };

export { MILITARY_INSTALLATION_ELEMENT_CAP } from './military-installations/constants.js';
export { quantizeMilitaryInstallationBox } from './military-installations/query.js';
export { militaryInstallationCacheKey } from './military-installations/query.js';
export { resolveMilitaryInstallationTier } from './military-installations/cache.js';
export { migrateMilitaryInstallationEntry } from './military-installations/cache.js';
export { militaryInstallationDiskFresh } from './military-installations/cache.js';
export { militaryInstallationDiskPath } from './military-installations/cache.js';
export { readMilitaryInstallationDisk } from './military-installations/cache.js';
export { writeMilitaryInstallationDisk } from './military-installations/cache.js';
export { validMilitaryInstallationBox } from './military-installations/query.js';
export { militaryInstallationFailureReason } from './military-installations/query.js';