/**
 * Reads every border post OpenStreetMap knows - the nodes, ways and
 * relations tagged barrier=border_control - through the public Overpass API,
 * in tiles of the world, gently, and keeps each answer in scripts/.osm-cache/border-crossings
 * (not committed) so an interrupted run carries on where it stopped.
 *
 *   npm run crossings:fetch
 *
 * Then scripts/build-border-crossings.mjs makes the file the map reads.
 * The data is OpenStreetMap's, ODbL-licensed and credited in the app;
 * nothing about anyone is sent. The world has about 8,200 such nodes and 1,400
 * ways and relations, two megabytes in all.
 */
import { existsSync, mkdirSync, writeFileSync } from 'node:fs';
import { dirname, join } from 'node:path';
import { fileURLToPath } from 'node:url';

const root = join(dirname(fileURLToPath(import.meta.url)), '..');
export const CROSSINGS_CACHE = join(root, 'scripts/.osm-cache/border-crossings');

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));

/** The tiles of the world: thirty degrees of longitude by twenty of latitude, from 60° south to 85° north. */
export function crossingTiles() {
  const tiles = [];
  for (let south = -60; south < 85; south += 20) {
    for (let west = -180; west < 180; west += 30) tiles.push([south, west, Math.min(south + 20, 85), west + 30]);
  }
  return tiles;
}

async function ask(tile) {
  const [south, west, north, east] = tile;
  const query = `[out:json][timeout:60];nwr["barrier"="border_control"](${south},${west},${north},${east});out center;`;
  for (let attempt = 1; attempt <= 6; attempt += 1) {
    try {
      const response = await fetch('https://overpass-api.de/api/interpreter', {
        method: 'POST',
        headers: { 'content-type': 'application/x-www-form-urlencoded', 'user-agent': '197-app border crossings build (197.world)' },
        body: `data=${encodeURIComponent(query)}`,
        signal: AbortSignal.timeout(90_000),
      });
      const text = await response.text();
      if (response.ok && text.startsWith('{')) return JSON.parse(text);
    } catch {
      // The public server is busy at times: wait, and ask again.
    }
    await sleep(8_000 * attempt);
  }
  return undefined;
}

if (process.argv[1] === fileURLToPath(import.meta.url)) {
  mkdirSync(CROSSINGS_CACHE, { recursive: true });
  const failed = [];
  let done = 0;
  for (const tile of crossingTiles()) {
    const file = join(CROSSINGS_CACHE, `tile_${tile.join('_')}.json`);
    if (existsSync(file)) {
      done += 1;
      continue;
    }
    const answer = await ask(tile);
    if (!answer) {
      failed.push(tile.join(','));
      continue;
    }
    writeFileSync(file, JSON.stringify(answer.elements ?? []));
    done += 1;
    await sleep(2_500);
  }
  console.log(JSON.stringify({ done, failed }));
  if (failed.length > 0) process.exitCode = 1;
}