/**
 * Pregenerates the globe's land dot pattern from Natural Earth coastlines.
 *
 *   node scripts/generate-land-dots.mjs
 *
 * Runs at author time only — world-atlas/topojson stay dev dependencies and the
 * browser gets a small quantized lat/lon table instead of a 400 KB topology.
 */
import { readFileSync, writeFileSync } from "node:fs";
import { createRequire } from "node:module";
import { feature } from "topojson-client";

const require = createRequire(import.meta.url);
const topology = JSON.parse(
  readFileSync(require.resolve("world-atlas/land-110m.json"), "utf8"),
);
const land = feature(topology, topology.objects.land);

// Flatten to rings, each with a bounding box so most tests exit immediately.
const rings = [];
for (const f of land.features) {
  const polygons =
    f.geometry.type === "Polygon" ? [f.geometry.coordinates] : f.geometry.coordinates;
  for (const polygon of polygons) {
    for (let i = 0; i < polygon.length; i++) {
      const coords = polygon[i];
      let minX = Infinity;
      let minY = Infinity;
      let maxX = -Infinity;
      let maxY = -Infinity;
      for (const [x, y] of coords) {
        if (x < minX) minX = x;
        if (x > maxX) maxX = x;
        if (y < minY) minY = y;
        if (y > maxY) maxY = y;
      }
      rings.push({ coords, hole: i > 0, minX, minY, maxX, maxY });
    }
  }
}

function inRing(lon, lat, ring) {
  if (lon < ring.minX || lon > ring.maxX || lat < ring.minY || lat > ring.maxY) {
    return false;
  }
  let inside = false;
  const c = ring.coords;
  for (let i = 0, j = c.length - 1; i < c.length; j = i++) {
    const [xi, yi] = c[i];
    const [xj, yj] = c[j];
    if (yi > lat !== yj > lat && lon < ((xj - xi) * (lat - yi)) / (yj - yi) + xi) {
      inside = !inside;
    }
  }
  return inside;
}

function isLand(lon, lat) {
  let hit = false;
  for (const ring of rings) {
    if (!inRing(lon, lat, ring)) continue;
    if (ring.hole) return false; // lake / inner ring
    hit = true;
  }
  return hit;
}

const SAMPLES = 26000;
const golden = Math.PI * (3 - Math.sqrt(5));
const out = [];

for (let i = 0; i < SAMPLES; i++) {
  const y = 1 - (i / (SAMPLES - 1)) * 2;
  const theta = golden * i;
  const lat = Math.asin(y) * (180 / Math.PI);
  const lon = Math.atan2(Math.sin(theta), Math.cos(theta)) * (180 / Math.PI);
  if (!isLand(lon, lat)) continue;
  // Quantized to 1/100 degree — far finer than a 2 px dot can show.
  out.push(Math.round(lat * 100), Math.round(lon * 100));
}

const header = `// Generated by scripts/generate-land-dots.mjs — do not edit by hand.
// ${out.length / 2} land points sampled from Natural Earth 110m coastlines,
// stored as [lat, lon] pairs in hundredths of a degree.
export const LAND_LATLON: number[] = [
`;

const body = [];
for (let i = 0; i < out.length; i += 20) {
  body.push("  " + out.slice(i, i + 20).join(",") + ",");
}

writeFileSync(
  new URL("../src/lib/land-dots.ts", import.meta.url),
  header + body.join("\n") + "\n];\n",
);

console.log(`wrote ${out.length / 2} land points from ${SAMPLES} samples`);