import { mulberry32 } from './game/seed';

// Pure deterministic per-airport weather (v0.11.0) — display-only per PLAN.md, no
// gameplay effects. The same ICAO always yields the same weather (stable across
// polls and sessions); an optional dayKey varies it by sim-day when wanted.

export type WeatherCondition = 'Clear' | 'Cloudy' | 'Rain' | 'Fog';

export interface AirportWeather {
  condition: WeatherCondition;
  // Meteorological convention: direction the wind blows FROM, degrees true [0, 360).
  windDirDeg: number;
  windKt: number;
  visibilityM: number;
}

// FNV-1a 32-bit — cheap, stable string hash (no Math.random, no Date anywhere).
function fnv1a(s: string): number {
  let h = 0x811c9dc5;
  for (let i = 0; i < s.length; i++) {
    h ^= s.charCodeAt(i);
    h = Math.imul(h, 0x01000193);
  }
  return h >>> 0;
}

export function weatherFor(icao: string, dayKey?: number): AirportWeather {
  const seed = (fnv1a(icao) ^ (dayKey === undefined ? 0 : Math.imul(dayKey | 0, 0x9e3779b9))) >>> 0;
  const rng = mulberry32(seed);

  const c = rng();
  let condition: WeatherCondition;
  if (c < 0.45) condition = 'Clear';
  else if (c < 0.75) condition = 'Cloudy';
  else if (c < 0.92) condition = 'Rain';
  else condition = 'Fog';

  const windDirDeg = Math.floor(rng() * 360);
  const windKt = Math.round(2 + rng() * 28); // 2–30 kt

  let visibilityM: number;
  if (condition === 'Fog') visibilityM = 500 + Math.floor(rng() * 1500); // 0.5–2 km
  else if (condition === 'Rain') visibilityM = 4000 + Math.floor(rng() * 6000); // 4–10 km
  else visibilityM = 8000 + Math.floor(rng() * 32000); // 8–40 km

  return { condition, windDirDeg, windKt, visibilityM };
}