How to Build a Snow Day Calculator

interface WeatherData {
  snowfallInches: number;
  temperatureF: number;
  windChillF: number;
  iceAccumulationInches: number;
  windSpeedMph: number;
  stormTiming: "overnight" | "morning_commute" | "during_school" | "afternoon" | "already_falling";
  precipType: "snow" | "freezing_rain" | "sleet" | "mixed" | "none";
  }

  interface DistrictProfile {
  type: "urban" | "suburban" | "rural";
  region: "north" | "midwest" | "south" | "mountain_west";
  hasSnowEquipment: boolean;
  }

  interface SnowDayResult {
  probability: number;
  verdict: string;
  factors: { name: string; score: number; explanation: string }[];
  }

  function calculateSnowDayProbability(
  weather: WeatherData,
  district: DistrictProfile
  ): SnowDayResult {
  const factors: { name: string; score: number; explanation: string }[] = [];

  // Snowfall factor (biggest weight)
  let snowScore = 0;
  if (weather.snowfallInches >= 10) { snowScore = 90; }
  else if (weather.snowfallInches >= 6) { snowScore = 75; }
  else if (weather.snowfallInches >= 3) { snowScore = 50; }
  else if (weather.snowfallInches >= 1) { snowScore = 20; }
  else { snowScore = 5; }
  factors.push({ name: "Snowfall", score: snowScore, explanation: `${weather.snowfallInches}" forecasted` });

  // Temperature factor
  let tempScore = 0;
  if (weather.temperatureF < 0) { tempScore = 15; }
  else if (weather.temperatureF < 15) { tempScore = 10; }
  else if (weather.temperatureF < 25) { tempScore = 5; }
  factors.push({ name: "Temperature", score: tempScore, explanation: `${weather.temperatureF}°F` });

  // Wind chill factor
  let windChillScore = 0;
  if (weather.windChillF < -25) { windChillScore = 20; }
  else if (weather.windChillF < -10) { windChillScore = 15; }
  else if (weather.windChillF < 0) { windChillScore = 10; }
  factors.push({ name: "Wind Chill", score: windChillScore, explanation: `${weather.windChillF}°F feels like` });

  // Ice accumulation
  let iceScore = 0;
  if (weather.iceAccumulationInches >= 0.25) { iceScore = 40; }
  else if (weather.precipType === "freezing_rain" || weather.precipType === "mixed") { iceScore = 25; }
  factors.push({ name: "Ice/Freezing Rain", score: iceScore, explanation: weather.precipType });

  // Storm timing
  let timingScore = 0;
  if (weather.stormTiming === "morning_commute") { timingScore = 15; }
  else if (weather.stormTiming === "overnight") { timingScore = 10; }
  else if (weather.stormTiming === "already_falling") { timingScore = 5; }
  factors.push({ name: "Storm Timing", score: timingScore, explanation: weather.stormTiming.replace("_", " ") });

  // Wind speed (blowing/drifting)
  let windScore = 0;
  if (weather.windSpeedMph >= 35 && weather.snowfallInches >= 1) { windScore = 15; }
  else if (weather.windSpeedMph >= 25) { windScore = 10; }
  else if (weather.windSpeedMph >= 15) { windScore = 5; }
  factors.push({ name: "Wind/Drifting", score: windScore, explanation: `${weather.windSpeedMph} mph` });

  // District modifier
  let districtMod = 0;
  if (district.type === "rural") districtMod += 10;
  if (district.type === "urban") districtMod -= 10;
  if (district.region === "south" || !district.hasSnowEquipment) districtMod += 15;
  factors.push({ name: "District Type", score: districtMod, explanation: `${district.type}, ${district.region}` });

  const rawProbability = factors.reduce((sum, f) => sum + f.score, 0);
  const probability = Math.min(99, Math.max(0, rawProbability));

  let verdict = "";
  if (probability >= 80) verdict = "Almost certain. Set that alarm to OFF.";
  else if (probability >= 60) verdict = "Looking very good. Keep your fingers crossed.";
  else if (probability >= 40) verdict = "Coin flip. Do your homework just in case.";
  else if (probability >= 20) verdict = "Unlikely, but stranger things have happened.";
  else verdict = "Go to bed. You have school tomorrow.";

  return { probability, verdict, factors };
  }