Browser (Next.js 14 App Router, TypeScript, Tailwind, Recharts, Leaflet)
   |
   |-- /api/air      -> Open-Meteo Air Quality (no key) or WAQI (token)
   |-- /api/bedrock  -> Amazon Bedrock: advisories and guidance
   |-- /api/alert    -> Amazon SNS: school directive to subscribers
   |-- /api/reports  -> Amazon DynamoDB: crowd-sourced reports

Hosting: AWS Amplify (Next.js SSR)

type Band = { aqiLo: number; aqiHi: number; cLo: number; cHi: number };

const CPCB_PM25: Band[] = [
  { aqiLo: 0,   aqiHi: 50,  cLo: 0,   cHi: 30 },
  { aqiLo: 51,  aqiHi: 100, cLo: 31,  cHi: 60 },
  { aqiLo: 101, aqiHi: 200, cLo: 61,  cHi: 90 },
  { aqiLo: 201, aqiHi: 300, cLo: 91,  cHi: 120 },
  { aqiLo: 301, aqiHi: 400, cLo: 121, cHi: 250 },
  { aqiLo: 401, aqiHi: 500, cLo: 250, cHi: 500 },
];

export function aqiToPm25(aqi: number, bands = CPCB_PM25): number {
  const b = bands.find(x => aqi >= x.aqiLo && aqi <= x.aqiHi) ?? bands[bands.length - 1];
  const t = (aqi - b.aqiLo) / (b.aqiHi - b.aqiLo);
  return b.cLo + t * (b.cHi - b.cLo);
}

inhaled mass (µg) = concentration (µg/m³) × ventilation (m³/min) × minutes

// Rough population-level anchors: [heart rate bpm, ventilation L/min]
const ANCHORS: [number, number][] = [[60, 6], [100, 20], [140, 45], [170, 70]];

export function ventilationFromHr(bpm: number): number {
  if (bpm <= ANCHORS[0][0]) return ANCHORS[0][1];
  for (let i = 1; i < ANCHORS.length; i++) {
    const [h1, v1] = ANCHORS[i];
    const [h0, v0] = ANCHORS[i - 1];
    if (bpm <= h1) return v0 + ((bpm - h0) / (h1 - h0)) * (v1 - v0);
  }
  return ANCHORS[ANCHORS.length - 1][1];
}

export function inhaledMicrograms(pm25: number, bpm: number, minutes: number): number {
  const m3PerMin = ventilationFromHr(bpm) / 1000; // L -> m³
  return pm25 * m3PerMin * minutes;
}

import { BedrockRuntimeClient, ConverseCommand } from '@aws-sdk/client-bedrock-runtime';

const client = new BedrockRuntimeClient({ region: process.env.APP_AWS_REGION });

export async function writeDirective(facts: {
  school: string; tier: string; pm25: number; observedAt: string;
}) {
  const system = [{ text:
    'You write short safety notices for school staff. Use only the facts provided. ' +
    'Do not invent readings, do not give medical diagnoses. Max 3 sentences, plain language.' }];

  const out = await client.send(new ConverseCommand({
    modelId: process.env.APP_BEDROCK_MODEL_ID!,
    system,
    messages: [{ role: 'user', content: [{ text: JSON.stringify(facts) }] }],
    inferenceConfig: { maxTokens: 200, temperature: 0.2 },
  }));

  return out.output?.message?.content?.[0]?.text ?? null;
}

import { SNSClient, PublishCommand } from '@aws-sdk/client-sns';

const sns = new SNSClient({ region: process.env.APP_AWS_REGION });

export async function sendDirective(subject: string, message: string) {
  await sns.send(new PublishCommand({
    TopicArn: process.env.APP_SNS_TOPIC_ARN,
    Subject: subject.slice(0, 100),
    Message: message,
  }));
}

version: 1
frontend:
  phases:
    preBuild:
      commands:
        - npm ci
    build:
      commands:
        - env | grep -e APP_ >> .env.production
        - npm run build
  artifacts:
    baseDirectory: .next
    files:
      - '**/*'
  cache:
    paths:
      - node_modules/**/*
      - .next/cache/**/*

const HR_SERVICE = 0x180d;
const HR_MEASUREMENT = 0x2a37;

export async function connectHeartRate(onBpm: (bpm: number) => void) {
  const device = await navigator.bluetooth.requestDevice({
    filters: [{ services: [HR_SERVICE] }],
  });
  const server = await device.gatt!.connect();
  const service = await server.getPrimaryService(HR_SERVICE);
  const ch = await service.getCharacteristic(HR_MEASUREMENT);
  await ch.startNotifications();
  ch.addEventListener('characteristicvaluechanged', (e: any) => {
    const dv: DataView = e.target.value;
    const is16 = dv.getUint8(0) & 0x01;
    onBpm(is16 ? dv.getUint16(1, true) : dv.getUint8(1));
  });
  return device;
}

const stream = await navigator.mediaDevices.getUserMedia({
  audio: { echoCancellation: false, noiseSuppression: false, autoGainControl: false },
});