Data Collector Pattern

Name: data-collector
Rating: 87
Author: ohall

Collector Interface

Every collector must implement this interface:

typescript

// src/collectors/base.ts
export interface RawRecord {
  [key: string]: unknown;
}

export interface Incident {
  sourceId: string;
  sourceName: string;
  sourceUrl?: string;
  category: 'fire' | 'police' | 'traffic' | 'transit' | 'weather' | 'utility';
  subcategory?: string;
  severity: 'critical' | 'high' | 'moderate' | 'low' | 'info';
  title: string;
  description?: string;
  location: { type: 'Point'; coordinates: [number, number] } | null;
  locationText?: string;
  eventTime: Date;
  dedupeKey: string;
  rawData: RawRecord;
}

export interface Collector {
  name: string;
  pollIntervalMs: number;
  fetch(): Promise<RawRecord[]>;
  transform(raw: RawRecord): Incident | null;
}

Example: NYC Open Data (Socrata API)

typescript

// src/collectors/fdny-dispatch.ts
import { Collector, RawRecord, Incident } from './base';

interface FDNYRecord {
  starfire_incident_id: string;
  incident_datetime: string;
  incident_type_desc: string;
  alarm_level: string;
  borough: string;
  street_highway: string;
  latitude: string;
  longitude: string;
}

function mapSeverity(alarmLevel: string): Incident['severity'] {
  const level = parseInt(alarmLevel, 10);
  if (level >= 4) return 'critical';
  if (level >= 3) return 'high';
  if (level >= 2) return 'moderate';
  return 'low';
}

export const fdnyDispatchCollector: Collector = {
  name: 'fdny-dispatch',
  pollIntervalMs: 60_000, // 1 minute
  
  async fetch() {
    const url = 'https://data.cityofnewyork.us/resource/8m42-w767.json';
    const since = new Date(Date.now() - 3600000).toISOString(); // Last hour
    
    const params = new URLSearchParams({
      '$where': `incident_datetime > '${since}'`,
      '$limit': '100',
      '$order': 'incident_datetime DESC',
      '$$app_token': process.env.NYC_OPEN_DATA_TOKEN!,
    });
    
    const res = await fetch(`${url}?${params}`, {
      headers: { 'Accept': 'application/json' },
    });
    
    if (!res.ok) {
      throw new Error(`FDNY API error: ${res.status}`);
    }
    
    return res.json();
  },
  
  transform(raw: RawRecord): Incident | null {
    const record = raw as FDNYRecord;
    
    // Skip records missing required fields
    if (!record.starfire_incident_id || !record.incident_datetime) {
      return null;
    }
    
    // Parse coordinates
    const lat = parseFloat(record.latitude);
    const lng = parseFloat(record.longitude);
    const hasLocation = !isNaN(lat) && !isNaN(lng);
    
    return {
      sourceId: record.starfire_incident_id,
      sourceName: 'FDNY Dispatch',
      sourceUrl: 'https://data.cityofnewyork.us/d/8m42-w767',
      category: 'fire',
      subcategory: record.incident_type_desc,
      severity: mapSeverity(record.alarm_level || '1'),
      title: `${record.incident_type_desc || 'Fire Incident'} - ${record.borough || 'NYC'}`,
      description: `Alarm level ${record.alarm_level}`,
      location: hasLocation 
        ? { type: 'Point', coordinates: [lng, lat] }
        : null,
      locationText: record.street_highway 
        ? `${record.street_highway}, ${record.borough}`
        : record.borough,
      eventTime: new Date(record.incident_datetime),
      dedupeKey: `fdny-dispatch-${record.starfire_incident_id}`,
      rawData: record,
    };
  },
};

Example: REST API (511NY)

typescript

// src/collectors/511ny-incidents.ts
import { Collector, RawRecord, Incident } from './base';

interface NY511Event {
  id: string;
  headline: string;
  description: string;
  event_type: string;
  severity: string;
  geography: {
    coordinates: [number, number];
  };
  start_time: string;
  road_name: string;
}

function mapSeverity(severity: string): Incident['severity'] {
  switch (severity.toLowerCase()) {
    case 'major': return 'critical';
    case 'moderate': return 'high';
    case 'minor': return 'moderate';
    default: return 'low';
  }
}

export const ny511IncidentsCollector: Collector = {
  name: '511ny-incidents',
  pollIntervalMs: 60_000,
  
  async fetch() {
    const url = 'https://511ny.org/api/v2/get/event';
    
    const res = await fetch(url, {
      headers: {
        'Authorization': `Bearer ${process.env.NY511_API_KEY}`,
        'Accept': 'application/json',
      },
    });
    
    if (!res.ok) {
      throw new Error(`511NY API error: ${res.status}`);
    }
    
    const data = await res.json();
    return data.events || [];
  },
  
  transform(raw: RawRecord): Incident | null {
    const event = raw as NY511Event;
    
    if (!event.id || !event.geography?.coordinates) {
      return null;
    }
    
    return {
      sourceId: event.id,
      sourceName: '511NY Traffic',
      category: 'traffic',
      subcategory: event.event_type,
      severity: mapSeverity(event.severity),
      title: event.headline,
      description: event.description,
      location: {
        type: 'Point',
        coordinates: event.geography.coordinates,
      },
      locationText: event.road_name,
      eventTime: new Date(event.start_time),
      dedupeKey: `511ny-${event.id}`,
      rawData: event,
    };
  },
};

Example: NWS Weather Alerts (No Auth)

typescript

// src/collectors/nws-alerts.ts
import { Collector, RawRecord, Incident } from './base';

interface NWSAlert {
  id: string;
  properties: {
    headline: string;
    description: string;
    severity: string;
    urgency: string;
    event: string;
    effective: string;
    expires: string;
    areaDesc: string;
  };
  geometry?: {
    coordinates: number[][][];
  };
}

function mapSeverity(severity: string): Incident['severity'] {
  switch (severity.toLowerCase()) {
    case 'extreme': return 'critical';
    case 'severe': return 'critical';
    case 'moderate': return 'high';
    case 'minor': return 'moderate';
    default: return 'low';
  }
}

export const nwsAlertsCollector: Collector = {
  name: 'nws-alerts',
  pollIntervalMs: 60_000,
  
  async fetch() {
    // NYC metro zone IDs
    const zones = ['NYZ072', 'NYZ073', 'NYZ074', 'NYZ075', 'NYZ176'];
    const url = `https://api.weather.gov/alerts/active?zone=${zones.join(',')}`;
    
    const res = await fetch(url, {
      headers: {
        'User-Agent': process.env.NWS_USER_AGENT || 'SituationMonitor/1.0',
        'Accept': 'application/geo+json',
      },
    });
    
    if (!res.ok) {
      throw new Error(`NWS API error: ${res.status}`);
    }
    
    const data = await res.json();
    return data.features || [];
  },
  
  transform(raw: RawRecord): Incident | null {
    const alert = raw as NWSAlert;
    const props = alert.properties;
    
    if (!alert.id || !props.headline) {
      return null;
    }
    
    // Use centroid of NYC if no geometry
    const defaultLocation: [number, number] = [-73.98, 40.75];
    
    return {
      sourceId: alert.id,
      sourceName: 'NWS Weather',
      category: 'weather',
      subcategory: props.event,
      severity: mapSeverity(props.severity),
      title: props.headline,
      description: props.description?.slice(0, 1000),
      location: {
        type: 'Point',
        coordinates: defaultLocation,
      },
      locationText: props.areaDesc,
      eventTime: new Date(props.effective),
      dedupeKey: `nws-${alert.id}`,
      rawData: alert,
    };
  },
};

Registering Collectors

typescript

// src/collectors/index.ts
import { Collector } from './base';
import { fdnyDispatchCollector } from './fdny-dispatch';
import { ny511IncidentsCollector } from './511ny-incidents';
import { nwsAlertsCollector } from './nws-alerts';

export const collectors: Collector[] = [
  fdnyDispatchCollector,
  ny511IncidentsCollector,
  nwsAlertsCollector,
];

export function getCollectorByName(name: string): Collector | undefined {
  return collectors.find(c => c.name === name);
}

Processor

typescript

// src/pipeline/processor.ts
import { Collector, Incident } from '@/collectors/base';
import { upsertIncident } from '@/db/queries';
import { updateSourceHealth } from '@/db/source-health';

export async function processCollector(collector: Collector): Promise<void> {
  const startTime = Date.now();
  
  try {
    // Fetch raw data
    const rawRecords = await collector.fetch();
    
    // Transform records
    const incidents: Incident[] = [];
    for (const raw of rawRecords) {
      try {
        const incident = collector.transform(raw);
        if (incident) {
          incidents.push(incident);
        }
      } catch (err) {
        console.error(`Transform error in ${collector.name}:`, err);
      }
    }
    
    // Upsert to database
    let successCount = 0;
    for (const incident of incidents) {
      try {
        await upsertIncident(incident);
        successCount++;
      } catch (err) {
        console.error(`Upsert error in ${collector.name}:`, err);
      }
    }
    
    // Update source health
    await updateSourceHealth(collector.name, {
      lastSuccessAt: new Date(),
      consecutiveFailures: 0,
      lastRecordCount: successCount,
      avgLatencyMs: Date.now() - startTime,
      status: 'healthy',
    });
    
  } catch (err) {
    console.error(`Collector ${collector.name} failed:`, err);
    
    await updateSourceHealth(collector.name, {
      lastFailureAt: new Date(),
      consecutiveFailures: sql`consecutive_failures + 1`,
      status: sql`CASE WHEN consecutive_failures >= 3 THEN 'failing' ELSE 'degraded' END`,
    });
  }
}

Dedupe Key Guidelines

•Always deterministic — same input produces same key
•Include source name — prevent cross-source collisions
•Use source's unique ID — most reliable identifier
•Lowercase and normalize — consistent formatting

typescript

function generateDedupeKey(sourceName: string, sourceId: string): string {
  const normalized = sourceName
    .toLowerCase()
    .replace(/\s+/g, '-')
    .replace(/[^a-z0-9-]/g, '');
  return `${normalized}-${sourceId}`;
}

Error Handling Best Practices

•Fail gracefully — skip bad records, don't abort entire batch
•Log with context — include collector name and record ID
•Track health — update source_health table on success/failure
•Retry logic — use exponential backoff for transient failures
•Rate limiting — respect API rate limits (usually in headers)

Testing Collectors

typescript

// __tests__/collectors/fdny-dispatch.test.ts
import { fdnyDispatchCollector } from '@/collectors/fdny-dispatch';

describe('fdnyDispatchCollector', () => {
  it('transforms valid record', () => {
    const raw = {
      starfire_incident_id: 'SF-2026-12345',
      incident_datetime: '2026-01-11T10:30:00',
      incident_type_desc: 'STRUCTURAL FIRE',
      alarm_level: '3',
      borough: 'MANHATTAN',
      street_highway: '5TH AVE',
      latitude: '40.7580',
      longitude: '-73.9855',
    };
    
    const result = fdnyDispatchCollector.transform(raw);
    
    expect(result).not.toBeNull();
    expect(result?.category).toBe('fire');
    expect(result?.severity).toBe('high');
    expect(result?.dedupeKey).toBe('fdny-dispatch-SF-2026-12345');
  });
  
  it('returns null for invalid record', () => {
    const raw = { incomplete: true };
    expect(fdnyDispatchCollector.transform(raw)).toBeNull();
  });
});