What I've learned building VSCarbon

Learning by building is exciting in the way that I figure things out as I go, feeling like I’m on a quest as each level requires new skills.

Full development cycle

Design pattern

Adapter. When interest arises, there’s a need to extend VSCarbon to EU countries. It means I have to integrate other APIs (e.g., Electricity Maps, Carbon Aware Computing), creating a new strutural challenge. Luckily, someone recommended adapter pattern. Instead of rewriting core logic for each provider, I can abstract data layer (this feels deja vu because a CTO mentioned abstraction as a way to deal with business diversity in a job interview).
I was worried it’s gonna be heavy for a VS Code extension because it sounds like big enterprise-y layers, but in my case, it looks less like design pattern boilerplate and more like a simple translation function per API.

Anw, I can define a common interface like this

type CarbonData = {
  timestamp: string
  region: string
  carbonIntensity: number // gCO2/kWh
  generationMix?: Record<string, number> // sadly some APIs don't provide energy mix
}

Adapters here are functions that normalise responses. I can add more providers later without changing much UI/logic. So, it’s a cleaner way to avoid if (provider === “UK”) else if (“EU”) everywhere

// National Grid adapter for UK users
export async function fetchUKCarbonData(): Promise<CarbonData[]> {
  const res = await fetch('https://api.carbonintensity.org.uk/regional')
  const json = await res.json()

  return json.data.map((region: any) => ({
    timestamp: region.from,
    region: region.shortname,
    carbonIntensity: region.intensity.actual,
    generationMix: region.generationmix.reduce(
      (acc: any, g: any) => ({ ...acc, [g.fuel]: g.perc }),
      {}
    )
  }))
}

// Otherwise Electricity Maps adapter for EU/global users
export async function fetchEUCarbonData(
  countryCode: string
): Promise<CarbonData> {
  const res = await fetch(
    `https://api.electricitymap.org/v3/carbon-intensity/latest?zone=${countryCode}`,
    { headers: { 'auth-token': process.env.ELECTRICITYMAP_TOKEN! } }
  )
  const json = await res.json()

  return {
    timestamp: json.datetime,
    region: json.zone,
    carbonIntensity: json.carbonIntensity,
    generationMix: json.productionMix
  }
}

Transforming and normalising data

My tool integrates data from two distinct APIs - the UK’s National Grid Carbon Intensity API and the Electricity Maps API. Each provides carbon intensity data but with different structures, requiring transformation and normalisation to present a unified interface.

UK National Grid API returns nested regional data:

{
  "data": [
    {
      "shortname": "England",
      "data": [
        {
          "intensity": {
            "forecast": 245,
            "index": "moderate"
          },
          "generationmix": [
            { "fuel": "gas", "perc": 40.2 },
            { "fuel": "wind", "perc": 25.1 }
          ]
        }
      ]
    }
  ]
}

Electricity Maps API uses a flatter structure:

{
  "zone": "GB",
  "carbonIntensity": 245,
  "datetime": "2024-01-15T10:00:00.000Z",
  "powerConsumptionBreakdown": {
    "gas": 15420,
    "wind": 9630,
    "solar": 2100
  }
}

1. Unified Data Schema

So I defined a common interface CarbonData that both adapters transform to

interface CarbonData {
  intensity: number // gCO₂/kWh
  index?: CarbonIntensityIndex
  region: string
  timestamp: Date
  mix?: GenerationMix[]
  source: DataSource
}

2. Adapter Pattern Implementation

Each API gets its own adapter with transformation logic:

UK Adapter

const transformNationalGridResponse = (
  response: NationalGridResponse
): CarbonData => {
  const regionalData = response.data[0]
  const intensityData = regionalData.data[0]

  return {
    intensity: intensityData.intensity.forecast,
    index: intensityData.intensity.index as CarbonIntensityIndex,
    region: regionalData.shortname || 'England',
    timestamp: new Date(),
    mix: intensityData.generationmix?.map((item) => ({
      fuel: item.fuel,
      perc: item.perc
    })),
    source: 'national-grid'
  }
}

EU Adapter

// Transform power consumption to percentages
const calculatePercentages = (powerBreakdown: Record<string, number>) => {
  const totalConsumption = Object.values(powerBreakdown)
    .filter((value) => value > 0)
    .reduce((sum, value) => sum + value, 0)

  const percentages: Record<string, number> = {}
  for (const [fuelType, value] of Object.entries(powerBreakdown)) {
    if (value > 0) {
      percentages[fuelType] = (value / totalConsumption) * 100
    }
  }
  return percentages
}

// Map Electricity Maps API  fuel types to our standard
const fuelTypeMapping = {
  nuclear: 'nuclear',
  wind: 'wind',
  solar: 'solar',
  gas: 'gas',
  coal: 'coal',
  'hydro discharge': 'hydro',
  biomass: 'biomass'
}

const groupedByFuel: Record<string, number> = {}
for (const [fuelType, percentage] of Object.entries(percentages)) {
  const mappedFuel = fuelTypeMapping[fuelType.toLowerCase()] || 'other'
  groupedByFuel[mappedFuel] = (groupedByFuel[mappedFuel] || 0) + percentage
}

Privacy

Instead of detecting user location (which may be inaccurate due to devs using VPN), I let users input their regional postcode (more private and practical as well)

Performance, SEO

Writing

Promoting

and I’m grateful that VSCarbon is receiving interest and support beyond the UK.

(Draft) What I've learned building VSCarbon