wip: calculate emissions from page speed results

Author: jonoliver

package-lock.json

@@ -22,7 +22,7 @@
     "node": ">=14.0.0"
   },
   "dependencies": {
+    "@tgwf/co2": "^0.16.9",
     "archiver": "^5.3.1"
-  },
-  "devDependencies": {}
-}
+  }
+}

package.json

@@ -0,0 +1,38 @@
+import { co2 } from "@tgwf/co2";
+
+/**
+ * Calculates the carbon emissions for a web page based on the results from Google's PageSpeed Insights (Lighthouse).
+ *
+ * @param {Object} pageSpeedResults - The PageSpeed Insights (Lighthouse) result object.
+ * @returns {Object} An object containing:
+ *   @property {number} emissionsOneByte - Estimated emissions CO2e (in grams) from the OneByte model.
+ *   @property {number} emissionsSWD - Estimated emissions CO2e (in grams) from the Sustainable Web Design model.
+ * TODO: This function currently returns emissions for both the OneByte and SWD models. Not sure which one we ultimately want to use.
+ */
+export const calculateEmissionsFromPageSpeedResults = (pageSpeedResults) => {
+  const totalByteWeight = pageSpeedResults.lighthouseResult.audits['total-byte-weight'].numericValue;
+  // this appears to be the same number as totalByteWeight:
+  // const totalByteWeightSummed = pageSpeedResults.lighthouseResult.audits['network-requests'].details.items.reduce((total, item) => total + item.transferSize, 0);
+
+  // OneByte model
+  // https://developers.thegreenwebfoundation.org/co2js/models/#using-the-onebyte-model
+  const perByte = new co2({ model: "1byte" });
+  const emissionsOneByte = perByte.perByte(totalByteWeight);
+
+  // Sustainable Web Design (SWD) model
+  // https://developers.thegreenwebfoundation.org/co2js/models/#using-the-sustainable-web-design-model-default-v0110
+  const swd = new co2({ model: "swd" });
+  const emissionsSWD = swd.perVisit(totalByteWeight);
+
+  return { emissionsOneByte, emissionsSWD };
+}
+
+// TODO: The code below is for testing purposes only.
+// It should be removed once it's able to be integrated with https://sparkbox.atlassian.net/browse/BLDL-9
+// tempdata.json should also be removed.
+(async () => {
+  const pageSpeedResults = (await import("./tempdata.json", { with: { type: "json" } })).default;
+  const results = calculateEmissionsFromPageSpeedResults(pageSpeedResults)
+  console.log("Emissions Calculation Results:", results);
+})();
+