feat: fetch currency exchange rate

exchange rates are fetched at script startup, and at most once daily, then cached. attribution is added as per ExchangeRate-API's requirements

src/content/config.ts

@@ -3,6 +3,9 @@ export const storage_lastUpdateTime = 'tf2wikipricing_lastUpdate';
 export const storage_schema = 'tf2wikipricing_schema';
 export const storage_version = 'tf2wikipricing_version';
 export const storage_priceprefix = 'tf2wikipricing_sku_';
+export const storage_exchangerates = 'tf2wikipricing_exchangerates';
+export const storage_exchangerates_update = 'tf2wikipricing_exchangerates_update';
+export const storage_exchangerates_next = 'tf2wikipricing_exchangerates_next';
 export const conversion_ref_usd = 0.0265;
 export const defindex_key = 5021;
 export const defindex_metal_refined = 5002;

src/content/content.ts

@@ -9,7 +9,9 @@ import { fetchPrice, fetchKeyPrice, ItemPriceData } from './priceService'
 import { createPriceRow, createStoreButton } from './uiRenderer'
 import { findFirstElement, findFirstChildElement } from './utils/dom'
 import { extractPageTitleFromURL } from './utils/url';
+import { ExchangeRates, prepareExchangeRates } from './exchangeRateService';
 var itemSchema: ItemSchema | null;
+var exchangeRates: ExchangeRates | null;
 
 var locale: string = 'en'
 
@@ -425,7 +427,8 @@ async function inject() {
 		label.style.fontSize = "85%";
 		const updateText = $T("Updated %@.", locale).replace('%@', updateTime.toLocaleString(locale, { year: 'numeric', month: 'long', day: 'numeric', hour: '2-digit', minute: '2-digit', timeZoneName: 'short' }))
 		const attributionText = $T("Trade prices sourced from %@. Currency conversions are approximate.", locale).replace('%@', '<a rel="nofollow" class="external text" href="https://prices.tf">prices.tf</a>');
-		label.innerHTML = `${updateText}<br>${attributionText}`;
+		const exchangeRateAttribution = `<a rel="nofollow" class="external text" href="https://www.exchangerate-api.com">Rates By Exchange Rate API</a>.`;
+		label.innerHTML = `${updateText}<br>${attributionText}<br>${exchangeRateAttribution}`;
 		row.appendChild(label);
 
 		priceProgressRow.insertAdjacentElement('afterend', row);
@@ -440,15 +443,22 @@ function addStyles() {
 	style.innerHTML = styleCss;
 }
 
-prepareSchema().then(function (schema) {
+prepareSchema()
+.then(schema => {
 	itemSchema = schema;
 	if (!itemSchema) {
-		logError("No item schema ready, exiting.");
 		wipeSchema(); // FIXME: ugly hack. requires additional page reload. if prepareSchema returns null, we should handle it properly
-		return;
+		throw new Error("No item schema ready");
 	}
+})
+.then(prepareExchangeRates)
+.then(rates => exchangeRates = rates)
+.then(() => {
 	locale = extractLocaleFromURL(document.URL)
 	addStyles();
 	inject();
 	// TODO: Purge expired price data
-});
+})
+.catch((error) => {
+	logError(error);
+})

src/content/exchangeRateService.ts

@@ -0,0 +1,55 @@
+import { getStorageValue, setStorageValue } from './storage'
+import { logDebug, log, logError } from './utils/log'
+import { storage_exchangerates, storage_exchangerates_next, storage_exchangerates_update } from './config'
+declare function GM_fetch(input: string | URL | globalThis.Request, init?: RequestInit): Promise<Response>
+import './GM_fetch'
+
+export interface ExchangeRates {
+  [key: string]: number;
+}
+
+export async function wipeExchangeRates(): Promise<void> {
+	await setStorageValue(storage_exchangerates, null)
+	await setStorageValue(storage_exchangerates_update, new Date().toISOString())
+	await setStorageValue(storage_exchangerates_next, new Date().toISOString())
+	logDebug(`Exchange rates wiped`)
+}
+
+export async function prepareExchangeRates(): Promise<ExchangeRates> {
+	var needsUpdate: Boolean = false
+  var rates: ExchangeRates | null = null
+
+  rates = await getStorageValue(storage_exchangerates, null);
+	const update = await getStorageValue(storage_exchangerates_update, null)
+	const nextUpdate = await getStorageValue(storage_exchangerates_next, null)
+	if (update && nextUpdate) {
+		const lastUpdateTime = new Date(update);
+		const nextUpdateTime = new Date(nextUpdate);
+		log(`Exchange rates updated at ${lastUpdateTime}`);
+		if (rates == null || Object.keys(rates).length === 0 || lastUpdateTime.getTime() > nextUpdateTime.getTime()) {
+			needsUpdate = true
+		}
+	} else {
+    needsUpdate = true
+  }
+
+  if(needsUpdate) {
+    log("Exchange rates out of Date. Rebuilding...");
+    const url = "https://open.er-api.com/v6/latest/USD"
+    const response = await GM_fetch(url);
+    if (response.ok) {
+      await setStorageValue(storage_exchangerates_update, new Date().toISOString())
+      var json = await response.json()
+      if(json != null){
+        rates = json['rates']
+        await setStorageValue(storage_exchangerates, rates)
+        await setStorageValue(storage_exchangerates_next, json['time_next_update_utc'])
+      }
+			logDebug(`Exchange rates updated at ${new Date()}`)
+    } else {
+      logError(`Failed to fetch exchange rates. Status code: ${response.status}`, response)
+    }
+  }
+
+  return rates
+}