Convert display prices on current rates

src/m2m-schema.ts

@@ -15,6 +15,12 @@ type LockCurrencyPriceInput = {
   rateDate?: string | null
 }
 
+type ConvertCurrencyForDisplayInput = {
+  amount: number
+  sourceCurrency: string
+  displayCurrency: string
+}
+
 export const m2mTypeDefs = `#graphql
   input LockCurrencyPriceInput {
     sourceAmount: Float!
@@ -24,6 +30,24 @@ export const m2mTypeDefs = `#graphql
     rateDate: String
   }
 
+  input ConvertCurrencyForDisplayInput {
+    amount: Float!
+    sourceCurrency: String!
+    displayCurrency: String!
+  }
+
+  type DisplayCurrencyConversion {
+    sourceAmount: Float!
+    sourceCurrency: String!
+    displayAmount: Float!
+    displayCurrency: String!
+    exchangeRate: Float!
+    rateSnapshotUuid: String
+    rateEffectiveDate: String!
+    rateQuotedAt: String!
+    provider: String!
+  }
+
   type LockedCurrencyPrice {
     sourceAmount: Float!
     sourceCurrency: String!
@@ -41,6 +65,7 @@ export const m2mTypeDefs = `#graphql
 
   type Query {
     health: String!
+    convertCurrencyForDisplay(input: ConvertCurrencyForDisplayInput!): DisplayCurrencyConversion!
   }
 
   type Mutation {
@@ -118,9 +143,49 @@ async function lockCurrencyPrice(
   }
 }
 
+async function convertCurrencyForDisplay(
+  _: unknown,
+  args: { input: ConvertCurrencyForDisplayInput },
+) {
+  const sourceAmount = Number(args.input.amount)
+  if (!Number.isFinite(sourceAmount) || sourceAmount < 0) {
+    throw new GraphQLError('amount must be a non-negative finite number')
+  }
+  const sourceCurrency = currencyCode(args.input.sourceCurrency)
+  const displayCurrency = currencyCode(args.input.displayCurrency)
+  if (sourceCurrency === displayCurrency) {
+    const quotedAt = new Date()
+    return {
+      sourceAmount,
+      sourceCurrency,
+      displayAmount: sourceAmount,
+      displayCurrency,
+      exchangeRate: 1,
+      rateSnapshotUuid: null,
+      rateEffectiveDate: quotedAt.toISOString().slice(0, 10),
+      rateQuotedAt: quotedAt.toISOString(),
+      provider: 'identity',
+    }
+  }
+  const snapshot = await latestCurrencyRatesSnapshot()
+  const exchangeRate = convertMoney(1, sourceCurrency, displayCurrency, snapshot)
+  return {
+    sourceAmount,
+    sourceCurrency,
+    displayAmount: sourceAmount * exchangeRate,
+    displayCurrency,
+    exchangeRate,
+    rateSnapshotUuid: snapshot.uuid,
+    rateEffectiveDate: snapshot.effectiveDate.toISOString().slice(0, 10),
+    rateQuotedAt: snapshot.updatedAt.toISOString(),
+    provider: snapshot.provider,
+  }
+}
+
 export const m2mResolvers = {
   Query: {
     health: () => 'ok',
+    convertCurrencyForDisplay,
   },
   Mutation: {
     lockCurrencyPrice,