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import { entries, fromEntries, keys } from "remeda";
import { z } from "zod";
import type { CurrencyCode } from "~app/utils/currency";
import type { UnauthorizedContext } from "~web/handlers/context";
import type { CacheInstance } from "~web/providers/cache-db";
import { getCacheInstance } from "~web/providers/cache-db";
import { env } from "~web/utils/env";
export type ExchangeRateOptions = {
mock?: {
fn: (from: CurrencyCode, to: CurrencyCode) => Promise<number>;
};
};
type ExchangeRateInput = { fromCode: CurrencyCode; toCode: CurrencyCode };
// see https://github.com/fawazahmed0/exchange-api
const CDN_MAIN_BASE_URL = `https://cdn.jsdelivr.net/npm/@fawazahmed0/currency-api@latest/v1/currencies/{fromCode}.min.json`;
// see https://github.com/fawazahmed0/exchange-api/blob/main/README.md#additional-fallback-url-on-cloudflare
const CDN_BACKUP_BASE_URL = `https://latest.currency-api.pages.dev/v1/currencies/{fromCode}.min.json`;
const fetchCDNRate =
(baseUrl: string) =>
async (fromCode: CurrencyCode, toCodes: CurrencyCode[]) => {
const fromCodeLower = fromCode.toLowerCase();
const toCodesLower = toCodes.map((code) => code.toLowerCase()) as [
string,
...string[],
];
const response = await fetch(baseUrl.replace("{fromCode}", fromCodeLower));
if (response.status !== 200) {
throw new Error(
`Response to exchange rate request is ${response.status}`,
);
}
const json: unknown = await response.json();
const parsedJson = z
.object({
[fromCodeLower]: z.record(z.string(), z.float32()).refine((obj) => {
const actualKeys = keys(obj);
return toCodesLower.every((code) => actualKeys.includes(code));
}),
})
.safeParse(json);
if (!parsedJson.success) {
throw parsedJson.error;
}
return toCodesLower.map((toCodeLower) =>
Number(
// We just verified it exists
// oxlint-disable-next-line typescript/no-non-null-assertion
parsedJson.data[fromCodeLower]![toCodeLower]!.toFixed(6),
),
);
};
// see https://www.exchangerate-api.com/docs/standard-requests
const ERA_BASE_URL = "https://v6.exchangerate-api.com/v6/";
const fetchERARate = async (
fromCode: CurrencyCode,
toCodes: CurrencyCode[],
) => {
const { ERA_API_KEY } = env;
if (!ERA_API_KEY) {
throw new Error(`Expected to have env.ERA_API_KEY`);
}
const fromCodeUpper = fromCode.toUpperCase();
const toCodesUpper = toCodes.map((code) => code.toUpperCase());
const response = await fetch(
`${ERA_BASE_URL}${ERA_API_KEY}/latest/${fromCodeUpper}`,
);
if (response.status !== 200) {
throw new Error(`Response to exchange rate request is ${response.status}`);
}
const json: unknown = await response.json();
const parsedJson = z
.discriminatedUnion("result", [
z.object({
result: z.literal("success"),
base_code: z.literal(fromCodeUpper),
conversion_rates: z.record(z.string(), z.number()),
}),
z.object({
result: z.literal("error"),
"error-type": z.string(),
}),
])
.safeParse(json);
if (!parsedJson.success) {
throw parsedJson.error;
}
const { data } = parsedJson;
if (data.result === "error") {
throw new Error(`Error fetching ERA result: "${data["error-type"]}"`);
}
return toCodesUpper.map((toCodeUpper) => {
const matchedRate = data.conversion_rates[toCodeUpper];
if (!matchedRate) {
throw new Error(
`Error getting ERA rate for "${fromCodeUpper}" -> "${toCodeUpper}"`,
);
}
return Number(matchedRate.toFixed(6));
});
};
const fetchWithBatches = async (
inputs: readonly ExchangeRateInput[],
fetcher: (
fromCode: CurrencyCode,
toCodes: CurrencyCode[],
) => Promise<number[]>,
) => {
const batches = inputs.reduce<Record<CurrencyCode, CurrencyCode[]>>(
(acc, input) => {
const batch = acc[input.fromCode] || [];
if (!batch.includes(input.toCode)) {
batch.push(input.toCode);
}
return { ...acc, [input.fromCode]: batch };
},
{},
);
const batchResults = await Promise.all(
entries(batches).map(async ([fromCode, toCodes]) => {
const batchResult = await fetcher(fromCode, toCodes);
return {
fromCode,
toRates: toCodes.map((toCode, index) => {
const toRate = batchResult[index];
if (toRate === undefined) {
throw new Error("Expected length to match in response");
}
return {
code: toCode,
rate: toRate,
};
}),
};
}),
);
return inputs.map((input) => {
const matchedBatch = batchResults.find(
({ fromCode }) => fromCode === input.fromCode,
);
if (!matchedBatch) {
throw new Error(`No batch from code "${input.fromCode}"`);
}
const matchedRate = matchedBatch.toRates.find(
({ code }) => code === input.toCode,
);
if (!matchedRate) {
throw new Error(
`No batch from code "${input.fromCode}" to code "${input.toCode}"`,
);
}
return matchedRate.rate;
});
};
const fetchPipeline = (fetchers: (() => Promise<number[]>)[]) =>
fetchers.reduce<Promise<number[] | Error[]>>(async (acc, fetcher) => {
const results = await acc;
try {
if (typeof results[0] !== "number") {
return await fetcher();
}
return results;
} catch (error) {
return [...(results as Error[]), error as Error];
}
}, Promise.resolve([]));
const SCHEDULE_DELAY = 100;
const exchangeRateDataloader = new Dataloader<
ExchangeRateInput,
number,
string
>(
async (inputs) => {
const result = await fetchPipeline([
() => fetchWithBatches(inputs, fetchCDNRate(CDN_MAIN_BASE_URL)),
() => fetchWithBatches(inputs, fetchCDNRate(CDN_BACKUP_BASE_URL)),
() => fetchWithBatches(inputs, fetchERARate),
]);
if (typeof result[0] === "number") {
return result;
}
throw new AggregateError(
result,
"All exchange rate resolution options failed",
);
},
{
batchScheduleFn: (callback) => {
setTimeout(callback, SCHEDULE_DELAY);
},
cacheKeyFn: JSON.stringify,
name: "exchange-rate",
},
);
// Seconds
const CACHE_TTL = 24 * 60 * 1000;
const getKey = (fromCode: CurrencyCode, toCode: CurrencyCode): string =>
`${fromCode}->${toCode}`;
export const getExchangeRates = async (
ctx: UnauthorizedContext,
fromCode: CurrencyCode,
toCodes: CurrencyCode[],
): Promise<Record<CurrencyCode, number>> => {
let cacheInstance: CacheInstance | null = null;
try {
cacheInstance = await getCacheInstance(ctx);
} catch {
/* empty */
}
const rates = await Promise.all(
toCodes.map(async (toCode) => {
const cacheKey = getKey(fromCode, toCode);
const cachedRate = cacheInstance
? await cacheInstance.getValue(cacheKey)
: null;
if (cachedRate) {
return { toCode, rate: Number(cachedRate) };
}
const fetchedRate = await (ctx.exchangeRateOptions.mock
? ctx.exchangeRateOptions.mock.fn(fromCode, toCode)
: exchangeRateDataloader.load({
fromCode,
toCode,
}));
cacheInstance
?.setValue(cacheKey, fetchedRate.toString(), { expiryInS: CACHE_TTL })
.catch((error) => {
// Failing on this action doesn't matter much
ctx.logger.warn("Cache DB setex action failed", error);
});
return { toCode, rate: fetchedRate };
}),
);
return fromEntries(rates.map(({ toCode, rate }) => [toCode, rate]));
};
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