nullcart/backend/src/modules/exchangeRate/services/ExchangeRateService.ts

import { Injectable, Logger, OnModuleInit } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';
import { Cron, CronExpression } from '@nestjs/schedule';
import { plainToInstance } from 'class-transformer';
import { validateSync } from 'class-validator';
import axios from 'axios';
import type { Config } from '../../../types/Config';
import { getErrorMessage } from '../../../utils/getErrorMessage';
import { COINGECKO_ID_BY_PAYMENT_METHOD } from '../const/coingeckoIds';
import { COINPAPRIKA_ID_BY_PAYMENT_METHOD } from '../const/coinPaprikaIds';
import { EXCHANGE_RATE_PAYMENT_METHODS, type ExchangeRatePaymentMethod } from '../const/exchangeRatePaymentMethods';
import { CoingeckoSimplePriceResponseDto } from '../dto/CoingeckoSimplePriceResponseDto';
import { CoinPaprikaTickerResponseDto } from '../dto/CoinPaprikaTickerResponseDto';
import type { FiatPerCryptoRates } from '../types/FiatPerCryptoRates';
import { extractCoingeckoSimplePrice } from '../utils/extractCoingeckoSimplePrice';
import { extractCoinPaprikaTickerPrice } from '../utils/extractCoinPaprikaTickerPrice';

@Injectable()
export class ExchangeRateService implements OnModuleInit {
    private readonly logger = new Logger(ExchangeRateService.name);

    private liveFiatPerCrypto = Object.fromEntries(
        EXCHANGE_RATE_PAYMENT_METHODS.map(method => [method, null])
    ) as Record<ExchangeRatePaymentMethod, number | null>;

    constructor(private readonly configService: ConfigService) {}

    async onModuleInit(): Promise<void> {
        await this.fetchLiveRates();
    }

    getLiveFiatPerCrypto(method: ExchangeRatePaymentMethod): number | null {
        return this.liveFiatPerCrypto[method];
    }

    @Cron(CronExpression.EVERY_5_MINUTES)
    async fetchLiveRates(): Promise<void> {
        const { shopFiatCurrency } = this.configService.get('shopSettings') as Config['shopSettings'];

        try {
            const rates = await this.fetchRatesFromCoingecko();

            this.applyRates(rates);
        } catch {
            this.logger.warn(`CoinGecko rate fetch failed for ${shopFiatCurrency}, trying CoinPaprika`);

            try {
                const rates = await this.fetchRatesFromCoinPaprika();

                this.applyRates(rates);

                this.logger.log(`Successfully fetched live rates from CoinPaprika for ${shopFiatCurrency}`);
            } catch (error) {
                this.logger.error(
                    `Failed to fetch live rates from CoinGecko and CoinPaprika for ${shopFiatCurrency}: ${getErrorMessage(error)}`
                );
            }
        }
    }

    private async fetchRatesFromCoingecko(): Promise<FiatPerCryptoRates> {
        const { rateFetchTimeoutMs } = this.configService.get('coingecko') as Config['coingecko'];
        const { shopFiatCurrency } = this.configService.get('shopSettings') as Config['shopSettings'];

        const url = this.buildCoingeckoRateUrl();

        const { data } = await axios.get<unknown>(url, {
            timeout: rateFetchTimeoutMs
        });

        const coinIds = EXCHANGE_RATE_PAYMENT_METHODS.map(method => COINGECKO_ID_BY_PAYMENT_METHOD[method]);

        const dto = plainToInstance(CoingeckoSimplePriceResponseDto, {
            response: data,
            shopFiatCurrency,
            coinIds
        });

        const errors = validateSync(dto);

        if (errors.length > 0) {
            throw new Error('CoinGecko response validation failed');
        }

        const rates = {} as FiatPerCryptoRates;

        for (const method of EXCHANGE_RATE_PAYMENT_METHODS) {
            const coinId = COINGECKO_ID_BY_PAYMENT_METHOD[method];

            const price = extractCoingeckoSimplePrice(dto.response, coinId, shopFiatCurrency);

            if (price === null) {
                throw new Error(`CoinGecko response validation failed for coin ${coinId}`);
            }

            rates[method] = price;
        }

        return rates;
    }

    private async fetchRatesFromCoinPaprika(): Promise<FiatPerCryptoRates> {
        const { apiBaseUrl, rateFetchTimeoutMs } = this.configService.get('coinPaprika') as Config['coinPaprika'];
        const { shopFiatCurrency } = this.configService.get('shopSettings') as Config['shopSettings'];

        const rates = {} as FiatPerCryptoRates;

        await Promise.all(
            EXCHANGE_RATE_PAYMENT_METHODS.map(async method => {
                const coinId = COINPAPRIKA_ID_BY_PAYMENT_METHOD[method];
                const url = `${apiBaseUrl}/tickers/${coinId}?quotes=${shopFiatCurrency}`;

                const { data } = await axios.get<unknown>(url, {
                    timeout: rateFetchTimeoutMs
                });

                const dto = plainToInstance(CoinPaprikaTickerResponseDto, {
                    response: data,
                    shopFiatCurrency
                });

                const errors = validateSync(dto);

                if (errors.length > 0) {
                    throw new Error(`CoinPaprika response validation failed for coin ${coinId}`);
                }

                const price = extractCoinPaprikaTickerPrice(dto.response, shopFiatCurrency);

                if (price === null) {
                    throw new Error(`CoinPaprika response validation failed for coin ${coinId}`);
                }

                rates[method] = price;
            })
        );

        return rates;
    }

    private buildCoingeckoRateUrl(): string {
        const { apiBaseUrl } = this.configService.get('coingecko') as Config['coingecko'];
        const { shopFiatCurrency } = this.configService.get('shopSettings') as Config['shopSettings'];

        const coinIds = EXCHANGE_RATE_PAYMENT_METHODS.map(method => COINGECKO_ID_BY_PAYMENT_METHOD[method]).join(',');
        const vs = shopFiatCurrency.toLowerCase();

        return `${apiBaseUrl}/simple/price?ids=${coinIds}&vs_currencies=${vs}`;
    }

    private applyRates(rates: FiatPerCryptoRates): void {
        for (const method of EXCHANGE_RATE_PAYMENT_METHODS) {
            this.liveFiatPerCrypto[method] = rates[method];
        }
    }
}