alexradzin · June 9, 2022 16:16 · Jun 9, 2022
diff --git a/ExchangeRate.java b/ExchangeRate.java
@@ -0,0 +1,27 @@
+package com.exercise;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+import java.util.Map;
+
+@JsonIgnoreProperties(ignoreUnknown = true)
+public class ExchangeRate {
+    private final String base;
+    private final Map<String, Double> rates;
+
+    @JsonCreator
+    public ExchangeRate(@JsonProperty("base") String base, @JsonProperty("rates") Map<String, Double> rates) {
+        this.base = base;
+        this.rates = rates;
+    }
+
+    public String getBase() {
+        return base;
+    }
+
+    public Map<String, Double> getRates() {
+        return rates;
+    }
+}
diff --git a/README.txt b/README.txt
@@ -0,0 +1,10 @@
+Implement code that calculates amounts of money in national currencies useing CSV file like
+
+Base,Sum,Target
+USD,100,ILS
+USD,150,GBP
+...
+
+Use exchangeratesapi.io to retrieve currency rates. Print resutls to STDOUT. 
+
+(Interview question of Correlate)
diff --git a/SumCalculator.java b/SumCalculator.java
@@ -0,0 +1,98 @@
+package com.exercise;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.apache.logging.log4j.util.BiConsumer;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.net.URL;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.stream.Stream;
+
+import static java.lang.String.format;
+import static java.util.stream.Collectors.toList;
+import static java.util.stream.Collectors.toMap;
+
+public class SumCalculator {
+    private static final String RATES_URL_TEMPLATE = "https://api.exchangeratesapi.io/latest?base=%s&symbols=%s&access_key=d6943c813d6c3a3d1ca6793e8232a096";
+    private final ObjectMapper mapper = new ObjectMapper();
+
+    public List<Double> sums(InputStream transactions) throws IOException {
+        if(!transactions.markSupported()) {
+            throw new IllegalArgumentException("Given input stream does not support mark");
+        }
+
+        transactions.mark(Integer.MAX_VALUE);
+        Map<String, List<String>> currencies = retrieveAllUsedCurrencies(transactions);
+        transactions.reset();
+
+        Map<String, Map<String, Double>> rates = getRates(currencies).stream().collect(toMap(ExchangeRate::getBase, ExchangeRate::getRates));
+
+        return calculate(transactions, rates);
+    }
+
+
+    private List<Double> calculate(InputStream transactions, Map<String, Map<String, Double>> rates) throws IOException {
+        List<Double> results = new LinkedList<>();
+
+        return readTransactions(transactions, results, (results1, transaction) -> {
+            String base = transaction.getBase();
+            String target = transaction.getTarget();
+            int sum = transaction.getSum();
+
+            double rate = Optional.ofNullable(rates.get(base)).map(baseCurrency -> baseCurrency.get(target)).orElse(Double.NaN);
+            double result = sum * rate;
+            results.add(result);
+        });
+    }
+
+    private Map<String, List<String>> retrieveAllUsedCurrencies(InputStream transactions) throws IOException {
+        Map<String, List<String>> currencies = new HashMap<>();
+
+        return readTransactions(transactions, currencies, (currencies1, transaction) -> {
+            String base = transaction.getBase();
+            String target = transaction.getTarget();
+            currencies1.merge(base, List.of(target), (existingTargets, newTargets) -> Stream.concat(existingTargets.stream(), newTargets.stream()).collect(toList()));
+        });
+    }
+
+    private <T> T readTransactions(InputStream transactions, T result, BiConsumer<T, Transaction> adder) throws IOException {
+        BufferedReader reader = new BufferedReader(new InputStreamReader(transactions));
+        boolean header = true;
+        for (String line = reader.readLine(); line != null; line = reader.readLine()) {
+            if (header) {
+                header = false;
+                continue;
+            }
+            Transaction transaction = parseLineToTransaction(line);
+            adder.accept(result, transaction);
+        }
+        return result;
+    }
+
+    private List<ExchangeRate> getRates(Map<String, List<String>> currencyNames) throws IOException {
+        List<ExchangeRate> exchangeRates = new LinkedList<>();
+        for (Map.Entry<String, List<String>> entry : currencyNames.entrySet()) {
+            String base = entry.getKey();
+            String targets = String.join(",", entry.getValue());
+            String url = format(RATES_URL_TEMPLATE, base, targets);
+            ExchangeRate exchangeRate = mapper.readValue(new URL(url), ExchangeRate.class);
+            if (exchangeRate.getBase() != null) {
+                exchangeRates.add(exchangeRate);
+            }
+        }
+
+        return exchangeRates;
+    }
+
+    private Transaction parseLineToTransaction(String line) {
+        String[] parts = line.split(",");
+        return new Transaction(parts[0], Integer.parseInt(parts[1]), parts[2]);
+    }
+}
diff --git a/SumCalculatorCli.java b/SumCalculatorCli.java
@@ -0,0 +1,14 @@
+package com.exercise;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.List;
+
+public class SumCalculatorCli {
+    public static void main(String[] args) throws IOException {
+        try (InputStream in = SumCalculatorCli.class.getResourceAsStream("/transactions.csv")) {
+            List<Double> results = new SumCalculator().sums(in);
+            System.out.println(results);
+        }
+    }
+}
diff --git a/Transaction.java b/Transaction.java
@@ -0,0 +1,25 @@
+package com.exercise;
+
+public class Transaction {
+    private final String base;
+    private final int sum;
+    private final String target;
+
+    public Transaction(String base, int sum, String target) {
+        this.base = base;
+        this.sum = sum;
+        this.target = target;
+    }
+
+    public String getBase() {
+        return base;
+    }
+
+    public int getSum() {
+        return sum;
+    }
+
+    public String getTarget() {
+        return target;
+    }
+}
diff --git a/transactions.csv b/transactions.csv
@@ -0,0 +1,6 @@
+Base,Sum,Target
+USD,100,ILS
+USD,150,GBP
+ILS,100,USD
+EUR,300,ETH
+CAD,50,KRW