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UnitsConverter.java
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package com.thealgorithms.conversions;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import org.apache.commons.lang3.tuple.Pair;
public final class UnitsConverter {
private final Map<Pair<String, String>, AffineConverter> conversions;
private final Set<String> units;
private static void putIfNeeded(Map<Pair<String, String>, AffineConverter> conversions, final String inputUnit, final String outputUnit, final AffineConverter converter) {
if (!inputUnit.equals(outputUnit)) {
final var key = Pair.of(inputUnit, outputUnit);
conversions.putIfAbsent(key, converter);
}
}
private static Map<Pair<String, String>, AffineConverter> addInversions(final Map<Pair<String, String>, AffineConverter> knownConversions) {
Map<Pair<String, String>, AffineConverter> res = new HashMap<Pair<String, String>, AffineConverter>();
for (final var curConversion : knownConversions.entrySet()) {
final var inputUnit = curConversion.getKey().getKey();
final var outputUnit = curConversion.getKey().getValue();
putIfNeeded(res, inputUnit, outputUnit, curConversion.getValue());
putIfNeeded(res, outputUnit, inputUnit, curConversion.getValue().invert());
}
return res;
}
private static Map<Pair<String, String>, AffineConverter> addCompositions(final Map<Pair<String, String>, AffineConverter> knownConversions) {
Map<Pair<String, String>, AffineConverter> res = new HashMap<Pair<String, String>, AffineConverter>();
for (final var first : knownConversions.entrySet()) {
final var firstKey = first.getKey();
putIfNeeded(res, firstKey.getKey(), firstKey.getValue(), first.getValue());
for (final var second : knownConversions.entrySet()) {
final var secondKey = second.getKey();
if (firstKey.getValue().equals(secondKey.getKey())) {
final var newConversion = second.getValue().compose(first.getValue());
putIfNeeded(res, firstKey.getKey(), secondKey.getValue(), newConversion);
}
}
}
return res;
}
private static Map<Pair<String, String>, AffineConverter> addAll(final Map<Pair<String, String>, AffineConverter> knownConversions) {
final var res = addInversions(knownConversions);
return addCompositions(res);
}
private static Map<Pair<String, String>, AffineConverter> computeAllConversions(final Map<Pair<String, String>, AffineConverter> basicConversions) {
var tmp = basicConversions;
var res = addAll(tmp);
while (res.size() != tmp.size()) {
tmp = res;
res = addAll(tmp);
}
return res;
}
private static Set<String> extractUnits(final Map<Pair<String, String>, AffineConverter> conversions) {
Set<String> res = new HashSet<>();
for (final var conversion : conversions.entrySet()) {
res.add(conversion.getKey().getKey());
}
return res;
}
public UnitsConverter(final Map<Pair<String, String>, AffineConverter> basicConversions) {
conversions = computeAllConversions(basicConversions);
units = extractUnits(conversions);
}
public double convert(final String inputUnit, final String outputUnit, final double value) {
if (inputUnit.equals(outputUnit)) {
throw new IllegalArgumentException("inputUnit must be different from outputUnit.");
}
final var conversionKey = Pair.of(inputUnit, outputUnit);
return conversions.computeIfAbsent(conversionKey, k -> { throw new NoSuchElementException("No converter for: " + k); }).convert(value);
}
public Set<String> availableUnits() {
return units;
}
}