package org.apidesign.apifest08.currency;

 import java.util.*;

 /**

  * ConvertorProvider class is introduced to handle

  */

 public final class OfflineConverterProvider implements CurrencyConverterProvider {

 	// we can't synchronize on DEFAULT as it's not final and can even be null in synchronized section

 	private static final Object LOCK = new Object();

 	private static CurrencyConverterProvider DEFAULT;

 	// this is not nice and could be static, but future usage is uncertain and it's pretty easy to create

 	private final Map<Currency, Double> rates;

 	private OfflineConverterProvider() {

 		rates = new HashMap<Currency, Double>();

 		// simple initialization just for Task1Test

 		rates.put(Currency.getInstance("USD"), 100.0);

 		rates.put(Currency.getInstance("CZK"), 1700.0);

 		rates.put(Currency.getInstance("SKK"), 2125.0);

 	}

 	/**

 	 * Provides default implementation of ConvertorProvider. This Converter does nos not ensure accuracy

 	 * of exchange rates, but should be functional at any circumstances including being offline.

 	 *

 	 * @return

 	 */

 	public static CurrencyConverterProvider getInstance() {

 		// should be necessary in current implementation as creating CurrencyConverterProvider is cheap, but for future

 		if (DEFAULT == null)

 			synchronized (LOCK) {

 				if (DEFAULT == null)

 					DEFAULT = new OfflineConverterProvider();

 			}

 		return DEFAULT;

 	}

 	@Override

 	public CurrencyConverter getConverter(double amount1, /*@NotNull*/ String currency1,

 									   double amount2, /*@NotNull*/ String currency2)

 			throws IllegalArgumentException {

 		return getConverter(amount1, Currency.getInstance(currency2), amount2, Currency.getInstance(currency1));

 	}

 	/**

 	 * Retrieves converter that is capable of converting values between currency1 and currency2. The exchange is

 	 * specified in easy to understand way. By specifying values in two currencies that are equal. For example

 	 * CurrencyConverter.getConverter(25, "CZK", 1, "EUR"); means 25CKZ is equal to 1EUR. This enables user to

 	 * use this method without having to calculate anything. In general this can be expressed by formula

 	 * amount1[currency1] = amount2[currency2].

 	 *

 	 * @param amount1

 	 * @param currency1

 	 * @param amount2

 	 * @param currency2

 	 *

 	 * @return

 	 *

 	 * @throws IllegalArgumentException

 	 * @throws CurrencyNotAvailableException

 	 *

 	 */

 	@Override

 	public CurrencyConverter getConverter(double amount1, /*@NotNull*/ Currency currency1,

 									   double amount2, /*@NotNull*/ Currency currency2)

 			throws IllegalArgumentException, CurrencyNotAvailableException {

 		if (amount1 <= 0.0 || amount2 <= 0.0)

 			throw new IllegalArgumentException(

 					String.format("The specified currency values (%1$s, %2$s)", amount1, amount2));

 		return new ConstantRateConverter(currency2, currency1, amount2 / amount1);

 	}

 	/**

 	 * Creates a new converter that is able to convert between all specified currencies.

 	 *

 	 * @param currencies that the converter should be created for

 	 *

 	 * @return converter able to convert between all specified currencies

 	 *

 	 * @throws CurrencyNotAvailableException

 	 *          thrown when one of the currencies is not available

 	 */

 	@Override

 	public CurrencyConverter getConverter(/*@NotNull*/ Currency... currencies) throws CurrencyNotAvailableException {

 		for (Currency c : currencies) {

 			if (c == null)

 				throw new NullPointerException("One of the specified currencies is null");

 			if (!rates.containsKey(c))

 				throw new CurrencyNotAvailableException(c);

 		}

 		return new MultiCurrencyConstantRateConverter(rates);

 	}

 	/**

 	 * Creates a new converter that is able to convert between all specified currencies.

 	 *

 	 * @param currencies that the converter should be created for

 	 *

 	 * @return converter able to convert between all specified currencies

 	 *

 	 * @throws CurrencyNotAvailableException

 	 *                                  thrown when one of the currencies is not available

 	 * @throws NullPointerException	 if any of the specified currencies is null

 	 * @throws IllegalArgumentException if any of the specified currencies is not a valid ISO code

 	 */

 	@Override

 	public CurrencyConverter getConverter(/*@NotNull*/ String... currencies)

 			throws CurrencyNotAvailableException, IllegalArgumentException, NullPointerException {

 		Currency[] c2 = new Currency[currencies.length];

 		for (int i = 0; i < c2.length; i++)

 			c2[i] = Currency.getInstance(currencies[i]);

 		return getConverter(c2);

 	}

 }