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);

	}

}