/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.math.fraction;

import java.text.FieldPosition;
import java.text.NumberFormat;
import java.text.ParsePosition;

import org.apache.commons.math.MathRuntimeException;
import org.apache.commons.math.util.MathUtils;

/**
 * Formats a Fraction number in proper format. The number format for each of the
 * whole number, numerator and, denominator can be configured.
 * <p>
 * Minus signs are only allowed in the whole number part - i.e., "-3 1/2" is
 * legitimate and denotes -7/2, but "-3 -1/2" is invalid and will result in a
 * <code>ParseException</code>.
 * </p>
 * 
 * @since 1.1
 * @version $Revision$ $Date$
 */
public class ProperFractionFormat extends FractionFormat {

	/** Serializable version identifier */
	private static final long serialVersionUID = 760934726031766749L;

	/** The format used for the whole number. */
	private NumberFormat wholeFormat;

	/**
	 * Create a proper formatting instance with the default number format for
	 * the whole, numerator, and denominator.
	 */
	public ProperFractionFormat() {
		this(getDefaultNumberFormat());
	}

	/**
	 * Create a proper formatting instance with a custom number format for the
	 * whole, numerator, and denominator.
	 * 
	 * @param format
	 *            the custom format for the whole, numerator, and denominator.
	 */
	public ProperFractionFormat(NumberFormat format) {
		this(format, (NumberFormat) format.clone(), (NumberFormat) format.clone());
	}

	/**
	 * Create a proper formatting instance with a custom number format for each
	 * of the whole, numerator, and denominator.
	 * 
	 * @param wholeFormat
	 *            the custom format for the whole.
	 * @param numeratorFormat
	 *            the custom format for the numerator.
	 * @param denominatorFormat
	 *            the custom format for the denominator.
	 */
	public ProperFractionFormat(NumberFormat wholeFormat, NumberFormat numeratorFormat,
			NumberFormat denominatorFormat) {
		super(numeratorFormat, denominatorFormat);
		setWholeFormat(wholeFormat);
	}

	/**
	 * Formats a {@link Fraction} object to produce a string. The fraction is
	 * output in proper format.
	 *
	 * @param fraction
	 *            the object to format.
	 * @param toAppendTo
	 *            where the text is to be appended
	 * @param pos
	 *            On input: an alignment field, if desired. On output: the
	 *            offsets of the alignment field
	 * @return the value passed in as toAppendTo.
	 */
	@Override
	public StringBuffer format(Fraction fraction, StringBuffer toAppendTo, FieldPosition pos) {

		pos.setBeginIndex(0);
		pos.setEndIndex(0);

		int num = fraction.getNumerator();
		int den = fraction.getDenominator();
		int whole = num / den;
		num = num % den;

		if (whole != 0) {
			getWholeFormat().format(whole, toAppendTo, pos);
			toAppendTo.append(' ');
			num = Math.abs(num);
		}
		getNumeratorFormat().format(num, toAppendTo, pos);
		toAppendTo.append(" / ");
		getDenominatorFormat().format(den, toAppendTo, pos);

		return toAppendTo;
	}

	/**
	 * Access the whole format.
	 * 
	 * @return the whole format.
	 */
	public NumberFormat getWholeFormat() {
		return wholeFormat;
	}

	/**
	 * Parses a string to produce a {@link Fraction} object. This method expects
	 * the string to be formatted as a proper fraction.
	 * <p>
	 * Minus signs are only allowed in the whole number part - i.e., "-3 1/2" is
	 * legitimate and denotes -7/2, but "-3 -1/2" is invalid and will result in
	 * a <code>ParseException</code>.
	 * </p>
	 * 
	 * @param source
	 *            the string to parse
	 * @param pos
	 *            input/ouput parsing parameter.
	 * @return the parsed {@link Fraction} object.
	 */
	@Override
	public Fraction parse(String source, ParsePosition pos) {
		// try to parse improper fraction
		Fraction ret = super.parse(source, pos);
		if (ret != null) {
			return ret;
		}

		int initialIndex = pos.getIndex();

		// parse whitespace
		parseAndIgnoreWhitespace(source, pos);

		// parse whole
		Number whole = getWholeFormat().parse(source, pos);
		if (whole == null) {
			// invalid integer number
			// set index back to initial, error index should already be set
			// character examined.
			pos.setIndex(initialIndex);
			return null;
		}

		// parse whitespace
		parseAndIgnoreWhitespace(source, pos);

		// parse numerator
		Number num = getNumeratorFormat().parse(source, pos);
		if (num == null) {
			// invalid integer number
			// set index back to initial, error index should already be set
			// character examined.
			pos.setIndex(initialIndex);
			return null;
		}

		if (num.intValue() < 0) {
			// minus signs should be leading, invalid expression
			pos.setIndex(initialIndex);
			return null;
		}

		// parse '/'
		int startIndex = pos.getIndex();
		char c = parseNextCharacter(source, pos);
		switch (c) {
		case 0:
			// no '/'
			// return num as a fraction
			return new Fraction(num.intValue(), 1);
		case '/':
			// found '/', continue parsing denominator
			break;
		default:
			// invalid '/'
			// set index back to initial, error index should be the last
			// character examined.
			pos.setIndex(initialIndex);
			pos.setErrorIndex(startIndex);
			return null;
		}

		// parse whitespace
		parseAndIgnoreWhitespace(source, pos);

		// parse denominator
		Number den = getDenominatorFormat().parse(source, pos);
		if (den == null) {
			// invalid integer number
			// set index back to initial, error index should already be set
			// character examined.
			pos.setIndex(initialIndex);
			return null;
		}

		if (den.intValue() < 0) {
			// minus signs must be leading, invalid
			pos.setIndex(initialIndex);
			return null;
		}

		int w = whole.intValue();
		int n = num.intValue();
		int d = den.intValue();
		return new Fraction(((Math.abs(w) * d) + n) * MathUtils.sign(w), d);
	}

	/**
	 * Modify the whole format.
	 * 
	 * @param format
	 *            The new whole format value.
	 * @throws IllegalArgumentException
	 *             if <code>format</code> is <code>null</code>.
	 */
	public void setWholeFormat(NumberFormat format) {
		if (format == null) {
			throw MathRuntimeException.createIllegalArgumentException("whole format can not be null");
		}
		this.wholeFormat = format;
	}
}
