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/*******************************************************************************
 * Copyright 2012 Anteros Tecnologia
 *  
 * Licensed 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 br.com.anteros.bean.validation.constraints.validators;

import java.util.ArrayList;
import java.util.List;
import java.util.regex.Pattern;

import br.com.anteros.validation.api.ConstraintValidatorContext;

/**
 * ModCheckBase contains all shared methods and options used by Mod Check Validators
 *
 * http://en.wikipedia.org/wiki/Check_digit
 *
 * @author George Gastaldi
 * @author Hardy Ferentschik
 * @author Victor Rezende dos Santos
 */
public abstract class ModCheckBase {

	private static final Pattern NUMBERS_ONLY_REGEXP = Pattern.compile( "[^0-9]" );

	private static final int DEC_RADIX = 10;

	/**
	 * The start index for the checksum calculation
	 */
	private int startIndex;

	/**
	 * The end index for the checksum calculation
	 */
	private int endIndex;

	/**
	 * The index of the checksum digit
	 */
	private int checkDigitIndex;

	private boolean ignoreNonDigitCharacters;

	public boolean isValid(final CharSequence value, final ConstraintValidatorContext context) {
		if ( value == null ) {
			return true;
		}

		String valueAsString = value.toString();
		String digitsAsString;
		char checkDigit;
		try {
			digitsAsString = extractVerificationString( valueAsString );
			checkDigit = extractCheckDigit( valueAsString );
		}
		catch (IndexOutOfBoundsException e) {
			return false;
		}
		digitsAsString = stripNonDigitsIfRequired( digitsAsString );

		List digits;
		try {
			digits = extractDigits( digitsAsString );
		}
		catch (NumberFormatException e) {
			return false;
		}

		return this.isCheckDigitValid( digits, checkDigit );
	}

	public abstract boolean isCheckDigitValid(List digits, char checkDigit);

	protected void initialize(int startIndex, int endIndex, int checkDigitIndex, boolean ignoreNonDigitCharacters) {
		this.startIndex = startIndex;
		this.endIndex = endIndex;
		this.checkDigitIndex = checkDigitIndex;
		this.ignoreNonDigitCharacters = ignoreNonDigitCharacters;

		this.validateOptions();
	}

	/**
	 * Returns the numeric {@code int} value of a {@code char}
	 *
	 * @param value the input {@code char} to be parsed
	 *
	 * @return the numeric {@code int} value represented by the character.
	 *
	 * @throws NumberFormatException in case character is not a digit
	 */
	protected int extractDigit(char value) throws NumberFormatException {
		if ( Character.isDigit( value ) ) {
			return Character.digit( value, DEC_RADIX );
		}
		else {
			throw new NumberFormatException("'"+value+"' is not a digit.");
		}
	}

	/**
	 * Parses the {@link String} value as a {@link List} of {@link Integer} objects
	 *
	 * @param value the input string to be parsed
	 *
	 * @return List of {@code Integer} objects.
	 *
	 * @throws NumberFormatException in case any of the characters is not a digit
	 */
	private List extractDigits(final String value) throws NumberFormatException {
		List digits = new ArrayList( value.length() );
		char[] chars = value.toCharArray();
		for ( char c : chars ) {
			digits.add( extractDigit( c ) );
		}
		return digits;
	}

	private boolean validateOptions() {
		if ( this.startIndex < 0 ) {
			throw new IllegalArgumentException("Start index cannot be negative: "+this.startIndex);
		}

		if ( this.endIndex < 0 ) {
			throw new IllegalArgumentException("End index cannot be negative: "+this.endIndex);
		}

		if ( this.startIndex > this.endIndex ) {
			throw new IllegalArgumentException("Invalid Range: "+startIndex+" > "+endIndex);
		}

		if ( this.checkDigitIndex > 0 && this.startIndex <= this.checkDigitIndex && this.endIndex > this.checkDigitIndex ) {
			throw new IllegalArgumentException("A explicitly specified check digit must lie outside the interval: ["+startIndex+", "+endIndex+"].");
		}

		return true;
	}

	private String stripNonDigitsIfRequired(String value) {
		if ( ignoreNonDigitCharacters ) {
			return NUMBERS_ONLY_REGEXP.matcher( value ).replaceAll( "" );
		}
		else {
			return value;
		}
	}

	private String extractVerificationString(String value) throws IndexOutOfBoundsException {
		// the string contains the check digit, just return the digits to verify
		if ( endIndex == Integer.MAX_VALUE ) {
			return value.substring( 0, value.length() - 1 );
		}
		else if ( checkDigitIndex == -1 ) {
			return value.substring( startIndex, endIndex );
		}
		else {
			return value.substring( startIndex, endIndex + 1 );
		}
	}

	private char extractCheckDigit(String value) throws IndexOutOfBoundsException {
		// take last character of string to be validated unless the index is given explicitly
		if ( checkDigitIndex == -1 ) {
			if ( endIndex == Integer.MAX_VALUE ) {
				return value.charAt( value.length() - 1 );
			}
			else {
				return value.charAt( endIndex );
			}
		}
		else {
			return value.charAt( checkDigitIndex );
		}
	}

}