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This is the api to interact with Concourse, a schemaless and distributed version control database with optimistic availability, serializable transactions and full-text search. Concourse provides a more intuitive approach to data management that is easy to deploy, access and scale with minimal tuning while also maintaining the referential integrity and ACID characteristics of traditional database systems.

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/*
 * The MIT License (MIT)
 * 
 * Copyright (c) 2013 Jeff Nelson, Cinchapi Software Collective
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.cinchapi.concourse.util;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Random;

/**
 * A random string generator.
 * 
 * @see http
 *      ://stackoverflow.com/questions/41107/how-to-generate-a-random-alpha-
 *      numeric -string-in-java
 * @author jnelson
 */
public class RandomStringGenerator {

	Random random;

	private static final int MAX_DISTRIBUTION_OF_SPACE_CHARS = 5;
	private static final int MAX_RANDOM_STRING_LENGTH = 100;
	private static final char spaceChar = (char) ' ';
	private static final Character[] digits = new Character[10];
	private static final Character[] letters = new Character[26];

	static {
		for (int i = 0; i < digits.length; i++) {
			digits[i] = (char) ('0' + i);
		}
		for (int i = 0; i < letters.length; i++) {
			letters[i] = (char) ('a' + i);
		}
	}

	/**
	 * Create a new generator with a seed that is very likely to be distinct
	 * from any other invocation of this constructor.
	 */
	public RandomStringGenerator() {
		this(0);
	}

	/**
	 * Create a new generator with the specified seed.
	 * 
	 * @param seed
	 */
	public RandomStringGenerator(long seed) {
		random = seed == 0 ? new Random() : new Random(seed);
	}

	/**
	 * Generate a string of random length and no digits
	 * 
	 * @return random string
	 */
	public String nextString() {
		return nextString(random.nextInt(MAX_RANDOM_STRING_LENGTH) + 1);
	}

	/**
	 * Generate a string of the specified length and no digits
	 * 
	 * @param length
	 * @return random string
	 */
	public String nextString(int length) {
		Character[] spaces = new Character[random
				.nextInt(MAX_DISTRIBUTION_OF_SPACE_CHARS)];
		for (int i = 0; i < spaces.length; i++) {
			spaces[i] = spaceChar;
		}
		ArrayList source = new ArrayList();
		source.addAll(Arrays.asList(letters));
		source.addAll(Arrays.asList(spaces));
		Collections.shuffle(source);
		return build(length, source);
	}

	/**
	 * Generate a string of random length, possibly with digits
	 * 
	 * @return random string
	 */
	public String nextStringAllowDigits() {
		return nextStringAllowDigits(random.nextInt(MAX_RANDOM_STRING_LENGTH) + 1);
	}

	/**
	 * Generate a string of the specified length, possibly with digits
	 * 
	 * @param length
	 * @return random string
	 */
	public String nextStringAllowDigits(int length) {
		Character[] spaces = new Character[random
				.nextInt(MAX_DISTRIBUTION_OF_SPACE_CHARS)];
		for (int i = 0; i < spaces.length; i++) {
			spaces[i] = spaceChar;
		}
		ArrayList source = new ArrayList();
		source.addAll(Arrays.asList(letters));
		source.addAll(Arrays.asList(digits));
		source.addAll(Arrays.asList(spaces));
		Collections.shuffle(source);
		return build(length, source);
	}

	/**
	 * Build a random string of {@code length} using the characters in
	 * {@code source}
	 * 
	 * @param length
	 * @param source
	 * @return random string
	 */
	private String build(int length, List source) {
		if(length < 1) {
			throw new IllegalArgumentException(
					"Cannot generate a string with fewer than 1 characters.");
		}
		StringBuilder builder = new StringBuilder();
		for (int i = 0; i < length; i++) {
			int index = random.nextInt(source.size());
			builder.append(source.get(index));
		}
		return builder.toString().trim();
	}

}