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TOVAL comprises a set of java classes for common programming issues. It includes utils for arrays, lists, sets and collections for convenient handling and modification, but also support for mathematic definitions concerning logic (clauses + resolution) together with some algorithms for permutations, powersets and resolution. Additionally it contains a number of types for multisets, matrices with object keys and much more.
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package de.invation.code.toval.misc;

public class FormatUtils {

	private static final double BASE = 1024, KB = BASE, MB = KB * BASE, GB = MB * BASE;

	/**
	 * Format used for representing integers.
	 */
	public static final String INTEGER_FORMAT = "%d";
	/**
	 * Generator-String used for creating formats for representing non-integers.
	 * 

	 * It can be parameterized by the desired precision.
	 * 
	 * @see #getFloatFormat(int)
	 */
	private static final String FLOAT_FORMAT = "%%.%df";
	/**
	 * Format used for representing strings.
	 */
	public static final String STRING_FORMAT = "%s";
	/**
	 * Generator-String used for creating indexed formats.

	 * It can be parameterized by the desired index and the format itself
	 * (integer, float, string).
	 * 
	 * @see #getIndexedFormat(int, String)
	 */
	private static final String INDEXED_FORMAT = "%%%s$%s";
	/**
	 * Generator-String used for creating generator-strings for creating formats
	 * with trim-constraints.

	 * It provides a basis for generating formatted output with a fixed length
	 * and can be parameterized by the desired length.
	 * 
	 * @see #getTrimmedFormat(String, int)
	 */
	private static final String TRIM_BASE_FORMAT = "%%%s%%s";
	/**
	 * Default precision used for generating formats for non-integers.
	 */
	public static final int DEFAULT_PRECISION = 2;

	/**
	 * Returns a String representation of the given object using an appropriate
	 * format.
	 * 
	 * @param o
	 *            Object for which a String representation is desired.
	 * @return String representation of the given object using an appropriate
	 *         format
	 * @see #getFormat(Object)
	 * @see #getFormat(Object, int)
	 */
	public static String format(Object o) {
		return format(o, DEFAULT_PRECISION);
	}

	/**
	 * Returns a String representation of the given object using an appropriate
	 * format and the specified precision in case the object is a non-integer
	 * number.
	 * 
	 * @param o
	 *            Object for which a String representation is desired.
	 * @param precision
	 *            Desired precision
	 * @return String representation of the given object using an appropriate
	 *         format
	 */
	public static String format(Object o, int precision) {
		return String.format(getFormat(o, precision), o);
	}

	/**
	 * Returns a String representation of the given object using an appropriate
	 * format trimmed to the specified length.
	 * 
	 * @param o
	 *            Object for which a String representation is desired.
	 * @param length
	 *            Length of the trimmed string.
	 * @return String representation of the given object using an appropriate
	 *         format
	 * @see #getFormat(Object)
	 * @see #getFormat(Object, int)
	 */
	public static String formatTrimmed(Object o, int length) {
		return formatTrimmed(o, DEFAULT_PRECISION, length);
	}

	/**
	 * Returns a String representation of the given object using an appropriate
	 * format and the specified precision in case the object is a non-integer
	 * number, trimmed to the specified length.
	 * 
	 * @param o
	 *            Object for which a String representation is desired.
	 * @param precision
	 *            Desired precision
	 * @param length
	 *            Length of the trimmed string.
	 * @return String representation of the given object using an appropriate
	 *         format
	 */
	public static String formatTrimmed(Object o, int precision, int length) {
		return String.format(getTrimmedFormat(getFormat(o, precision), length), o);
	}

	/**
	 * Returns a format for non-integers using the default precision.
	 * 
	 * @return The default format for non-integers
	 */
	public static String getFloatFormat() {
		return getFloatFormat(DEFAULT_PRECISION);
	}

	/**
	 * Returns a format for non-integers using the specified precision.
	 * 
	 * @param precision
	 *            Desired precision
	 * @return Format for non-integers with the specified precision
	 */
	public static String getFloatFormat(int precision) {
		if (precision < 0)
			throw new IllegalArgumentException();
		return String.format(FLOAT_FORMAT, precision);
	}

	/**
	 * Returns an appropriate format for the given object.

	 * 
	 * case 1: object is of type Float or Double
	 * -> float format
	 * case 2: object is a whole number -> integer format
	 * case 3: object is of any other type -> string format
	 * 
	 * 
	 * @param o
	 *            Object for which a format has to be assigned
	 * @return An appropriate format for the given object
	 */
	public static String getFormat(Object o) {
		return getFormat(o, DEFAULT_PRECISION);
	}

	/**
	 * Returns an appropriate format for the given object, considering the
	 * specified precision in case the object is a non-integer number.

	 * 
	 * case 1: object is of type Float or Double
	 * -> float format with the specified precision
	 * case 2: object is a whole number -> integer format
	 * case 3: object is of any other type -> string format
	 * 
	 * 
	 * @param o
	 *            Object for which a format has to be assigned
	 * @param precision
	 *            Desired precision
	 * @return An appropriate format for the given object
	 */
	public static String getFormat(Object o, int precision) {
		if (o instanceof Double || o instanceof Float)
			return getFloatFormat(precision);
		if (o instanceof Integer || o instanceof Long || o instanceof Short || o instanceof Byte)
			return INTEGER_FORMAT;
		return STRING_FORMAT;
	}

	/**
	 * Returns an indexed format by placing the specified index before the given
	 * format.
	 * 
	 * @param index
	 *            Desired index for the given format
	 * @param format
	 *            Format to be indexed
	 * @return The format format indexed with index
	 */
	public static String getIndexedFormat(int index, String format) {
		if (index < 1)
			throw new IllegalArgumentException();
		if (format == null)
			throw new NullPointerException();
		if (format.length() == 0)
			throw new IllegalArgumentException();
		return String.format(INDEXED_FORMAT, index, format);
	}

	/**
	 * Extends a given format by additional constraints for trimmed
	 * (length-limited) outputs.

	 * It assumes that the given String is a valid format.
	 * 
	 * @param format
	 *            Format to extend
	 * @param length
	 *            Desired fixed output length for formatted output
	 * @return Extended version of format by trim-constraints
	 */
	public static String getTrimmedFormat(String format, int length) {
		return String.format('%' + String.format(TRIM_BASE_FORMAT, length), format.substring(1));
	}

	public static String formatFileSize(double size) {
		if (size >= GB) {
			return format(size / GB, 2) + " GB";
		}
		if (size >= MB) {
			return format(size / MB, 2) + " MB";
		}
		if (size >= KB) {
			return format(size / KB, 2) + " KB";
		}
		return "" + (int) size + " bytes";
	}

}