package appeng.util;


import java.math.RoundingMode;
import java.text.DecimalFormat;
import java.text.DecimalFormatSymbols;
import java.text.Format;


/**
 * Converter class to convert a large number into a SI system.
 *
 * @author thatsIch
 * @version rv2
 * @since rv2
 */
public enum ReadableNumberConverter implements ISlimReadableNumberConverter, IWideReadableNumberConverter
{
	INSTANCE;

	/**
	 * Defines the base for a division, non-si standard could be 1024 for kilobytes
	 */
	private static final int DIVISION_BASE = 1000;

	/**
	 * String representation of the sorted postfixes
	 */
	private static final char[] ENCODED_POSTFIXES = "KMGTPE".toCharArray();

	private final Format format;

	/**
	 * Initializes the specific decimal format with special format for negative and positive numbers
	 */
	ReadableNumberConverter()
	{
		final DecimalFormatSymbols symbols = new DecimalFormatSymbols();
		symbols.setDecimalSeparator( '.' );
		final DecimalFormat format = new DecimalFormat( ".#;0.#" );
		format.setDecimalFormatSymbols( symbols );
		format.setRoundingMode( RoundingMode.DOWN );

		this.format = format;
	}

	@Override
	public String toSlimReadableForm( long number )
	{
		return this.toReadableFormRestrictedByWidth( number, 3 );
	}

	/**
	 * restricts a string representation of a number to a specific width
	 *
	 * @param number to be formatted number
	 * @param width  width limitation of the resulting number
	 *
	 * @return formatted number restricted by the width limitation
	 */
	private String toReadableFormRestrictedByWidth( long number, int width )
	{
		assert number >= 0;

		// handles low numbers more efficiently since no format is needed
		final String numberString = Long.toString( number );
		int numberSize = numberString.length();
		if( numberSize <= width )
		{
			return numberString;
		}

		long base = number;
		double last = base * 1000;
		int exponent = -1;
		String postFix = "";

		while( numberSize > width )
		{
			last = base;
			base /= DIVISION_BASE;

			exponent++;

			// adds +1 due to the postfix
			numberSize = Long.toString( base ).length() + 1;
			postFix = String.valueOf( ENCODED_POSTFIXES[exponent] );
		}

		final String withPrecision = this.format.format( last / DIVISION_BASE ) + postFix;
		final String withoutPrecision = Long.toString( base ) + postFix;

		final String slimResult = ( withPrecision.length() <= width ) ? withPrecision : withoutPrecision;

		// post condition
		assert slimResult.length() <= width;

		return slimResult;
	}

	@Override
	public String toWideReadableForm( final long number )
	{
		return this.toReadableFormRestrictedByWidth( number, 4 );
	}
}