package bjc.utils.funcutils;

import java.util.regex.Pattern;

/*
 * Checks if a string would pass Double.parseDouble.
 *
 * Uses a regex from the javadoc for Double.valueOf()
 */
class DoubleMatcher {
	private static final String Digits = "(\\p{Digit}+)";
	private static final String HexDigits = "(\\p{XDigit}+)";
	
	/*
	 * an exponent is 'e' or 'E' followed by an optionally signed decimal
	 * integer.
	 */
	private static final String Exp = "[eE][+-]?" + Digits;

	private static final String fpRegex    = ("[\\x00-\\x20]*" +  // Optional leading "whitespace"
		 "[+-]?(" +         // Optional sign character
		 "NaN|" +           // "NaN" string
		 "Infinity|" +      // "Infinity" string

		 /* A decimal floating-point string representing a finite positive
		  * number without a leading sign has at most five basic pieces:
		  * Digits . Digits ExponentPart FloatTypeSuffix
		  *
		  * Since this method allows integer-only strings as input
		  * in addition to strings of floating-point literals, the
		  * two sub-patterns below are simplifications of the grammar
		  * productions from section 3.10.2 of
		  * The Java™ Language Specification.
		  */

		 /*
		  * Digits ._opt Digits_opt ExponentPart_opt FloatTypeSuffix_opt
		  */
		 "((("+Digits+"(\\.)?("+Digits+"?)("+Exp+")?)|"+

		 /*
		  * . Digits ExponentPart_opt FloatTypeSuffix_opt
		  */
		 "(\\.("+Digits+")("+Exp+")?)|"+

		 /*
		  * Hexadecimal strings
		  */
		 "((" +
		 /*
		  * 0[xX] HexDigits ._opt BinaryExponent FloatTypeSuffix_opt
		  */
		 "(0[xX]" + HexDigits + "(\\.)?)|" +

		 /*
		  * 0[xX] HexDigits_opt . HexDigits BinaryExponent FloatTypeSuffix_opt
		  */
		 "(0[xX]" + HexDigits + "?(\\.)" + HexDigits + ")" +

		 ")[pP][+-]?" + Digits + "))" +
		 "[fFdD]?))" +
		 "[\\x00-\\x20]*"); // Optional trailing "whitespace"

	public static final Pattern floatingLiteral = Pattern.compile("\\A" + fpRegex + "\\Z");
}