package bjc.dicelang.v2;

import java.util.regex.Pattern;

/**
 * Checks if a string would pass Double.parseDouble.
 *
 * Uses a regex from the javadoc for Double.valueOf()
 */
public 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(fpRegex);

}