/*
 * This file is subject to the license.txt file in the main folder
 * of this project.
 */

package stanhebben.zenscript.parser;

/**
 * Represents a character stream. Suitable for character by character parsing.
 *
 * Used in the regular expression parser.
 * 
 * @author Stan Hebben
 */
public class CharStream {
	private char[] data;
	private int index;

	/**
	 * Constructs a character stream from a data string.
	 *
	 * @param data data string
	 */
	public CharStream(String data) {
		this.data = data.toCharArray();
		index = 0;
	}

	/**
	 * Checks if the next character in the stream equals the specified
	 * character.
	 *
	 * @param ch checked character
	 * @return true if the next character equals the specified character
	 */
	public boolean peek(char ch) {
		if (index == data.length)
			return false;
		return data[index] == ch;
	}

	/**
	 * Processes an optional character. If the next character does not equal the
	 * specified character, nothing will happen.
	 *
	 * @param ch checked character
	 * @return true if the next character equals the specified character
	 */
	public boolean optional(char ch) {
		if (index == data.length)
			return false;
		if (data[index] == ch) {
			index++;
			return true;
		} else {
			return false;
		}
	}

	/**
	 * Processes an optional range of characters. If the next character is not
	 * within the specified bounds, nothing will happen.
	 *
	 * @param from lower character value bound, inclusive
	 * @param to upper character value bound, inclusive
	 * @return the processed character
	 */
	public char optional(char from, char to) {
		if (index == data.length)
			return 0;
		if (data[index] >= from && data[index] <= to) {
			return data[index++];
		} else {
			return 0;
		}
	}

	/**
	 * Processes a required character. If the next character does not equal the
	 * specified character, an IllegalArgumentException is thrown.
	 *
	 * @param ch required character
	 */
	public void required(char ch) {
		if (data[index] != ch) {
			throw new IllegalArgumentException("Unexpected character: " + data[index]);
		}
		index++;
	}

	/**
	 * Processes a required character range. If the next character is not within
	 * the specified bounds, an IllegalArgumentException is thrown.
	 *
	 * @param from lower character value bound, inclusive
	 * @param to upper character value bound, inclusive
	 * @return the processed character
	 */
	public char required(char from, char to) {
		if (data[index] < from || data[index] > to) {
			throw new IllegalArgumentException("Unexpected character: " + data[index]);
		}
		return data[index++];
	}

	/**
	 * Returns the next character in the stream.
	 *
	 * @return the next character
	 */
	public char next() {
		return data[index++];
	}

	/**
	 * Checks if the end of the stream has been reached.
	 *
	 * @return true if there are more characters in the stream
	 */
	public boolean hasMore() {
		return index < data.length;
	}
}