/*******************************************************************************
 * Copyright (c) 2009 IBM Corporation and others All rights reserved. This
 * program and the accompanying materials are made available under the terms of
 * the Eclipse Public License v1.0 which accompanies this distribution, and is
 * available at http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors: IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.e4.pde.internal.webui;

import java.math.BigDecimal;
import java.text.CharacterIterator;
import java.text.StringCharacterIterator;
import java.util.*;

// JSON <--> Java
//------------------
// string <--> java.lang.String
// number <--> java.math.Number (BigDecimal)
// object <--> java.util.Map (HashMap)
// array <--> java.util.Collection (ArrayList)
// true <--> java.lang.Boolean.TRUE
// false <--> java.lang.Boolean.FALSE
// null <--> null

public class JSONUtil {
	private static final String EMPTY_STRING = ""; //$NON-NLS-1$
	private static final String NULL = "null"; //$NON-NLS-1$

	public static Object read(String jsonString) {
		return parse(new StringCharacterIterator(jsonString));
	}

	public static String write(Object jsonObject) {
		StringBuffer buffer = new StringBuffer();
		writeValue(jsonObject, buffer);
		return buffer.toString();
	}

	private static RuntimeException error(String message, CharacterIterator it) {
		return new IllegalStateException("[" + it.getIndex() + "] " + message); //$NON-NLS-1$//$NON-NLS-2$
	}

	private static RuntimeException error(String message) {
		return new IllegalStateException(message);
	}

	private static Object parse(CharacterIterator it) {
		parseWhitespace(it);
		Object result = parseValue(it);
		parseWhitespace(it);

		if (it.current() != CharacterIterator.DONE)
			throw error("should be done", it); //$NON-NLS-1$
		return result;
	}

	private static void parseWhitespace(CharacterIterator it) {
		char c = it.current();
		while (Character.isWhitespace(c))
			c = it.next();
	}

	private static Object parseValue(CharacterIterator it) {
		switch (it.current()) {
			case '{' :
				return parseObject(it);
			case '[' :
				return parseArray(it);
			case '"' :
				return parseString(it);
			case '-' :
			case '0' :
			case '1' :
			case '2' :
			case '3' :
			case '4' :
			case '5' :
			case '6' :
			case '7' :
			case '8' :
			case '9' :
				return parseNumber(it);
			case 't' :
				parseText(Boolean.TRUE.toString(), it);
				return Boolean.TRUE;
			case 'f' :
				parseText(Boolean.FALSE.toString(), it);
				return Boolean.FALSE;
			case 'n' :
				parseText(NULL, it);
				return null;
		}
		throw error("Bad JSON starting character '" + it.current() + "'", it); //$NON-NLS-1$ //$NON-NLS-2$;
	}

	private static Map parseObject(CharacterIterator it) {
		it.next();
		parseWhitespace(it);
		if (it.current() == '}') {
			it.next();
			return Collections.EMPTY_MAP;
		}

		Map map = new HashMap();
		while (true) {
			if (it.current() != '"')
				throw error("expected a string start '\"' but was '" + it.current() + "'", it); //$NON-NLS-1$ //$NON-NLS-2$
			String key = parseString(it);
			if (map.containsKey(key))
				throw error("' already defined" + "key '" + key, it); //$NON-NLS-1$ //$NON-NLS-2$
			parseWhitespace(it);
			if (it.current() != ':')
				throw error("expected a pair separator ':' but was '" + it.current() + "'", it); //$NON-NLS-1$ //$NON-NLS-2$
			it.next();
			parseWhitespace(it);
			Object value = parseValue(it);
			map.put(key, value);
			parseWhitespace(it);
			if (it.current() == ',') {
				it.next();
				parseWhitespace(it);
				continue;
			}

			if (it.current() != '}')
				throw error("expected an object close '}' but was '" + it.current() + "'", it); //$NON-NLS-1$ //$NON-NLS-2$
			break;
		}
		it.next();
		return map;
	}

	private static List parseArray(CharacterIterator it) {
		it.next();
		parseWhitespace(it);
		if (it.current() == ']') {
			it.next();
			return Collections.EMPTY_LIST;
		}

		List list = new ArrayList();
		while (true) {
			Object value = parseValue(it);
			list.add(value);
			parseWhitespace(it);
			if (it.current() == ',') {
				it.next();
				parseWhitespace(it);
				continue;
			}

			if (it.current() != ']')
				throw error("expected an array close ']' but was '" + it.current() + "'", it); //$NON-NLS-1$ //$NON-NLS-2$
			break;
		}
		it.next();
		return list;
	}

	private static void parseText(String string, CharacterIterator it) {
		int length = string.length();
		char c = it.current();
		for (int i = 0; i < length; i++) {
			if (c != string.charAt(i))
				throw error("expected to parse '" + string + "' but character " + (i + 1) + " was '" + c + "'", it); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$ //$NON-NLS-4$;
			c = it.next();
		}
	}

	private static Object parseNumber(CharacterIterator it) {
		StringBuffer buffer = new StringBuffer();
		char c = it.current();
		while (Character.isDigit(c) || c == '-' || c == '+' || c == '.' || c == 'e' || c == 'E') {
			buffer.append(c);
			c = it.next();
		}
		try {
			return new BigDecimal(buffer.toString());
		} catch (NumberFormatException e) {
			throw error("expected a number but was '" + buffer.toString() + "'", it); //$NON-NLS-1$ //$NON-NLS-2$;
		}
	}

	private static String parseString(CharacterIterator it) {
		char c = it.next();
		if (c == '"') {
			it.next();
			return EMPTY_STRING;
		}
		StringBuffer buffer = new StringBuffer();
		while (c != '"') {
			if (Character.isISOControl(c))
				throw error("illegal iso control character: '" + Integer.toHexString(c) + "'", it); //$NON-NLS-1$ //$NON-NLS-2$);

			if (c == '\\') {
				c = it.next();
				switch (c) {
					case '"' :
					case '\\' :
					case '/' :
						buffer.append(c);
						break;
					case 'b' :
						buffer.append('\b');
						break;
					case 'f' :
						buffer.append('\f');
						break;
					case 'n' :
						buffer.append('\n');
						break;
					case 'r' :
						buffer.append('\r');
						break;
					case 't' :
						buffer.append('\t');
						break;
					case 'u' :
						StringBuffer unicode = new StringBuffer(4);
						for (int i = 0; i < 4; i++) {
							unicode.append(it.next());
						}
						try {
							buffer.append((char) Integer.parseInt(unicode.toString(), 16));
						} catch (NumberFormatException e) {
							throw error("expected a unicode hex number but was '" + unicode.toString() + "'", it); //$NON-NLS-1$ //$NON-NLS-2$););
						}
						break;
					default :
						throw error("illegal escape character '" + c + "'", it); //$NON-NLS-1$ //$NON-NLS-2$););
				}
			} else
				buffer.append(c);

			c = it.next();
		}
		c = it.next();
		return buffer.toString();
	}

	private static void writeValue(Object value, StringBuffer buffer) {
		if (value == null)
			buffer.append(NULL);
		else if (value instanceof Boolean || value instanceof Number)
			buffer.append(value.toString());
		else if (value instanceof String)
			writeString((String) value, buffer);
		else if (value instanceof Collection)
			writeArray((Collection) value, buffer);
		else if (value instanceof Map)
			writeObject((Map) value, buffer);
		else
			throw error("Unexpected object instance type was '" + value.getClass().getName() + "'"); //$NON-NLS-1$ //$NON-NLS-2$););
	}

	private static void writeObject(Map map, StringBuffer buffer) {
		buffer.append('{');
		for (Iterator iterator = map.keySet().iterator(); iterator.hasNext();) {
			Object key = iterator.next();
			if (!(key instanceof String))
				throw error("Map keys must be an instance of String but was '" + key.getClass().getName() + "'"); //$NON-NLS-1$ //$NON-NLS-2$););
			writeString((String) key, buffer);
			buffer.append(':');
			writeValue(map.get(key), buffer);
			buffer.append(',');
		}
		if (buffer.charAt(buffer.length() - 1) == ',')
			buffer.setCharAt(buffer.length() - 1, '}');
		else
			buffer.append('}');
	}

	private static void writeArray(Collection collection, StringBuffer buffer) {
		buffer.append('[');
		for (Iterator iterator = collection.iterator(); iterator.hasNext();) {
			writeValue(iterator.next(), buffer);
			buffer.append(',');
		}
		if (buffer.charAt(buffer.length() - 1) == ',')
			buffer.setCharAt(buffer.length() - 1, ']');
		else
			buffer.append(']');
	}

	private static void writeString(String string, StringBuffer buffer) {
		buffer.append('"');
		int length = string.length();
		for (int i = 0; i < length; i++) {
			char c = string.charAt(i);
			switch (c) {
				case '"' :
				case '\\' :
				case '/' :
					buffer.append('\\');
					buffer.append(c);
					break;
				case '\b' :
					buffer.append("\\b"); //$NON-NLS-1$
					break;
				case '\f' :
					buffer.append("\\f"); //$NON-NLS-1$
					break;
				case '\n' :
					buffer.append("\\n"); //$NON-NLS-1$
					break;
				case '\r' :
					buffer.append("\\r"); //$NON-NLS-1$
					break;
				case '\t' :
					buffer.append("\\t"); //$NON-NLS-1$
					break;
				default :
					if (Character.isISOControl(c)) {
						buffer.append("\\u"); //$NON-NLS-1$
						String hexString = Integer.toHexString(c);
						for (int j = hexString.length(); j < 4; j++)
							buffer.append('0');
						buffer.append(hexString);
					} else
						buffer.append(c);
			}
		}
		buffer.append('"');
	}
}