/*
 * Copyright 2012-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.boot.json;

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import org.springframework.util.StringUtils;

Really basic JSON parser for when you have nothing else available. Comes with some
limitations with respect to the JSON specification (e.g. only supports String values),
so users will probably prefer to have a library handle things instead (Jackson or Snake
YAML are supported).
Author:
Dave Syer, Jean de Klerk, Stephane Nicoll
See Also:
JsonParserFactory
Since:
1.2.0/**
 * Really basic JSON parser for when you have nothing else available. Comes with some
 * limitations with respect to the JSON specification (e.g. only supports String values),
 * so users will probably prefer to have a library handle things instead (Jackson or Snake
 * YAML are supported).
 *
 * @author Dave Syer
 * @author Jean de Klerk
 * @author Stephane Nicoll
 * @since 1.2.0
 * @see JsonParserFactory
 */
public class BasicJsonParser extends AbstractJsonParser {

	@Override
	public Map<String, Object> parseMap(String json) {
		return parseMap(json, this::parseMapInternal);
	}

	@Override
	public List<Object> parseList(String json) {
		return parseList(json, this::parseListInternal);
	}

	private List<Object> parseListInternal(String json) {
		List<Object> list = new ArrayList<>();
		json = trimLeadingCharacter(trimTrailingCharacter(json, ']'), '[').trim();
		for (String value : tokenize(json)) {
			list.add(parseInternal(value));
		}
		return list;
	}

	private Object parseInternal(String json) {
		if (json.startsWith("[")) {
			return parseListInternal(json);
		}
		if (json.startsWith("{")) {
			return parseMapInternal(json);
		}
		if (json.startsWith("\"")) {
			return trimTrailingCharacter(trimLeadingCharacter(json, '"'), '"');
		}
		try {
			return Long.valueOf(json);
		}
		catch (NumberFormatException ex) {
			// ignore
		}
		try {
			return Double.valueOf(json);
		}
		catch (NumberFormatException ex) {
			// ignore
		}
		return json;
	}

	private static String trimTrailingCharacter(String string, char c) {
		if (!string.isEmpty() && string.charAt(string.length() - 1) == c) {
			return string.substring(0, string.length() - 1);
		}
		return string;
	}

	private static String trimLeadingCharacter(String string, char c) {
		if (!string.isEmpty() && string.charAt(0) == c) {
			return string.substring(1);
		}
		return string;
	}

	private Map<String, Object> parseMapInternal(String json) {
		Map<String, Object> map = new LinkedHashMap<>();
		json = trimLeadingCharacter(trimTrailingCharacter(json, '}'), '{').trim();
		for (String pair : tokenize(json)) {
			String[] values = StringUtils.trimArrayElements(StringUtils.split(pair, ":"));
			String key = trimLeadingCharacter(trimTrailingCharacter(values[0], '"'), '"');
			Object value = parseInternal(values[1]);
			map.put(key, value);
		}
		return map;
	}

	private List<String> tokenize(String json) {
		List<String> list = new ArrayList<>();
		int index = 0;
		int inObject = 0;
		int inList = 0;
		boolean inValue = false;
		boolean inEscape = false;
		StringBuilder build = new StringBuilder();
		while (index < json.length()) {
			char current = json.charAt(index);
			if (inEscape) {
				build.append(current);
				index++;
				inEscape = false;
				continue;
			}
			if (current == '{') {
				inObject++;
			}
			if (current == '}') {
				inObject--;
			}
			if (current == '[') {
				inList++;
			}
			if (current == ']') {
				inList--;
			}
			if (current == '"') {
				inValue = !inValue;
			}
			if (current == ',' && inObject == 0 && inList == 0 && !inValue) {
				list.add(build.toString());
				build.setLength(0);
			}
			else if (current == '\\') {
				inEscape = true;
			}
			else {
				build.append(current);
			}
			index++;
		}
		if (build.length() > 0) {
			list.add(build.toString().trim());
		}
		return list;
	}

}