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/*
 * Copyright 2003-2012 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
 *
 *     http://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 groovy.json;

import static groovy.json.JsonTokenType.*;
import groovy.io.LineColumnReader;

import java.io.Reader;
import java.io.StringReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * JSON slurper which parses text or reader content into a data structure of lists and maps.
 * 
 * Example usage:
 * 
 * def slurper = new JsonSlurper()
 * def result = slurper.parseText('{"person":{"name":"Guillaume","age":33,"pets":["dog","cat"]}}')
 *
 * assert result.person.name == "Guillaume"
 * assert result.person.age == 33
 * assert result.person.pets.size() == 2
 * assert result.person.pets[0] == "dog"
 * assert result.person.pets[1] == "cat"
 * 
 *
 * @author Guillaume Laforge
 * @since 1.8.0
 */
public class JsonSlurper {

    /**
     * Parse a text representation of a JSON data structure
     *
     * @param text JSON text to parse
     * @return a data structure of lists and maps
     */
    public Object parseText(String text) {
        if (text == null || text.length() == 0) {
            throw new IllegalArgumentException("The JSON input text should neither be null nor empty.");
        }

        return parse(new LineColumnReader(new StringReader(text)));
    }

    /**
     * Parse a JSON data structure from content from a reader
     *
     * @param reader reader over a JSON content
     * @return a data structure of lists and maps
     */
    public Object parse(Reader reader) {
        Object content;

        JsonLexer lexer = new JsonLexer(reader);

        JsonToken token = lexer.nextToken();
        if (token.getType() == OPEN_CURLY) {
            content = parseObject(lexer);
        } else if (token.getType() == OPEN_BRACKET) {
            content = parseArray(lexer);
        } else {
            throw new JsonException(
                    "A JSON payload should start with " + OPEN_CURLY.getLabel() +
                    " or " + OPEN_BRACKET.getLabel() + ".\n" +
                    "Instead, '" + token.getText() + "' was found " +
                    "on line: " + token.getStartLine() + ", " +
                    "column: " + token.getStartColumn()
            );
        }

        return content;
    }

    /**
     * Parse an array from the lexer
     *
     * @param lexer the lexer
     * @return a list of JSON values
     */
    private List parseArray(JsonLexer lexer) {
        List content = new ArrayList();

        JsonToken currentToken;

        for(;;) {
            currentToken = lexer.nextToken();

            if (currentToken == null) {
                throw new JsonException(
                        "Expected a value on line: " + lexer.getReader().getLine() + ", " +
                        "column: " + lexer.getReader().getColumn() + ".\n" +
                        "But got an unterminated array."
                );
            }

            if (currentToken.getType() == OPEN_CURLY) {
                content.add(parseObject(lexer));
            } else if (currentToken.getType() == OPEN_BRACKET) {
                content.add(parseArray(lexer));
            } else if (currentToken.getType().ordinal() >= NULL.ordinal()) {
                content.add(currentToken.getValue());
            } else if (currentToken.getType() == CLOSE_BRACKET) {
                return content;
            } else {
                throw new JsonException(
                        "Expected a value, an array, or an object " +
                        "on line: " + currentToken.getStartLine() + ", " +
                        "column: " + currentToken.getStartColumn() + ".\n" +
                        "But got '" + currentToken.getText() + "' instead."
                );
            }

            currentToken = lexer.nextToken();

            if (currentToken == null) {
                throw new JsonException(
                        "Expected " + CLOSE_BRACKET.getLabel() + " " +
                        "or " + COMMA.getLabel() + " " +
                        "on line: " + lexer.getReader().getLine() + ", " +
                        "column: " + lexer.getReader().getColumn() + ".\n" +
                        "But got an unterminated array."
                );
            }

            // Expect a comma for an upcoming value
            // or a closing bracket for the end of the array
            if (currentToken.getType() == CLOSE_BRACKET) {
                break;
            } else if (currentToken.getType() != COMMA) {
                throw new JsonException(
                        "Expected a value or " + CLOSE_BRACKET.getLabel() + " " +
                        "on line: " + currentToken.getStartLine() + " " +
                        "column: " + currentToken.getStartColumn() + ".\n" +
                        "But got '" + currentToken.getText() + "' instead."
                );
            }
        }

        return content;
    }

    /**
     * Parses an object from the lexer
     *
     * @param lexer the lexer
     * @return a Map representing a JSON object
     */
    private Map parseObject(JsonLexer lexer) {
        Map content = new HashMap();

        JsonToken previousToken = null;
        JsonToken currentToken = null;

        for(;;) {
            currentToken = lexer.nextToken();

            if (currentToken == null) {
                throw new JsonException(
                        "Expected a String key on line: " + lexer.getReader().getLine() + ", " +
                        "column: " + lexer.getReader().getColumn() + ".\n" +
                        "But got an unterminated object."
                );
            }

            // expect a string key, or already a closing curly brace

            if (currentToken.getType() == CLOSE_CURLY) {
                return content;
            } else if (currentToken.getType() != STRING) {
                throw new JsonException(
                        "Expected " + STRING.getLabel() + " key " +
                        "on line: " + currentToken.getStartLine() + ", " +
                        "column: " + currentToken.getStartColumn() + ".\n" +
                        "But got '" + currentToken.getText() + "' instead."
                );
            }

            String mapKey = (String) currentToken.getValue();

            currentToken = lexer.nextToken();

            if (currentToken == null) {
                throw new JsonException(
                        "Expected a " + COLON.getLabel() + " " +
                        "on line: " + lexer.getReader().getLine() + ", " +
                        "column: " + lexer.getReader().getColumn() + ".\n" +
                        "But got an unterminated object."
                );
            }

            // expect a colon between the key and value pair

            if (currentToken.getType() != COLON) {
                throw new JsonException(
                        "Expected " + COLON.getLabel() + " " +
                        "on line: " + currentToken.getStartLine() + ", " +
                        "column: " + currentToken.getStartColumn() + ".\n" +
                        "But got '" + currentToken.getText() +  "' instead."
                );
            }

            currentToken = lexer.nextToken();

            if (currentToken == null) {
                throw new JsonException(
                        "Expected a value " + 
                        "on line: " + lexer.getReader().getLine() + ", " +
                        "column: " + lexer.getReader().getColumn() + ".\n" +
                        "But got an unterminated object."
                );
            }

            // value can be an object, an array, a number, string, boolean or null values

            if (currentToken.getType() == OPEN_CURLY) {
                content.put(mapKey, parseObject(lexer));
            } else if (currentToken.getType() == OPEN_BRACKET) {
                content.put(mapKey, parseArray(lexer));
            } else if (currentToken.getType().ordinal() >= NULL.ordinal()) {
                content.put(mapKey, currentToken.getValue());
            } else {
                throw new JsonException(
                        "Expected a value, an array, or an object " +
                        "on line: " + currentToken.getStartLine() + ", " +
                        "column: " + currentToken.getStartColumn() + ".\n" +
                        "But got '" + currentToken.getText() + "' instead."
                );
            }

            previousToken = currentToken;
            currentToken = lexer.nextToken();

            // premature end of the object

            if (currentToken == null) {
                throw new JsonException(
                        "Expected " + CLOSE_CURLY.getLabel() + " or " + COMMA.getLabel() + " " +
                        "on line: " + previousToken.getEndLine() + ", " +
                        "column: " + previousToken.getEndColumn() + ".\n" +
                        "But got an unterminated object."
                );
            }

            // Expect a comma for an upcoming key/value pair
            // or a closing curly brace for the end of the object
            if (currentToken.getType() == CLOSE_CURLY) {
                break;
            } else if (currentToken.getType() != COMMA) {
                throw new JsonException(
                        "Expected a value or " + CLOSE_CURLY.getLabel() + " " +
                        "on line: " + currentToken.getStartLine() + ", " +
                        "column: " + currentToken.getStartColumn() + ".\n" +
                        "But got '" + currentToken.getText() + "' instead."
                );
            }
        }

        return content;
    }
}