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A set of Java interfaces, which defines the common JSON data behaviors, can be used to decouple programming logic from JSON implementations such as Jackson, Gson, org.json and Jakarta...
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/*
 *
 * Copyright 2020 Wei-Ming Wu
 *
 * 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 com.github.wnameless.json.base;

/**
 * 
 * {@link JsonPrinter} reprints any JSON input into minimal or pretty form. It only uses Java native
 * string processing to generate the output and no additional explicit JSON library is required.
 * 
 * @author Wei-Ming Wu
 *
 */
public final class JsonPrinter {

  private JsonPrinter() {}

  /**
   * Returns a minimal print JSON of any JSON input.
   * 
   * @param json any JSON
   * @return a minimal print JSON
   */
  public static String minimalPrint(String json) {
    if (json == null) new NullPointerException();
    StringBuilder minimalPrintBuilder = new StringBuilder();

    int lookback = -1;
    int backslashCount = 0;
    boolean inQuote = false;
    for (char jsonChar : json.toCharArray()) {
      switch (jsonChar) {
        case '"':
          if (lookback != '\\' || backslashCount % 2 == 0) {
            inQuote = !inQuote;
            minimalPrintBuilder.append(jsonChar);
            break;
          }
        default:
          if (inQuote || !Character.toString(jsonChar).matches("\\s")) {
            minimalPrintBuilder.append(jsonChar);
          }
      }
      if (jsonChar == '\\') {
        backslashCount++;
      } else {
        backslashCount = 0;
      }
      lookback = jsonChar;
    }

    return minimalPrintBuilder.toString();
  }

  /**
   * Returns a pretty print JSON of any JSON input.
   * 
   * @param json any JSON
   * @return a pretty print JSON
   */
  public static String prettyPrint(String json) {
    return prettyPrint(json, "  ");
  }

  /**
   * Returns a pretty print JSON of any JSON input.
   * 
   * @param json any JSON
   * @param indentStr a string to use as an indent
   * @return a pretty print JSON
   */
  public static String prettyPrint(String json, String indentStr) {
    if (json == null) new NullPointerException();
    StringBuilder prettyPrintBuilder = new StringBuilder();

    int lookback = -1;
    int backslashCount = 0;
    int indentLevel = 0;
    boolean inQuote = false;
    boolean inBracket = false;
    for (char jsonChar : json.toCharArray()) {
      switch (jsonChar) {
        case '"':
          if (lookback != '\\' || backslashCount % 2 == 0) {
            inQuote = !inQuote;
            prettyPrintBuilder.append(jsonChar);
            break;
          }
        case '{':
          prettyPrintBuilder.append(jsonChar);
          if (!inQuote) {
            indentLevel++;
            appendNewLine(prettyPrintBuilder, indentLevel, indentStr);
          }
          break;
        case '}':
          if (!inQuote) {
            indentLevel--;
            appendNewLine(prettyPrintBuilder, indentLevel, indentStr);
          }
          prettyPrintBuilder.append(jsonChar);
          break;
        case '[':
          prettyPrintBuilder.append(jsonChar);
          if (!inQuote) {
            inBracket = true;
            prettyPrintBuilder.append(' ');
          }
          break;
        case ']':
          if (!inQuote) {
            inBracket = false;
            prettyPrintBuilder.append(' ');
          }
          prettyPrintBuilder.append(jsonChar);
          break;
        case ',':
          prettyPrintBuilder.append(jsonChar);
          if (!inQuote) {
            if (inBracket) {
              prettyPrintBuilder.append(' ');
            } else {
              appendNewLine(prettyPrintBuilder, indentLevel, indentStr);
            }
          }
          break;
        case ':':
          if (inQuote) {
            prettyPrintBuilder.append(jsonChar);
          } else {
            prettyPrintBuilder.append(' ');
            prettyPrintBuilder.append(jsonChar);
            prettyPrintBuilder.append(' ');
          }
          break;
        default:
          if (inQuote || !Character.toString(jsonChar).matches("\\s")) {
            prettyPrintBuilder.append(jsonChar);
          }
      }
      if (jsonChar == '\\') {
        backslashCount++;
      } else {
        backslashCount = 0;
      }
      lookback = jsonChar;
    }

    return prettyPrintBuilder.toString();
  }

  private static void appendNewLine(StringBuilder stringBuilder, int indentLevel,
      String indentStr) {
    stringBuilder.append('\n');
    for (int i = 0; i < indentLevel; i++) {
      stringBuilder.append(indentStr);
    }
  }

  /**
   * Converts any Java String to the JSON string representation, which is quoted and escaped
   * properly.
   * 
   * @param javaString any Java String
   * @return a representation of JSON string
   */
  public static String toJsonString(String javaString) {
    if (javaString == null || javaString.isEmpty()) {
      return "\"\"";
    }

    StringBuilder sb = new StringBuilder();

    sb.append('"');
    for (int i = 0; i < javaString.length(); i++) {
      char c = javaString.charAt(i);
      switch (c) {
        case '"':
          sb.append('\\');
          sb.append(c);
          break;
        case '\\':
          sb.append("\\\\");
          break;
        case '\b':
          sb.append("\\b");
          break;
        case '\n':
          sb.append("\\n");
          break;
        case '\t':
          sb.append("\\t");
          break;
        case '\f':
          sb.append("\\f");
          break;
        case '\r':
          sb.append("\\r");
          break;
        default:
          sb.append(c);
      }
    }
    sb.append('"');

    return sb.toString();
  }

}