/*
 * Copyright (c) 2003, PostgreSQL Global Development Group
 * See the LICENSE file in the project root for more information.
 */

package org.postgresql.core;

import java.io.IOException;

Predicts encoding for error messages based on some heuristics.

For certain languages, it is known how "FATAL" is translated
For Japanese, several common words are hardcoded
Then try various LATIN encodings

/**
 * <p>Predicts encoding for error messages based on some heuristics.</p>
 *
 * <ol>
 * <li>For certain languages, it is known how "FATAL" is translated</li>
 * <li>For Japanese, several common words are hardcoded</li>
 * <li>Then try various LATIN encodings</li>
 * </ol>
 */
public class EncodingPredictor {
  
In certain cases the encoding is not known for sure (e.g. before authentication).
In such cases, backend might send messages in "native to database" encoding,
thus pgjdbc has to guess the encoding nad
/**
   * In certain cases the encoding is not known for sure (e.g. before authentication).
   * In such cases, backend might send messages in "native to database" encoding,
   * thus pgjdbc has to guess the encoding nad
   */
  public static class DecodeResult {
    public final String result;
    public final String encoding; // JVM name

    DecodeResult(String result, String encoding) {
      this.result = result;
      this.encoding = encoding;
    }
  }

  static class Translation {
    public final String fatalText;
    private final String[] texts;
    public final String language;
    public final String[] encodings;

    Translation(String fatalText, String[] texts, String language, String... encodings) {
      this.fatalText = fatalText;
      this.texts = texts;
      this.language = language;
      this.encodings = encodings;
    }
  }

  private static final Translation[] FATAL_TRANSLATIONS =
      new Translation[]{
          new Translation("ВАЖНО", null, "ru", "WIN", "ALT", "KOI8"),
          new Translation("致命错误", null, "zh_CN", "EUC_CN", "GBK", "BIG5"),
          new Translation("KATASTROFALNY", null, "pl", "LATIN2"),
          new Translation("FATALE", null, "it", "LATIN1", "LATIN9"),
          new Translation("FATAL", new String[]{"は存在しません" /* ~ does not exist */,
              "ロール" /* ~ role */, "ユーザ" /* ~ user */}, "ja", "EUC_JP", "SJIS"),
          new Translation(null, null, "fr/de/es/pt_BR", "LATIN1", "LATIN3", "LATIN4", "LATIN5",
              "LATIN7", "LATIN9"),
      };

  public static DecodeResult decode(byte[] bytes, int offset, int length) {
    Encoding defaultEncoding = Encoding.defaultEncoding();
    for (Translation tr : FATAL_TRANSLATIONS) {
      for (String encoding : tr.encodings) {
        Encoding encoder = Encoding.getDatabaseEncoding(encoding);
        if (encoder == defaultEncoding) {
          continue;
        }

        // If there is a translation for "FATAL", then try typical encodings for that language
        if (tr.fatalText != null) {
          byte[] encoded;
          try {
            byte[] tmp = encoder.encode(tr.fatalText);
            encoded = new byte[tmp.length + 2];
            encoded[0] = 'S';
            encoded[encoded.length - 1] = 0;
            System.arraycopy(tmp, 0, encoded, 1, tmp.length);
          } catch (IOException e) {
            continue;// should not happen
          }

          if (!arrayContains(bytes, offset, length, encoded, 0, encoded.length)) {
            continue;
          }
        }

        // No idea how to tell Japanese from Latin languages, thus just hard-code certain Japanese words
        if (tr.texts != null) {
          boolean foundOne = false;
          for (String text : tr.texts) {
            try {
              byte[] textBytes = encoder.encode(text);
              if (arrayContains(bytes, offset, length, textBytes, 0, textBytes.length)) {
                foundOne = true;
                break;
              }
            } catch (IOException e) {
              // do not care, will try other encodings
            }
          }
          if (!foundOne) {
            // Error message does not have key parts, will try other encodings
            continue;
          }
        }

        try {
          String decoded = encoder.decode(bytes, offset, length);
          if (decoded.indexOf(65533) != -1) {
            // bad character in string, try another encoding
            continue;
          }
          return new DecodeResult(decoded, encoder.name());
        } catch (IOException e) {
          // do not care
        }
      }
    }
    return null;
  }

  private static boolean arrayContains(
      byte[] first, int firstOffset, int firstLength,
      byte[] second, int secondOffset, int secondLength
  ) {
    if (firstLength < secondLength) {
      return false;
    }

    for (int i = 0; i < firstLength; i++) {
      for (; i < firstLength && first[firstOffset + i] != second[secondOffset]; i++) {
        // find the first matching byte
      }

      int j = 1;
      for (; j < secondLength && first[firstOffset + i + j] == second[secondOffset + j]; j++) {
        // compare arrays
      }
      if (j == secondLength) {
        return true;
      }
    }
    return false;
  }
}