/*
 * Jooby https://jooby.io
 * Apache License Version 2.0 https://jooby.io/LICENSE.txt
 * Copyright 2014 Edgar Espina
 */
package io.jooby.internal.apt.escape;

import java.io.IOException;
import java.io.StringWriter;
import java.io.UncheckedIOException;
import java.io.Writer;
import java.util.Locale;
import java.util.Objects;

/**
 * An API for translating text. Its core use is to escape and unescape text. Because escaping and
 * unescaping is completely contextual, the API does not present two separate signatures.
 *
 * @since 1.0
 */
abstract class CharSequenceTranslator {

  /** Array containing the hexadecimal alphabet. */
  static final char[] HEX_DIGITS = {
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
  };

  /**
   * Returns an upper case hexadecimal {@code String} for the given character.
   *
   * @param codePoint The code point to convert.
   * @return An upper case hexadecimal {@code String}
   */
  public static String hex(final int codePoint) {
    return Integer.toHexString(codePoint).toUpperCase(Locale.ENGLISH);
  }

  /**
   * Helper for non-Writer usage.
   *
   * @param input CharSequence to be translated
   * @return String output of translation
   */
  public final String translate(final CharSequence input) {
    try {
      final StringWriter writer = new StringWriter(input.length() * 2);
      translate(input, writer);
      return writer.toString();
    } catch (final IOException ioe) {
      // this should never ever happen while writing to a StringWriter
      throw new UncheckedIOException(ioe);
    }
  }

  /**
   * Translate a set of code points, represented by an int index into a CharSequence, into another
   * set of code points. The number of code points consumed must be returned, and the only
   * IOExceptions thrown must be from interacting with the Writer so that the top level API may
   * reliably ignore StringWriter IOExceptions.
   *
   * @param input CharSequence that is being translated
   * @param index int representing the current point of translation
   * @param writer Writer to translate the text to
   * @return int count of code points consumed
   * @throws IOException if and only if the Writer produces an IOException
   */
  public abstract int translate(CharSequence input, int index, Writer writer) throws IOException;

  /**
   * Translate an input onto a Writer. This is intentionally final as its algorithm is tightly
   * coupled with the abstract method of this class.
   *
   * @param input CharSequence that is being translated
   * @param writer Writer to translate the text to
   * @throws IOException if and only if the Writer produces an IOException
   */
  public final void translate(final CharSequence input, final Writer writer) throws IOException {
    Objects.requireNonNull(writer, "The Writer must not be null");
    int pos = 0;
    final int len = input.length();
    while (pos < len) {
      final int consumed = translate(input, pos, writer);
      if (consumed == 0) {
        // inlined implementation of
        // Character.toChars(Character.codePointAt(input, pos))
        // avoids allocating temp char arrays and duplicate checks
        final char c1 = input.charAt(pos);
        writer.write(c1);
        pos++;
        if (Character.isHighSurrogate(c1) && pos < len) {
          final char c2 = input.charAt(pos);
          if (Character.isLowSurrogate(c2)) {
            writer.write(c2);
            pos++;
          }
        }
        continue;
      }
      // contract with translators is that they have to understand code points
      // and they just took care of a surrogate pair
      for (int pt = 0; pt < consumed; pt++) {
        pos += Character.charCount(Character.codePointAt(input, pos));
      }
    }
  }

  /**
   * Helper method to create a merger of this translator with another set of translators. Useful in
   * customizing the standard functionality.
   *
   * @param translators CharSequenceTranslator array of translators to merge with this one
   * @return CharSequenceTranslator merging this translator with the others
   */
  public final CharSequenceTranslator with(final CharSequenceTranslator... translators) {
    final CharSequenceTranslator[] newArray = new CharSequenceTranslator[translators.length + 1];
    newArray[0] = this;
    System.arraycopy(translators, 0, newArray, 1, translators.length);
    return new AggregateTranslator(newArray);
  }
}
