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A set of utilities for classes of the java.lang and the java.util packages.
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/*
 * Copyright 2021 Objectos Software LTDA.
 *
 * Reprodução parcial ou total proibida.
 */
package br.com.objectos.lang;

import static br.com.objectos.lang.Lang.checkNotNull;

abstract class ToJava {

  static final ToJava TO_JAVA_IDENTIFIER = new ToJavaIdentifier();

  static final ToJava TO_JAVA_UPPER_NAME = new ToJavaName(State.UPPER_NAME_START);

  static final ToJava TO_JAVA_VARIABLE_NAME = new ToJavaName(State.VARIABLE_NAME_START);

  private final State startingState;

  ToJava(State startingState) {
    this.startingState = startingState;
  }

  public final String apply(String string) {
    checkNotNull(string, "string == null");

    if (string.isEmpty()) {
      return "";
    }

    State state;
    state = startingState;

    int[] points;
    points = Strings.toCodePoints(string);

    StringBuilder result;
    result = new StringBuilder(points.length);

    for (int point : points) {
      state = consume(state, point, result);
    }

    return result.toString();
  }

  abstract State consume(State state, int point, StringBuilder result);

  private enum State {

    IDENTIFIER_PART,

    IDENTIFIER_START,

    NAME_PART,

    NAME_UPPER,

    UPPER_NAME_START,

    VARIABLE_NAME_START;

  }

  private static class ToJavaIdentifier extends ToJava {

    ToJavaIdentifier() {
      super(State.IDENTIFIER_START);
    }

    @Override
    final State consume(State state, int point, StringBuilder result) {
      switch (state) {
        case IDENTIFIER_PART:
          if (Character.isJavaIdentifierPart(point)) {
            result.appendCodePoint(point);
          }

          return state;
        case IDENTIFIER_START:
          if (Character.isJavaIdentifierStart(point)) {
            result.appendCodePoint(point);

            return State.IDENTIFIER_PART;
          } else {
            return state;
          }
        default:
          throw new UnsupportedOperationException("Implement me @ " + state);
      }
    }

  }

  private static class ToJavaName extends ToJava {

    ToJavaName(State startingState) {
      super(startingState);
    }

    @Override
    final State consume(State state, int point, StringBuilder result) {
      int converted;

      switch (state) {
        case UPPER_NAME_START:
          if (Character.isJavaIdentifierStart(point)) {
            converted = Character.toUpperCase(point);

            result.appendCodePoint(converted);

            return State.NAME_PART;
          } else {
            return state;
          }
        case NAME_PART:
          if (Character.isJavaIdentifierPart(point)) {
            result.appendCodePoint(point);

            return state;
          } else {
            return State.NAME_UPPER;
          }
        case NAME_UPPER:
          if (Character.isJavaIdentifierPart(point)) {
            converted = Character.toUpperCase(point);

            result.appendCodePoint(converted);

            return State.NAME_PART;
          } else {
            return state;
          }
        case VARIABLE_NAME_START:
          if (Character.isJavaIdentifierStart(point)) {
            converted = Character.toLowerCase(point);

            result.appendCodePoint(converted);

            return State.NAME_PART;
          } else {
            return state;
          }
        default:
          throw new UnsupportedOperationException("Implement me @ " + state);
      }
    }

  }

}