com.lokalized.StringInterpolator Maven / Gradle / Ivy

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/*
 * Copyright 2017 Product Mog LLC.
 *
 * 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.lokalized;

import javax.annotation.Nonnull;
import javax.annotation.concurrent.ThreadSafe;
import java.util.Map;
import java.util.Optional;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import static java.lang.String.format;

/**
 * Merges data into a string using {@code {{placeholder}} syntax}.
 *
 * @author Mark Allen
 */
@ThreadSafe
class StringInterpolator {
  @Nonnull
  private static final Pattern PLACEHOLDER_PATTERN;

  static {
    PLACEHOLDER_PATTERN = Pattern.compile("\\{\\{\\p{Alnum}+}}");
  }

  @Nonnull
  public String interpolate(@Nonnull String string, @Nonnull Map context) {
    Matcher matcher = PLACEHOLDER_PATTERN.matcher(string);

    // Matcher#appendReplacement only accepts StringBuffer, not StringBuilder
    StringBuffer stringBuffer = new StringBuffer();

    while (matcher.find()) {
      String name = matcher.group();
      name = name.substring("{{".length(), name.length() - "}}".length());
      Object value = context.get(name);

      if (value instanceof Optional)
        value = ((Optional) value).orElse(null);

      if (value == null)
        matcher.appendReplacement(stringBuffer, format("{{%s}}", name));
      else
        matcher.appendReplacement(stringBuffer, value == null ? "" : value.toString());
    }

    matcher.appendTail(stringBuffer);

    return stringBuffer.toString();
  }
}