1 files changed, 77 insertions, 0 deletions
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/fixes/StringModifier.java b/gerrit-server/src/main/java/com/google/gerrit/server/fixes/StringModifier.java
new file mode 100644
index 0000000000..ccd40b3d4f
--- /dev/null
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/fixes/StringModifier.java
@@ -0,0 +1,77 @@
+// Copyright (C) 2017 The Android Open Source Project
+//
+// 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.google.gerrit.server.fixes;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * A modifier of a string. It allows to replace multiple parts of a string by indicating those parts
+ * with indices based on the unmodified string. There is one limitation though: Replacements which
+ * affect lower indices of the string must be specified before replacements for higher indices.
+ */
+class StringModifier {
+
+  private final StringBuilder stringBuilder;
+
+  private int characterShift = 0;
+  private int previousEndOffset = Integer.MIN_VALUE;
+
+  StringModifier(String string) {
+    checkNotNull(string, "string must not be null");
+    stringBuilder = new StringBuilder(string);
+  }
+
+  /**
+   * Replaces part of the string with another content. When called multiple times, the calls must be
+   * ordered according to increasing start indices. Overlapping replacement regions aren't
+   * supported.
+   *
+   * @param startIndex the beginning index in the unmodified string (inclusive)
+   * @param endIndex the ending index in the unmodified string (exclusive)
+   * @param replacement the string which should be used instead of the original content
+   * @throws StringIndexOutOfBoundsException if the start index is smaller than the end index of a
+   *     previous call of this method
+   */
+  public void replace(int startIndex, int endIndex, String replacement) {
+    checkNotNull(replacement, "replacement string must not be null");
+    if (previousEndOffset > startIndex) {
+      throw new StringIndexOutOfBoundsException(
+          String.format(
+              "Not supported to replace the content starting at index %s after previous "
+                  + "replacement which ended at index %s",
+              startIndex, previousEndOffset));
+    }
+    int shiftedStartIndex = startIndex + characterShift;
+    int shiftedEndIndex = endIndex + characterShift;
+    if (shiftedEndIndex > stringBuilder.length()) {
+      throw new StringIndexOutOfBoundsException(
+          String.format("end %s > length %s", shiftedEndIndex, stringBuilder.length()));
+    }
+    stringBuilder.replace(shiftedStartIndex, shiftedEndIndex, replacement);
+
+    int replacedContentLength = endIndex - startIndex;
+    characterShift += replacement.length() - replacedContentLength;
+    previousEndOffset = endIndex;
+  }
+
+  /**
+   * Returns the modified string including all specified replacements.
+   *
+   * @return the modified string
+   */
+  public String getResult() {
+    return stringBuilder.toString();
+  }
+}