1 files changed, 110 insertions, 0 deletions
diff --git a/java/com/google/gerrit/server/fixes/LineIdentifier.java b/java/com/google/gerrit/server/fixes/LineIdentifier.java
new file mode 100644
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+++ b/java/com/google/gerrit/server/fixes/LineIdentifier.java
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+// 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 java.util.Objects.requireNonNull;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * An identifier of lines in a string. Lines are sequences of characters which are separated by any
+ * Unicode linebreak sequence as defined by the regular expression {@code \R}. If data for several
+ * lines is requested, calls which are ordered according to ascending line numbers are the most
+ * efficient.
+ */
+class LineIdentifier {
+
+  private static final Pattern LINE_SEPARATOR_PATTERN = Pattern.compile("\\R");
+  private final Matcher lineSeparatorMatcher;
+
+  private int nextLineNumber;
+  private int nextLineStartIndex;
+  private int currentLineStartIndex;
+  private int currentLineEndIndex;
+
+  LineIdentifier(String string) {
+    requireNonNull(string);
+    lineSeparatorMatcher = LINE_SEPARATOR_PATTERN.matcher(string);
+    reset();
+  }
+
+  /**
+   * Returns the start index of the indicated line within the given string. Start indices are
+   * zero-based while line numbers are one-based.
+   *
+   * <p><b>Note:</b> Requesting data for several lines is more efficient if those calls occur with
+   * increasing line number.
+   *
+   * @param lineNumber the line whose start index should be determined
+   * @return the start index of the line
+   * @throws StringIndexOutOfBoundsException if the line number is negative, zero or greater than
+   *     the identified number of lines
+   */
+  public int getStartIndexOfLine(int lineNumber) {
+    findLine(lineNumber);
+    return currentLineStartIndex;
+  }
+
+  /**
+   * Returns the length of the indicated line in the given string. The character(s) used to separate
+   * lines aren't included in the count. Line numbers are one-based.
+   *
+   * <p><b>Note:</b> Requesting data for several lines is more efficient if those calls occur with
+   * increasing line number.
+   *
+   * @param lineNumber the line whose length should be determined
+   * @return the length of the line
+   * @throws StringIndexOutOfBoundsException if the line number is negative, zero or greater than
+   *     the identified number of lines
+   */
+  public int getLengthOfLine(int lineNumber) {
+    findLine(lineNumber);
+    return currentLineEndIndex - currentLineStartIndex;
+  }
+
+  private void findLine(int targetLineNumber) {
+    if (targetLineNumber <= 0) {
+      throw new StringIndexOutOfBoundsException("Line number must be positive");
+    }
+    if (targetLineNumber < nextLineNumber) {
+      reset();
+    }
+    while (nextLineNumber < targetLineNumber + 1 && lineSeparatorMatcher.find()) {
+      currentLineStartIndex = nextLineStartIndex;
+      currentLineEndIndex = lineSeparatorMatcher.start();
+      nextLineStartIndex = lineSeparatorMatcher.end();
+      nextLineNumber++;
+    }
+
+    // End of string
+    if (nextLineNumber == targetLineNumber) {
+      currentLineStartIndex = nextLineStartIndex;
+      currentLineEndIndex = lineSeparatorMatcher.regionEnd();
+    }
+    if (nextLineNumber < targetLineNumber) {
+      throw new StringIndexOutOfBoundsException(
+          String.format("Line %d isn't available", targetLineNumber));
+    }
+  }
+
+  private void reset() {
+    nextLineNumber = 1;
+    nextLineStartIndex = 0;
+    currentLineStartIndex = 0;
+    currentLineEndIndex = 0;
+    lineSeparatorMatcher.reset();
+  }
+}