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Common Expression Language Runtime for Java
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// Copyright 2024 Google 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
//
//      https://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 dev.cel.common;

import static com.google.common.base.Preconditions.checkArgument;

import com.google.common.collect.ImmutableList;
import dev.cel.common.annotations.Internal;
import dev.cel.common.internal.CelCodePointArray;
import java.util.List;
import java.util.Optional;

/**
 * Helper methods for common source handling in CEL.
 *
 * CEL Library Internals. Do Not Use.
 */
@Internal
public final class CelSourceHelper {

  /** Extract the snippet text that corresponds to {@code line}. */
  public static Optional getSnippet(CelCodePointArray content, int line) {
    checkArgument(line > 0);
    ImmutableList lineOffsets = content.lineOffsets();
    int start = findLineOffset(lineOffsets, line);
    if (start == -1) {
      return Optional.empty();
    }
    int end = findLineOffset(lineOffsets, line + 1);
    if (end == -1) {
      end = content.size();
    } else {
      end--;
    }
    return Optional.of(end != start ? content.slice(start, end).toString() : "");
  }

  /**
   * Get the line and column in the source expression text for the given code point {@code offset}.
   */
  public static Optional getOffsetLocation(
      CelCodePointArray content, int offset) {
    checkArgument(offset >= 0);
    LineAndOffset lineAndOffset = findLine(content.lineOffsets(), offset);
    return Optional.of(CelSourceLocation.of(lineAndOffset.line, offset - lineAndOffset.offset));
  }

  private static LineAndOffset findLine(List lineOffsets, int offset) {
    int line = 1;
    for (Integer lineOffset : lineOffsets) {
      if (lineOffset > offset) {
        break;
      }
      line++;
    }
    if (line == 1) {
      return new LineAndOffset(line, 0);
    }
    return new LineAndOffset(line, lineOffsets.get(line - 2));
  }

  private static final class LineAndOffset {
    private LineAndOffset(int line, int offset) {
      this.line = line;
      this.offset = offset;
    }

    private final int line;
    private final int offset;
  }

  static int findLineOffset(List lineOffsets, int line) {
    if (line == 1) {
      return 0;
    }
    if (line > 1 && line <= lineOffsets.size()) {
      return lineOffsets.get(line - 2);
    }
    return -1;
  }

  private CelSourceHelper() {}
}