/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.hadoop.hbase.regionserver;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.junit.jupiter.api.Assertions.assertTrue;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellComparatorImpl;
import org.apache.hadoop.hbase.ExtendedCell;
import org.apache.hadoop.hbase.KeyValue;
import org.apache.hadoop.hbase.testclassification.RegionServerTests;
import org.apache.hadoop.hbase.testclassification.SmallTests;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.hbase.util.CollectionBackedScanner;
import org.junit.jupiter.api.Tag;
import org.junit.jupiter.api.Test;

@Tag(RegionServerTests.TAG)
@Tag(SmallTests.TAG)
public class TestKeyValueHeap {

  private byte[] row1 = Bytes.toBytes("row1");
  private byte[] fam1 = Bytes.toBytes("fam1");
  private byte[] col1 = Bytes.toBytes("col1");
  private byte[] data = Bytes.toBytes("data");

  private byte[] row2 = Bytes.toBytes("row2");
  private byte[] fam2 = Bytes.toBytes("fam2");
  private byte[] col2 = Bytes.toBytes("col2");

  private byte[] col3 = Bytes.toBytes("col3");
  private byte[] col4 = Bytes.toBytes("col4");
  private byte[] col5 = Bytes.toBytes("col5");

  // Variable name encoding. kv<row#><fam#><col#>
  ExtendedCell kv111 = new KeyValue(row1, fam1, col1, data);
  ExtendedCell kv112 = new KeyValue(row1, fam1, col2, data);
  ExtendedCell kv113 = new KeyValue(row1, fam1, col3, data);
  ExtendedCell kv114 = new KeyValue(row1, fam1, col4, data);
  ExtendedCell kv115 = new KeyValue(row1, fam1, col5, data);
  ExtendedCell kv121 = new KeyValue(row1, fam2, col1, data);
  ExtendedCell kv122 = new KeyValue(row1, fam2, col2, data);
  ExtendedCell kv211 = new KeyValue(row2, fam1, col1, data);
  ExtendedCell kv212 = new KeyValue(row2, fam1, col2, data);
  ExtendedCell kv213 = new KeyValue(row2, fam1, col3, data);

  TestScanner s1 = new TestScanner(Arrays.asList(kv115, kv211, kv212));
  TestScanner s2 = new TestScanner(Arrays.asList(kv111, kv112));
  TestScanner s3 = new TestScanner(Arrays.asList(kv113, kv114, kv121, kv122, kv213));

  List<KeyValueScanner> scanners = new ArrayList<>(Arrays.asList(s1, s2, s3));

  /*
   * Uses {@code scanners} to build a KeyValueHeap, iterates over it and asserts that returned Cells
   * are same as {@code expected}.
   * @return List of Cells returned from scanners.
   */
  public List<Cell> assertCells(List<Cell> expected, List<KeyValueScanner> scanners)
    throws IOException {
    // Creating KeyValueHeap
    try (KeyValueHeap kvh = new KeyValueHeap(scanners, CellComparatorImpl.COMPARATOR)) {
      List<Cell> actual = new ArrayList<>();
      while (kvh.peek() != null) {
        actual.add(kvh.next());
      }

      assertEquals(expected, actual);
      return actual;
    }
  }

  @Test
  public void testSorted() throws IOException {
    // Cases that need to be checked are:
    // 1. The "smallest" Cell is in the same scanners as current
    // 2. Current scanner gets empty

    List<Cell> expected =
      Arrays.asList(kv111, kv112, kv113, kv114, kv115, kv121, kv122, kv211, kv212, kv213);

    List<Cell> actual = assertCells(expected, scanners);

    // Check if result is sorted according to Comparator
    for (int i = 0; i < actual.size() - 1; i++) {
      int ret = CellComparatorImpl.COMPARATOR.compare(actual.get(i), actual.get(i + 1));
      assertTrue(ret < 0);
    }
  }

  @Test
  public void testSeek() throws IOException {
    // Cases:
    // 1. Seek Cell that is not in scanner
    // 2. Check that smallest that is returned from a seek is correct
    List<Cell> expected = Arrays.asList(kv211);

    // Creating KeyValueHeap
    try (KeyValueHeap kvh = new KeyValueHeap(scanners, CellComparatorImpl.COMPARATOR)) {
      ExtendedCell seekKv = new KeyValue(row2, fam1, null, null);
      kvh.seek(seekKv);

      List<Cell> actual = Arrays.asList(kvh.peek());

      assertEquals(expected, actual, "Expected = " + Arrays.toString(expected.toArray())
        + "\n Actual = " + Arrays.toString(actual.toArray()));
    }
  }

  @Test
  public void testScannerLeak() throws IOException {
    // Test for unclosed scanners (HBASE-1927)

    TestScanner s4 = new TestScanner(new ArrayList<>());
    scanners.add(s4);

    // Creating KeyValueHeap
    try (KeyValueHeap kvh = new KeyValueHeap(scanners, CellComparatorImpl.COMPARATOR)) {
      for (;;) {
        if (kvh.next() == null) {
          break;
        }
      }
      // Once the internal scanners go out of Cells, those will be removed from KVHeap's priority
      // queue and added to a Set for lazy close. The actual close will happen only on
      // KVHeap#close()
      assertEquals(4, kvh.scannersForDelayedClose.size());
      assertTrue(kvh.scannersForDelayedClose.contains(s1));
      assertTrue(kvh.scannersForDelayedClose.contains(s2));
      assertTrue(kvh.scannersForDelayedClose.contains(s3));
      assertTrue(kvh.scannersForDelayedClose.contains(s4));
    }

    for (KeyValueScanner scanner : scanners) {
      assertTrue(((TestScanner) scanner).isClosed());
    }
  }

  @Test
  public void testScannerException() throws IOException {
    // Test for NPE issue when exception happens in scanners (HBASE-13835)

    TestScanner s1 = new SeekTestScanner(Arrays.asList(kv115, kv211, kv212));
    TestScanner s2 = new SeekTestScanner(Arrays.asList(kv111, kv112));
    TestScanner s3 = new SeekTestScanner(Arrays.asList(kv113, kv114, kv121, kv122, kv213));
    TestScanner s4 = new SeekTestScanner(new ArrayList<>());

    List<KeyValueScanner> scanners = new ArrayList<>(Arrays.asList(s1, s2, s3, s4));

    // Creating KeyValueHeap
    try (KeyValueHeap kvh = new KeyValueHeap(scanners, CellComparatorImpl.COMPARATOR)) {
      for (KeyValueScanner scanner : scanners) {
        ((SeekTestScanner) scanner).setRealSeekDone(false);
      }
      // The pollRealKV should throw IOE.
      assertThrows(IOException.class, () -> {
        for (;;) {
          if (kvh.next() == null) {
            break;
          }
        }
      });
    }
    // It implies there is no NPE thrown from kvh.close() if getting here
    for (KeyValueScanner scanner : scanners) {
      // Verify that close is called and only called once for each scanner
      assertTrue(((SeekTestScanner) scanner).isClosed());
      assertEquals(1, ((SeekTestScanner) scanner).getClosedNum());
    }
  }

  @Test
  public void testPriorityId() throws IOException {
    ExtendedCell kv113A = new KeyValue(row1, fam1, col3, Bytes.toBytes("aaa"));
    ExtendedCell kv113B = new KeyValue(row1, fam1, col3, Bytes.toBytes("bbb"));
    TestScanner scan1 = new TestScanner(Arrays.asList(kv111, kv112, kv113A), 1);
    TestScanner scan2 = new TestScanner(Arrays.asList(kv113B), 2);
    List<Cell> expected = Arrays.asList(kv111, kv112, kv113B, kv113A);
    assertCells(expected, Arrays.asList(scan1, scan2));

    scan1 = new TestScanner(Arrays.asList(kv111, kv112, kv113A), 2);
    scan2 = new TestScanner(Arrays.asList(kv113B), 1);
    expected = Arrays.asList(kv111, kv112, kv113A, kv113B);
    assertCells(expected, Arrays.asList(scan1, scan2));
  }

  @Test
  public void testGetFilesRead() throws IOException {
    // Create test scanners with file paths
    Path file1 = new Path("/test/file1");
    Path file2 = new Path("/test/file2");
    Path file3 = new Path("/test/file3");

    FileTrackingScanner scanner1 =
      new FileTrackingScanner(Arrays.asList(kv115, kv211, kv212), file1);
    FileTrackingScanner scanner2 = new FileTrackingScanner(Arrays.asList(kv111, kv112), file2);
    FileTrackingScanner scanner3 =
      new FileTrackingScanner(Arrays.asList(kv113, kv114, kv121, kv122, kv213), file3);

    // Add a non-file-based scanner (e.g., memstore scanner) that doesn't return files
    TestScanner memStoreScanner = new TestScanner(Arrays.asList(kv114));

    List<KeyValueScanner> scanners =
      new ArrayList<>(Arrays.asList(scanner1, scanner2, scanner3, memStoreScanner));

    // Create KeyValueHeap and scan through all cells
    KeyValueHeap keyValueHeap = new KeyValueHeap(scanners, CellComparatorImpl.COMPARATOR);

    // Before closing, should return empty set even after scanning
    // Scan through all cells first
    while (keyValueHeap.peek() != null) {
      keyValueHeap.next();
    }

    // Verify that before closing, files are not returned
    Set<Path> filesReadBeforeClose = keyValueHeap.getFilesRead();
    assertTrue(filesReadBeforeClose.isEmpty(), "Should return empty set before closing heap");
    assertEquals(0, filesReadBeforeClose.size(), "Should have 0 files before closing");

    // Now close the heap
    keyValueHeap.close();

    // After closing, should return all files from file-based scanners only
    // Non-file-based scanners (like memstore) should not contribute files
    Set<Path> filesReadAfterClose = keyValueHeap.getFilesRead();
    assertEquals(3, filesReadAfterClose.size(),
      "Should return set with 3 file paths after closing (excluding non-file scanner)");
    assertTrue(filesReadAfterClose.contains(file1), "Should contain file1");
    assertTrue(filesReadAfterClose.contains(file2), "Should contain file2");
    assertTrue(filesReadAfterClose.contains(file3), "Should contain file3");

    // Verify that non-file-based scanner doesn't contribute any files
    // (memStoreScanner.getFilesRead() should return empty set)
    Set<Path> memStoreFiles = memStoreScanner.getFilesRead();
    assertTrue(memStoreFiles.isEmpty(), "Non-file-based scanner should return empty set");
  }

  private static class TestScanner extends CollectionBackedScanner {
    private boolean closed = false;
    private long scannerOrder = 0;

    public TestScanner(List<ExtendedCell> list) {
      super(list);
    }

    public TestScanner(List<ExtendedCell> list, long scannerOrder) {
      this(list);
      this.scannerOrder = scannerOrder;
    }

    @Override
    public long getScannerOrder() {
      return scannerOrder;
    }

    @Override
    public void close() {
      closed = true;
    }

    public boolean isClosed() {
      return closed;
    }
  }

  private static class SeekTestScanner extends TestScanner {
    private int closedNum = 0;
    private boolean realSeekDone = true;

    public SeekTestScanner(List<ExtendedCell> list) {
      super(list);
    }

    @Override
    public void close() {
      super.close();
      closedNum++;
    }

    public int getClosedNum() {
      return closedNum;
    }

    @Override
    public boolean realSeekDone() {
      return realSeekDone;
    }

    public void setRealSeekDone(boolean done) {
      realSeekDone = done;
    }

    @Override
    public void enforceSeek() throws IOException {
      throw new IOException("enforceSeek must not be called on a " + "non-lazy scanner");
    }
  }

  private static class FileTrackingScanner extends TestScanner {
    private final Path filePath;
    private boolean closed = false;

    public FileTrackingScanner(List<ExtendedCell> list, Path filePath) {
      super(list);
      this.filePath = filePath;
    }

    @Override
    public void close() {
      super.close();
      closed = true;
    }

    @Override
    public Set<Path> getFilesRead() {
      // Only return the file path after the scanner is closed
      return closed ? Collections.singleton(filePath) : Collections.emptySet();
    }
  }
}