/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the "Elastic License
 * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
 * Public License v 1"; you may not use this file except in compliance with, at
 * your election, the "Elastic License 2.0", the "GNU Affero General Public
 * License v3.0 only", or the "Server Side Public License, v 1".
 */
package org.elasticsearch.watcher;

import org.apache.lucene.tests.util.LuceneTestCase;
import org.elasticsearch.core.IOUtils;
import org.elasticsearch.test.ESTestCase;

import java.io.BufferedWriter;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.nio.file.attribute.FileTime;
import java.util.ArrayList;
import java.util.List;

import static org.hamcrest.Matchers.contains;
import static org.hamcrest.Matchers.containsInAnyOrder;
import static org.hamcrest.Matchers.empty;
import static org.hamcrest.Matchers.equalTo;
import static org.hamcrest.Matchers.hasSize;

@LuceneTestCase.SuppressFileSystems("ExtrasFS")
public class FileWatcherTests extends ESTestCase {
    private class RecordingChangeListener implements FileChangesListener {
        private Path rootDir;

        private RecordingChangeListener(Path rootDir) {
            this.rootDir = rootDir;
        }

        private String getRelativeFileName(Path file) {
            return rootDir.toUri().relativize(file.toUri()).getPath();
        }

        private List<String> notifications = new ArrayList<>();

        @Override
        public void onFileInit(Path file) {
            notifications.add("onFileInit: " + getRelativeFileName(file));
        }

        @Override
        public void onDirectoryInit(Path file) {
            notifications.add("onDirectoryInit: " + getRelativeFileName(file));
        }

        @Override
        public void onFileCreated(Path file) {
            notifications.add("onFileCreated: " + getRelativeFileName(file));
        }

        @Override
        public void onFileDeleted(Path file) {
            notifications.add("onFileDeleted: " + getRelativeFileName(file));
        }

        @Override
        public void onFileChanged(Path file) {
            notifications.add("onFileChanged: " + getRelativeFileName(file));
        }

        @Override
        public void onDirectoryCreated(Path file) {
            notifications.add("onDirectoryCreated: " + getRelativeFileName(file));
        }

        @Override
        public void onDirectoryDeleted(Path file) {
            notifications.add("onDirectoryDeleted: " + getRelativeFileName(file));
        }

        public List<String> notifications() {
            return notifications;
        }
    }

    public void testSimpleFileOperations() throws IOException {

        Path tempDir = createTempDir();
        RecordingChangeListener changes = new RecordingChangeListener(tempDir);
        Path testFile = tempDir.resolve("test.txt");
        touch(testFile);
        FileWatcher fileWatcher = new FileWatcher(testFile);
        fileWatcher.addListener(changes);
        fileWatcher.init();
        assertThat(changes.notifications(), contains(equalTo("onFileInit: test.txt")));

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), hasSize(0));

        append("Test", testFile, Charset.defaultCharset());
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), contains(equalTo("onFileChanged: test.txt")));

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), hasSize(0));

        // change modification date, but not contents [we set the time in the future to guarantee a change]
        Files.setLastModifiedTime(testFile, FileTime.fromMillis(System.currentTimeMillis() + 1));
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), contains(equalTo("onFileChanged: test.txt")));

        changes.notifications().clear();
        Files.delete(testFile);
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), contains(equalTo("onFileDeleted: test.txt")));
    }

    public void testSimpleFileOperationsWithContentChecking() throws IOException {
        Path tempDir = createTempDir();
        RecordingChangeListener changes = new RecordingChangeListener(tempDir);
        Path testFile = tempDir.resolve("test.txt");
        touch(testFile);
        FileWatcher fileWatcher = new FileWatcher(testFile, true);
        fileWatcher.addListener(changes);
        fileWatcher.init();
        assertThat(changes.notifications(), contains(equalTo("onFileInit: test.txt")));

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), empty());

        append("Test", testFile, Charset.defaultCharset());
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), contains(equalTo("onFileChanged: test.txt")));

        changes.notifications().clear();

        // change modification date, but not contents
        Files.setLastModifiedTime(testFile, FileTime.fromMillis(System.currentTimeMillis() + 1));
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), empty());

        changes.notifications().clear();

        // change modification date again, but not contents
        Files.setLastModifiedTime(testFile, FileTime.fromMillis(System.currentTimeMillis() + 2));
        fileWatcher.checkAndNotify();
        // This will not trigger a notification because the hash was calculated last time
        assertThat(changes.notifications(), empty());

        // Change file length without changing modification time
        final FileTime modifiedTime = Files.getLastModifiedTime(testFile);
        append("Modified", testFile, Charset.defaultCharset());
        Files.setLastModifiedTime(testFile, modifiedTime);

        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), contains(equalTo("onFileChanged: test.txt")));

        changes.notifications().clear();
        Files.delete(testFile);
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), contains(equalTo("onFileDeleted: test.txt")));
    }

    public void testSimpleDirectoryOperations() throws IOException {
        Path tempDir = createTempDir();
        RecordingChangeListener changes = new RecordingChangeListener(tempDir);
        Path testDir = tempDir.resolve("test-dir");
        Files.createDirectories(testDir);
        touch(testDir.resolve("test.txt"));
        touch(testDir.resolve("test0.txt"));

        FileWatcher fileWatcher = new FileWatcher(testDir);
        fileWatcher.addListener(changes);
        fileWatcher.init();
        assertThat(
            changes.notifications(),
            contains(
                equalTo("onDirectoryInit: test-dir/"),
                equalTo("onFileInit: test-dir/test.txt"),
                equalTo("onFileInit: test-dir/test0.txt")
            )
        );

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), hasSize(0));

        for (int i = 0; i < 4; i++) {
            touch(testDir.resolve("test" + i + ".txt"));
        }
        // Make sure that first file is modified
        append("Test", testDir.resolve("test0.txt"), Charset.defaultCharset());

        fileWatcher.checkAndNotify();
        assertThat(
            changes.notifications(),
            contains(
                equalTo("onFileChanged: test-dir/test0.txt"),
                equalTo("onFileCreated: test-dir/test1.txt"),
                equalTo("onFileCreated: test-dir/test2.txt"),
                equalTo("onFileCreated: test-dir/test3.txt")
            )
        );

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), hasSize(0));

        Files.delete(testDir.resolve("test1.txt"));
        Files.delete(testDir.resolve("test2.txt"));

        fileWatcher.checkAndNotify();
        assertThat(
            changes.notifications(),
            contains(equalTo("onFileDeleted: test-dir/test1.txt"), equalTo("onFileDeleted: test-dir/test2.txt"))
        );

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), hasSize(0));

        Files.delete(testDir.resolve("test0.txt"));
        touch(testDir.resolve("test2.txt"));
        touch(testDir.resolve("test4.txt"));
        fileWatcher.checkAndNotify();

        assertThat(
            changes.notifications(),
            contains(
                equalTo("onFileDeleted: test-dir/test0.txt"),
                equalTo("onFileCreated: test-dir/test2.txt"),
                equalTo("onFileCreated: test-dir/test4.txt")
            )
        );

        changes.notifications().clear();

        Files.delete(testDir.resolve("test3.txt"));
        Files.delete(testDir.resolve("test4.txt"));
        fileWatcher.checkAndNotify();
        assertThat(
            changes.notifications(),
            contains(equalTo("onFileDeleted: test-dir/test3.txt"), equalTo("onFileDeleted: test-dir/test4.txt"))
        );

        changes.notifications().clear();
        if (Files.exists(testDir)) {
            IOUtils.rm(testDir);
        }
        fileWatcher.checkAndNotify();

        assertThat(
            changes.notifications(),
            contains(
                equalTo("onFileDeleted: test-dir/test.txt"),
                equalTo("onFileDeleted: test-dir/test2.txt"),
                equalTo("onDirectoryDeleted: test-dir")
            )
        );

    }

    public void testSimpleDirectoryOperationsWithContentChecking() throws IOException {

        final long startTime = System.currentTimeMillis();

        Path tempDir = createTempDir();
        RecordingChangeListener changes = new RecordingChangeListener(tempDir);
        Path testDir = tempDir.resolve("test-dir");
        Files.createDirectories(testDir);
        for (String fileName : List.of("test1.txt", "test2.txt", "test3.txt", "test4.txt")) {
            Files.writeString(testDir.resolve(fileName), "initial", StandardCharsets.UTF_8);
        }

        FileWatcher fileWatcher = new FileWatcher(testDir, true);
        fileWatcher.addListener(changes);
        fileWatcher.init();
        assertThat(
            changes.notifications(),
            contains(
                equalTo("onDirectoryInit: test-dir/"),
                equalTo("onFileInit: test-dir/test1.txt"),
                equalTo("onFileInit: test-dir/test2.txt"),
                equalTo("onFileInit: test-dir/test3.txt"),
                equalTo("onFileInit: test-dir/test4.txt")
            )
        );

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), hasSize(0));

        // Modify the length of file #1
        append("Test-1", testDir.resolve("test1.txt"), Charset.defaultCharset());

        // Change lastModified on file #2 (set it to before this test started so there's no chance of accidental matching)
        // However the contents haven't changed, so it won't be notified
        Files.setLastModifiedTime(testDir.resolve("test2.txt"), FileTime.fromMillis(startTime - 100));

        // Add a new file
        Files.writeString(testDir.resolve("test5.txt"), "abc", StandardCharsets.UTF_8);

        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), containsInAnyOrder("onFileChanged: test-dir/test1.txt", "onFileCreated: test-dir/test5.txt"));

        // Change file #2 but don't change the size
        Files.writeString(testDir.resolve("test2.txt"), "changed", StandardCharsets.UTF_8);
        // Change lastModified on file #3 (newer than the last update, but still before the test started)
        // But no change to contents, so no notification
        Files.setLastModifiedTime(testDir.resolve("test3.txt"), FileTime.fromMillis(startTime - 50));

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), containsInAnyOrder(equalTo("onFileChanged: test-dir/test2.txt")));

        // change the contents of files #2 (change in size) and #3 (same size)
        Files.writeString(testDir.resolve("test2.txt"), "new contents", StandardCharsets.UTF_8);
        Files.writeString(testDir.resolve("test3.txt"), "updated", StandardCharsets.UTF_8);

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(
            changes.notifications(),
            containsInAnyOrder(equalTo("onFileChanged: test-dir/test2.txt"), equalTo("onFileChanged: test-dir/test3.txt"))
        );

        // Change lastModified on files #2 & #3, but not the contents
        Files.setLastModifiedTime(testDir.resolve("test2.txt"), FileTime.fromMillis(System.currentTimeMillis() + 3));
        Files.setLastModifiedTime(testDir.resolve("test3.txt"), FileTime.fromMillis(System.currentTimeMillis() + 3));

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), hasSize(0));

        // Do nothing
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), hasSize(0));

        // Delete files
        Files.delete(testDir.resolve("test1.txt"));
        Files.delete(testDir.resolve("test2.txt"));

        fileWatcher.checkAndNotify();
        assertThat(
            changes.notifications(),
            contains(equalTo("onFileDeleted: test-dir/test1.txt"), equalTo("onFileDeleted: test-dir/test2.txt"))
        );
    }

    public void testNestedDirectoryOperations() throws IOException {
        Path tempDir = createTempDir();
        RecordingChangeListener changes = new RecordingChangeListener(tempDir);
        Path testDir = tempDir.resolve("test-dir");
        Files.createDirectories(testDir);
        touch(testDir.resolve("test.txt"));
        Files.createDirectories(testDir.resolve("sub-dir"));
        touch(testDir.resolve("sub-dir/test0.txt"));

        FileWatcher fileWatcher = new FileWatcher(testDir);
        fileWatcher.addListener(changes);
        fileWatcher.init();
        assertThat(
            changes.notifications(),
            contains(
                equalTo("onDirectoryInit: test-dir/"),
                equalTo("onDirectoryInit: test-dir/sub-dir/"),
                equalTo("onFileInit: test-dir/sub-dir/test0.txt"),
                equalTo("onFileInit: test-dir/test.txt")
            )
        );

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), hasSize(0));

        // Create new file in subdirectory
        touch(testDir.resolve("sub-dir/test1.txt"));
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), contains(equalTo("onFileCreated: test-dir/sub-dir/test1.txt")));

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), hasSize(0));

        // Create new subdirectory in subdirectory
        Files.createDirectories(testDir.resolve("first-level"));
        touch(testDir.resolve("first-level/file1.txt"));
        Files.createDirectories(testDir.resolve("first-level/second-level"));
        touch(testDir.resolve("first-level/second-level/file2.txt"));
        fileWatcher.checkAndNotify();
        assertThat(
            changes.notifications(),
            contains(
                equalTo("onDirectoryCreated: test-dir/first-level/"),
                equalTo("onFileCreated: test-dir/first-level/file1.txt"),
                equalTo("onDirectoryCreated: test-dir/first-level/second-level/"),
                equalTo("onFileCreated: test-dir/first-level/second-level/file2.txt")
            )
        );

        changes.notifications().clear();
        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), hasSize(0));

        // Delete a directory, check notifications for
        Path path = testDir.resolve("first-level");
        if (Files.exists(path)) {
            IOUtils.rm(path);
        }
        fileWatcher.checkAndNotify();
        assertThat(
            changes.notifications(),
            contains(
                equalTo("onFileDeleted: test-dir/first-level/file1.txt"),
                equalTo("onFileDeleted: test-dir/first-level/second-level/file2.txt"),
                equalTo("onDirectoryDeleted: test-dir/first-level/second-level"),
                equalTo("onDirectoryDeleted: test-dir/first-level")
            )
        );
    }

    public void testFileReplacingDirectory() throws IOException {
        Path tempDir = createTempDir();
        RecordingChangeListener changes = new RecordingChangeListener(tempDir);
        Path testDir = tempDir.resolve("test-dir");
        Files.createDirectories(testDir);
        Path subDir = testDir.resolve("sub-dir");
        Files.createDirectories(subDir);
        touch(subDir.resolve("test0.txt"));
        touch(subDir.resolve("test1.txt"));

        FileWatcher fileWatcher = new FileWatcher(testDir);
        fileWatcher.addListener(changes);
        fileWatcher.init();
        assertThat(
            changes.notifications(),
            contains(
                equalTo("onDirectoryInit: test-dir/"),
                equalTo("onDirectoryInit: test-dir/sub-dir/"),
                equalTo("onFileInit: test-dir/sub-dir/test0.txt"),
                equalTo("onFileInit: test-dir/sub-dir/test1.txt")
            )
        );

        changes.notifications().clear();

        if (Files.exists(subDir)) {
            IOUtils.rm(subDir);
        }
        touch(subDir);
        fileWatcher.checkAndNotify();
        assertThat(
            changes.notifications(),
            contains(
                equalTo("onFileDeleted: test-dir/sub-dir/test0.txt"),
                equalTo("onFileDeleted: test-dir/sub-dir/test1.txt"),
                equalTo("onDirectoryDeleted: test-dir/sub-dir"),
                equalTo("onFileCreated: test-dir/sub-dir")
            )
        );

        changes.notifications().clear();

        Files.delete(subDir);
        Files.createDirectories(subDir);

        fileWatcher.checkAndNotify();
        assertThat(
            changes.notifications(),
            contains(equalTo("onFileDeleted: test-dir/sub-dir/"), equalTo("onDirectoryCreated: test-dir/sub-dir/"))
        );
    }

    public void testEmptyDirectory() throws IOException {
        Path tempDir = createTempDir();
        RecordingChangeListener changes = new RecordingChangeListener(tempDir);
        Path testDir = tempDir.resolve("test-dir");
        Files.createDirectories(testDir);
        touch(testDir.resolve("test0.txt"));
        touch(testDir.resolve("test1.txt"));

        FileWatcher fileWatcher = new FileWatcher(testDir);
        fileWatcher.addListener(changes);
        fileWatcher.init();
        changes.notifications().clear();

        Files.delete(testDir.resolve("test0.txt"));
        Files.delete(testDir.resolve("test1.txt"));
        fileWatcher.checkAndNotify();
        assertThat(
            changes.notifications(),
            contains(equalTo("onFileDeleted: test-dir/test0.txt"), equalTo("onFileDeleted: test-dir/test1.txt"))
        );
    }

    public void testNoDirectoryOnInit() throws IOException {
        Path tempDir = createTempDir();
        RecordingChangeListener changes = new RecordingChangeListener(tempDir);
        Path testDir = tempDir.resolve("test-dir");

        FileWatcher fileWatcher = new FileWatcher(testDir);
        fileWatcher.addListener(changes);
        fileWatcher.init();
        assertThat(changes.notifications(), hasSize(0));
        changes.notifications().clear();

        Files.createDirectories(testDir);
        touch(testDir.resolve("test0.txt"));
        touch(testDir.resolve("test1.txt"));

        fileWatcher.checkAndNotify();
        assertThat(
            changes.notifications(),
            contains(
                equalTo("onDirectoryCreated: test-dir/"),
                equalTo("onFileCreated: test-dir/test0.txt"),
                equalTo("onFileCreated: test-dir/test1.txt")
            )
        );
    }

    public void testNoFileOnInit() throws IOException {
        Path tempDir = createTempDir();
        RecordingChangeListener changes = new RecordingChangeListener(tempDir);
        Path testFile = tempDir.resolve("testfile.txt");

        FileWatcher fileWatcher = new FileWatcher(testFile);
        fileWatcher.addListener(changes);
        fileWatcher.init();
        assertThat(changes.notifications(), hasSize(0));
        changes.notifications().clear();

        touch(testFile);

        fileWatcher.checkAndNotify();
        assertThat(changes.notifications(), contains(equalTo("onFileCreated: testfile.txt")));
    }

    static void touch(Path path) throws IOException {
        Files.newOutputStream(path).close();
    }

    static void append(String string, Path path, Charset cs) throws IOException {
        try (BufferedWriter writer = Files.newBufferedWriter(path, cs, StandardOpenOption.APPEND)) {
            writer.append(string);
        }
    }
}