Add option to perform no-conflicts-only update and revert

src/main/java/org/wildfly/installationmanager/CandidateType.java

@@ -0,0 +1,8 @@
+package org.wildfly.installationmanager;
+
+/**
+ * Supported candidate types
+ */
+public enum CandidateType {
+    UPDATE, REVERT
+}

src/main/java/org/wildfly/installationmanager/FileConflict.java

@@ -0,0 +1,101 @@
+/*
+ * JBoss, Home of Professional Open Source.
+ * Copyright 2024 Red Hat, Inc., and individual contributors
+ * as indicated by the @author tags.
+ *
+ * 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 org.wildfly.installationmanager;
+
+import java.nio.file.Path;
+import java.util.Objects;
+
+/**
+ * Represents a file modified by both the update and by the user. Such files cause a conflict and are resolved using
+ * a backup file to preserve either user or update changes.
+ */
+public class FileConflict {
+
+    /**
+     * Describes the change to the file - it can be modified, removed, added, or not-existing (e.g. when a new file was added by user
+     * and doesn't exist in the update).
+     */
+    public enum Status {
+        MODIFIED,
+        REMOVED,
+        ADDED,
+        NONE }
+    private Path relativePath;
+    private Status userChanges;
+    private Status updateChanges;
+    private boolean overwritten;
+
+    public FileConflict(Path relativePath, Status userChanges, Status updateChanges, boolean overwritten) {
+        this.relativePath = relativePath;
+        this.userChanges = userChanges;
+        this.updateChanges = updateChanges;
+        this.overwritten = overwritten;
+    }
+
+    /**
+     * File's Relative path to the server root
+     */
+    public Path getRelativePath() {
+        return relativePath;
+    }
+
+    /**
+     * The change to the current copy of the file, i.e. compared to previous installation/update state.
+     */
+    public Status getUserChanges() {
+        return userChanges;
+    }
+
+    /**
+     * The change performed in the update compared to the previous installation/update state.
+     */
+    public Status getUpdateChanges() {
+        return updateChanges;
+    }
+
+    /**
+     * Whether the user or update changes have been used to resolve conflict. Set to true if the update state overrides user changes, false otherwise.
+     */
+    public boolean isOverwritten() {
+        return overwritten;
+    }
+
+    @Override
+    public String toString() {
+        return "FileConflict{" +
+                "relativePath=" + relativePath +
+                ", userChanges=" + userChanges +
+                ", updateChanges=" + updateChanges +
+                ", overwritten=" + overwritten +
+                '}';
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        FileConflict that = (FileConflict) o;
+        return overwritten == that.overwritten && Objects.equals(relativePath, that.relativePath) && userChanges == that.userChanges && updateChanges == that.updateChanges;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(relativePath, userChanges, updateChanges, overwritten);
+    }
+}

src/main/java/org/wildfly/installationmanager/spi/InstallationManager.java

@@ -18,6 +18,8 @@
 
 package org.wildfly.installationmanager.spi;
 
+import org.wildfly.installationmanager.CandidateType;
+import org.wildfly.installationmanager.FileConflict;
 import org.wildfly.installationmanager.InstallationChanges;
 import org.wildfly.installationmanager.Channel;
 import org.wildfly.installationmanager.HistoryResult;
@@ -29,7 +31,6 @@
 import java.nio.file.Path;
 import java.util.Collection;
 import java.util.List;
-import java.util.Optional;
 
 public interface InstallationManager {
     /**
@@ -161,6 +162,7 @@ public interface InstallationManager {
      * @return a CLI command.
      * @throws OperationNotAvailableException - if the installation manager CLI support is not installed
      */
+    @Deprecated
     String generateApplyUpdateCommand(Path scriptHome, Path candidatePath, OsShell shell) throws OperationNotAvailableException;
 
     /**
@@ -173,12 +175,49 @@ public interface InstallationManager {
      * @return a CLI command.
      * @throws OperationNotAvailableException - if the installation manager CLI support is not installed
      */
+    @Deprecated
     String generateApplyRevertCommand(Path scriptHome, Path candidatePath, OsShell shell) throws OperationNotAvailableException;
 
+    /**
+     * Generate an apply update CLI command.
+     * The generated command can be run in separate process to apply changes.
+     *
+     * @param candidatePath - Specify the directory path of the candidate installation to apply.
+     * @param scriptHome - Specify the directory path containing the script used to execute the apply command.
+     * @param shell - Specify what shell should the script be runnable in
+     * @param noConflictsOnly - Specify whether the command should fail if file conflicts are present
+     * @return a CLI command.
+     * @throws OperationNotAvailableException - if the installation manager CLI support is not installed
+     */
+    String generateApplyUpdateCommand(Path scriptHome, Path candidatePath, OsShell shell, boolean noConflictsOnly) throws OperationNotAvailableException;
+
+    /**
+     * Generate an apply rollback CLI command.
+     * The generated command can be run in separate process to apply changes.
+     *
+     * @param candidatePath - Specify the directory path of the candidate installation to apply.
+     * @param scriptHome - Specify the directory path containing the script used to execute the apply command.
+     * @param shell - Specify what shell should the script be runnable in
+     * @param noConflictsOnly - Specify whether the command should fail if file conflicts are present
+     * @return a CLI command.
+     * @throws OperationNotAvailableException - if the installation manager CLI support is not installed
+     */
+    String generateApplyRevertCommand(Path scriptHome, Path candidatePath, OsShell shell, boolean noConflictsOnly) throws OperationNotAvailableException;
+
     /**
      * Reports latest versions of manifests used in latest update/install operation for each registered channels.
      * @return list of {@link ManifestVersion}s
      * @throws Exception if there was an error reading the version information
      */
     Collection<ManifestVersion> getInstalledVersions() throws Exception;
+
+    /**
+     * Checks a candidate for update or revert at {@code candidatePath} and generates a list of potential file conflicts.
+     *
+     * @param candidatePath - location of the candidate server
+     * @param candidateType - the type of the candidate server
+     * @return collection of the {@code FileConflicts} or an empty collection if no conflicts were found.
+     * @throws Exception - if there was an exception accessing the server information or if the candidate is invalid
+     */
+    Collection<FileConflict> verifyCandidate(Path candidatePath, CandidateType candidateType) throws Exception;
 }