New utility class.

org.jdrupes.vmoperator.util/src/org/jdrupes/vmoperator/util/FsdUtils.java

@@ -0,0 +1,168 @@
+/*
+ * VM-Operator
+ * Copyright (C) 2023 Michael N. Lipp
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package org.jdrupes.vmoperator.util;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * Utilities to access configurable file system directories. Based on
+ * the [FHS](https://refspecs.linuxfoundation.org/FHS_3.0/fhs/index.html) and the
+ * [XDG Base Directory Specification](https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html).
+ */
+@SuppressWarnings("PMD.UseUtilityClass")
+public class FsdUtils {
+
+    /**
+     * Adds a directory with the user's name to the path.
+     * If such a directory does not exist yet, creates it.
+     * If this file or the directory is not writable,
+     * return the given path.
+     *
+     * @param path the path
+     * @return the path
+     */
+    public static Path addUser(Path path) {
+        String user = System.getProperty("user.name");
+        if (user == null) {
+            return path;
+        }
+        Path dir = path.resolve(user);
+        if (Files.exists(dir)) {
+            return dir;
+        }
+        try {
+            Files.createDirectories(dir);
+        } catch (IOException e) { // NOPMD
+            // Just trying, doesn't matter
+        }
+        if (!Files.isWritable(dir)) {
+            return path;
+        }
+        return dir;
+    }
+
+    /**
+     * Returns the directory for temporary storage.
+     *
+     * @return the path
+     */
+    public static Path tmpDir() {
+        return Path.of(System.getProperty("java.io.tmpdir", "/tmp"));
+    }
+
+    /**
+     * Returns the real home directory of the user or, if not
+     * available, a sub directory in {@link #tmpDir()} with
+     * the user's name. 
+     *
+     * @return the path
+     */
+    public static Path userHome() {
+        Path home = Optional.ofNullable(System.getProperty("user.home"))
+            .map(Path::of).orElse(null);
+        if (home != null) {
+            return home;
+        }
+        return addUser(tmpDir());
+    }
+
+    /**
+     * Returns the data home.
+     *
+     * @param appName the application name
+     * @return the path
+     */
+    public static Path dataHome(String appName) {
+        return Optional.ofNullable(System.getenv().get("XDG_DATA_HOME"))
+            .map(Path::of).orElse(userHome().resolve(".local").resolve("share"))
+            .resolve(appName);
+    }
+
+    /**
+     * Returns the config home.
+     *
+     * @param appName the application name
+     * @return the path
+     */
+    public static Path configHome(String appName) {
+        return Optional.ofNullable(System.getenv().get("XDG_CONFIG_HOME"))
+            .map(Path::of).orElse(userHome().resolve(".config"))
+            .resolve(appName);
+    }
+
+    /**
+     * Returns the state directory.
+     *
+     * @param appName the application name
+     * @return the path
+     */
+    public static Path stateHome(String appName) {
+        return Optional.ofNullable(System.getenv().get("XDG_STATE_HOME"))
+            .map(Path::of)
+            .orElse(userHome().resolve(".local").resolve("state"))
+            .resolve(appName);
+    }
+
+    /**
+     * Returns the runtime directory.
+     *
+     * @param appName the application name
+     * @return the path
+     */
+    public static Path runtimeDir(String appName) {
+        return Optional.ofNullable(System.getenv("XDG_RUNTIME_DIR"))
+            .map(Path::of).orElseGet(() -> {
+                var runtimeBase = Path.of("/run");
+                var dir = addUser(runtimeBase);
+                if (!dir.equals(runtimeBase)) {
+                    return dir;
+                }
+                return addUser(tmpDir());
+            }).resolve(appName);
+    }
+
+    /**
+     * Find a configuration file. The given filename is searched for in:
+     * 
+     * 1. the current working directory,
+     * 1. the {@link #configHome(String)}
+     * 1. the subdirectory `appName` of `/etc`
+     *
+     * @param appName the application name
+     * @param filename the filename
+     * @return the optional
+     */
+    public static Optional<Path> findConfigFile(String appName,
+            String filename) {
+        var candidates = List.of(Path.of(filename),
+            configHome(appName).resolve(filename),
+            Path.of("/etc").resolve(appName).resolve(filename));
+        for (var candidate : candidates) {
+            if (Files.exists(candidate)) {
+                return Optional.of(candidate);
+            }
+        }
+        return Optional.empty();
+    }
+
+}