Move config file to standard location

The user's config directory is taken as ~\AppData\Local\ on Windows and
is XDG-compliant elsewhere.  The config file's location is <config
dir>/SevenUnits/config.txt.  The SevenUnits directory is created if
nonexistent.

The previous location inside the git directory would not work for
someone actually installing and using 7Units, so this change was made.

1 files changed, 42 insertions, 6 deletions

diff --git a/src/main/java/sevenUnitsGUI/Presenter.java b/src/main/java/sevenUnitsGUI/Presenter.java
index abdd1f6..3ecfba6 100644
--- a/src/main/java/sevenUnitsGUI/Presenter.java
+++ b/src/main/java/sevenUnitsGUI/Presenter.java
@@ -21,6 +21,7 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
@@ -57,9 +58,8 @@ import sevenUnits.utils.UncertainDouble;
  * @since 2021-12-15
  */
 public final class Presenter {
-	/** The default place where settings are stored. */
-	private static final Path DEFAULT_SETTINGS_FILEPATH = Path
-			.of("settings.txt");
+	/** The place where settings are stored. */
+	private static final Optional<Path> CONFIG_FILE = getConfigPath();
 	/** The default place where units are stored. */
 	private static final String DEFAULT_UNITS_FILEPATH = "/unitsfile.txt";
 	/** The default place where dimensions are stored. */
@@ -67,6 +67,38 @@ public final class Presenter {
 	/** The default place where exceptions are stored. */
 	private static final String DEFAULT_EXCEPTIONS_FILEPATH = "/metric_exceptions.txt";
 	
+	/** Gets the configuration file, creating the directory if needed. */
+	private static final Optional<Path> getConfigPath() {
+		final Path configDir;
+		if (System.getProperty("os.name").startsWith("Windows")) {
+			final String envFolder = System.getenv("LOCALAPPDATA");
+			if (envFolder == null || "".equals(envFolder)) {
+				configDir = Paths.get(System.getenv("USERPROFILE"), "AppData", "Local", "SevenUnits");
+			} else {
+				configDir = Paths.get(envFolder, "SevenUnits");
+			}
+		} else {
+			final String envFolder = System.getenv("XDG_CONFIG_HOME");
+			if (envFolder == null || "".equals(envFolder)) {
+				configDir = Paths.get(System.getenv("HOME"), ".config", "SevenUnits");
+			} else {
+				configDir = Paths.get(envFolder, "SevenUnits");
+			}
+		}
+
+		// try to create config directory
+		if (!Files.exists(configDir)) {
+			try {
+				Files.createDirectory(configDir);
+			} catch (IOException e) {
+				e.printStackTrace();
+				return Optional.empty();
+			}
+		}
+
+		return Optional.of(configDir.resolve("config.txt"));
+	}
+
 	/**
 	 * Adds default units and dimensions to a database.
 	 * 
@@ -267,7 +299,9 @@ public final class Presenter {
 		}
 		
 		// set default settings temporarily
-		this.loadSettings(DEFAULT_SETTINGS_FILEPATH);
+		CONFIG_FILE.ifPresentOrElse(this::loadSettings, () -> {
+			this.view.showErrorMessage("Config Loading Error", "Could not load config file - using default settings.");
+		});
 		
 		// a Predicate that returns true iff the argument is a full base unit
 		final Predicate<Unit> isFullBase = unit -> unit instanceof LinearUnit
@@ -661,10 +695,12 @@ public final class Presenter {
 	/**
 	 * Saves the presenter's current settings to its default filepath.
 	 * 
+	 * @return true iff this operation succeeded
 	 * @since 2022-04-19
 	 */
-	public void saveSettings() {
-		this.saveSettings(DEFAULT_SETTINGS_FILEPATH);
+	public boolean saveSettings() {
+		CONFIG_FILE.ifPresent(this::saveSettings);
+		return CONFIG_FILE.isPresent();
 	}
 	
 	/**