feat: include uninstallation logic

lib/src/installer/completion_installation.dart

@@ -304,6 +304,82 @@ ${configuration!.sourceLineTemplate(scriptPath)}''';
 
     logger.info('Added config to $configFilePath');
   }
+
+  /// Uninstalls the completion for the command [executableName] on the current
+  /// shell.
+  ///
+  /// Before uninstalling, it checks if the completion is installed:
+  /// - The shell has an existing RCFile with a completion
+  /// [ScriptConfigurationEntry].
+  /// - The shell has an exisiting completion configuration file with a
+  /// [ScriptConfigurationEntry] for the [executableName].
+  ///
+  /// If any of the above is not true, it throws a
+  /// [CompletionUnistallationException].
+  ///
+  /// Upon a successful uninstallation the executable [ScriptConfigurationEntry]
+  /// is removed from the shell configuration file. If after this removal the
+  /// latter is empty, it is deleted together with the the executable completion
+  /// script and the completion [ScriptConfigurationEntry] from the shell RC
+  /// file. In the case that there are no other completion scripts installed on
+  /// other shells the completion config directory is deleted, leaving the
+  /// user's system as it was before the installation.
+  void uninstall(String executableName) {
+    final configuration = this.configuration!;
+    logger.detail(
+      '''Uninstalling completion for the command $executableName on ${configuration.shell.name}''',
+    );
+
+    final shellRCFile = File(_shellRCFilePath);
+    if (!shellRCFile.existsSync()) {
+      throw CompletionUnistallationException(
+        executableName: executableName,
+        message: 'No shell RC file found at ${shellRCFile.path}',
+      );
+    }
+
+    const completionEntry = ScriptConfigurationEntry('Completion');
+    if (!completionEntry.existsIn(shellRCFile)) {
+      throw CompletionUnistallationException(
+        executableName: executableName,
+        message: 'Completion is not installed at ${shellRCFile.path}',
+      );
+    }
+
+    final shellCompletionConfigurationFile = File(
+      path.join(
+        completionConfigDir.path,
+        configuration.completionConfigForShellFileName,
+      ),
+    );
+    final executableEntry = ScriptConfigurationEntry(executableName);
+    if (!executableEntry.existsIn(shellCompletionConfigurationFile)) {
+      throw CompletionUnistallationException(
+        executableName: executableName,
+        message:
+            '''No shell script file found at ${shellCompletionConfigurationFile.path}''',
+      );
+    }
+
+    final executableShellCompletionScriptFile = File(
+      path.join(
+        completionConfigDir.path,
+        '$executableName.${configuration.shell.name}',
+      ),
+    );
+    if (executableShellCompletionScriptFile.existsSync()) {
+      executableShellCompletionScriptFile.deleteSync();
+    }
+
+    executableEntry.removeFrom(shellCompletionConfigurationFile);
+    if (!shellCompletionConfigurationFile.existsSync()) {
+      completionEntry.removeFrom(shellRCFile, shouldDelete: false);
+    }
+
+    if (completionConfigDir.listSync().isEmpty) {
+      completionConfigDir.deleteSync();
+    }
+  }
 }
 
 /// Resolve the home from a path string

lib/src/installer/exceptions.dart

@@ -18,3 +18,24 @@ class CompletionInstallationException implements Exception {
   String toString() => 'Could not install completion scripts for $rootCommand: '
       '$message';
 }
+
+/// {@template completion_unistallation_exception}
+/// Describes an exception during the installation of completion scripts.
+/// {@endtemplate}
+class CompletionUnistallationException implements Exception {
+  /// {@macro completion_unistallation_exception}
+  CompletionUnistallationException({
+    required this.message,
+    required this.executableName,
+  });
+
+  /// The error message for this exception
+  final String message;
+
+  /// The command for which the installation failed.
+  final String executableName;
+
+  @override
+  String toString() =>
+      '''Could not uninstall completion scripts for $executableName: $message''';
+}

lib/src/installer/script_configuration_entry.dart

@@ -38,16 +38,46 @@ class ScriptConfigurationEntry {
       file.createSync(recursive: true);
     }
 
-    final entry = StringBuffer()
+    final stringBuffer = StringBuffer()
       ..writeln()
-      ..writeln(_startComment)
-      ..writeln(content)
+      ..writeln(_startComment);
+    if (content != null) stringBuffer.writeln(content);
+    stringBuffer
       ..writeln(_endComment)
       ..writeln();
 
     file.writeAsStringSync(
-      entry.toString(),
+      stringBuffer.toString(),
       mode: FileMode.append,
     );
   }
+
+  /// Removes the entry with [name] from the [file].
+  ///
+  /// If the [file] does not exist, this will do nothing.
+  ///
+  /// If a file has multiple entries with the same [name], all of them will be
+  /// removed.
+  ///
+  /// If [shouldDelete] is true, the [file] will be deleted if it is empty after
+  /// removing the entry. Otherwise, the [file] will be left empty.
+  void removeFrom(File file, {bool shouldDelete = true}) {
+    if (!file.existsSync()) return;
+
+    final content = file.readAsStringSync();
+    final stringPattern = '\n$_startComment.*$_endComment\n\n'
+        .replaceAll('[', r'\[')
+        .replaceAll(']', r'\]');
+    final pattern = RegExp(
+      stringPattern,
+      multiLine: true,
+      dotAll: true,
+    );
+    final newContent = content.replaceAllMapped(pattern, (_) => '');
+    file.writeAsStringSync(newContent);
+
+    if (shouldDelete && newContent.trim().isEmpty) {
+      file.deleteSync();
+    }
+  }
 }