feat: add installation process for zsh (#7)

.gitignore

@@ -4,4 +4,6 @@
 .dart_tool/
 .packages
 build/
-pubspec.lock
+pubspec.lock
+
+coverage/

lib/install.dart

@@ -0,0 +1,5 @@
+/// Contains the functions related to the installation file
+library install;
+
+export 'src/install/install_completion.dart';
+export 'src/install/shell_completion_installation.dart';

lib/src/exceptions.dart

@@ -0,0 +1,20 @@
+/// {@template completion_installation_exception}
+/// Describes an exception during the installation of completion scripts.
+/// {@endtemplate}
+class CompletionInstallationException implements Exception {
+  /// {@macro completion_installation_exception}
+  CompletionInstallationException({
+    required this.message,
+    required this.rootCommand,
+  });
+
+  /// The error message for this exception
+  final String message;
+
+  /// The command for which the installation failed.
+  final String rootCommand;
+
+  @override
+  String toString() => 'Could not install completion scripts for $rootCommand: '
+      '$message';
+}

lib/src/install/install_completion.dart

@@ -0,0 +1,36 @@
+import 'package:cli_completion/src/exceptions.dart';
+import 'package:cli_completion/src/install/shell_completion_installation.dart';
+
+import 'package:mason_logger/mason_logger.dart';
+
+/// Install completion configuration hooks for a [rootCommand] in the
+/// current shell.
+void installCompletion({
+  required Logger logger,
+  required String rootCommand,
+  bool? isWindowsOverride,
+  Map<String, String>? environmentOverride,
+}) {
+  logger
+    ..detail('Completion installation for $rootCommand started')
+    ..detail('Identifying system shell');
+
+  final completionInstallation = ShellCompletionInstallation.fromCurrentShell(
+    logger: logger,
+    isWindowsOverride: isWindowsOverride,
+    environmentOverride: environmentOverride,
+  );
+
+  if (completionInstallation == null) {
+    throw CompletionInstallationException(
+      message: 'Unknown shell.',
+      rootCommand: rootCommand,
+    );
+  }
+
+  logger.detail(
+    'Shell identified as ${completionInstallation.configuration.name}',
+  );
+
+  completionInstallation.install(rootCommand);
+}

lib/src/install/shell_completion_configuration.dart

@@ -0,0 +1,70 @@
+import 'package:meta/meta.dart';
+
+/// A type definition for functions that creates the content of a
+/// completion script given a [rootCommand]
+typedef CompletionScriptTemplate = String Function(String rootCommand);
+
+/// A type definition for functions that describes
+/// the source line given a [scriptPath]
+typedef SourceStringTemplate = String Function(String scriptPath);
+
+/// {@template shell_completion_configuration}
+/// Describes the configuration of a completion script in a specific shell.
+///
+/// See:
+/// - [zshConfiguration] for zsh
+@immutable
+class ShellCompletionConfiguration {
+  /// {@macro shell_completion_configuration}
+  @visibleForTesting
+  const ShellCompletionConfiguration({
+    required this.name,
+    required this.shellRCFile,
+    required this.sourceLineTemplate,
+    required this.scriptTemplate,
+  });
+
+  /// A descriptive string to identify the shell among others.
+  final String name;
+
+  /// The location of a config file that is run upon shell start.
+  /// Eg: .bashrc or .zshrc
+  final String shellRCFile;
+
+  /// Generates a line to sources of a script file.
+  final SourceStringTemplate sourceLineTemplate;
+
+  /// Generates the contents of a completion script.
+  final CompletionScriptTemplate scriptTemplate;
+
+  /// The name for the config file for this shell.
+  String get completionConfigForShellFileName => '$name-config.$name';
+}
+
+/// A [ShellCompletionConfiguration] for zsh.
+final zshConfiguration = ShellCompletionConfiguration(
+  name: 'zsh',
+  shellRCFile: '~/.zshrc',
+  sourceLineTemplate: (String scriptPath) {
+    return '[[ -f $scriptPath ]] && . $scriptPath || true';
+  },
+  scriptTemplate: (String rootCommand) {
+    // Completion script for zsh.
+    //
+    // Based on https://github.com/mklabs/tabtab/blob/master/lib/scripts/zsh.sh
+    return '''
+if type compdef &>/dev/null; then
+  _${rootCommand}_completion () {
+    local reply
+    local si=\$IFS
+
+    IFS=\$'\n' reply=(\$(COMP_CWORD="\$((CURRENT-1))" COMP_LINE="\$BUFFER" COMP_POINT="\$CURSOR" $rootCommand completion -- "\${words[@]}"))
+    IFS=\$si
+
+    _describe 'values' reply
+  }
+  compdef _${rootCommand}_completion $rootCommand
+fi
+''';
+  },
+);