Initialize Nest CLI library.

.gitignore

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+# IDEA
+.idea/
+*.iml
+
+# Composer
+vendor/

composer.json

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+{
+	"version": "1.0",
+	"name": "nest/cli",
+	"description": "Nest CLI service and engine.",
+	"type": "library",
+	"authors": [
+		{
+			"name": "Madeorsk",
+			"email": "madeorsk@protonmail.com"
+		}
+	],
+	"autoload": {
+		"psr-4": {
+			"Nest\\Cli\\": "src/"
+		}
+	},
+	"repositories": [
+		{
+			"type": "vcs",
+			"url": "https://code.zeptotech.net/Nest/Core"
+		}
+	],
+	"require": {
+		"php": "^8.3",
+		"nest/core": "dev-main"
+	}
+}

composer.lock

@@ -0,0 +1,56 @@
+{
+    "_readme": [
+        "This file locks the dependencies of your project to a known state",
+        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
+        "This file is @generated automatically"
+    ],
+    "content-hash": "fc6ba9501cee8e0307bbf953ce6c5ec9",
+    "packages": [
+        {
+            "name": "nest/core",
+            "version": "dev-main",
+            "source": {
+                "type": "git",
+                "url": "https://code.zeptotech.net/Nest/Core",
+                "reference": "22296b8d7c8b528089189a8d9500395424cb6468"
+            },
+            "require": {
+                "php": "^8.3"
+            },
+            "default-branch": true,
+            "type": "library",
+            "autoload": {
+                "psr-4": {
+                    "Nest\\": "src/"
+                },
+                "files": [
+                    "src/Utils/Array.php",
+                    "src/Utils/Paths.php",
+                    "src/Utils/Reflection.php",
+                    "src/Utils/String.php"
+                ]
+            },
+            "authors": [
+                {
+                    "name": "Madeorsk",
+                    "email": "madeorsk@protonmail.com"
+                }
+            ],
+            "description": "Nest framework core.",
+            "time": "2024-11-08T11:12:38+00:00"
+        }
+    ],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": {
+        "nest/core": 20
+    },
+    "prefer-stable": false,
+    "prefer-lowest": false,
+    "platform": {
+        "php": "^8.3"
+    },
+    "platform-dev": {},
+    "plugin-api-version": "2.6.0"
+}

src/Cli.php

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+<?php
+
+namespace Nest\Cli;
+
+use Nest\Application;
+use Nest\Cli\Commands\CommandContext;
+use Nest\Cli\Commands\CommandDefinition;
+use Nest\Cli\Commands\FlagDefinition;
+use Nest\Exceptions\Cli\Command\CommandException;
+use Nest\Exceptions\Cli\Command\InvalidCommandHandlerException;
+use Nest\Exceptions\Cli\IncompatibleCliHandlerSubcommands;
+use Throwable;
+
+/**
+ * CLI manager and engine.
+ */
+class Cli
+{
+	/**
+	 * Associative array of CLI commands.
+	 * @var array<string, CommandDefinition>
+	 */
+	protected array $commands;
+
+	/**
+	 * The CLI helper.
+	 * @var CliHelper
+	 */
+	protected CliHelper $helper;
+
+	/**
+	 * @param Application $application The application.
+	 * @param CliConfiguration $configuration CLI configuration.
+	 */
+	public function __construct(protected Application $application, protected CliConfiguration $configuration)
+	{
+	}
+
+	/**
+	 * Create a new command context for given arguments.
+	 * @param string[]|null $argv Command arguments, NULL to get the currently passed command arguments.
+	 * @return CommandContext The command context.
+	 * @throws CommandException
+	 */
+	public function newCommandContext(?array $argv = null): CommandContext
+	{
+		// Initialize command context with arguments.
+		return new CommandContext($this, $this->commands, $argv);
+	}
+
+	/**
+	 * Exception handler for the CLI.
+	 * @param Throwable $exception Exception to handle.
+	 * @return void
+	 */
+	protected function exceptionHandler(Throwable $exception): void
+	{
+		Out::error("Unhandled exception: {$exception->getMessage()}");
+		Out::error("in file ".Out::ITALIC_ATTRIBUTE."{$exception->getFile()}".Out::RESET_ATTRIBUTES.Color::Red->value." on line {$exception->getLine()}.");
+		echo Color::Red->value."{$exception->getTraceAsString()}".Color::Default->value."\n";
+	}
+
+	/**
+	 * Main engine function.
+	 * @return void
+	 * @throws InvalidCommandHandlerException
+	 * @throws IncompatibleCliHandlerSubcommands
+	 */
+	public function __invoke(): void
+	{
+		// Add exception handler.
+		$this->application->exceptionHandler()->add(fn (Throwable $exception) => $this->exceptionHandler($exception));
+
+		// Define configuration of this CLI.
+		$this->configuration->define($this);
+
+		// Get CLI helper.
+		$helper = $this->getHelper();
+
+		try
+		{
+			// Create and fill command context, then check its validity.
+			$commandContext = $this->newCommandContext();
+			$commandContext->checkValidity();
+
+			if ($commandContext->hasFlag(FlagDefinition::HELP_FLAG))
+			{ // If auto help flag has been provided, showing help no matter the rest.
+				$helper->help($this, $commandContext);
+			}
+			else
+			{ // Execute the command handler with all parameters.
+				$commandContext->getCommandHandler()(...$commandContext->getParameters());
+			}
+		}
+		catch (CommandException $commandException)
+		{ // If any command parse error happen, show it, then show help for the given context.
+			$helper->help($this, $commandException->commandContext, $commandException);
+		}
+	}
+
+	/**
+	 * Set CLI helper.
+	 * The role of CLI helper is to provide help when needed (either asked by user or after invalid arguments).
+	 * @param CliHelper $helper New CLI helper.
+	 * @return void
+	 */
+	public function setHelper(CliHelper $helper): void
+	{
+		$this->helper = $helper;
+	}
+
+	/**
+	 * Get CLI helper.
+	 * If none is set, return a default one.
+	 * @return CliHelper CLI helper instance.
+	 */
+	public function getHelper(): CliHelper
+	{
+		// Return defined helper, if there is one.
+		if (!empty($this->helper)) return $this->helper;
+
+		// Return a new default helper.
+		return new DefaultHelper();
+	}
+
+	/**
+	 * Get command definition of the given command.
+	 * Initialize a new command definition if it didn't exist.
+	 * @param string $command A command
+	 * @return CommandDefinition
+	 */
+	public function command(string $command): CommandDefinition
+	{
+		if (empty($this->commands[$command]))
+			// Initialize a new command definition because it doesn't exist.
+			$this->commands[$command] = new CommandDefinition();
+		// Return command definition of given command.
+		return $this->commands[$command];
+	}
+
+	/**
+	 * Get commands definitions for the CLI.
+	 * @return array<string, CommandDefinition> Commands definitions.
+	 */
+	public function getCommands(): array
+	{
+		return $this->commands;
+	}
+}

src/CliConfiguration.php

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+<?php
+
+namespace Nest\Cli;
+
+use Nest\Exceptions\Cli\Command\InvalidCommandHandlerException;
+use Nest\Exceptions\Cli\IncompatibleCliHandlerSubcommands;
+use Nest\Services\ServiceConfiguration;
+
+/**
+ * CLI configuration class.
+ */
+abstract class CliConfiguration extends ServiceConfiguration
+{
+	/**
+	 * Define commands of the CLI.
+	 * @param Cli $cli The CLI to configure.
+	 * @return void
+	 * @throws InvalidCommandHandlerException
+	 * @throws IncompatibleCliHandlerSubcommands
+	 */
+	public abstract function define(Cli $cli): void;
+}

src/CliHelper.php

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+<?php
+
+namespace Nest\Cli;
+
+use Nest\Cli\Commands\CommandContext;
+use Throwable;
+
+/**
+ * CLI helper interface.
+ */
+interface CliHelper
+{
+	/**
+	 * Show helper for a given command context in a CLI.
+	 * @param Cli $cli CLI of the helper.
+	 * @param CommandContext $command Command context which require help.
+	 * @param Throwable|null $exception Thrown exception that caused helper to be called.
+	 * @return void
+	 */
+	public function help(Cli $cli, CommandContext $command, ?Throwable $exception = null): void;
+}

src/CliService.php

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+<?php
+
+namespace Nest\Cli;
+
+use Nest\Exceptions\Services\Configuration\UndefinedServiceConfigurationException;
+
+/**
+ * CLI Nest service.
+ */
+trait CliService
+{
+	/**
+	 * The CLI.
+	 * @var Cli
+	 */
+	private Cli $cli;
+
+	/**
+	 * @return void
+	 * @throws UndefinedServiceConfigurationException
+	 */
+	protected function __nest__CliService(): void
+	{
+		// Initialize CLI.
+		$this->cli = new Cli($this, $this->getServiceConfiguration(CliConfiguration::class));
+	}
+
+	/**
+	 * Get the CLI.
+	 * @return Cli CLI instance.
+	 */
+	public function cli(): Cli
+	{
+		return $this->cli;
+	}
+}

src/Color.php

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+<?php
+
+namespace Nest\Cli;
+
+/**
+ * CLI out colors.
+ */
+enum Color: string
+{
+	case Default = "\e[39m";
+	case Black = "\e[30m";
+	case Red = "\e[31m";
+	case Green = "\e[32m";
+	case Yellow = "\e[33m";
+	case Blue = "\e[34m";
+	case Magenta = "\e[35m";
+	case Cyan = "\e[36m";
+	case LightGray = "\e[37m";
+	case DarkGray = "\e[90m";
+	case LightRed = "\e[91m";
+	case LightGreen = "\e[92m";
+	case LightYellow = "\e[93m";
+	case LightBlue = "\e[94m";
+	case LightMagenta = "\e[95m";
+	case LightCyan = "\e[96m";
+	case White = "\e[97m";
+}

src/Commands/CommandContext.php

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+<?php
+
+namespace Nest\Cli\Commands;
+
+use Nest\Cli\Cli;
+use Nest\Exceptions\Cli\Command\CommandException;
+use Nest\Exceptions\Cli\Command\IncompleteCommandException;
+use Nest\Exceptions\Cli\Command\InvalidCommandException;
+use Nest\Exceptions\Cli\Command\NotEnoughParametersException;
+use Nest\Exceptions\Cli\Command\MissingCommandException;
+use Nest\Exceptions\Cli\Command\MissingRequiredFlagException;
+use Nest\Exceptions\Cli\Command\UndefinedFlagException;
+use Nest\Exceptions\Cli\Command\UndefinedShortFlagException;
+use Nest\Exceptions\Cli\Command\UndefinedSubcommandsException;
+use Nest\Exceptions\Cli\FlagNotFoundException;
+
+/**
+ * Class of a command context.
+ */
+class CommandContext
+{
+	/**
+	 * Command executable.
+	 * @var string
+	 */
+	protected string $executable;
+
+	/**
+	 * Commands path (with all subcommands).
+	 * @var string[]
+	 */
+	protected array $commandsPath;
+
+	/**
+	 * Associated command definition.
+	 * @var CommandDefinition
+	 */
+	protected CommandDefinition $commandDefinition;
+
+	/**
+	 * Command parameters.
+	 * @var string[]
+	 */
+	protected array $parameters = [];
+
+	/**
+	 * Flags with their parameters (if there are some).
+	 * @var array<string, array>
+	 */
+	protected array $flags;
+
+	/**
+	 * Command handler callable, determined from command definition.
+	 * @var callable(mixed...): ?int
+	 */
+	protected $handler;
+
+	/**
+	 * Create a new command context and fill it using passed command arguments.
+	 * @param Cli $cli The CLI.
+	 * @param array<string, CommandDefinition> $commands Commands definitions.
+	 * @param array|null $argv Command arguments (with executable at first position), NULL to get the currently passed command arguments.
+	 * @throws CommandException
+	 */
+	public function __construct(protected Cli $cli, protected array $commands, ?array $argv = null)
+	{
+		// Parse command.
+		$this->parseCommand($argv);
+	}
+
+	/**
+	 * Parse passed command arguments.
+	 * @param array|null $args Command arguments, NULL to get the currently passed command arguments.
+	 * @return void
+	 * @throws CommandException
+	 */
+	protected function parseCommand(?array $args = null): void
+	{
+		// Get command arguments.
+		global $argv;
+
+		// If args are not defined, get it from argv.
+		if (is_null($args)) $args = $argv;
+
+		// Save used executable.
+		$this->executable = $args[0];
+
+		if (empty($args[1]))
+			// No command.
+			throw new MissingCommandException($this);
+
+		// Parse commands path from first argument.
+		$this->commandsPath = array_map(fn (string $command) => trim($command), explode(":", $args[1]));
+
+		// Find associated command definition from commands path.
+		$this->findCommandDefinition();
+
+		if (!empty($args[2]))
+			// Find command flags and parameters, if there are some.
+			$this->findCommandFlagsAndParams(array_slice($args, 2));
+	}
+
+	/**
+	 * Find associated command definition from commands path.
+	 * @param int $currentIndex Current index in commands path.
+	 * @param CommandDefinition|null $currentCommandDefinition Current command definition, for recursive calls.
+	 * @return void
+	 * @throws CommandException
+	 */
+	protected function findCommandDefinition(int $currentIndex = 0, ?CommandDefinition $currentCommandDefinition = null): void
+	{
+		if (empty($this->commandsPath[$currentIndex]))
+		{ // We reached the end of the commands path, set the current command definition as the current one.
+			$this->commandDefinition = $currentCommandDefinition;
+
+			if ($this->commandDefinition->hasHandler())
+			{ // Check that a command handler is defined for the current command.
+				// Get command handler.
+				$commandHandler = $this->commandDefinition->getHandler();
+				// Instantiate handler class to call the object.
+				$this->handler = new $commandHandler($this->cli, $this);
+			}
+			else
+				// If there is no handler for the current command definition, the given command is incomplete.
+				throw new IncompleteCommandException($this);
+		}
+		else
+		{ // Get the next command definition, if there is one.
+
+			// Get current command part.
+			$commandPart = $this->commandsPath[$currentIndex];
+
+			if (empty($currentCommandDefinition))
+			{ // Try to read root command.
+				if (empty($this->commands[$commandPart]))
+					// Invalid command.
+					throw new InvalidCommandException($commandPart, $this);
+
+				// Recursive call to find the right command definition.
+				$this->findCommandDefinition($currentIndex + 1, $this->commands[$commandPart]);
+			}
+			else
+			{ // Try to read a subcommand.
+				if ($currentCommandDefinition->hasSubcommands())
+				{ // Try to get subcommands.
+					$subcommands = $currentCommandDefinition->getSubcommands();
+
+					if (is_array($subcommands))
+					{ // If it's an array, try to get the right command definition.
+						if (empty($subcommands[$commandPart]))
+							// Invalid command.
+							throw new InvalidCommandException($commandPart, $this);
+
+						// Recursive call to find the right command definition.
+						$this->findCommandDefinition($currentIndex + 1, $subcommands[$commandPart]);
+					}
+					else
+					{ // A subcommands handler is defined, we just need to call it with the right subcommand.
+						$subcommandsHandler = $currentCommandDefinition->getSubcommands();
+
+						// Instantiate handler class to call the object.
+						$callable = new $subcommandsHandler($this->cli, $this);
+
+						// Get remaining subcommands.
+						$subcommandsPath = array_slice($this->commandsPath, $currentIndex);
+
+						// Set current command definition as definitive command definition.
+						$this->commandDefinition = $currentCommandDefinition;
+						// Create a new handler which will pass subcommands path as first parameter of the callable.
+						$this->handler = function (mixed ...$parameters) use ($callable, $subcommandsPath) {
+							return $callable($subcommandsPath, ...$parameters);
+						};
+					}
+				}
+				else
+					// No subcommands for the current command, throwing an exception.
+					throw new UndefinedSubcommandsException($commandPart, $this);
+			}
+		}
+	}
+
+	/**
+	 * Find command flags and parameters.
+	 * @param string[] $args Raw arguments array.
+	 * @return void
+	 * @throws UndefinedFlagException
+	 */
+	protected function findCommandFlagsAndParams(array $args): void
+	{
+		// Initialize current flag (full) name.
+		$currentFlagName = null;
+
+		foreach ($args as $arg)
+		{ // Reading each argument one by one, to determine if it's a flag, a flag parameter or a positional parameter.
+
+			if (str_starts_with($arg, "--"))
+			{ // Current argument is a flag.
+				// Get current flag name.
+				$currentFlagName = substr($arg, 2);
+
+				if (empty($this->commandDefinition->getFlagDefinition($currentFlagName)) && $currentFlagName != FlagDefinition::HELP_FLAG)
+					// If the flag is undefined, throw an exception. Explicitly allow auto help flag.
+					throw new UndefinedFlagException($currentFlagName, $this);
+
+				// Initialize flag in the context.
+				$this->flags[$currentFlagName] = [];
+			}
+			elseif (str_starts_with($arg, "-"))
+			{ // Current argument is a (short) flag.
+				// Get current flag name from short flag name.
+				$currentFlagName = $this->commandDefinition->getShortFlagName($shortFlagName = substr($arg, 1));
+
+				if (empty($currentFlagName))
+					// If the short flag is undefined, throw an exception.
+					throw new UndefinedShortFlagException($shortFlagName, $this);
+
+				// Initialize flag in the context.
+				$this->flags[$currentFlagName] = [];
+			}
+			else
+			{ // Current argument is a parameter.
+				if (!empty($currentFlagName) && count($this->flags[$currentFlagName]) < $this->commandDefinition->getFlagDefinition($currentFlagName)->getParametersCount())
+				{ // If there is a current flag and we did not read all its parameters, considering this parameter is a flag parameter.
+					$this->flags[$currentFlagName][] = $arg;
+				}
+				else
+					// No current flag (no current flag or no remaining parameters for it), the parameter is a command parameter.
+					$this->parameters[] = $arg;
+			}
+		}
+	}
+
+	/**
+	 * Check command validity: the current command context should fulfill requirements of the command definition.
+	 * Throw a CommandException if anything is wrong.
+	 * @return void
+	 * @throws CommandException
+	 */
+	public function checkValidity(): void
+	{
+		// Check there are enough parameters to match the required count.
+		if (($providedCount = !empty($this->parameters) ? count($this->parameters) : 0) < ($expectedCount = $this->commandDefinition->getRequiredParametersCount()))
+			throw new NotEnoughParametersException($providedCount, $expectedCount, $this);
+
+		// Check that all the required flags are set.
+		foreach ($this->commandDefinition->getRequiredFlags() as $requiredFlag)
+		{ // Check each required flag existence.
+			if (!$this->hasFlag($requiredFlag))
+				// Required flag is not defined, throw an exception.
+				throw new MissingRequiredFlagException($requiredFlag, $this);
+		}
+	}
+
+	/**
+	 * Get used executable.
+	 * @return string Command executable.
+	 */
+	public function getExecutable(): string
+	{
+		return $this->executable;
+	}
+
+	/**
+	 * Get full command (with all its subcommands).
+	 * @return string Full command.
+	 */
+	public function getFullCommand(): string
+	{
+		return implode(":", $this->commandsPath);
+	}
+
+	/**
+	 * Get commands path (all subcommands).
+	 * @return string[]
+	 */
+	public function getCommandsPath(): array
+	{
+		return $this->commandsPath;
+	}
+
+	/**
+	 * Get associated command definition, or NULL if it couldn't be found.
+	 * @return CommandDefinition|null
+	 */
+	public function getCommandDefinition(): ?CommandDefinition
+	{
+		return $this->commandDefinition ?? null;
+	}
+
+	/**
+	 * Get command handler callable.
+	 * @return callable(mixed...): ?int
+	 */
+	public function getCommandHandler(): callable
+	{
+		return $this->handler;
+	}
+
+	/**
+	 * Get command positional parameters.
+	 * @return array
+	 */
+	public function getParameters(): array
+	{
+		return $this->parameters;
+	}
+
+	/**
+	 * Determine if a flag has been provided in the command.
+	 * @param string $flag Flag (full) name.
+	 * @return bool True if the flag have been provided, false otherwise.
+	 */
+	public function hasFlag(string $flag): bool
+	{
+		return isset($this->flags[$flag]);
+	}
+
+	/**
+	 * Get flag parameters of a flag, if they were provided.
+	 * @param string $flag Flag (full) name.
+	 * @return array Flag parameters.
+	 * @throws FlagNotFoundException
+	 */
+	public function getFlagParameters(string $flag): array
+	{
+		if (!$this->hasFlag($flag))
+			// Flag not provided, throw an exception.
+			throw new FlagNotFoundException($flag);
+
+		return $this->flags[$flag]; // Return flag parameters.
+	}
+}

src/Commands/CommandDefinition.php

@@ -0,0 +1,274 @@
+<?php
+
+namespace Nest\Cli\Commands;
+
+use Nest\Exceptions\Cli\Command\InvalidCommandHandlerException;
+use Nest\Exceptions\Cli\IncompatibleCliHandlerSubcommands;
+
+/**
+ * A command definition object.
+ */
+class CommandDefinition
+{
+	/**
+	 * The command description.
+	 * @var string|null
+	 */
+	protected ?string $description = null;
+
+	/**
+	 * Parameters array for the current command.
+	 * @var array<string, ParameterDefinition>
+	 */
+	protected array $parameters = [];
+
+	/**
+	 * Flags array for the current command.
+	 * @var array<string, FlagDefinition>
+	 */
+	protected array $flags = [];
+
+	/**
+	 * Short flags matching array.
+	 * Associate every short flag with its matching full flag.
+	 * @var array<string, string>
+	 */
+	protected array $shortFlags = [];
+
+	/**
+	 * Command handler.
+	 * @var string
+	 */
+	protected string $handler;
+
+	/**
+	 * Subcommands handler or subcommands definitions.
+	 * @var string|array<string, CommandDefinition>
+	 */
+	protected string|array $subcommands;
+
+	/**
+	 * Set the description of the command.
+	 * @param string $description The description of the command.
+	 * @return $this
+	 */
+	public function description(string $description): static
+	{
+		// Set description.
+		$this->description = $description;
+		return $this;
+	}
+
+	/**
+	 * Define a parameter for the command.
+	 * @param string $name Parameter name.
+	 * @param (callable(ParameterDefinition): ParameterDefinition)|null $parameterDefinition Parameter definition function.
+	 * @return $this
+	 */
+	public function parameter(string $name, ?callable $parameterDefinition = null): static
+	{
+		// Add the given parameter with its definition.
+		$this->parameters[$name] = new ParameterDefinition();
+
+		if (!empty($parameterDefinition))
+			// A parameter definition function is defined, calling it.
+			$this->parameters[$name] = $parameterDefinition($this->parameters[$name]);
+
+		return $this;
+	}
+
+	/**
+	 * Define a flag for the command.
+	 * @param string $flag Flag name.
+	 * @param (callable(FlagDefinition): FlagDefinition)|null $flagDefinition Flag definition function.
+	 * @return $this
+	 */
+	public function flag(string $flag, ?callable $flagDefinition = null): static
+	{
+		// Add the given flag with its definition.
+		$this->flags[$flag] = new FlagDefinition();
+
+		if (!empty($flagDefinition))
+			// A flag definition function is defined, calling it.
+			$this->flags[$flag] = $flagDefinition($this->flags[$flag]);
+
+		if (!empty($short = $this->flags[$flag]->getShort()))
+			// If a short flag is defined, add it to short flag matching array.
+			$this->shortFlags[$short] = $flag;
+
+		return $this;
+	}
+
+	/**
+	 * Define an handler for the command.
+	 * Cannot be used when subcommands are defined.
+	 * @param string $handler Command handler class.
+	 * @return $this
+	 * @throws IncompatibleCliHandlerSubcommands
+	 * @throws InvalidCommandHandlerException
+	 */
+	public function handler(string $handler): static
+	{
+		if (!empty($this->subcommands))
+			// Subcommands are already defined, throwing an exception.
+			throw new IncompatibleCliHandlerSubcommands();
+
+		// Check that the command handler has the right type.
+		if (!is_a($handler, CommandHandler::class, true))
+			throw new InvalidCommandHandlerException($handler);
+
+		// Set the current command handler.
+		$this->handler = $handler;
+
+		return $this;
+	}
+
+	/**
+	 * Define subcommands for the command.
+	 * Cannot be used when handler is defined.
+	 * @param string|array<string, callable(CommandDefinition): CommandDefinition> $subcommands Subcommands handler or subcommands definitions array.
+	 * @return $this
+	 * @throws IncompatibleCliHandlerSubcommands
+	 * @throws InvalidCommandHandlerException
+	 */
+	public function subcommands(string|array $subcommands): static
+	{
+		if (!empty($this->handler))
+			// A handler is already defined, throwing an exception.
+			throw new IncompatibleCliHandlerSubcommands();
+
+		if (is_string($subcommands))
+		{ // If subcommands is a handler class, check that the subcommands handler has the right type.
+			if (!is_a($subcommands, CommandHandler::class, true))
+				throw new InvalidCommandHandlerException($subcommands);
+			// Set subcommands handler.
+			$this->subcommands = $subcommands;
+		}
+		else
+		{ // Set subcommands definition array.
+			foreach ($subcommands as $subcommand => $definitionCallable)
+			{ // For each subcommand definition, call its definition function.
+				$this->subcommands[$subcommand] = $definitionCallable(new CommandDefinition());
+			}
+		}
+
+		return $this;
+	}
+
+	/**
+	 * Return true if a command handler is defined for this command.
+	 * @return bool
+	 */
+	public function hasHandler(): bool
+	{
+		return !empty($this->handler);
+	}
+
+	/**
+	 * Get defined command handler class.
+	 * @return string Command handler class.
+	 */
+	public function getHandler(): string
+	{
+		return $this->handler;
+	}
+
+	/**
+	 * Return true if subcommands are defined for this command.
+	 * @return bool
+	 */
+	public function hasSubcommands(): bool
+	{
+		return !empty($this->subcommands);
+	}
+
+	/**
+	 * Get subcommands definition.
+	 * @return string|array<string, callable(CommandDefinition): CommandDefinition> Subcommands handler or subcommands definitions.
+	 */
+	public function getSubcommands(): string|array
+	{
+		return $this->subcommands;
+	}
+
+	/**
+	 * Get required parameters count.
+	 * @return int Required parameters count.
+	 */
+	public function getRequiredParametersCount(): int
+	{
+		// Check every parameter to count the required ones.
+		return array_reduce(
+			$this->parameters,
+			// Add 1 everytime we see a required parameter.
+			fn (int $total, ParameterDefinition $parameter) => $total + ($parameter->isRequired() ? 1 : 0),
+			0,
+		);
+	}
+
+	/**
+	 * Get command description.
+	 * @return string
+	 */
+	public function getDescription(): string
+	{
+		return $this->description ?? "";
+	}
+
+	/**
+	 * Get defined parameters for the command.
+	 * @return array<string, ParameterDefinition> Defined parameters.
+	 */
+	public function getParameters(): array
+	{
+		return $this->parameters;
+	}
+
+	/**
+	 * Get short flag full name.
+	 * @param string $shortFlag Short flag name.
+	 * @return string|null Flag full name. NULL if undefined.
+	 */
+	public function getShortFlagName(string $shortFlag): ?string
+	{
+		return $this->shortFlags[$shortFlag] ?? null;
+	}
+
+	/**
+	 * Get flag definition for the given flag (full) name.
+	 * @param string $flag Flag (full) name.
+	 * @return FlagDefinition|null Flag definition. NULL if undefined.
+	 */
+	public function getFlagDefinition(string $flag): ?FlagDefinition
+	{
+		return $this->flags[$flag] ?? null;
+	}
+
+	/**
+	 * Get required flags list.
+	 * @return string[] Required flags names.
+	 */
+	public function getRequiredFlags(): array
+	{
+		// Initialize required flags list.
+		$requiredFlags = [];
+
+		foreach ($this->flags as $flag => $definition)
+		{ // For each flag, if it is required, add it in the list.
+			if ($definition->isRequired())
+				// The current flag is required, adding it to the list.
+				$requiredFlags[] = $flag;
+		}
+
+		return $requiredFlags;
+	}
+
+	/**
+	 * Get defined flags for the command.
+	 * @return array<string, FlagDefinition> Defined flags.
+	 */
+	public function getFlags(): array
+	{
+		return $this->flags;
+	}
+}

src/Commands/CommandHandler.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace Nest\Cli\Commands;
+
+use Nest\Cli\Cli;
+
+/**
+ * A CLI command handler.
+ */
+abstract class CommandHandler
+{
+	/**
+	 * Initialize a CLI command handler.
+	 * @param Cli $cli The CLI of the command.
+	 * @param CommandContext $context Current command context.
+	 */
+	public function __construct(protected Cli $cli, protected CommandContext $context)
+	{}
+}

src/Commands/FlagDefinition.php

@@ -0,0 +1,125 @@
+<?php
+
+namespace Nest\Cli\Commands;
+
+/**
+ * A flag definition object.
+ */
+class FlagDefinition
+{
+	/**
+	 * Help flag name.
+	 */
+	const string HELP_FLAG = "help";
+
+	/**
+	 * Short version of the flag.
+	 * @var string|null
+	 */
+	protected ?string $short = null;
+
+	/**
+	 * Flag description.
+	 * @var string|null
+	 */
+	protected ?string $description = null;
+
+	/**
+	 * Positional parameters array for the current flag.
+	 * @var object{name: string, description: string}[]
+	 */
+	protected array $parameters = [];
+
+	/**
+	 * Set if the flag is required or not. A flag is NOT required by default.
+	 * @var bool
+	 */
+	protected bool $required = false;
+
+	/**
+	 * Set the short version of the flag.
+	 * @param string $short Short version of the flag.
+	 * @return $this
+	 */
+	public function short(string $short): static
+	{
+		$this->short = $short;
+		return $this;
+	}
+
+	/**
+	 * Set the description of the flag.
+	 * @param string $description The description of the flag.
+	 * @return $this
+	 */
+	public function description(string $description): static
+	{
+		// Set description.
+		$this->description = $description;
+		return $this;
+	}
+
+	/**
+	 * Add a positional parameter to the flag.
+	 * @param string $name Parameter name.
+	 * @param string $description Parameter description.
+	 * @return $this
+	 */
+	public function parameter(string $name, string $description): static
+	{
+		// Add a positional parameter to the next position, with given metadata.
+		$this->parameters[] = (object) [
+			"name" => $name,
+			"description" => $description,
+		];
+
+		return $this;
+	}
+
+	/**
+	 * Set the flag as required (or not).
+	 * @param bool $require True to set the flag as required.
+	 * @return $this
+	 */
+	public function require(bool $require = true): static
+	{
+		$this->required = $require;
+		return $this;
+	}
+
+	/**
+	 * Get short version of the flag, if there is one.
+	 * @return string|null
+	 */
+	public function getShort(): ?string
+	{
+		return $this->short;
+	}
+
+	/**
+	 * Get flag description.
+	 * @return string
+	 */
+	public function getDescription(): string
+	{
+		return $this->description ?? "";
+	}
+
+	/**
+	 * Get flag parameters count.
+	 * @return int
+	 */
+	public function getParametersCount(): int
+	{
+		return count($this->parameters);
+	}
+
+	/**
+	 * Determine if the flag is required or not.
+	 * @return bool True if the flag is required.
+	 */
+	public function isRequired(): bool
+	{
+		return $this->required;
+	}
+}

src/Commands/ParameterDefinition.php

@@ -0,0 +1,71 @@
+<?php
+
+namespace Nest\Cli\Commands;
+
+/**
+ * A parameter definition object.
+ */
+class ParameterDefinition
+{
+	/**
+	 * Parameter description.
+	 * @var string|null
+	 */
+	protected ?string $description = null;
+
+	/**
+	 * Set if the parameter is optional or not. By default, it is NOT optional.
+	 * @var bool
+	 */
+	protected bool $optional = false;
+
+	/**
+	 * Set the description of the parameter.
+	 * @param string $description The description of the parameter.
+	 * @return $this
+	 */
+	public function description(string $description): static
+	{
+		// Set description.
+		$this->description = $description;
+		return $this;
+	}
+
+	/**
+	 * Set the parameter as optional (or not).
+	 * @param bool $optional True to set the parameter as optional.
+	 * @return $this
+	 */
+	public function optional(bool $optional = true): static
+	{
+		$this->optional = $optional;
+		return $this;
+	}
+
+	/**
+	 * Set the parameter as required.
+	 * @return $this
+	 */
+	public function require(): static
+	{
+		return $this->optional(false);
+	}
+
+	/**
+	 * Get parameter description.
+	 * @return string
+	 */
+	public function getDescription(): string
+	{
+		return $this->description ?? "";
+	}
+
+	/**
+	 * Determine if the parameter is required or not.
+	 * @return bool True if the parameter is required.
+	 */
+	public function isRequired(): bool
+	{
+		return !$this->optional;
+	}
+}

src/DefaultHelper.php

@@ -0,0 +1,217 @@
+<?php
+
+namespace Nest\Cli;
+
+use Nest\Cli\Commands\CommandContext;
+use Nest\Cli\Commands\CommandDefinition;
+use Throwable;
+
+/**
+ * Default CLI helper.
+ */
+class DefaultHelper implements CliHelper
+{
+	public const string REQUIRED_FIELD_PREFIX = "{";
+	public const string REQUIRED_FIELD_SUFFIX = "}";
+
+	public const string OPTIONAL_FIELD_PREFIX = "[";
+	public const string OPTIONAL_FIELD_SUFFIX = "]";
+
+	/**
+	 * The command context.
+	 * @var CommandContext
+	 */
+	private CommandContext $command;
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function help(Cli $cli, CommandContext $command, ?Throwable $exception = null): void
+	{
+		// Save command context in class property.
+		$this->command = $command;
+
+		if (!empty($exception))
+			// If an exception has been thrown, show its message.
+			Out::error($exception->getMessage());
+
+		echo "\n";
+
+		if (!empty($commandDefinition = $command->getCommandDefinition()))
+		{ // A command definition have been provided. Showing help for this command especially.
+			$this->showHelp($command->getFullCommand(), $commandDefinition, true);
+		}
+		else
+		{
+			echo Out::BOLD_ATTRIBUTE."Available commands: ".Out::RESET_ATTRIBUTES."\n\n";
+			foreach ($cli->getCommands() as $command => $commandDefinition)
+			{ // Showing help for each command.
+				// Dimmed list tick.
+				echo Out::DIM_ATTRIBUTE;
+				echo " -  ";
+				echo Out::RESET_ATTRIBUTES;
+				// Command help.
+				$this->showHelp($command, $commandDefinition);
+			}
+		}
+	}
+
+	/**
+	 * Show help for a specific command definition.
+	 * @param string $command Current command to show.
+	 * @param CommandDefinition $commandDefinition Full command definition.
+	 * @param bool $details If true, help will show detailed information about parameters and flags.
+	 * @return void
+	 */
+	private function showHelp(string $command, CommandDefinition $commandDefinition, bool $details = false): void
+	{
+		if ($details)
+		{ // Details requested.
+			if ($commandDefinition->hasSubcommands())
+			{ // If there are subcommands, showing all subcommands.
+				$subcommands = $commandDefinition->getSubcommands();
+				if (is_array($subcommands))
+				{ // Showing subcommands array details.
+					echo Out::BOLD_ATTRIBUTE." Subcommands: ".Out::RESET_ATTRIBUTES."\n\n";
+
+					foreach ($subcommands as $subcommand => $subcommandDefinition)
+					{
+						// Dimmed list tick.
+						echo Out::DIM_ATTRIBUTE;
+						echo " -  ";
+						echo Out::RESET_ATTRIBUTES;
+						// Show subcommand help.
+						$this->showHelp("$command:$subcommand", $subcommandDefinition);
+					}
+				}
+				else
+				{ // Showing generic subcommands manual.
+					echo "{$this->command->getExecutable()} $command";
+					echo ":{}";
+					echo "\n\n";
+					echo Out::DIM_ATTRIBUTE." Customized subcommands are not documented.".Out::RESET_ATTRIBUTES;
+				}
+			}
+			elseif ($commandDefinition->hasHandler())
+			{ // If there is an handler, showing all parameters with details.
+				echo "{$this->command->getExecutable()} $command";
+
+				$this->printParameters($commandDefinition);
+				$this->printFlags($commandDefinition);
+
+				echo "\n\n";
+
+				if (!empty($commandDefinition->getParameters()))
+				{ // Show full parameters details.
+					echo Out::BOLD_ATTRIBUTE." Parameters: ".Out::RESET_ATTRIBUTES."\n\n";
+					foreach ($commandDefinition->getParameters() as $parameter => $parameterDefinition)
+					{ // Show details of each parameter.
+
+						// Dimmed list tick.
+						echo Out::DIM_ATTRIBUTE;
+						if (!$parameterDefinition->isRequired())
+							echo "  *  (optional) ";
+						else
+							echo "  -  ";
+						echo Out::RESET_ATTRIBUTES;
+
+						echo "$parameter: ".Out::ITALIC_ATTRIBUTE."{$parameterDefinition->getDescription()}".Out::RESET_ATTRIBUTES;
+						echo "\n";
+					}
+
+					// Parameters end.
+					echo "\n";
+				}
+				else
+					echo Out::DIM_ATTRIBUTE." No parameters.\n".Out::RESET_ATTRIBUTES;
+
+				if (!empty($commandDefinition->getFlags()))
+				{ // Show full flags details.
+					// Show flags in yellow.
+					echo Color::LightYellow->value;
+
+					// Show full flags details.
+					echo Out::BOLD_ATTRIBUTE." Flags: ".Out::RESET_ATTRIBUTES.Color::LightYellow->value."\n";
+
+					foreach ($commandDefinition->getFlags() as $flag => $flagDefinition)
+					{ // Show details of each parameter.
+
+						echo "\n";
+
+						$flagColor = $flagDefinition->isRequired() ? Color::LightRed->value : Color::LightYellow->value;
+
+						// Dimmed list tick.
+						echo $flagColor.Out::DIM_ATTRIBUTE;
+						echo "  -  ";
+						if ($flagDefinition->isRequired()) echo "(required) ";
+						echo Out::RESET_ATTRIBUTES.$flagColor;
+
+						echo "--$flag";
+						if (!empty($short = $flagDefinition->getShort()))
+						{ // If a short equivalent is defined, showing it.
+							echo " (alt.: -$short)";
+						}
+						echo ": ".Out::ITALIC_ATTRIBUTE."{$flagDefinition->getDescription()}".Out::RESET_ATTRIBUTES.Color::LightYellow->value;
+					}
+
+					// Flags end.
+					echo Color::Default->value;
+				}
+				else
+					echo Out::DIM_ATTRIBUTE." No flags.\n".Out::RESET_ATTRIBUTES;
+			}
+			else
+			{ // Something is wrong with the definition.
+				echo "\n";
+				Out::error("Invalid command definition.");
+			}
+		}
+		else
+		{ // Details not requested, simply show parameters and flags.
+			echo "{$this->command->getExecutable()} $command";
+
+			$this->printParameters($commandDefinition);
+			$this->printFlags($commandDefinition);
+
+			if (!empty($description = $commandDefinition->getDescription()))
+			{
+				echo "\n";
+				echo Out::ITALIC_ATTRIBUTE."    $description".Out::RESET_ATTRIBUTES;
+			}
+		}
+
+		echo "\n\n";
+	}
+
+	/**
+	 * Print parameters of a command.
+	 * @param CommandDefinition $commandDefinition Command definition.
+	 * @return void
+	 */
+	private function printParameters(CommandDefinition $commandDefinition): void
+	{
+		foreach ($commandDefinition->getParameters() as $parameter => $parameterDefinition)
+		{ // Show every parameter according to its definition.
+			echo " ";
+			echo $parameterDefinition->isRequired() ? static::REQUIRED_FIELD_PREFIX : static::OPTIONAL_FIELD_PREFIX;
+			echo $parameter;
+			echo $parameterDefinition->isRequired() ? static::REQUIRED_FIELD_SUFFIX : static::OPTIONAL_FIELD_SUFFIX;
+		}
+	}
+
+	/**
+	 * Print flags of a command.
+	 * @param CommandDefinition $commandDefinition Command definition.
+	 * @return void
+	 */
+	private function printFlags(CommandDefinition $commandDefinition): void
+	{
+		foreach ($commandDefinition->getFlags() as $flag => $flagDefinition)
+		{ // Show every flag according to its definition.
+			echo " ";
+			echo $flagDefinition->isRequired() ? static::REQUIRED_FIELD_PREFIX : static::OPTIONAL_FIELD_PREFIX;
+			echo "--$flag";
+			echo $flagDefinition->isRequired() ? static::REQUIRED_FIELD_SUFFIX : static::OPTIONAL_FIELD_SUFFIX;
+		}
+	}
+}

src/Exceptions/CliException.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace Nest\Cli\Exceptions;
+
+use Nest\Exceptions\Exception;
+
+class CliException extends Exception
+{
+}

src/Exceptions/Command/CommandException.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Nest\Cli\Exceptions\Command;
+
+use Nest\Cli\Commands\CommandContext;
+use Nest\Cli\Exceptions\CliException;
+use Throwable;
+
+/**
+ * Exception thrown when parsing a command.
+ */
+class CommandException extends CliException
+{
+	/**
+	 * @param CommandContext $commandContext Command context.
+	 * @param string $message [optional] The Exception message to throw.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public CommandContext $commandContext, string $message = "", int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct($message, $code, $previous);
+	}
+}

src/Exceptions/Command/IncompleteCommandException.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace Nest\Cli\Exceptions\Command;
+
+use Nest\Cli\Commands\CommandContext;
+use Throwable;
+
+/**
+ * Exception thrown when an incomplete command has been used.
+ */
+class IncompleteCommandException extends CommandException
+{
+	/**
+	 * @param CommandContext $commandContext Command context.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(CommandContext $commandContext, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct($commandContext, "Incomplete command.", $code, $previous);
+	}
+}

src/Exceptions/Command/InvalidCommandException.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Nest\Cli\Exceptions\Command;
+
+use Nest\Cli\Commands\CommandContext;
+use Throwable;
+
+/**
+ * Exception thrown when an invalid command has been used.
+ */
+class InvalidCommandException extends CommandException
+{
+	/**
+	 * @param string $invalidCommand Invalid command in context.
+	 * @param CommandContext $commandContext Command context.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public string $invalidCommand, CommandContext $commandContext, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct($commandContext, "Invalid command $this->invalidCommand in this context.", $code, $previous);
+	}
+}

src/Exceptions/Command/InvalidCommandHandlerException.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Nest\Cli\Exceptions\Command;
+
+use Nest\Cli\Commands\CommandHandler;
+use Nest\Exceptions\Cli\CliException;
+use Throwable;
+
+/**
+ * Exception thrown when a given command handler is not of the right type.
+ */
+class InvalidCommandHandlerException extends CliException
+{
+	/**
+	 * @param string $commandHandlerClass Class of command handler with invalid type.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public string $commandHandlerClass, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct("$this->commandHandlerClass must be of type ".CommandHandler::class, $code, $previous);
+	}
+}

src/Exceptions/Command/InvalidParametersException.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Nest\Cli\Exceptions\Command;
+
+use Nest\Cli\Commands\CommandContext;
+use Throwable;
+
+/**
+ * Exception thrown when invalid command parameters have been provided.
+ */
+class InvalidParametersException extends CommandException
+{
+	/**
+	 * @param CommandContext $commandContext Command context.
+	 * @param string $message [optional] The Exception message to throw.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(CommandContext $commandContext, string $message = "", int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct($commandContext, "Invalid parameters".(!empty($message) ? ": $message" : "."), $code, $previous);
+	}
+}

src/Exceptions/Command/MissingCommandException.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace Nest\Cli\Exceptions\Command;
+
+use Nest\Cli\Commands\CommandContext;
+use Throwable;
+
+/**
+ * Exception thrown when no command have been provided.
+ */
+class MissingCommandException extends CommandException
+{
+	/**
+	 * @param CommandContext $commandContext Command context.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(CommandContext $commandContext, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct($commandContext, "Please provide a command to execute.", $code, $previous);
+	}
+}

src/Exceptions/Command/MissingRequiredFlagException.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Nest\Cli\Exceptions\Command;
+
+use Nest\Cli\Commands\CommandContext;
+use Throwable;
+
+/**
+ * Exception thrown when a required flag is missing.
+ */
+class MissingRequiredFlagException extends CommandException
+{
+	/**
+	 * @param string $flag Missing flag.
+	 * @param CommandContext $commandContext Command context.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public string $flag, CommandContext $commandContext, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct($commandContext, "The required flag $this->flag is missing.", $code, $previous);
+	}
+}

src/Exceptions/Command/NotEnoughParametersException.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Nest\Cli\Exceptions\Command;
+
+use Nest\Cli\Commands\CommandContext;
+use Throwable;
+
+/**
+ * Exception thrown when not enough parameters have been provided.
+ */
+class NotEnoughParametersException extends InvalidParametersException
+{
+	/**
+	 * @param int $providedCount Provided parameters count.
+	 * @param int $expectedCount Expected parameters count.
+	 * @param CommandContext $commandContext Command context.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public int $providedCount, public int $expectedCount, CommandContext $commandContext, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct($commandContext, "Not enough parameters: $this->providedCount provided, expected $this->expectedCount.", $code, $previous);
+	}
+}

src/Exceptions/Command/UndefinedFlagException.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Nest\Cli\Exceptions\Command;
+
+use Nest\Cli\Commands\CommandContext;
+use Throwable;
+
+/**
+ * Exception thrown when an undefined flag has been provided.
+ */
+class UndefinedFlagException extends CommandException
+{
+	/**
+	 * @param string $flag Undefined flag.
+	 * @param CommandContext $commandContext Command context.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public string $flag, CommandContext $commandContext, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct($commandContext, "Provided flag $this->flag is not defined for this command.", $code, $previous);
+	}
+}

src/Exceptions/Command/UndefinedShortFlagException.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace Nest\Cli\Exceptions\Command;
+
+/**
+ * Exception thrown when an undefined short flag has been provided.
+ */
+class UndefinedShortFlagException extends UndefinedFlagException
+{
+}

src/Exceptions/Command/UndefinedSubcommandsException.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Nest\Cli\Exceptions\Command;
+
+use Nest\Cli\Commands\CommandContext;
+use Throwable;
+
+/**
+ * Exception thrown when no subcommands are defined for the given command.
+ */
+class UndefinedSubcommandsException extends CommandException
+{
+	/**
+	 * @param string $invalidCommand Command with no subcommands.
+	 * @param CommandContext $commandContext Command context.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public string $invalidCommand, CommandContext $commandContext, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct($commandContext, "No defined subcommands for $this->invalidCommand.", $code, $previous);
+	}
+}

src/Exceptions/FlagNotFoundException.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace Nest\Cli\Exceptions;
+
+use Throwable;
+
+/**
+ * Exception thrown when a requested flag is not found.
+ */
+class FlagNotFoundException extends CliException
+{
+	/**
+	 * @param string $flag Request flag (full) name.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public string $flag, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct("$this->flag was not provided in the command.", $code, $previous);
+	}
+}

src/Exceptions/IncompatibleCliHandlerSubcommands.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Nest\Cli\Exceptions;
+
+use Throwable;
+
+/**
+ * Exception thrown when a handler and subcommands are defined at the same time in a command definition.
+ */
+class IncompatibleCliHandlerSubcommands extends CliException
+{
+	/**
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct("Cannot define a command handler and subcommands for the same command.", $code, $previous);
+	}
+}

src/Out.php

@@ -0,0 +1,94 @@
+<?php
+
+namespace Nest\Cli;
+
+/**
+ * CLI out functions.
+ */
+class Out
+{
+	/**
+	 * Reset attributes special character.
+	 */
+	public const string RESET_ATTRIBUTES = "\e[0m";
+	/**
+	 * Bold attribute special character.
+	 */
+	public const string BOLD_ATTRIBUTE = "\e[1m";
+	/**
+	 * Italic attribute special character.
+	 */
+	public const string ITALIC_ATTRIBUTE = "\e[3m";
+	/**
+	 * Dim attribute special character.
+	 */
+	public const string DIM_ATTRIBUTE = "\e[2m";
+
+	/**
+	 * Print a message.
+	 * @param string $message Message to print.
+	 * @param string $symbol Prefix symbol.
+	 * @param Color $color Text color.
+	 * @param bool $bold Set text to bold.
+	 * @param bool $dim Set text to dim.
+	 * @return void
+	 */
+	public static function print(string $message, string $symbol = "❯", Color $color = Color::Default, bool $bold = false, bool $dim = false): void
+	{
+		echo
+			// Set color and attributes.
+			$color->value.($bold ? self::BOLD_ATTRIBUTE : "").($dim ? self::DIM_ATTRIBUTE : "").
+			// Print message with its symbol.
+			"$symbol $message".
+			// Reset colors and attributes.
+			Color::Default->value.self::RESET_ATTRIBUTES."\n";
+	}
+
+	/**
+	 * Print an informational message.
+	 * @param string $message Message to print.
+	 * @param bool $bold Set text to bold.
+	 * @param bool $dim Set text to dim.
+	 * @return void
+	 */
+	public static function info(string $message, bool $bold = false, bool $dim = false): void
+	{
+		self::print($message, "ℹ", Color::Cyan, $bold, $dim);
+	}
+
+	/**
+	 * Print a success message.
+	 * @param string $message Message to print.
+	 * @param bool $bold Set text to bold.
+	 * @param bool $dim Set text to dim.
+	 * @return void
+	 */
+	public static function success(string $message, bool $bold = false, bool $dim = false): void
+	{
+		self::print($message, "✔", Color::Green, $bold, $dim);
+	}
+
+	/**
+	 * Print a warning message.
+	 * @param string $message Message to print.
+	 * @param bool $bold Set text to bold.
+	 * @param bool $dim Set text to dim.
+	 * @return void
+	 */
+	public static function warning(string $message, bool $bold = false, bool $dim = false): void
+	{
+		self::print($message, "!", Color::Yellow, $bold, $dim);
+	}
+
+	/**
+	 * Print an error message.
+	 * @param string $message Message to print.
+	 * @param bool $bold Set text to bold.
+	 * @param bool $dim Set text to dim.
+	 * @return void
+	 */
+	public static function error(string $message, bool $bold = false, bool $dim = false): void
+	{
+		self::print($message, "‼", Color::Red, $bold, $dim);
+	}
+}