Fix availability feature

- Bring back some missing functionality which got missing
  during the rework to new command model.
- Polish some classes.
- Restore origin sample.
- Add availability things into help templates and its
  representation model.
- Fixes #423

spring-shell-core/src/main/java/org/springframework/shell/CommandNotCurrentlyAvailable.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 the original author or authors.
+ * Copyright 2017-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -13,7 +13,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.shell;
 
 /**
@@ -23,20 +22,21 @@ package org.springframework.shell;
  */
 public class CommandNotCurrentlyAvailable extends RuntimeException {
 
-    private final String command;
-    private final Availability availability;
+	private final String command;
+	private final Availability availability;
 
-    public CommandNotCurrentlyAvailable(String command, Availability availability) {
-        super(String.format("Command '%s' exists but is not currently available because %s", command, availability.getReason()));
-        this.command = command;
-        this.availability = availability;
-    }
+	public CommandNotCurrentlyAvailable(String command, Availability availability) {
+		super(String.format("Command '%s' exists but is not currently available because %s", command,
+				availability.getReason()));
+		this.command = command;
+		this.availability = availability;
+	}
 
-    public String getCommand() {
-        return command;
-    }
+	public String getCommand() {
+		return command;
+	}
 
-    public Availability getAvailability() {
-        return availability;
-    }
+	public Availability getAvailability() {
+		return availability;
+	}
 }

spring-shell-core/src/main/java/org/springframework/shell/command/CommandExecution.java

@@ -29,6 +29,8 @@ import org.springframework.core.convert.ConversionService;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.handler.invocation.HandlerMethodArgumentResolver;
 import org.springframework.messaging.support.MessageBuilder;
+import org.springframework.shell.Availability;
+import org.springframework.shell.CommandNotCurrentlyAvailable;
 import org.springframework.shell.command.CommandParser.CommandParserException;
 import org.springframework.shell.command.CommandParser.CommandParserResults;
 import org.springframework.shell.command.CommandRegistration.TargetInfo;
@@ -95,6 +97,11 @@ public interface CommandExecution {
 		}
 
 		public Object evaluate(CommandRegistration registration, String[] args) {
+			// fast fail with availability before doing anything else
+			Availability availability = registration.getAvailability();
+			if (availability != null && !availability.isAvailable()) {
+				return new CommandNotCurrentlyAvailable(registration.getCommand(), availability);
+			}
 
 			List<CommandOption> options = registration.getOptions();
 			CommandParser parser = CommandParser.of(conversionService);

spring-shell-core/src/test/java/org/springframework/shell/command/CommandExecutionTests.java

@@ -26,6 +26,8 @@ import org.junit.jupiter.params.provider.ValueSource;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.messaging.handler.invocation.HandlerMethodArgumentResolver;
+import org.springframework.shell.Availability;
+import org.springframework.shell.CommandNotCurrentlyAvailable;
 import org.springframework.shell.command.CommandExecution.CommandParserExceptionsException;
 import org.springframework.shell.command.CommandRegistration.OptionArity;
 
@@ -459,4 +461,22 @@ public class CommandExecutionTests extends AbstractCommandTests {
 			execution.evaluate(r1, new String[]{});
 		}).isInstanceOf(CommandParserExceptionsException.class);
 	}
+
+	@Test
+	public void testCommandNotAvailable() {
+		CommandRegistration r1 = CommandRegistration.builder()
+			.command("command1")
+			.description("help")
+			.withOption()
+				.longNames("arg1")
+				.description("some arg1")
+				.and()
+			.availability(() -> Availability.unavailable("fake reason"))
+			.withTarget()
+				.function(function1)
+				.and()
+			.build();
+		Object result = execution.evaluate(r1, new String[]{"--arg1", "myarg1value"});
+		assertThat(result).isInstanceOf(CommandNotCurrentlyAvailable.class);
+	}
 }

spring-shell-core/src/test/java/org/springframework/shell/command/CommandRegistrationTests.java

@@ -18,6 +18,7 @@ package org.springframework.shell.command;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.core.ResolvableType;
+import org.springframework.shell.Availability;
 import org.springframework.shell.command.CommandRegistration.OptionArity;
 import org.springframework.shell.command.CommandRegistration.TargetInfo.TargetType;
 import org.springframework.shell.context.InteractionMode;
@@ -410,4 +411,27 @@ public class CommandRegistrationTests extends AbstractCommandTests {
 		assertThat(registration.getExitCode()).isNotNull();
 		assertThat(registration.getExitCode().getMappingFunctions()).hasSize(4);
 	}
+
+	@Test
+	public void testAvailability() {
+		CommandRegistration registration;
+		registration = CommandRegistration.builder()
+			.command("command1")
+			.withTarget()
+				.function(function1)
+				.and()
+			.build();
+		assertThat(registration.getAvailability()).isNotNull();
+		assertThat(registration.getAvailability().isAvailable()).isTrue();
+
+		registration = CommandRegistration.builder()
+			.command("command1")
+			.availability(() -> Availability.unavailable("fake"))
+			.withTarget()
+				.function(function1)
+				.and()
+			.build();
+		assertThat(registration.getAvailability()).isNotNull();
+		assertThat(registration.getAvailability().isAvailable()).isFalse();
+	}
 }