Flow system for UI components

- Implement basic flow system with builder patterns
  to easily use components and hook those together
  as a flow.
- Fixes #364

spring-shell-samples/src/main/java/org/springframework/shell/samples/standard/ComponentFlowCommands.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.shell.samples.standard;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.springframework.shell.component.flow.ComponentFlow;
+import org.springframework.shell.component.flow.SelectItem;
+import org.springframework.shell.standard.AbstractShellComponent;
+import org.springframework.shell.standard.ShellComponent;
+import org.springframework.shell.standard.ShellMethod;
+
+@ShellComponent
+public class ComponentFlowCommands extends AbstractShellComponent {
+
+	@ShellMethod(key = "flow showcase", value = "Showcase", group = "Flow")
+	public void showcase() {
+		Map<String, String> single1SelectItems = new HashMap<>();
+		single1SelectItems.put("key1", "value1");
+		single1SelectItems.put("key2", "value2");
+		List<SelectItem> multi1SelectItems = Arrays.asList(SelectItem.of("key1", "value1"),
+				SelectItem.of("key2", "value2"), SelectItem.of("key3", "value3"));
+		ComponentFlow flow = ComponentFlow.builder(getTerminal())
+				.resourceLoader(getResourceLoader())
+				.templateExecutor(getTemplateExecutor())
+				.withStringInput("field1")
+					.name("Field1")
+					.defaultValue("defaultField1Value")
+					.and()
+				.withStringInput("field2")
+					.name("Field2")
+					.and()
+				.withConfirmationInput("confirmation1")
+					.name("Confirmation1")
+					.and()
+				.withPathInput("path1")
+					.name("Path1")
+					.and()
+				.withSingleItemSelector("single1")
+					.name("Single1")
+					.selectItems(single1SelectItems)
+					.and()
+				.withMultiItemSelector("multi1")
+					.name("Multi1")
+					.selectItems(multi1SelectItems)
+					.and()
+				.build();
+		flow.run();
+	}
+
+	@ShellMethod(key = "flow conditional", value = "Second component based on first", group = "Flow")
+	public void conditional() {
+		Map<String, String> single1SelectItems = new HashMap<>();
+		single1SelectItems.put("Field1", "field1");
+		single1SelectItems.put("Field2", "field2");
+		ComponentFlow flow = ComponentFlow.builder(getTerminal())
+				.resourceLoader(getResourceLoader())
+				.templateExecutor(getTemplateExecutor())
+				.withSingleItemSelector("single1")
+					.name("Single1")
+					.selectItems(single1SelectItems)
+					.next(ctx -> ctx.getResultItem().get().getItem())
+					.and()
+				.withStringInput("field1")
+					.name("Field1")
+					.defaultValue("defaultField1Value")
+					.next(ctx -> null)
+					.and()
+				.withStringInput("field2")
+					.name("Field2")
+					.defaultValue("defaultField2Value")
+					.next(ctx -> null)
+					.and()
+				.build();
+		flow.run();
+	}
+}