commit 6d6c56518c2b0c121dc92bbd3c5e738b81c34b06
Author: Florian THIERRY <fthierry@ippon.fr>
Date:   Fri Jul 30 18:36:02 2021 +0200

    Initial commit.

diff --git a/.gitignore b/.gitignore
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index 0000000..549e00a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,33 @@
+HELP.md
+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
diff --git a/pom.xml b/pom.xml
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+++ b/pom.xml
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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>org.springframework.boot</groupId>
+		<artifactId>spring-boot-starter-parent</artifactId>
+		<version>2.5.3</version>
+		<relativePath/> <!-- lookup parent from repository -->
+	</parent>
+	<groupId>org.takiguchi.workflow-validator</groupId>
+	<artifactId>workflow-validator</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+	<name>workflow-validator</name>
+	<description>Demo project for Spring Boot</description>
+	<properties>
+		<java.version>11</java.version>
+	</properties>
+	<dependencies>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter</artifactId>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-test</artifactId>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.springframework.boot</groupId>
+				<artifactId>spring-boot-maven-plugin</artifactId>
+			</plugin>
+		</plugins>
+	</build>
+
+</project>
diff --git a/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/WorkflowValidatorApplication.java b/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/WorkflowValidatorApplication.java
new file mode 100644
index 0000000..d3cb7a6
--- /dev/null
+++ b/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/WorkflowValidatorApplication.java
@@ -0,0 +1,13 @@
+package org.takiguchi.workflowvalidator.workflowvalidator;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class WorkflowValidatorApplication {
+
+	public static void main(String[] args) {
+		SpringApplication.run(WorkflowValidatorApplication.class, args);
+	}
+
+}
diff --git a/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/model/Step.java b/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/model/Step.java
new file mode 100644
index 0000000..93f62c7
--- /dev/null
+++ b/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/model/Step.java
@@ -0,0 +1,122 @@
+package org.takiguchi.workflowvalidator.workflowvalidator.model;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+
+import static org.takiguchi.workflowvalidator.workflowvalidator.model.StepType.FINAL;
+import static org.takiguchi.workflowvalidator.workflowvalidator.model.StepType.INITIAL;
+
+public class Step {
+    private String name;
+    private StepType type;
+    private List<Step> previousSteps;
+    private List<Step> nextSteps;
+
+    public Step(String name, StepType type, List<Step> previousSteps, List<Step> nextSteps) {
+        this.name = name;
+        this.type = type;
+        this.previousSteps = previousSteps;
+        this.nextSteps = nextSteps;
+    }
+
+    public static Builder oneStep() {
+        return new Builder();
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public StepType getType() {
+        return type;
+    }
+
+    public void setType(StepType type) {
+        this.type = type;
+    }
+
+    public List<Step> getPreviousSteps() {
+        return previousSteps;
+    }
+
+    public void setPreviousSteps(List<Step> previousSteps) {
+        this.previousSteps = previousSteps;
+    }
+
+    public List<Step> getNextSteps() {
+        return nextSteps;
+    }
+
+    public void setNextSteps(List<Step> nextSteps) {
+        this.nextSteps = nextSteps;
+    }
+
+    public boolean hasAtLeastOneNextStep() {
+        return !Optional.ofNullable(nextSteps)
+                .map(List::isEmpty)
+                .orElse(false);
+    }
+
+    public boolean hasAtLeastOnePreviousStep() {
+        return !Optional.ofNullable(previousSteps)
+                .map(List::isEmpty)
+                .orElse(false);
+    }
+
+    public boolean isInitialStep() {
+        return type == INITIAL;
+    }
+
+    public boolean isFinalStep() {
+        return type == FINAL;
+    }
+
+    public void addPreviousStep(Step step) {
+        previousSteps.add(step);
+    }
+
+    public void addNextStep(Step step) {
+        nextSteps.add(step);
+    }
+
+    @Override
+    public String toString() {
+        return "Step{" + name + '}';
+    }
+
+    public static class Builder {
+        private String name;
+        private StepType type;
+        private List<Step> previousSteps = new ArrayList<>();
+        private List<Step> nextSteps = new ArrayList<>();
+
+        public Builder name(String name) {
+            this.name = name;
+            return this;
+        }
+
+        public Builder type(StepType type) {
+            this.type = type;
+            return this;
+        }
+
+        public Builder previousSteps(List<Step> previousSteps) {
+            this.previousSteps = previousSteps;
+            return this;
+        }
+
+        public Builder nextSteps(List<Step> nextSteps) {
+            this.nextSteps = nextSteps;
+            return this;
+        }
+
+        public Step build() {
+            return new Step(name, type, previousSteps, nextSteps);
+        }
+    }
+}
diff --git a/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/model/StepType.java b/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/model/StepType.java
new file mode 100644
index 0000000..58a3f1b
--- /dev/null
+++ b/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/model/StepType.java
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+package org.takiguchi.workflowvalidator.workflowvalidator.model;
+
+public enum StepType {
+    INITIAL, MIDDLE, FINAL
+}
diff --git a/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/model/Workflow.java b/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/model/Workflow.java
new file mode 100644
index 0000000..a3c2ee0
--- /dev/null
+++ b/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/model/Workflow.java
@@ -0,0 +1,15 @@
+package org.takiguchi.workflowvalidator.workflowvalidator.model;
+
+import java.util.List;
+
+public class Workflow {
+    private final List<Step> steps;
+
+    public Workflow(List<Step> steps) {
+        this.steps = steps;
+    }
+
+    public List<Step> getSteps() {
+        return steps;
+    }
+}
diff --git a/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/service/WorkflowValidator.java b/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/service/WorkflowValidator.java
new file mode 100644
index 0000000..fe32e93
--- /dev/null
+++ b/src/main/java/org/takiguchi/workflowvalidator/workflowvalidator/service/WorkflowValidator.java
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+package org.takiguchi.workflowvalidator.workflowvalidator.service;
+
+import org.springframework.util.CollectionUtils;
+import org.takiguchi.workflowvalidator.workflowvalidator.model.Step;
+import org.takiguchi.workflowvalidator.workflowvalidator.model.Workflow;
+
+public class WorkflowValidator {
+    public void validate(Workflow workflow) {
+        if (CollectionUtils.isEmpty(workflow.getSteps())) {
+            throw new IllegalStateException("Workflow should have at least one step.");
+        }
+        workflow.getSteps().forEach(this::validateStep);
+    }
+
+    private void validateStep(Step step) {
+        if (step.hasAtLeastOneNextStep()) {
+            if (step.isFinalStep()) {
+                throw new IllegalStateException(String.format("The step %s is final, but it has at least one next step, but it shouldn't.", step));
+            }
+
+            // Non final step, that has at least one next step.
+            validatePreviousStepsOf(step);
+        } else {
+            if (!step.isFinalStep()) {
+                throw new IllegalStateException(String.format("The step %s should have at least one next step.", step));
+            }
+
+            // Final Step, that hasn't any next step.
+            validatePreviousStepsOf(step);
+        }
+    }
+
+    private void validatePreviousStepsOf(Step step) {
+        if (step.hasAtLeastOnePreviousStep()) {
+            if (step.isInitialStep()) {
+                throw new IllegalStateException(String.format("The step %s is initial, but is has at least one previous step, but it shouldn't.", step));
+            }
+
+            // Non initial step, that has at least one previous step.
+
+            if (canPreviousStepsReachAnInitialStep(step)) {
+                // Ok
+            } else {
+                throw new IllegalStateException(String.format("The step %s hasn't any previous step that can reach an initial step.", step));
+            }
+        } else {
+            if (!step.isInitialStep()) {
+                throw new IllegalStateException(String.format("The step %s han't any previous step while it is not an initial step.", step));
+            }
+
+            // Initial step, that hasn't any previous step.
+        }
+    }
+
+    private boolean canPreviousStepsReachAnInitialStep(Step step) {
+        return step.getPreviousSteps().stream()
+                .anyMatch(this::canStepReachAnInitialStep);
+    }
+
+    private boolean canStepReachAnInitialStep(Step step) {
+        boolean result;
+
+        if (step.hasAtLeastOnePreviousStep()) {
+            result = canPreviousStepsReachAnInitialStep(step);
+        } else {
+            result = step.isInitialStep();
+        }
+
+        return result;
+    }
+}
diff --git a/src/main/resources/application.properties b/src/main/resources/application.properties
new file mode 100644
index 0000000..8b13789
--- /dev/null
+++ b/src/main/resources/application.properties
@@ -0,0 +1 @@
+
diff --git a/src/test/java/org/takiguchi/workflowvalidator/workflowvalidator/service/WorkflowValidatorTest.java b/src/test/java/org/takiguchi/workflowvalidator/workflowvalidator/service/WorkflowValidatorTest.java
new file mode 100644
index 0000000..705fdf5
--- /dev/null
+++ b/src/test/java/org/takiguchi/workflowvalidator/workflowvalidator/service/WorkflowValidatorTest.java
@@ -0,0 +1,147 @@
+package org.takiguchi.workflowvalidator.workflowvalidator.service;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.takiguchi.workflowvalidator.workflowvalidator.model.Step;
+import org.takiguchi.workflowvalidator.workflowvalidator.model.StepType;
+import org.takiguchi.workflowvalidator.workflowvalidator.model.Workflow;
+
+import java.util.List;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.catchThrowableOfType;
+import static org.takiguchi.workflowvalidator.workflowvalidator.model.Step.oneStep;
+import static org.takiguchi.workflowvalidator.workflowvalidator.model.StepType.*;
+
+class WorkflowValidatorTest {
+    /** Tested validator. */
+    private WorkflowValidator validator;
+
+    @BeforeEach
+    void setUp() {
+        validator = new WorkflowValidator();
+    }
+
+    @ParameterizedTest
+    @MethodSource("should_validate_data")
+    void should_validate(Workflow workflow) {
+        // when
+        validator.validate(workflow);
+    }
+
+    private static Stream<Arguments> should_validate_data() {
+        return Stream.of(
+                Arguments.of(workflowGood1()),
+                Arguments.of(workflowGood2()),
+                Arguments.of(workflowGood3())
+        );
+    }
+
+    private static Step buildOneStep(String name, StepType type) {
+        return oneStep()
+                .name(name)
+                .type(type)
+                .build();
+    }
+
+    private static Workflow workflowGood1() {
+        Step stepInitial = buildOneStep("A", INITIAL);
+
+        Step stepFinal = buildOneStep("B", FINAL);
+
+        stepInitial.addNextStep(stepFinal);
+        stepFinal.addPreviousStep(stepInitial);
+
+        return new Workflow(List.of(stepInitial, stepFinal));
+    }
+
+    private static Workflow workflowGood2() {
+        Step stepInitial =  buildOneStep("A", INITIAL);
+        Step stepB = buildOneStep("B", MIDDLE);
+        Step stepFinal = buildOneStep("B", FINAL);
+
+        stepInitial.addNextStep(stepB);
+
+        stepB.addPreviousStep(stepInitial);
+        stepB.addNextStep(stepFinal);
+
+        stepFinal.addPreviousStep(stepB);
+
+        return new Workflow(List.of(stepInitial, stepB, stepFinal));
+    }
+
+    private static Object workflowGood3() {
+        Step stepInitial =  buildOneStep("A", INITIAL);
+        Step stepB = buildOneStep("B", MIDDLE);
+        Step stepC = buildOneStep("C", MIDDLE);
+        Step stepFinal = buildOneStep("D", FINAL);
+
+        stepInitial.addNextStep(stepB);
+        stepInitial.addNextStep(stepC);
+
+        stepB.addPreviousStep(stepInitial);
+        stepB.addNextStep(stepFinal);
+
+        stepC.addPreviousStep(stepInitial);
+        stepC.addNextStep(stepFinal);
+
+        stepFinal.addPreviousStep(stepB);
+        stepFinal.addPreviousStep(stepC);
+
+        return new Workflow(List.of(stepInitial, stepB, stepC, stepFinal));
+    }
+
+    @ParameterizedTest
+    @MethodSource("should_throw_an_exception_data")
+    void should_throw_an_exception(Workflow workflow) {
+        // when
+        IllegalStateException exception = catchThrowableOfType(() -> validator.validate(workflow), IllegalStateException.class);
+
+        assertThat(exception).isNotNull();
+    }
+
+    private static Stream<Arguments> should_throw_an_exception_data() {
+        return Stream.of(
+                Arguments.of(workflowBad1()),
+                Arguments.of(workflowBad2()),
+                Arguments.of(workflowBad3()),
+                Arguments.of(workflowBad4())
+        );
+    }
+
+    private static Workflow workflowBad1() {
+        Step stepInitial = buildOneStep("A", INITIAL);
+
+        return new Workflow(List.of(stepInitial));
+    }
+
+    private static Workflow workflowBad2() {
+        Step stepFinal = buildOneStep("B", FINAL);
+
+        return new Workflow(List.of(stepFinal));
+    }
+
+    private static Workflow workflowBad3() {
+        Step stepInitial = buildOneStep("A", INITIAL);
+        Step stepFinal = buildOneStep("B", FINAL);
+
+        stepInitial.addNextStep(stepFinal);
+
+        return new Workflow(List.of(stepInitial, stepFinal));
+    }
+
+    private static Workflow workflowBad4() {
+        Step stepInitial = buildOneStep("A", INITIAL);
+        Step stepFinal = buildOneStep("B", FINAL);
+
+        stepFinal.addPreviousStep(stepInitial);
+
+        return new Workflow(List.of(stepInitial, stepFinal));
+    }
+
+
+}
\ No newline at end of file