diff --git a/README.md b/README.md
index 4a80115..19aec56 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,4 @@
+[![Review Assignment Due Date](https://classroom.github.com/assets/deadline-readme-button-22041afd0340ce965d47ae6ef1cefeee28c7c493a6346c4f15d667ab976d596c.svg)](https://classroom.github.com/a/TvkQWWs6)
 # Features of modern Java
 
 # Цели и задачи л/р:
diff --git a/build.gradle.kts b/build.gradle.kts
index 79bf52a..e4d3ceb 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -5,6 +5,12 @@ plugins {
 group = "org.lab"
 version = "1.0-SNAPSHOT"
 
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(26)
+    }
+}
+
 repositories {
     mavenCentral()
 }
@@ -17,4 +23,19 @@ dependencies {
 
 tasks.test {
     useJUnitPlatform()
+}
+
+// 2. Включаем preview-фичи для компиляции
+tasks.withType<JavaCompile>().configureEach {
+    options.compilerArgs.add("--enable-preview")
+}
+
+// 3. Включаем preview-фичи для запуска тестов
+tasks.withType<Test>().configureEach {
+    jvmArgs("--enable-preview")
+}
+
+// 4. Включаем preview-фичи для запуска приложения через run
+tasks.withType<JavaExec>().configureEach {
+    jvmArgs("--enable-preview")
 }
\ No newline at end of file
diff --git a/src/main/java/org/lab/Main.java b/src/main/java/org/lab/Main.java
index 22028ef..183bc87 100644
--- a/src/main/java/org/lab/Main.java
+++ b/src/main/java/org/lab/Main.java
@@ -1,4 +1,40 @@
+import org.lab.model.bug.Bug;
+import org.lab.model.bug.BugStatus;
+import org.lab.model.milestone.MilestoneStatus;
+import org.lab.model.users.Developer;
+import org.lab.model.users.Manager;
+
+import java.util.Date;
+
 void main() {
-    IO.println("Hello and welcome!");
+    Manager manager = new Manager("Manager");
+    var project =  manager.createProject("Lab 4");
+    IO.println("Manager " + manager.getName() + " create project " + project.getName());
+
+    var developer = new Developer("Backend");
+    manager.addDeveloper(project, developer);
+
+    var milestone = manager.createMilestone("MVP", new Date(), project);
+    manager.setMilestoneStatus(milestone, MilestoneStatus.ACTIVE);
+
+    var _ = manager.createTicket("Do backend", project, milestone, developer);
+
+    var bug = developer.createBug(project, "can't start backend");
+    var newBug = new Bug("can't start backend", project, BugStatus.NEW);
+    IO.println(bug == newBug);
+
+    Bug[] bugs = new Bug[2];
+    bugs[0] = bug;
+    bugs[1] = newBug;
+
+    var fixedBug = developer.resolveBug();
+    IO.println(bug == fixedBug);
+    IO.println(developer.getFirstBug() == fixedBug);
+    IO.println(developer.getFirstBug() == bug);
+
+    Object[] closedBugs = Arrays.stream(bugs).map(Bug::withFixed).map(Bug::withTested).map(Bug::withClosed).toArray();
+    IO.println(closedBugs[0] == closedBugs[1]);
+
+    var _ = new Developer("python backend");
 }
 
diff --git a/src/main/java/org/lab/Point.java b/src/main/java/org/lab/Point.java
new file mode 100644
index 0000000..8c457fe
--- /dev/null
+++ b/src/main/java/org/lab/Point.java
@@ -0,0 +1,22 @@
+package org.lab;
+
+public value class Point {
+    private final double x;
+    private final double y;
+
+    public Point(double x, double y) {
+        this.x = x;
+        this.y = y;
+    }
+
+    public double x() { return x; }
+    public double y() { return y; }
+
+    public Point withX(double newX) {
+        return new Point(newX, this.y);
+    }
+
+    public Point withY(double newY) {
+        return new Point(this.x, newY);
+    }
+}
diff --git a/src/main/java/org/lab/model/bug/Bug.java b/src/main/java/org/lab/model/bug/Bug.java
new file mode 100644
index 0000000..12e8c0b
--- /dev/null
+++ b/src/main/java/org/lab/model/bug/Bug.java
@@ -0,0 +1,25 @@
+package org.lab.model.bug;
+
+import org.lab.model.project.Project;
+
+public value record Bug(String name, Project project, BugStatus status) {
+    public Bug(String name, Project project) {
+        this(name, project, BugStatus.NEW);
+    }
+
+    public Bug withProject(Project project) {
+        return new Bug(this.name, project, this.status);
+    }
+
+    public Bug withFixed() {
+        return new Bug(this.name, this.project, BugStatus.FIXED);
+    }
+
+    public Bug withTested() {
+        return new Bug(this.name, this.project, BugStatus.FIXED);
+    }
+
+    public Bug withClosed() {
+        return new Bug(this.name, this.project, BugStatus.CLOSED);
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/org/lab/model/bug/BugStatus.java b/src/main/java/org/lab/model/bug/BugStatus.java
new file mode 100644
index 0000000..9983871
--- /dev/null
+++ b/src/main/java/org/lab/model/bug/BugStatus.java
@@ -0,0 +1,8 @@
+package org.lab.model.bug;
+
+public enum BugStatus {
+    NEW,
+    FIXED,
+    TESTED,
+    CLOSED,
+}
diff --git a/src/main/java/org/lab/model/milestone/Milestone.java b/src/main/java/org/lab/model/milestone/Milestone.java
new file mode 100644
index 0000000..b9361a9
--- /dev/null
+++ b/src/main/java/org/lab/model/milestone/Milestone.java
@@ -0,0 +1,50 @@
+package org.lab.model.milestone;
+
+import org.lab.model.project.Project;
+import org.lab.model.ticket.Ticket;
+
+import java.util.ArrayList;
+import java.util.Date;
+import java.util.SequencedCollection;
+
+public class Milestone {
+    private final String name;
+    private final Date date;
+    private final Project project;
+    private final SequencedCollection<Ticket> tickets = new ArrayList<>();
+    private MilestoneStatus status = MilestoneStatus.OPEN;
+
+    public Milestone(String name, Date date, Project project) {
+        this.name = name;
+        this.date = date;
+        this.project = project;
+    }
+
+    public void setStatus(MilestoneStatus status) {
+        this.status = status;
+    }
+
+    public void addTicket(Ticket ticket) {
+        this.tickets.addFirst(ticket);
+    }
+
+    public SequencedCollection<Ticket> getTickets() {
+        return this.tickets;
+    }
+
+    public Date getDate() {
+        return date;
+    }
+
+    public Project getProject() {
+        return project;
+    }
+
+    public MilestoneStatus getStatus() {
+        return status;
+    }
+
+    public String getName() {
+        return this.name;
+    }
+}
diff --git a/src/main/java/org/lab/model/milestone/MilestoneStatus.java b/src/main/java/org/lab/model/milestone/MilestoneStatus.java
new file mode 100644
index 0000000..fa936cc
--- /dev/null
+++ b/src/main/java/org/lab/model/milestone/MilestoneStatus.java
@@ -0,0 +1,7 @@
+package org.lab.model.milestone;
+
+public enum MilestoneStatus {
+    OPEN,
+    ACTIVE,
+    CLOSED,
+}
diff --git a/src/main/java/org/lab/model/project/Project.java b/src/main/java/org/lab/model/project/Project.java
new file mode 100644
index 0000000..f28e32e
--- /dev/null
+++ b/src/main/java/org/lab/model/project/Project.java
@@ -0,0 +1,114 @@
+package org.lab.model.project;
+
+import org.lab.model.bug.Bug;
+import org.lab.model.milestone.Milestone;
+import org.lab.model.users.*;
+
+import java.util.*;
+
+public class Project {
+    String name;
+    Leader leader;
+    Manager manager;
+    List<Developer> developers = new ArrayList<>();
+    List<Tester> testers = new ArrayList<>();
+
+    List<Milestone> milestones = new ArrayList<>();
+    SequencedCollection<Bug> bugs = new ArrayList<>();
+
+    public Project(String name) {
+        this.name = name;
+    }
+
+    public void addManager(Manager manager) {
+        if (this.manager != null) {
+            this.removeUser(manager);
+        }
+        this.manager = manager;
+        manager.addProject(this);
+    }
+    
+    public void removeUser(User user) {
+        StringBuilder sb = new StringBuilder();
+        sb.append("Remove ");
+        switch (user) {
+            case Developer developer -> {
+                this.developers.remove(developer);
+                developer.removeProject(this);
+                sb.append("developer ").append(developer.getName());
+            }
+            case Tester tester -> {
+                this.testers.remove(tester);
+                tester.removeProject(this);
+                sb.append("tester ").append(tester.getName());
+            }
+            case Manager manager -> {
+                this.manager = null;
+                manager.removeProject(this);
+                sb.append("manager ").append(manager.getName());
+            }
+            case Leader leader -> {
+                this.leader = null;
+                leader.removeProject(this);
+                sb.append("leader ").append(leader.getName());
+            }
+            default -> throw new IllegalStateException("Unexpected value: " + user);
+        }
+        sb.append(" from project ").append(this.getName());
+        String result = sb.toString();
+        System.out.println(result);
+    }
+
+    public void addUser(User user) {
+        StringBuilder sb = new StringBuilder();
+        sb.append("Add ");
+        switch (user) {
+            case Developer developer -> {
+                this.developers.add(developer);
+                developer.addProject(this);
+                sb.append("developer ").append(developer.getName());
+            }
+            case Tester tester -> {
+                this.testers.add(tester);
+                tester.addProject(this);
+                sb.append("tester ").append(tester.getName());
+            }
+            case Manager manager -> {
+                if (this.manager != null) {
+                    this.removeUser(manager);
+                }
+                this.manager = manager;
+                manager.addProject(this);
+                sb.append("manager ").append(manager.getName());
+            }
+            case Leader leader -> {
+                if (this.leader != null) {
+                    this.removeUser(this.leader);
+                }
+                this.leader = leader;
+                leader.addProject(this);
+                sb.append("leader ").append(leader.getName());
+            }
+            default -> throw new IllegalStateException("Unexpected value: " + user);
+        }
+        sb.append(" to project ").append(this.getName());
+        String result = sb.toString();
+        System.out.println(result);
+    }
+
+    public void addMilestone(Milestone milestone) {
+        this.milestones.add(milestone);
+    }
+
+    public void addBug(Bug bug) {
+        this.bugs.addLast(bug);
+    }
+
+    public boolean isManager(Manager manager) {
+        return this.manager == manager;
+    }
+
+    public String getName() {
+        return this.name;
+    }
+}
diff --git a/src/main/java/org/lab/model/ticket/Ticket.java b/src/main/java/org/lab/model/ticket/Ticket.java
new file mode 100644
index 0000000..1b0b194
--- /dev/null
+++ b/src/main/java/org/lab/model/ticket/Ticket.java
@@ -0,0 +1,11 @@
+package org.lab.model.ticket;
+
+import org.lab.model.milestone.Milestone;
+import org.lab.model.project.Project;
+import org.lab.model.users.Developer;
+
+public record Ticket(String name, Project project, Developer developer, Milestone milestone, TicketStatus status) {
+    public Ticket(String name, Project project, Developer developer, Milestone milestone) {
+        this(name, project, developer, milestone, TicketStatus.NEW);
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/org/lab/model/ticket/TicketStatus.java b/src/main/java/org/lab/model/ticket/TicketStatus.java
new file mode 100644
index 0000000..00cd6d6
--- /dev/null
+++ b/src/main/java/org/lab/model/ticket/TicketStatus.java
@@ -0,0 +1,8 @@
+package org.lab.model.ticket;
+
+public enum TicketStatus {
+    NEW,
+    ACCEPTED,
+    IN_PROGRESS,
+    COMPLETED,
+}
diff --git a/src/main/java/org/lab/model/users/Developer.java b/src/main/java/org/lab/model/users/Developer.java
new file mode 100644
index 0000000..96bf1b2
--- /dev/null
+++ b/src/main/java/org/lab/model/users/Developer.java
@@ -0,0 +1,26 @@
+package org.lab.model.users;
+
+import org.lab.model.bug.Bug;
+import org.lab.model.project.Project;
+
+public final class Developer extends User {
+    public Developer(String name) {
+        if (name.contains("python")) throw new IllegalArgumentException("we can't create python developers");
+        super(name);
+    }
+
+    public Bug createBug(Project project, String name) {
+        var bug = new Bug(name, project);
+        project.addBug(bug);
+        this.bugs.addLast(bug);
+        return bug;
+    }
+
+    public Bug resolveBug() {
+        var bug = this.bugs.getFirst();
+        bug = bug.withFixed();
+        this.bugs.removeFirst();
+        this.bugs.addFirst(bug);
+        return bug;
+    }
+}
diff --git a/src/main/java/org/lab/model/users/Leader.java b/src/main/java/org/lab/model/users/Leader.java
new file mode 100644
index 0000000..6c8438f
--- /dev/null
+++ b/src/main/java/org/lab/model/users/Leader.java
@@ -0,0 +1,7 @@
+package org.lab.model.users;
+
+public final class Leader extends User {
+    public Leader(String name) {
+        super(name);
+    }
+}
diff --git a/src/main/java/org/lab/model/users/Manager.java b/src/main/java/org/lab/model/users/Manager.java
new file mode 100644
index 0000000..a96b5b8
--- /dev/null
+++ b/src/main/java/org/lab/model/users/Manager.java
@@ -0,0 +1,68 @@
+package org.lab.model.users;
+
+import org.lab.model.milestone.Milestone;
+import org.lab.model.milestone.MilestoneStatus;
+import org.lab.model.project.Project;
+import org.lab.model.ticket.Ticket;
+import org.lab.model.ticket.TicketStatus;
+
+import java.util.Date;
+
+public final class Manager extends User {
+    public Manager(String name) {
+        super(name);
+    }
+
+    public void addLeader(Project project, Leader leader) {
+        if (project.isManager(this)) {
+            return;
+        }
+        project.addUser(leader);
+        leader.addProject(project);
+    }
+
+    public void addDeveloper(Project project, Developer developer) {
+        if (project.isManager(this)) {
+            return;
+        }
+        project.addUser(developer);
+        developer.addProject(project);
+    }
+
+    public void addTester(Project project, Tester tester) {
+        if (project.isManager(this)) {
+            return;
+        }
+        project.addUser(tester);
+        tester.addProject(project);
+    }
+
+    public Milestone createMilestone(String name, Date date, Project project) {
+        var milestone = new Milestone(name, date, project);
+        IO.println("Manager " + this.getName() + " create milestone " + milestone.getName());
+        return milestone;
+    }
+
+    public void setMilestoneStatus(Milestone milestone, MilestoneStatus status) {
+        StringBuilder sb = new StringBuilder();
+        sb.append("Manager ").append(this.getName());
+        sb.append(" milestone ").append(milestone.getName());
+        sb.append(" switch status from ").append(milestone.getStatus());
+        milestone.setStatus(status);
+        sb.append(" to ").append(milestone.getStatus());
+        String result = sb.toString();
+        System.out.println(result);
+    }
+
+    public Ticket createTicket(String name, Project project, Milestone milestone, Developer developer) {
+        var ticket = new Ticket(name, project, developer, milestone);
+        developer.addTicket(ticket);
+        milestone.addTicket(ticket);
+        IO.println("Manager " + this.getName() + " create ticket " + ticket.name());
+        return ticket;
+    }
+
+    public boolean checkTicketSuccess(Ticket ticket) {
+        return ticket.status() == TicketStatus.COMPLETED;
+    }
+}
diff --git a/src/main/java/org/lab/model/users/Tester.java b/src/main/java/org/lab/model/users/Tester.java
new file mode 100644
index 0000000..8fdc442
--- /dev/null
+++ b/src/main/java/org/lab/model/users/Tester.java
@@ -0,0 +1,7 @@
+package org.lab.model.users;
+
+public final class Tester extends User{
+    public Tester(String name) {
+        super(name);
+    }
+}
diff --git a/src/main/java/org/lab/model/users/User.java b/src/main/java/org/lab/model/users/User.java
new file mode 100644
index 0000000..40d5658
--- /dev/null
+++ b/src/main/java/org/lab/model/users/User.java
@@ -0,0 +1,64 @@
+package org.lab.model.users;
+
+import org.lab.model.bug.Bug;
+import org.lab.model.project.Project;
+import org.lab.model.ticket.Ticket;
+
+import java.util.*;
+
+public sealed class User permits Developer, Tester, Manager, Leader {
+    protected final String name;
+    protected final Set<Project> projects = new HashSet<>();
+    protected final SequencedCollection<Ticket> tickets = new ArrayList<>();
+    protected final SequencedCollection<Bug> bugs = new ArrayList<>();
+
+    public User(String name) {
+        this.name = name;
+    }
+
+    public Project createProject(String name) {
+        var project = new Project(name);
+        this.projects.add(project);
+        return project;
+    }
+
+    public void removeProject(Project project) {
+        this.projects.remove(project);
+    }
+
+    public void addProject(Project project) {
+        this.projects.add(project);
+    }
+
+    public List<Project> getAllProjects() {
+        return this.projects.stream().toList();
+    }
+
+    public void addTicket(Ticket ticket) {
+        this.tickets.addLast(ticket);
+    }
+
+    public Ticket getFirstTicket() {
+        return this.tickets.getFirst();
+    }
+
+    public List<Ticket> getAllTickets() {
+        return this.tickets.stream().toList();
+    }
+
+    public void addBug(Bug bug) {
+        this.bugs.addLast(bug);
+    }
+
+    public Bug getFirstBug() {
+        return this.bugs.getFirst();
+    }
+
+    public List<Bug> getAllBugs() {
+        return this.bugs.stream().toList();
+    }
+
+    public String getName() {
+        return this.name;
+    }
+}