Implemented node service and controller

src/main/java/ru/dragonestia/loadbalancer/controller/NodeController.java

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+package ru.dragonestia.loadbalancer.controller;
+
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.HttpStatusCode;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.*;
+import ru.dragonestia.loadbalancer.controller.response.NodeDetailsResponse;
+import ru.dragonestia.loadbalancer.controller.response.NodeListResponse;
+import ru.dragonestia.loadbalancer.controller.response.NodeRegisterResponse;
+import ru.dragonestia.loadbalancer.model.Node;
+import ru.dragonestia.loadbalancer.model.type.LoadBalancingMethod;
+import ru.dragonestia.loadbalancer.service.NodeService;
+import ru.dragonestia.loadbalancer.util.NamingValidator;
+
+@RestController
+@RequestMapping("/nodes")
+@RequiredArgsConstructor
+public class NodeController {
+
+    private final NodeService nodeService;
+
+    @GetMapping
+    NodeListResponse allNodes() {
+        return new NodeListResponse(nodeService.allNodes());
+    }
+
+    @PostMapping
+    NodeRegisterResponse registerNode(@RequestParam(name = "identifier") String identifier,
+                                      @RequestParam(name = "method") LoadBalancingMethod method) {
+
+        try {
+            nodeService.createNode(new Node(identifier, method));
+        } catch (IllegalArgumentException ex) {
+            return new NodeRegisterResponse(false, ex.getMessage());
+        } catch (Error error) {
+            new NodeRegisterResponse(false, error.getMessage());
+        }
+
+        return new NodeRegisterResponse(true, "");
+    }
+
+    @GetMapping("/{identifier}")
+    ResponseEntity<NodeDetailsResponse> nodeDetails(@PathVariable("identifier") String identifier) {
+        if (!NamingValidator.validateNodeIdentifier(identifier)) {
+            return new ResponseEntity<>(HttpStatusCode.valueOf(404));
+        }
+
+        var nodeOpt = nodeService.findNode(identifier);
+        return nodeOpt.map(node -> ResponseEntity.ok(new NodeDetailsResponse(node)))
+                .orElseGet(() -> new ResponseEntity<>(HttpStatusCode.valueOf(404)));
+    }
+
+    @DeleteMapping("/{identifier}")
+    ResponseEntity<?> removeNode(@PathVariable("identifier") String identifier) {
+        if (!NamingValidator.validateNodeIdentifier(identifier)) {
+            return ResponseEntity.ok().build();
+        }
+
+        var nodeOpt = nodeService.findNode(identifier);
+        nodeOpt.ifPresent(nodeService::removeNode);
+
+        return ResponseEntity.ok().build();
+    }
+}

src/main/java/ru/dragonestia/loadbalancer/controller/response/NodeDetailsResponse.java

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+package ru.dragonestia.loadbalancer.controller.response;
+
+import ru.dragonestia.loadbalancer.model.Node;
+
+public record NodeDetailsResponse(Node node) {}

src/main/java/ru/dragonestia/loadbalancer/controller/response/NodeListResponse.java

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+package ru.dragonestia.loadbalancer.controller.response;
+
+import ru.dragonestia.loadbalancer.model.Node;
+
+import java.util.List;
+
+public record NodeListResponse(List<Node> nodes) {}

src/main/java/ru/dragonestia/loadbalancer/controller/response/NodeRegisterResponse.java

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+package ru.dragonestia.loadbalancer.controller.response;
+
+public record NodeRegisterResponse(boolean success, String message) {}

src/main/java/ru/dragonestia/loadbalancer/service/impl/NodeServiceImpl.java

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+package ru.dragonestia.loadbalancer.service.impl;
+
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+import ru.dragonestia.loadbalancer.model.Node;
+import ru.dragonestia.loadbalancer.repository.NodeRepository;
+import ru.dragonestia.loadbalancer.service.NodeService;
+import ru.dragonestia.loadbalancer.util.NamingValidator;
+
+import java.util.List;
+import java.util.Optional;
+
+@Service
+@RequiredArgsConstructor
+public class NodeServiceImpl implements NodeService {
+
+    private final NodeRepository nodeRepository;
+
+    @Override
+    public void createNode(Node node) {
+        if (!NamingValidator.validateNodeIdentifier(node.identifier())) {
+            throw new Error("Invalid node identifier format");
+        }
+
+        nodeRepository.createNode(node);
+    }
+
+    @Override
+    public void removeNode(Node node) {
+        nodeRepository.deleteNode(node);
+    }
+
+    @Override
+    public List<Node> allNodes() {
+        return nodeRepository.all();
+    }
+
+    @Override
+    public Optional<Node> findNode(String identifier) {
+        return nodeRepository.findNode(identifier);
+    }
+}

src/main/java/ru/dragonestia/loadbalancer/util/NamingValidator.java

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+package ru.dragonestia.loadbalancer.util;
+
+import lombok.experimental.UtilityClass;
+
+@UtilityClass
+public class NamingValidator {
+
+    public boolean validateNodeIdentifier(String input) {
+        return input.matches("^[a-z\\d-]+$");
+    }
+}