feat: like and unlike backend endpoints

backend/src/main/java/online/wesal/wesal/controller/PostController.java

@@ -5,6 +5,7 @@ import io.swagger.v3.oas.annotations.tags.Tag;
 import jakarta.validation.Valid;
 import online.wesal.wesal.dto.ApiResponse;
 import online.wesal.wesal.dto.PostCreateRequestDTO;
+import online.wesal.wesal.dto.PostLikeRequestDTO;
 import online.wesal.wesal.dto.PostResponseDTO;
 import online.wesal.wesal.entity.Post;
 import online.wesal.wesal.service.PostService;
@@ -109,4 +110,78 @@ public class PostController {
             return ResponseEntity.status(500).body(ApiResponse.error("Something went wrong.. We're sorry but try again later"));
         }
     }
+    
+    @PostMapping(value = "/like", consumes = "application/json", produces = "application/json")
+    @Operation(summary = "Like post", description = "Like a post. Returns the updated post with new like count.")
+    public ResponseEntity<ApiResponse<PostResponseDTO>> likePost(
+            @Valid @RequestBody PostLikeRequestDTO request,
+            BindingResult bindingResult,
+            Authentication authentication) {
+        
+        if (bindingResult.hasErrors()) {
+            String errorMessage = bindingResult.getFieldErrors().stream()
+                .map(error -> {
+                    String field = error.getField();
+                    if ("postId".equals(field)) return "Valid post ID is required";
+                    return error.getDefaultMessage();
+                })
+                .findFirst()
+                .orElse("Invalid input");
+            return ResponseEntity.badRequest().body(ApiResponse.error(errorMessage));
+        }
+        
+        try {
+            PostResponseDTO response = postService.likePost(request.getPostId());
+            return ResponseEntity.ok(ApiResponse.success(response));
+        } catch (RuntimeException e) {
+            String message;
+            if (e.getMessage().contains("Post not found")) {
+                message = "Post not found";
+            } else if (e.getMessage().contains("User not found")) {
+                message = "Authentication error. Please log in again.";
+            } else {
+                message = "Something went wrong.. We're sorry but try again later";
+            }
+            return ResponseEntity.badRequest().body(ApiResponse.error(message));
+        } catch (Exception e) {
+            return ResponseEntity.status(500).body(ApiResponse.error("Something went wrong.. We're sorry but try again later"));
+        }
+    }
+    
+    @PostMapping(value = "/unlike", consumes = "application/json", produces = "application/json")
+    @Operation(summary = "Unlike post", description = "Unlike a post. Returns the updated post with new like count.")
+    public ResponseEntity<ApiResponse<PostResponseDTO>> unlikePost(
+            @Valid @RequestBody PostLikeRequestDTO request,
+            BindingResult bindingResult,
+            Authentication authentication) {
+        
+        if (bindingResult.hasErrors()) {
+            String errorMessage = bindingResult.getFieldErrors().stream()
+                .map(error -> {
+                    String field = error.getField();
+                    if ("postId".equals(field)) return "Valid post ID is required";
+                    return error.getDefaultMessage();
+                })
+                .findFirst()
+                .orElse("Invalid input");
+            return ResponseEntity.badRequest().body(ApiResponse.error(errorMessage));
+        }
+        
+        try {
+            PostResponseDTO response = postService.unlikePost(request.getPostId());
+            return ResponseEntity.ok(ApiResponse.success(response));
+        } catch (RuntimeException e) {
+            String message;
+            if (e.getMessage().contains("Post not found")) {
+                message = "Post not found";
+            } else if (e.getMessage().contains("User not found")) {
+                message = "Authentication error. Please log in again.";
+            } else {
+                message = "Something went wrong.. We're sorry but try again later";
+            }
+            return ResponseEntity.badRequest().body(ApiResponse.error(message));
+        } catch (Exception e) {
+            return ResponseEntity.status(500).body(ApiResponse.error("Something went wrong.. We're sorry but try again later"));
+        }
+    }
 }

backend/src/main/java/online/wesal/wesal/dto/PostLikeRequestDTO.java

@@ -0,0 +1,25 @@
+package online.wesal.wesal.dto;
+
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Positive;
+
+public class PostLikeRequestDTO {
+    
+    @NotNull(message = "Post ID is required")
+    @Positive(message = "Post ID must be a positive number")
+    private Long postId;
+    
+    public PostLikeRequestDTO() {}
+    
+    public PostLikeRequestDTO(Long postId) {
+        this.postId = postId;
+    }
+    
+    public Long getPostId() {
+        return postId;
+    }
+    
+    public void setPostId(Long postId) {
+        this.postId = postId;
+    }
+}

backend/src/main/java/online/wesal/wesal/entity/PostLike.java

@@ -0,0 +1,63 @@
+package online.wesal.wesal.entity;
+
+import jakarta.persistence.*;
+import java.time.LocalDateTime;
+
+@Entity
+@Table(name = "post_likes", uniqueConstraints = {
+    @UniqueConstraint(columnNames = {"post_id", "user_id"})
+})
+public class PostLike {
+    
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+    
+    @Column(nullable = false, name = "post_id")
+    private Long postId;
+    
+    @Column(nullable = false, name = "user_id")
+    private Long userId;
+    
+    @Column(nullable = false)
+    private LocalDateTime createdAt = LocalDateTime.now();
+    
+    public PostLike() {}
+    
+    public PostLike(Long postId, Long userId) {
+        this.postId = postId;
+        this.userId = userId;
+    }
+    
+    public Long getId() {
+        return id;
+    }
+    
+    public void setId(Long id) {
+        this.id = id;
+    }
+    
+    public Long getPostId() {
+        return postId;
+    }
+    
+    public void setPostId(Long postId) {
+        this.postId = postId;
+    }
+    
+    public Long getUserId() {
+        return userId;
+    }
+    
+    public void setUserId(Long userId) {
+        this.userId = userId;
+    }
+    
+    public LocalDateTime getCreatedAt() {
+        return createdAt;
+    }
+    
+    public void setCreatedAt(LocalDateTime createdAt) {
+        this.createdAt = createdAt;
+    }
+}

backend/src/main/java/online/wesal/wesal/repository/PostLikeRepository.java

@@ -0,0 +1,15 @@
+package online.wesal.wesal.repository;
+
+import online.wesal.wesal.entity.PostLike;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+import java.util.Optional;
+
+@Repository
+public interface PostLikeRepository extends JpaRepository<PostLike, Long> {
+    Optional<PostLike> findByPostIdAndUserId(Long postId, Long userId);
+    boolean existsByPostIdAndUserId(Long postId, Long userId);
+    void deleteByPostIdAndUserId(Long postId, Long userId);
+    long countByPostId(Long postId);
+}

backend/src/main/java/online/wesal/wesal/service/PostService.java

@@ -2,11 +2,14 @@ package online.wesal.wesal.service;
 
 import online.wesal.wesal.dto.PostResponseDTO;
 import online.wesal.wesal.entity.Post;
+import online.wesal.wesal.entity.PostLike;
 import online.wesal.wesal.entity.User;
+import online.wesal.wesal.repository.PostLikeRepository;
 import online.wesal.wesal.repository.PostRepository;
 import online.wesal.wesal.repository.UserRepository;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
 
 import java.time.LocalDateTime;
 import java.util.List;
@@ -19,6 +22,9 @@ public class PostService {
     @Autowired
     private PostRepository postRepository;
     
+    @Autowired
+    private PostLikeRepository postLikeRepository;
+    
     @Autowired
     private UserRepository userRepository;
     
@@ -64,4 +70,57 @@ public class PostService {
         post = postRepository.save(post);
         return new PostResponseDTO(post, currentUser);
     }
+    
+    @Transactional
+    public PostResponseDTO likePost(Long postId) {
+        User currentUser = userService.getCurrentUser();
+        Long userId = currentUser.getId();
+        
+        // Check if post exists
+        Post post = postRepository.findById(postId)
+                .orElseThrow(() -> new RuntimeException("Post not found"));
+        
+        // Check if user already liked this post
+        if (!postLikeRepository.existsByPostIdAndUserId(postId, userId)) {
+            // Add like record
+            PostLike postLike = new PostLike(postId, userId);
+            postLikeRepository.save(postLike);
+            
+            // Update post likes count
+            post.setLikes(post.getLikes() + 1);
+            post = postRepository.save(post);
+        }
+        
+        // Get creator for response
+        User creator = userRepository.findById(post.getCreatorId())
+                .orElseThrow(() -> new RuntimeException("Creator not found"));
+        
+        return new PostResponseDTO(post, creator);
+    }
+    
+    @Transactional
+    public PostResponseDTO unlikePost(Long postId) {
+        User currentUser = userService.getCurrentUser();
+        Long userId = currentUser.getId();
+        
+        // Check if post exists
+        Post post = postRepository.findById(postId)
+                .orElseThrow(() -> new RuntimeException("Post not found"));
+        
+        // Check if user has liked this post
+        if (postLikeRepository.existsByPostIdAndUserId(postId, userId)) {
+            // Remove like record
+            postLikeRepository.deleteByPostIdAndUserId(postId, userId);
+            
+            // Update post likes count
+            post.setLikes(Math.max(0, post.getLikes() - 1));
+            post = postRepository.save(post);
+        }
+        
+        // Get creator for response
+        User creator = userRepository.findById(post.getCreatorId())
+                .orElseThrow(() -> new RuntimeException("Creator not found"));
+        
+        return new PostResponseDTO(post, creator);
+    }
 }