feat: Followを送れるように

src/main/kotlin/dev/usbharu/hideout/domain/model/hideout/dto/SendFollowDto.kt

@@ -0,0 +1,5 @@
+package dev.usbharu.hideout.domain.model.hideout.dto
+
+import dev.usbharu.hideout.domain.model.hideout.entity.User
+
+data class SendFollowDto(val userId: User, val followTargetUserId: User)

src/main/kotlin/dev/usbharu/hideout/service/activitypub/ActivityPubSendFollowService.kt

@@ -0,0 +1,7 @@
+package dev.usbharu.hideout.service.activitypub
+
+import dev.usbharu.hideout.domain.model.hideout.dto.SendFollowDto
+
+interface ActivityPubSendFollowService {
+    suspend fun sendFollow(sendFollowDto: SendFollowDto)
+}

src/main/kotlin/dev/usbharu/hideout/service/activitypub/ActivityPubSendFollowServiceImpl.kt

@@ -0,0 +1,23 @@
+package dev.usbharu.hideout.service.activitypub
+
+import dev.usbharu.hideout.domain.model.ap.Follow
+import dev.usbharu.hideout.domain.model.hideout.dto.SendFollowDto
+import dev.usbharu.hideout.plugins.postAp
+import io.ktor.client.*
+import org.koin.core.annotation.Single
+
+@Single
+class ActivityPubSendFollowServiceImpl(private val httpClient: HttpClient) : ActivityPubSendFollowService {
+    override suspend fun sendFollow(sendFollowDto: SendFollowDto) {
+        val follow = Follow(
+            name = "Follow",
+            `object` = sendFollowDto.followTargetUserId.url,
+            actor = sendFollowDto.userId.url
+        )
+        httpClient.postAp(
+            urlString = sendFollowDto.followTargetUserId.inbox,
+            username = sendFollowDto.userId.url,
+            jsonLd = follow
+        )
+    }
+}

src/main/kotlin/dev/usbharu/hideout/service/impl/UserService.kt

@@ -2,17 +2,23 @@ package dev.usbharu.hideout.service.impl
 
 import dev.usbharu.hideout.config.Config
 import dev.usbharu.hideout.domain.model.hideout.dto.RemoteUserCreateDto
+import dev.usbharu.hideout.domain.model.hideout.dto.SendFollowDto
 import dev.usbharu.hideout.domain.model.hideout.dto.UserCreateDto
 import dev.usbharu.hideout.domain.model.hideout.entity.User
 import dev.usbharu.hideout.exception.UserNotFoundException
 import dev.usbharu.hideout.repository.IUserRepository
 import dev.usbharu.hideout.service.IUserAuthService
+import dev.usbharu.hideout.service.activitypub.ActivityPubSendFollowService
 import org.koin.core.annotation.Single
 import java.lang.Integer.min
 import java.time.Instant
 
 @Single
-class UserService(private val userRepository: IUserRepository, private val userAuthService: IUserAuthService) :
+class UserService(
+    private val userRepository: IUserRepository,
+    private val userAuthService: IUserAuthService,
+    private val activityPubSendFollowService: ActivityPubSendFollowService
+) :
     IUserService {
 
     private val maxLimit = 100
@@ -105,9 +111,19 @@ class UserService(private val userRepository: IUserRepository, private val userA
     }
 
     // TODO APのフォロー処理を作る
-    override suspend fun follow(id: Long, follower: Long): Boolean {
-        userRepository.createFollower(id, follower)
-        return false
+    override suspend fun follow(id: Long, followerId: Long): Boolean {
+        val user = userRepository.findById(id) ?: throw UserNotFoundException("$id was not found.")
+        val follower = userRepository.findById(followerId) ?: throw UserNotFoundException("$followerId was not found.")
+        if (follower.domain != Config.configData.domain) {
+            throw IllegalArgumentException("follower is not local user.")
+        }
+        return if (user.domain == Config.configData.domain) {
+            userRepository.createFollower(id, followerId)
+            true
+        } else {
+            activityPubSendFollowService.sendFollow(SendFollowDto(follower, user))
+            false
+        }
     }
 
     override suspend fun unfollow(id: Long, follower: Long): Boolean {

src/test/kotlin/dev/usbharu/hideout/service/impl/UserServiceTest.kt

@@ -29,7 +29,7 @@ class UserServiceTest {
             onBlocking { hash(anyString()) } doReturn "hashedPassword"
             onBlocking { generateKeyPair() } doReturn generateKeyPair
         }
-        val userService = UserService(userRepository, userAuthService)
+        val userService = UserService(userRepository, userAuthService, mock())
         userService.createLocalUser(UserCreateDto("test", "testUser", "XXXXXXXXXXXXX", "test"))
         verify(userRepository, times(1)).save(any())
         argumentCaptor<dev.usbharu.hideout.domain.model.hideout.entity.User> {
@@ -55,7 +55,7 @@ class UserServiceTest {
         val userRepository = mock<IUserRepository> {
             onBlocking { nextId() } doReturn 113345L
         }
-        val userService = UserService(userRepository, mock())
+        val userService = UserService(userRepository, mock(), mock())
         val user = RemoteUserCreateDto(
             "test",
             "example.com",