add getting of posts by page

src/main/kotlin/com/github/insanusmokrassar/postssystem/core/api/PostsAPI.kt

@@ -3,10 +3,13 @@ package com.github.insanusmokrassar.postssystem.core.api
 import com.github.insanusmokrassar.postssystem.core.post.Post
 import com.github.insanusmokrassar.postssystem.core.post.PostId
 import com.github.insanusmokrassar.postssystem.core.content.ContentId
+import com.github.insanusmokrassar.postssystem.core.utils.pagination.*
 import org.joda.time.DateTime
 
 interface PostsAPI {
     suspend fun getPostById(id: PostId): Post?
     suspend fun getPostsByContent(id: ContentId): List<Post>
     suspend fun getPostsByDates(from: DateTime? = null, to: DateTime? = null): List<Post>
+
+    suspend fun getPostsByPagination(pagination: Pagination): PaginationResult<Post>
 }

src/main/kotlin/com/github/insanusmokrassar/postssystem/core/utils/pagination/Pagination.kt

@@ -0,0 +1,6 @@
+package com.github.insanusmokrassar.postssystem.core.utils.pagination
+
+interface Pagination {
+    val page: Int
+    val size: Int
+}

src/main/kotlin/com/github/insanusmokrassar/postssystem/core/utils/pagination/PaginationRequest.kt

@@ -0,0 +1,9 @@
+package com.github.insanusmokrassar.postssystem.core.utils.pagination
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class PaginationRequest(
+    override val page: Int,
+    override val size: Int
+) : Pagination

src/main/kotlin/com/github/insanusmokrassar/postssystem/core/utils/pagination/PaginationResult.kt

@@ -0,0 +1,14 @@
+package com.github.insanusmokrassar.postssystem.core.utils.pagination
+
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.Transient
+
+@Serializable
+data class PaginationResult<T>(
+    override val page: Int,
+    val pagesNumber: Int,
+    val results: List<T>
+) : Pagination {
+    @Transient
+    override val size: Int = results.size
+}