Add pagination container

[Sone.git] / src / main / kotlin / net / pterodactylus / sone / utils / Pagination.kt

diff --git a/src/main/kotlin/net/pterodactylus/sone/utils/Pagination.kt b/src/main/kotlin/net/pterodactylus/sone/utils/Pagination.kt
new file mode 100644 (file)
index 0000000..130fe2e
--- /dev/null
+++ b/src/main/kotlin/net/pterodactylus/sone/utils/Pagination.kt
@@ -0,0 +1,42 @@
+package net.pterodactylus.sone.utils
+
+/**
+ * Helper class for lists that need pagination. Setting the page or the page
+ * size will automatically recalculate all other parameters, and the next call
+ * to [Pagination.items] retrieves all items on the current page.
+ * <p>
+ * A pagination object can be used as an [Iterable]. When the [Iterator]
+ * from [Pagination.iterator] is requested, the iterator over
+ * [Pagination.items] is returned.
+ *
+ * @param <T>
+ *            The type of the list elements
+ */
+class Pagination<out T>(private val originalItems: List<T>, pageSize: Int): Iterable<T> {
+
+       var page: Int = 0
+               set(value) {
+                       field = maxOf(0, minOf(value, lastPage))
+               }
+
+       var pageSize = pageSize
+               set(value) {
+                       val oldFirstIndex = page * field
+                       field = maxOf(1, value)
+                       page = oldFirstIndex / field
+               }
+
+       val pageNumber get() = page + 1
+       val pageCount get() = maxOf((originalItems.size - 1) / pageSize + 1, 1)
+       val itemCount get() = minOf(originalItems.size - page * pageSize, pageSize)
+       val items get() = originalItems.subList(page * pageSize, minOf(originalItems.size, (page + 1) * pageSize))
+       val isFirst get() = page == 0
+       val isLast get() = page == lastPage
+       val isNecessary get() = pageCount > 1
+       val previousPage get() = page - 1
+       val nextPage get() = page + 1
+       val lastPage get() = pageCount - 1
+
+       override fun iterator() = items.iterator()
+
+}