Removed "Inventory" from the GUI API names

src/main/kotlin/net/axay/kspigot/gui/GUIPageChange.kt

@@ -0,0 +1,143 @@
+package net.axay.kspigot.gui
+
+import net.axay.kspigot.runnables.task
+
+abstract class GUIPageChangeCalculator {
+
+    abstract fun calculateNewPage(currentPage: Int, pages: Collection<Int>): Int?
+
+    object GUIPreviousPageCalculator : GUIPageChangeCalculator() {
+        override fun calculateNewPage(currentPage: Int, pages: Collection<Int>) =
+            pages.sortedDescending().find { it < currentPage }
+    }
+
+    object GUINextPageCalculator : GUIPageChangeCalculator() {
+        override fun calculateNewPage(currentPage: Int, pages: Collection<Int>) =
+            pages.sorted().find { it > currentPage }
+    }
+
+    class GUIConsistentPageCalculator(private val toPage: Int) : GUIPageChangeCalculator() {
+        override fun calculateNewPage(currentPage: Int, pages: Collection<Int>) = toPage
+    }
+
+}
+
+enum class PageChangeEffect {
+    INSTANT,
+    SLIDE_HORIZONTALLY,
+    SLIDE_VERTICALLY,
+    SWIPE_HORIZONTALLY,
+    SWIPE_VERTICALLY,
+}
+
+enum class InventoryChangeEffect(
+    val effect: PageChangeEffect
+) {
+    INSTANT(PageChangeEffect.INSTANT)
+}
+
+internal fun GUI<*>.changePage(
+    effect: PageChangeEffect,
+    fromPage: GUIPage<*>,
+    toPage: GUIPage<*>
+) {
+
+    val fromPageInt = fromPage.number
+    val toPageInt = toPage.number
+
+    when (effect) {
+
+        PageChangeEffect.INSTANT -> loadPageUnsafe(toPage)
+
+        PageChangeEffect.SLIDE_HORIZONTALLY -> {
+
+            val width = data.guiType.dimensions.width
+
+            changePageEffect(fromPageInt, toPageInt, width) { currentOffset, ifInverted ->
+                if (ifInverted) {
+                    loadPageUnsafe(fromPage, offsetHorizontally = currentOffset)
+                    loadPageUnsafe(toPage, offsetHorizontally = -(width - currentOffset))
+                } else {
+                    loadPageUnsafe(fromPage, offsetHorizontally = -currentOffset)
+                    loadPageUnsafe(toPage, offsetHorizontally = width - currentOffset)
+                }
+            }
+
+        }
+
+        PageChangeEffect.SLIDE_VERTICALLY -> {
+
+            val height = data.guiType.dimensions.height
+
+            changePageEffect(fromPageInt, toPageInt, height) { currentOffset, ifInverted ->
+                if (ifInverted) {
+                    loadPageUnsafe(fromPage, offsetVertically = currentOffset)
+                    loadPageUnsafe(toPage, offsetVertically = -(height - currentOffset))
+                } else {
+                    loadPageUnsafe(fromPage, offsetVertically = -currentOffset)
+                    loadPageUnsafe(toPage, offsetVertically = height - currentOffset)
+                }
+            }
+
+        }
+
+        PageChangeEffect.SWIPE_HORIZONTALLY -> {
+
+            val width = data.guiType.dimensions.width
+
+            changePageEffect(fromPageInt, toPageInt, width) { currentOffset, ifInverted ->
+                if (ifInverted) {
+                    loadPageUnsafe(toPage, offsetHorizontally = -(width - currentOffset))
+                } else {
+                    loadPageUnsafe(toPage, offsetHorizontally = width - currentOffset)
+                }
+            }
+
+        }
+
+        PageChangeEffect.SWIPE_VERTICALLY -> {
+
+            val height = data.guiType.dimensions.height
+
+            changePageEffect(fromPageInt, toPageInt, height) { currentOffset, ifInverted ->
+                if (ifInverted) {
+                    loadPageUnsafe(toPage, offsetVertically = -(height - currentOffset))
+                } else {
+                    loadPageUnsafe(toPage, offsetVertically = height - currentOffset)
+                }
+            }
+
+        }
+
+    }
+}
+
+internal fun GUI<*>.changeGUI(
+    effect: InventoryChangeEffect,
+    fromPage: GUIPage<*>,
+    toPage: GUIPage<*>
+) = changePage(effect.effect, fromPage, toPage)
+
+private inline fun changePageEffect(
+    fromPage: Int,
+    toPage: Int,
+    doFor: Int,
+    crossinline effect: (currentOffset: Int, ifInverted: Boolean) -> Unit,
+) {
+
+    val ifInverted = fromPage >= toPage
+
+    var currentOffset = 1
+    task(
+        sync = true,
+        period = 1,
+        howOften = doFor.toLong()
+    ) {
+
+        effect.invoke(currentOffset, ifInverted)
+
+        currentOffset++
+
+    }
+
+}