1.4.0 pagination

Author: coderFlameyosFlow

src/main/java/me/flame/menus/menu/iterator/PageIterator.java

@@ -0,0 +1,150 @@
+package me.flame.menus.menu.iterator;
+
+import me.flame.menus.items.MenuItem;
+import me.flame.menus.menu.IterationDirection;
+import me.flame.menus.menu.Slot;
+import me.flame.menus.menu.Page;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import java.util.Optional;
+
+public class PageIterator implements Iterator<MenuItem> {
+    @NotNull
+    private final Page page;
+
+    @NotNull
+    private final IterationDirection direction;
+
+    @NotNull
+    private Slot position;
+
+    private Slot next;
+
+    private boolean isFirst = true;
+
+    private final int rows;
+
+    private static final String NOTHING_MORE_NEXT =
+            "Used PageIterator#next() but nothing more" +
+            "\nFix: Use hasNext() beforehand to avoid this error.";
+
+    private static final String NOTHING_MORE_NEXT_OPTIONAL =
+            "Used PageIterator#nextOptional() but nothing more" +
+            "\nFix: Use hasNext() beforehand to avoid this error.";
+
+    private static final String NOTHING_MORE_NEXT_NOT_NULL =
+            "Used PageIterator#nextNotNull() but nothing more";
+
+    private static final String GREATER_THAN_ONE_ONLY =
+            "Starting row and column must be 1 or greater only." +
+            "\nFix: If you're using an algorithm for rows/cols, you might wanna check it";
+
+    public PageIterator(int startingRow, int startingCol,
+                        @NotNull IterationDirection direction,
+                        @NotNull Page page) {
+        Slot prepos = new Slot(startingRow, startingCol);
+        if (!prepos.isSlot()) throw new IllegalArgumentException(GREATER_THAN_ONE_ONLY);
+        this.page = page;
+        this.rows = page.rows();
+        this.position = prepos;
+        this.direction = direction;
+    }
+
+    public PageIterator(@NotNull IterationDirection direction,
+                        @NotNull Page page) {
+        this.page = page;
+        this.rows = page.rows();
+        this.position = Slot.FIRST.copy();
+        this.direction = direction;
+    }
+
+    /**
+     * Retrieves the next slot in the menu.
+     *
+     * @param emptyOnly  a boolean indicating whether to retrieve only empty slots
+     * @return           the next empty slot in the menu, or null if no empty slot is found
+     */
+    public Slot nextSlot(boolean emptyOnly) {
+        if (!emptyOnly) return nextSlot();
+
+        while (true) {
+            MenuItem item = page.getItem(position);
+            if (item == null) break;
+
+            position = direction.shift(position, this.rows);
+            if (!position.isSlot()) return null;
+        }
+
+        // when it becomes empty
+        return position;
+    }
+
+    /**
+     * Retrieves the next slot in the menu.
+     * @return           the next empty slot in the menu, or null if no empty slot is found
+     */
+    public @Nullable Slot nextSlot() {
+        if (!isFirst) {
+            position = next;
+            next = null;
+            return position;
+        }
+        isFirst = false;
+        return position;
+    }
+
+    @Override
+    public boolean hasNext() {
+        if (next != null) return true;
+        next = direction.shift(position, this.rows);
+        return next.isSlot();
+    }
+
+    @Override
+    public MenuItem next() {
+        Slot slot = nextSlot();
+        if (slot != null) return page.getItem(slot.getSlot());
+        throw new NoSuchElementException(NOTHING_MORE_NEXT);
+    }
+
+    /**
+     * Retrieves the next non-null MenuItem in the menu.
+     *
+     * @return         	the next non-null MenuItem in the menu
+     */
+    public MenuItem nextNotNull() {
+        while (hasNext()) {
+            Slot slot = nextSlot();
+            if (slot == null)
+                throw new NoSuchElementException(
+                    NOTHING_MORE_NEXT_NOT_NULL +
+                    "\nFix: Everything after slot " + position.getSlot() + " is empty/null."
+                );
+
+            MenuItem item = page.getItem(slot.getSlot());
+            if (item != null) return item;
+        }
+
+        throw new NoSuchElementException(
+            NOTHING_MORE_NEXT_NOT_NULL +
+            "\nFix: Everything after slot " + position.getSlot() + " is empty/null."
+        );
+    }
+
+    /**
+     * Retrieves the next optional menu item.
+     *
+     * @return         	an Optional object containing the next MenuItem, if available.
+     *                  Returns an empty Optional if the slot in the menu is empty.
+     *                  Returns an empty Optional if there are no more items.
+     * @throws NoSuchElementException if there are no more items in the menu.
+     */
+    public Optional<MenuItem> nextOptional() {
+        Slot slot = nextSlot();
+        if (slot != null) return page.get(slot);
+        throw new NoSuchElementException(NOTHING_MORE_NEXT_OPTIONAL);
+    }
+}