package imgui;

import imgui.callback.ImListClipperCallback;

/**
 * Helper: Manually clip large list of items.
 * If you are submitting lots of evenly spaced items and you have a random access to the list, you can perform coarse
 * clipping based on visibility to save yourself from processing those items at all.
 * The clipper calculates the range of visible items and advance the cursor to compensate for the non-visible items we have skipped.
 * (Dear ImGui already clip items based on their bounds but it needs to measure text size to do so, whereas manual coarse clipping before submission makes this cost and your own data fetching/submission cost almost null)
 * <pre>
 *   ImGuiListClipper clipper;
 *   clipper.Begin(1000);         // We have 1000 elements, evenly spaced.
 *   while (clipper.Step())
 *       for (int i = clipper.DisplayStart; i {@code <} clipper.DisplayEnd; i++)
 *           ImGui::Text("line number %d", i);
 * </pre>
 * Generally what happens is:
 * - Clipper lets you process the first element (DisplayStart = 0, DisplayEnd = 1) regardless of it being visible or not.
 * - User code submit one element.
 * - Clipper can measure the height of the first element
 * - Clipper calculate the actual range of elements to display based on the current clipping rectangle, position the cursor before the first visible element.
 * - User code submit visible elements.
 * <p>
 * BINDING NOTICE:
 * It's impossible to implement the same API like in the original. Method {@link #forEach(int, int, ImListClipperCallback)} could be used instead.
 * <pre>
 *     ImGuiListClipper.forEach(1000, new ImListClipperCallback() {
 *         public void accept(int index) {
 *             ImGui.text(String.format("line number %d", index));
 *         }
 *     });
 * </pre>
 */
public final class ImGuiListClipper {
    private ImGuiListClipper() {
    }

    /*JNI
        #include <imgui.h>
        #include "jni_callbacks.h"
     */

    /**
     * @param itemsCount Use -1 to ignore (you can call Begin later).
     *                   Use INT_MAX if you don't know how many items you have (in which case the cursor won't be advanced in the final step).
     * @param callback action to do in iterations
     */
    public static void forEach(final int itemsCount, final ImListClipperCallback callback) {
        forEach(itemsCount, -1, callback);
    }

    /**
     * @param itemsCount Use -1 to ignore (you can call Begin later).
     *                   Use INT_MAX if you don't know how many items you have (in which case the cursor won't be advanced in the final step).
     * @param itemsHeight Use -1.0f to be calculated automatically on first step.
     *                    Otherwise pass in the distance between your items, typically GetTextLineHeightWithSpacing() or GetFrameHeightWithSpacing().
     * @param callback action to do in iterations
     */
    public static native void forEach(int itemsCount, int itemsHeight, ImListClipperCallback callback); /*
        ImGuiListClipper clipper;
        clipper.Begin(itemsCount, itemsHeight);
        while (clipper.Step()) {
            for (int i = clipper.DisplayStart; i < clipper.DisplayEnd; i++) {
                Jni::CallImListClipperCallback(env, callback, i);
            }
        }
    */
}