package de.geolykt.starloader.api.event.lifecycle;

import java.util.Objects;

import org.jetbrains.annotations.ApiStatus.AvailableSince;
import org.jetbrains.annotations.ApiStatus.Internal;
import org.jetbrains.annotations.Contract;
import org.jetbrains.annotations.NotNull;

import com.badlogic.gdx.graphics.g2d.PixmapPacker;
import com.badlogic.gdx.graphics.g2d.TextureAtlas;
import com.badlogic.gdx.graphics.g2d.TextureRegion;

import de.geolykt.starloader.api.event.Event;
import de.geolykt.starloader.api.gui.Drawing;
import de.geolykt.starloader.api.gui.DrawingImpl;

/**
 * Lifecycle event which is fired after the main texture atlas has been generated
 * via {@link PixmapPacker}. This {@link Event} will be fired after the {@link AtlasPackingEvent}
 * by necessity. However, the generated {@link TextureAtlas} will not be assigned
 * to its corresponding field in the game's 'GalFX' class (which in turn is used by
 * {@link Drawing} / {@link DrawingImpl}). This means that most graphical operations,
 * such as obtaining built-in fonts or specific texture regions, are only possible after
 * this event was fired.
 *
 * <p>The main usecase of this event is to preemptively store {@link TextureRegion}s
 * packed through {@link AtlasPackingEvent#packTexture(String, com.badlogic.gdx.graphics.Pixmap)}
 * via {@link TextureAtlas#findRegion(String)}.
 *
 * <p>For more information about the atlas packing process, see the documentation of
 * {@link AtlasPackingEvent}.
 *
 * <p>Like {@link AtlasPackingEvent}, this event should ideally only be fired once.
 * Changes to this behaviour will be considered an API compatibility break.
 *
 * <p>This event will be posted to the event bus immediately after
 * {@link PixmapPacker#generateTextureAtlas(com.badlogic.gdx.graphics.Texture.TextureFilter, com.badlogic.gdx.graphics.Texture.TextureFilter, boolean)}
 * is called.
 *
 * @since 2.0.0-a20260214
 * @apiNote Keep in mind that the constructor of Event classes are in general not public APIs,
 * unless specified otherwise. This also means that subclassing this class is not supported when
 * it comes to preserving ABI constraints.
 */
@AvailableSince("2.0.0-a20260214")
public class AtlasPackedEvent extends Event {
    @NotNull
    private final TextureAtlas atlas;

    /**
     * This constructor is not public API, do not invoke manually.
     *
     * @param atlas The {@link TextureAtlas} instance.
     * @since 2.0.0-a20260214
     */
    @Internal
    @Contract(pure = true, value = "null -> fail")
    public AtlasPackedEvent(@NotNull TextureAtlas atlas) {
        this.atlas = Objects.requireNonNull(atlas, "'atlas' may not be null");
    }

    /**
     * Obtains the {@link TextureAtlas} instance that was generated by the {@link AtlasPackingEvent}.
     *
     * @return The {@link TextureAtlas} generated by {@link AtlasPackingEvent}.
     * @since 2.0.0-a20260214
     */
    @NotNull
    @Contract(pure = true)
    @AvailableSince("2.0.0-a20260214")
    public TextureAtlas getAtlas() {
        return this.atlas;
    }
}