// License: GPL. For details, see LICENSE file.
package org.openstreetmap.josm.tools;

import java.awt.Dimension;
import java.awt.GraphicsConfiguration;
import java.awt.GraphicsEnvironment;
import java.awt.Image;
import java.awt.geom.AffineTransform;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.function.Function;
import java.util.function.UnaryOperator;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

import javax.swing.ImageIcon;

/**
 * Helper class for HiDPI support.
 *
 * Gives access to the class <code>BaseMultiResolutionImage</code> via reflection,
 * in case it is on classpath. This is to be expected for Java 9, but not for Java 8 runtime.
 *
 * @since 12722
 */
public final class HiDPISupport {

    private static final Class<? extends Image> baseMultiResolutionImageClass;
    private static final Constructor<? extends Image> baseMultiResolutionImageConstructor;
    private static final Method resolutionVariantsMethod;
    private static final Method resolutionVariantMethod;

    static {
        baseMultiResolutionImageClass = initBaseMultiResolutionImageClass();
        baseMultiResolutionImageConstructor = initBaseMultiResolutionImageConstructor();
        resolutionVariantsMethod = initResolutionVariantsMethod();
        resolutionVariantMethod = initResolutionVariantMethod();
    }

    private HiDPISupport() {
        // Hide default constructor
    }

    /**
     * Create a multi-resolution image from a base image and an {@link ImageResource}.
     * <p>
     * Will only return multi-resolution image, if HiDPI-mode is detected. Then
     * the image stack will consist of the base image and one that fits the
     * HiDPI scale of the main display.
     * @param base the base image
     * @param ir a corresponding image resource
     * @param resizeMode how to size/resize the image
     * @return multi-resolution image if necessary and possible, the base image otherwise
     */
    public static Image getMultiResolutionImage(Image base, ImageResource ir, ImageResizeMode resizeMode) {
        double uiScale = getHiDPIScale();
        if (uiScale != 1.0 && baseMultiResolutionImageConstructor != null) {
            if (resizeMode == ImageResizeMode.BOUNDED) {
                resizeMode = ImageResizeMode.AUTO;
            }
            ImageIcon zoomed = ir.getImageIconAlreadyScaled(new Dimension(
                    (int) Math.round(base.getWidth(null) * uiScale),
                    (int) Math.round(base.getHeight(null) * uiScale)), false, true, resizeMode);
            Image mrImg = getMultiResolutionImage(Arrays.asList(base, zoomed.getImage()));
            if (mrImg != null) return mrImg;
        }
        return base;
    }

    /**
     * Create a multi-resolution image from a list of images.
     * @param imgs the images, supposedly the same image at different resolutions,
     * must not be empty
     * @return corresponding multi-resolution image, if possible, the first image
     * in the list otherwise
     */
    public static Image getMultiResolutionImage(List<Image> imgs) {
        CheckParameterUtil.ensureThat(!imgs.isEmpty(), "imgs is empty");
        if (baseMultiResolutionImageConstructor != null) {
            try {
                return baseMultiResolutionImageConstructor.newInstance((Object) imgs.toArray(new Image[0]));
            } catch (InstantiationException | IllegalAccessException | InvocationTargetException ex) {
                Logging.error("Unexpected error while instantiating object of class BaseMultiResolutionImage: " + ex);
            }
        }
        return imgs.get(0);
    }

    /**
     * Wrapper for the method <code>java.awt.image.BaseMultiResolutionImage#getBaseImage()</code>.
     * <p>
     * Will return the argument <code>img</code> unchanged, if it is not a multi-resolution image.
     * @param img the image
     * @return if <code>img</code> is a <code>java.awt.image.BaseMultiResolutionImage</code>,
     * then the base image, otherwise the image itself
     */
    public static Image getBaseImage(Image img) {
        if (baseMultiResolutionImageClass == null || resolutionVariantsMethod == null) {
            return img;
        }
        if (baseMultiResolutionImageClass.isInstance(img)) {
            try {
                @SuppressWarnings("unchecked")
                List<Image> imgVars = (List<Image>) resolutionVariantsMethod.invoke(img);
                if (!imgVars.isEmpty()) {
                    return imgVars.get(0);
                }
            } catch (IllegalAccessException | InvocationTargetException ex) {
                Logging.error("Unexpected error while calling method: " + ex);
            }
        }
        return img;
    }

    /**
     * Wrapper for the method <code>java.awt.image.MultiResolutionImage#getResolutionVariants()</code>.
     * <p>
     * Will return the argument as a singleton list, in case it is not a multi-resolution image.
     * @param img the image
     * @return if <code>img</code> is a <code>java.awt.image.BaseMultiResolutionImage</code>,
     * then the result of the method <code>#getResolutionVariants()</code>, otherwise the image
     * itself as a singleton list
     */
    public static List<Image> getResolutionVariants(Image img) {
        if (baseMultiResolutionImageClass == null || resolutionVariantsMethod == null) {
            return Collections.singletonList(img);
        }
        if (baseMultiResolutionImageClass.isInstance(img)) {
            try {
                @SuppressWarnings("unchecked")
                List<Image> imgVars = (List<Image>) resolutionVariantsMethod.invoke(img);
                if (!imgVars.isEmpty()) {
                    return imgVars;
                }
            } catch (IllegalAccessException | InvocationTargetException ex) {
                Logging.error("Unexpected error while calling method: " + ex);
            }
        }
        return Collections.singletonList(img);
    }

    /**
     * Wrapper for method <code>java.awt.image.MultiResolutionImage#getResolutionVariant(double destImageWidth, double destImageHeight)</code>.
     * <p>
     * Will return the argument, in case it is not a multi-resolution image.
     * @param img the image
     * @param destImageWidth the width of the destination image
     * @param destImageHeight the height of the destination image
     * @return if <code>img</code> is a <code>java.awt.image.BaseMultiResolutionImage</code>,
     * then the result of the method <code>#getResolutionVariant(destImageWidth, destImageHeight)</code>,
     * otherwise the image itself
     */
    public static Image getResolutionVariant(Image img, double destImageWidth, double destImageHeight) {
        if (baseMultiResolutionImageClass == null || resolutionVariantsMethod == null) {
            return img;
        }
        if (baseMultiResolutionImageClass.isInstance(img)) {
            try {
                return (Image) resolutionVariantMethod.invoke(img, destImageWidth, destImageHeight);
            } catch (IllegalAccessException | InvocationTargetException ex) {
                Logging.error("Unexpected error while calling method: " + ex);
            }
        }
        return img;
    }

    /**
     * Detect the GUI scale for HiDPI mode.
     * <p>
     * This method may not work as expected for a multi-monitor setup. It will
     * only take the default screen device into account.
     * @return the GUI scale for HiDPI mode, a value of 1.0 means standard mode.
     */
    public static double getHiDPIScale() {
        if (GraphicsEnvironment.isHeadless())
            return 1.0;
        GraphicsConfiguration gc = GraphicsEnvironment
                .getLocalGraphicsEnvironment()
                .getDefaultScreenDevice().
                getDefaultConfiguration();
        AffineTransform transform = gc.getDefaultTransform();
        if (!Utils.equalsEpsilon(transform.getScaleX(), transform.getScaleY())) {
            Logging.warn("Unexpected ui transform: " + transform);
        }
        return transform.getScaleX();
    }

    /**
     * Perform an operation on multi-resolution images.
     *
     * When input image is not multi-resolution, it will simply apply the processor once.
     * Otherwise, the processor will be called for each resolution variant and the
     * resulting images assembled to become the output multi-resolution image.
     * @param img input image, possibly multi-resolution
     * @param processor processor taking a plain image as input and returning a single
     * plain image as output
     * @return multi-resolution image assembled from the output of calls to <code>processor</code>
     * for each resolution variant
     */
    public static Image processMRImage(Image img, UnaryOperator<Image> processor) {
        return processMRImages(Collections.singletonList(img), imgs -> processor.apply(imgs.get(0)));
    }

    /**
     * Perform an operation on multi-resolution images.
     *
     * When input images are not multi-resolution, it will simply apply the processor once.
     * Otherwise, the processor will be called for each resolution variant and the
     * resulting images assembled to become the output multi-resolution image.
     * @param imgs input images, possibly multi-resolution
     * @param processor processor taking a list of plain images as input and returning
     * a single plain image as output
     * @return multi-resolution image assembled from the output of calls to <code>processor</code>
     * for each resolution variant
     */
    public static Image processMRImages(List<Image> imgs, Function<List<Image>, Image> processor) {
        CheckParameterUtil.ensureThat(!imgs.isEmpty(), "at least one element expected");
        if (baseMultiResolutionImageClass != null) {
            return processor.apply(imgs);
        }
        List<List<Image>> allVars = imgs.stream().map(HiDPISupport::getResolutionVariants).collect(Collectors.toList());
        int maxVariants = allVars.stream().mapToInt(List<Image>::size).max().getAsInt();
        if (maxVariants == 1)
            return processor.apply(imgs);
        List<Image> imgsProcessed = IntStream.range(0, maxVariants)
                .mapToObj(
                        k -> processor.apply(
                                allVars.stream().map(vars -> vars.get(k)).collect(Collectors.toList())
                        )
                ).collect(Collectors.toList());
        return getMultiResolutionImage(imgsProcessed);
    }

    @SuppressWarnings("unchecked")
    private static Class<? extends Image> initBaseMultiResolutionImageClass() {
        try {
            return (Class<? extends Image>) Class.forName("java.awt.image.BaseMultiResolutionImage");
        } catch (ClassNotFoundException ex) {
            // class is not present in Java 8
            Logging.trace(ex);
            return null;
        }
    }

    private static Constructor<? extends Image> initBaseMultiResolutionImageConstructor() {
        try {
            return baseMultiResolutionImageClass != null
                    ? baseMultiResolutionImageClass.getConstructor(Image[].class)
                    : null;
        } catch (NoSuchMethodException ex) {
            Logging.error("Cannot find expected constructor: " + ex);
            return null;
        }
    }

    private static Method initResolutionVariantsMethod() {
        try {
            return baseMultiResolutionImageClass != null
                    ? baseMultiResolutionImageClass.getMethod("getResolutionVariants")
                    : null;
        } catch (NoSuchMethodException ex) {
            Logging.error("Cannot find expected method: " + ex);
            return null;
        }
    }

    private static Method initResolutionVariantMethod() {
        try {
            return baseMultiResolutionImageClass != null
                    ? baseMultiResolutionImageClass.getMethod("getResolutionVariant", Double.TYPE, Double.TYPE)
                    : null;
        } catch (NoSuchMethodException ex) {
            Logging.error("Cannot find expected method: " + ex);
            return null;
        }
    }
}