import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardCopyOption;

import javax.imageio.ImageIO;

/**
 * 由单张 PNG 源图生成 jpackage 各平台所需的应用图标。
 *
 * <p>jpackage 对各平台图标格式要求不同：Windows 用 {@code .ico}、macOS 用
 * {@code .icns}、Linux 用 {@code .png}。本工具基于纯 JDK（ImageIO + AWT）实现转换，
 * 不依赖 ImageMagick/Pillow 等外部工具，可在 Windows/macOS/Linux 的构建机上直接运行。</p>
 *
 * <p>用法：{@code java IconGen.java <sourcePng> <outputDir>}，输出
 * {@code icon.png}、{@code icon.ico}、{@code icon.icns}。</p>
 */
public final class IconGen {

    /** ICO 中包含的图标尺寸 */
    private static final int[] ICO_SIZES = {16, 24, 32, 48, 64, 128, 256};

    /** 尺寸不大于该值时使用 BMP 条目，否则使用 PNG 条目（兼容性最佳） */
    private static final int ICO_BMP_MAX_SIZE = 64;

    /** ICNS 条目：类型（4 字节）与其像素尺寸 */
    private static final Object[][] ICNS_ENTRIES = {
            {"ic11", 32},
            {"ic12", 64},
            {"ic07", 128},
            {"ic13", 256},
            {"ic08", 256},
            {"ic14", 512},
            {"ic09", 512},
    };

    private IconGen() {
    }

    /**
     * 程序入口。
     *
     * @param args 源 PNG 路径与输出目录
     * @throws IOException 读写失败
     */
    public static void main(String[] args) throws IOException {
        if (args.length < 2) {
            System.err.println("用法: java IconGen.java <sourcePng> <outputDir>");
            System.exit(2);
        }
        Path source = Paths.get(args[0]);
        Path outputDir = Paths.get(args[1]);
        Files.createDirectories(outputDir);

        BufferedImage sourceImage = ImageIO.read(source.toFile());
        if (sourceImage == null) {
            throw new IOException("无法读取源图标：" + source);
        }

        Files.copy(source, outputDir.resolve("icon.png"), StandardCopyOption.REPLACE_EXISTING);
        writeIco(sourceImage, outputDir.resolve("icon.ico"));
        writeIcns(sourceImage, outputDir.resolve("icon.icns"));

        System.out.println("已生成平台图标到 " + outputDir.toAbsolutePath());
    }

    /**
     * 生成 Windows ICO 文件。
     *
     * @param source 源图
     * @param out    输出文件
     * @throws IOException 写入失败
     */
    private static void writeIco(BufferedImage source, Path out) throws IOException {
        int count = ICO_SIZES.length;
        byte[][] images = new byte[count][];
        for (int i = 0; i < count; i++) {
            BufferedImage scaled = resize(source, ICO_SIZES[i]);
            images[i] = ICO_SIZES[i] <= ICO_BMP_MAX_SIZE ? toBmpEntry(scaled) : toPng(scaled);
        }

        try (OutputStream os = Files.newOutputStream(out)) {
            writeShortLE(os, 0);
            writeShortLE(os, 1);
            writeShortLE(os, count);
            // 图标数据区起始偏移：6 字节文件头 + 每项 16 字节目录项
            int offset = 6 + count * 16;
            for (int i = 0; i < count; i++) {
                int size = ICO_SIZES[i];
                os.write(size >= 256 ? 0 : size);
                os.write(size >= 256 ? 0 : size);
                os.write(0);
                os.write(0);
                writeShortLE(os, 1);
                writeShortLE(os, 32);
                writeIntLE(os, images[i].length);
                writeIntLE(os, offset);
                offset += images[i].length;
            }
            for (byte[] image : images) {
                os.write(image);
            }
        }
    }

    /**
     * 将图像编码为 ICO 中的 BMP 条目：BITMAPINFOHEADER + 32 位 BGRA 像素 + AND 掩码。
     *
     * @param image 图像
     * @return BMP 条目字节
     * @throws IOException 编码失败
     */
    private static byte[] toBmpEntry(BufferedImage image) throws IOException {
        int width = image.getWidth();
        int height = image.getHeight();
        ByteArrayOutputStream buffer = new ByteArrayOutputStream();

        // BITMAPINFOHEADER（高度为两倍，包含 XOR 图与 AND 掩码）
        writeIntLE(buffer, 40);
        writeIntLE(buffer, width);
        writeIntLE(buffer, height * 2);
        writeShortLE(buffer, 1);
        writeShortLE(buffer, 32);
        writeIntLE(buffer, 0);
        writeIntLE(buffer, 0);
        writeIntLE(buffer, 0);
        writeIntLE(buffer, 0);
        writeIntLE(buffer, 0);
        writeIntLE(buffer, 0);

        // XOR 图：32 位 BGRA，自下而上
        for (int y = height - 1; y >= 0; y--) {
            for (int x = 0; x < width; x++) {
                int argb = image.getRGB(x, y);
                buffer.write((argb) & 0xFF);
                buffer.write((argb >> 8) & 0xFF);
                buffer.write((argb >> 16) & 0xFF);
                buffer.write((argb >>> 24) & 0xFF);
            }
        }

        // AND 掩码：1 位/像素，行按 4 字节对齐，全 0（透明由 alpha 通道处理）
        int maskRowBytes = ((width + 31) / 32) * 4;
        byte[] maskRow = new byte[maskRowBytes];
        for (int y = 0; y < height; y++) {
            buffer.write(maskRow);
        }
        return buffer.toByteArray();
    }

    /**
     * 生成 macOS ICNS 文件（以 PNG 条目承载各尺寸）。
     *
     * @param source 源图
     * @param out    输出文件
     * @throws IOException 写入失败
     */
    private static void writeIcns(BufferedImage source, Path out) throws IOException {
        ByteArrayOutputStream body = new ByteArrayOutputStream();
        for (Object[] entry : ICNS_ENTRIES) {
            byte[] png = toPng(resize(source, (Integer) entry[1]));
            body.write(((String) entry[0]).getBytes("US-ASCII"));
            writeIntBE(body, png.length + 8);
            body.write(png);
        }
        byte[] bodyBytes = body.toByteArray();

        try (OutputStream os = Files.newOutputStream(out)) {
            os.write("icns".getBytes("US-ASCII"));
            writeIntBE(os, bodyBytes.length + 8);
            os.write(bodyBytes);
        }
    }

    /**
     * 缩放图像。
     *
     * @param source 源图
     * @param size   目标边长
     * @return 缩放后的 ARGB 图像
     */
    private static BufferedImage resize(BufferedImage source, int size) {
        BufferedImage target = new BufferedImage(size, size, BufferedImage.TYPE_INT_ARGB);
        Graphics2D graphics = target.createGraphics();
        try {
            graphics.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
                    RenderingHints.VALUE_INTERPOLATION_BICUBIC);
            graphics.setRenderingHint(RenderingHints.KEY_RENDERING,
                    RenderingHints.VALUE_RENDER_QUALITY);
            graphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                    RenderingHints.VALUE_ANTIALIAS_ON);
            graphics.drawImage(source, 0, 0, size, size, null);
        } finally {
            graphics.dispose();
        }
        return target;
    }

    /**
     * 将图像编码为 PNG 字节。
     *
     * @param image 图像
     * @return PNG 字节
     * @throws IOException 编码失败
     */
    private static byte[] toPng(BufferedImage image) throws IOException {
        ByteArrayOutputStream buffer = new ByteArrayOutputStream();
        ImageIO.write(image, "png", buffer);
        return buffer.toByteArray();
    }

    /**
     * 写出小端 2 字节整数。
     *
     * @param os  输出流
     * @param value 值
     * @throws IOException 写入失败
     */
    private static void writeShortLE(OutputStream os, int value) throws IOException {
        os.write(value & 0xFF);
        os.write((value >> 8) & 0xFF);
    }

    /**
     * 写出小端 4 字节整数。
     *
     * @param os  输出流
     * @param value 值
     * @throws IOException 写入失败
     */
    private static void writeIntLE(OutputStream os, int value) throws IOException {
        os.write(value & 0xFF);
        os.write((value >> 8) & 0xFF);
        os.write((value >> 16) & 0xFF);
        os.write((value >>> 24) & 0xFF);
    }

    /**
     * 写出大端 4 字节整数。
     *
     * @param os  输出流
     * @param value 值
     * @throws IOException 写入失败
     */
    private static void writeIntBE(OutputStream os, int value) throws IOException {
        os.write((value >>> 24) & 0xFF);
        os.write((value >> 16) & 0xFF);
        os.write((value >> 8) & 0xFF);
        os.write(value & 0xFF);
    }
}