package com.imyeyu.api.util;

import org.bytedeco.javacv.FFmpegFrameGrabber;
import org.bytedeco.javacv.Frame;
import org.bytedeco.javacv.Java2DFrameConverter;

import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

/// JavaCV 工具类
///
/// @author 夜雨
/// @since 2025-10-23 17:05
public class JavaCV {

	/// 单次跳转分片上限
	///
	/// 任何真实文件的当前位置加该值都不会溢出 long
	private static final long SKIP_PIECE = 1L << 40;

	/// 从视频流顺序解码并提取指定时间附近的一帧 PNG 图片
	///
	/// 不执行时间定位，避免为了取实时缩略图而把整个视频复制到临时文件
	///
	/// moov 原子位于文件尾部的视频（非 faststart）仍会触发 FFmpeg 回调 AVSEEK_SIZE 探测文件大小，
	/// 依赖底层流的 skip/reset 语义正确，因此必须配合 `SkipSafeInputStream` 规避 GridFS 的溢出缺陷
	///
	/// @param stream        视频输入流
	/// @param targetSeconds 目标时间，单位为秒
	/// @return PNG 图片字节流
	/// @throws Exception 视频解析或取帧失败
	public static ByteArrayOutputStream captureThumbnail(InputStream stream, double targetSeconds) throws Exception {
		long targetMicros = toMicros(targetSeconds);
		ByteArrayOutputStream firstFrame = new ByteArrayOutputStream();
		try (FFmpegFrameGrabber grabber = new FFmpegFrameGrabber(new SkipSafeInputStream(stream))) {
			grabber.start();
			try (Java2DFrameConverter converter = new Java2DFrameConverter()) {
				Frame frame;
				while ((frame = grabber.grabImage()) != null) {
					BufferedImage image = converter.getBufferedImage(frame);
					if (image == null) {
						continue;
					}
					if (!(0 < firstFrame.size())) {
						firstFrame = toPng(image);
					}
					if (grabber.getTimestamp() >= targetMicros) {
						return targetMicros == 0 ? firstFrame : toPng(image);
					}
				}
			}
		}
		// 短视频提前结束时退回首个有效帧
		return firstFrame;
	}

	private static long toMicros(double targetSeconds) {
		double seconds = Double.isFinite(targetSeconds) ? Math.max(0, targetSeconds) : 0;
		return Math.round(seconds * 1_000_000D);
	}

	private static ByteArrayOutputStream toPng(BufferedImage image) throws IOException {
		ByteArrayOutputStream output = new ByteArrayOutputStream();
		if (ImageIO.write(image, "png", output)) {
			return output;
		}
		return new ByteArrayOutputStream();
	}

	/// 分片跳转流包装
	///
	/// GridFSDownloadStreamImpl 的 skip 以 `currentPosition + n` 计算目标位置且不防护 long 溢出，
	/// 当 javacv 的 SeekCallback 以 `skip(Long.MAX_VALUE)` 探测流结尾时，位于流末尾的第二次调用
	/// 会因溢出落入正常分支，返回未实际跳过的 `Long.MAX_VALUE` 并污染内部位置，
	/// 导致 `avformat_open_input` 在 `while (true)` 内 100% CPU 死循环
	///
	/// 此包装将大额跳转拆分为不超过 {@link #SKIP_PIECE} 的分片，保证每次调用的目标位置不溢出
	private static class SkipSafeInputStream extends InputStream {

		private final InputStream stream;

		private SkipSafeInputStream(InputStream stream) {
			this.stream = stream;
		}

		@Override
		public int read() throws IOException {
			return stream.read();
		}

		@Override
		public int read(byte[] b, int off, int len) throws IOException {
			return stream.read(b, off, len);
		}

		@Override
		public long skip(long n) throws IOException {
			if (n <= 0) {
				return 0;
			}
			long total = 0;
			while (0 < n) {
				long skipped = stream.skip(Math.min(n, SKIP_PIECE));
				if (skipped <= 0) {
					break;
				}
				total += skipped;
				n -= skipped;
			}
			return total;
		}

		@Override
		public int available() throws IOException {
			return stream.available();
		}

		@Override
		public void close() throws IOException {
			stream.close();
		}

		@Override
		public synchronized void mark(int readlimit) {
			stream.mark(readlimit);
		}

		@Override
		public synchronized void reset() throws IOException {
			stream.reset();
		}

		@Override
		public boolean markSupported() {
			return stream.markSupported();
		}
	}
}