vision/preview.go

package vision

import (
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
)

// GenerateImagePreview 生成图片预览
// 支持缩放并裁剪以填充指定尺寸 (Fill 模式)
func GenerateImagePreview(srcPath, outPath string, width, height int) error {
	// 使用统一的 Load() 加载，内部已处理好 HEIC/sips/FFmpeg 的复杂格式兼容
	c, err := Load(srcPath)
	if err != nil {
		return err
	}
	c.Fill(width, height)

	if strings.HasSuffix(strings.ToLower(outPath), ".webp") {
		// 借用 FFmpeg 将生成的画布转为高质量 WebP
		tmpFile := filepath.Join(os.TempDir(), fmt.Sprintf("preview_%d.png", os.Getpid()))
		defer os.Remove(tmpFile)
		if err := Save(c, tmpFile); err != nil {
			return err
		}
		
		v, err := NewVideo()
		if err == nil {
			cmd := exec.Command(v.FFmpegPath, "-i", tmpFile, "-c:v", "libwebp", "-quality", "80", "-y", outPath)
			if err := cmd.Run(); err == nil {
				return nil
			}
		}
	}

	return Save(c, outPath)
}

// GenerateVideoPreview 生成视频预览 (动态 WebP)
// 支持缩放并裁剪以填充指定尺寸 (Fill 模式)
func GenerateVideoPreview(videoPath, outPath string, width, height int) error {
	v, err := NewVideo()
	if err != nil {
		return err
	}

	duration, err := getVideoDuration(videoPath)
	if err != nil {
		return err
	}

	// 动态计算帧数: 适合交给大模型 (VLM) 处理
	// 避免过多的帧浪费 Token，每 30 秒 1 帧，最少 3 帧，最多 8 帧
	frameCount := int(duration / 30.0)
	if frameCount < 3 {
		frameCount = 3
	} else if frameCount > 8 {
		frameCount = 8
	}

	// 在 10% 到 90% 之间均匀采样，跳过片头片尾的可能黑屏
	times := make([]float64, frameCount)
	if frameCount == 1 {
		times[0] = duration * 0.5
	} else {
		for i := 0; i < frameCount; i++ {
			times[i] = duration * (0.10 + 0.80*(float64(i)/float64(frameCount-1)))
		}
	}

	tmpDir, _ := os.MkdirTemp("", "frames")
	defer os.RemoveAll(tmpDir)

	// 使用 ffmpeg 的 scale 和 crop 滤镜实现 Fill 效果
	vf := fmt.Sprintf("scale=%d:%d:force_original_aspect_ratio=increase,crop=%d:%d", width, height, width, height)

	for i, t := range times {
		framePath := filepath.Join(tmpDir, fmt.Sprintf("frame_%02d.png", i))
		// 使用 -ss 快速 seek，性能极高
		cmd := exec.Command(v.FFmpegPath, "-ss", fmt.Sprintf("%f", t), "-i", videoPath, "-frames:v", "1", "-vf", vf, "-y", framePath)
		if err := cmd.Run(); err != nil {
			return err
		}
	}

	// 生成 WebP 动画，每秒 1 帧 (1000ms 间隔，让大模型能看清每一帧)
	cmd := exec.Command(v.FFmpegPath, "-framerate", "1", "-i", filepath.Join(tmpDir, "frame_%02d.png"), 
		"-c:v", "libwebp", "-lossless", "0", "-quality", "70", "-loop", "0", "-y", outPath)
	return cmd.Run()
}

// GenerateAudioPreview 提取 3 分钟内的音频用于预览或语音转写
// 格式: Ogg Opus, 16kHz, 单声道, 12kbps (极致压缩，保留人声特征)
func GenerateAudioPreview(mediaPath, outPath string) error {
	v, err := NewVideo()
	if err != nil {
		return err
	}
	// -vn: 禁用视频
	// -c:a libopus: 高效音频压缩
	// -ar 16000: 采样率 16k (转写标准)
	// -ac 1: 单声道
	// -b:a 12k: 极致压缩
	// -t 180: 最长 180 秒 (足以获得内容概要)
	cmd := exec.Command(v.FFmpegPath, "-i", mediaPath, "-vn", "-c:a", "libopus", "-ar", "16000", "-ac", "1", "-b:a", "12k", "-t", "180", "-y", outPath)
	return cmd.Run()
}

func getVideoDuration(videoPath string) (float64, error) {
	out, err := exec.Command("ffprobe", "-v", "error", "-show_entries", "format=duration", "-of", "default=noprint_wrappers=1:nokey=1", videoPath).Output()
	if err != nil {
		return 0, err
	}
	var duration float64
	_, err = fmt.Sscanf(strings.TrimSpace(string(out)), "%f", &duration)
	return duration, err
}