package camera

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
)

// VideoInfo holds metadata extracted by ffprobe before pipeline starts.
type VideoInfo struct {
	DurationSec float64 // total duration in seconds
	TotalFrames int     // estimated total frames at target FPS
}

// ProbeVideoInfo runs ffprobe to extract duration from a video file or URL.
// Returns zero values (no error) when duration is indeterminate (e.g. live streams).
func ProbeVideoInfo(input string, fps float64) VideoInfo {
	cmd := exec.Command("ffprobe",
		"-v", "error",
		"-select_streams", "v:0",
		"-show_entries", "format=duration",
		"-of", "csv=p=0",
		input,
	)
	out, err := cmd.Output()
	if err != nil {
		return VideoInfo{}
	}
	durStr := strings.TrimSpace(string(out))
	if durStr == "" || durStr == "N/A" {
		return VideoInfo{}
	}
	dur, err := strconv.ParseFloat(durStr, 64)
	if err != nil {
		return VideoInfo{}
	}
	if fps <= 0 {
		fps = 15
	}
	return VideoInfo{
		DurationSec: dur,
		TotalFrames: int(dur * fps),
	}
}

// VideoSource reads a video file or URL frame-by-frame using ffmpeg, outputting
// JPEG frames via stdout. Reuses the same JPEG SOI/EOI marker parsing
// pattern as FFmpegCamera.
type VideoSource struct {
	cmd         *exec.Cmd
	stdout      io.ReadCloser
	frameCh     chan []byte // decoded frames queue
	mu          sync.Mutex
	done        chan struct{}
	finished    bool
	err         error
	filePath    string // local file path (empty for URL sources)
	isURL       bool   // true when source is a URL, skip file cleanup
	totalFrames int64  // 0 means unknown
	frameCount  int64  // atomic counter incremented in readLoop
}

// NewVideoSource starts an ffmpeg process that decodes a video file
// and outputs MJPEG frames to stdout at the specified FPS.
func NewVideoSource(filePath string, fps float64) (*VideoSource, error) {
	return newVideoSource(filePath, fps, false, 0)
}

// NewVideoSourceWithSeek starts ffmpeg from a specific position (in seconds).
func NewVideoSourceWithSeek(filePath string, fps float64, seekSeconds float64) (*VideoSource, error) {
	return newVideoSource(filePath, fps, false, seekSeconds)
}

// NewVideoSourceFromURL starts an ffmpeg process that reads from a URL
// (HTTP, HTTPS, RTSP, etc.) and outputs MJPEG frames to stdout.
func NewVideoSourceFromURL(rawURL string, fps float64) (*VideoSource, error) {
	return newVideoSource(rawURL, fps, true, 0)
}

// NewVideoSourceFromURLWithSeek starts ffmpeg from a URL at a specific position.
func NewVideoSourceFromURLWithSeek(rawURL string, fps float64, seekSeconds float64) (*VideoSource, error) {
	return newVideoSource(rawURL, fps, true, seekSeconds)
}

// ResolveWithYTDLP uses yt-dlp to extract the direct video stream URL
// from platforms like YouTube, Vimeo, etc.
// Returns the resolved direct URL or an error.
func ResolveWithYTDLP(rawURL string) (string, error) {
	cmd := exec.Command("yt-dlp", "-f", "best[ext=mp4]/best", "--get-url", rawURL)
	out, err := cmd.Output()
	if err != nil {
		if exitErr, ok := err.(*exec.ExitError); ok {
			stderr := strings.TrimSpace(string(exitErr.Stderr))
			return "", fmt.Errorf("%s\n%s", friendlyYTDLPError(stderr), stderr)
		}
		return "", fmt.Errorf("yt-dlp 未安裝或無法執行: %w", err)
	}

	resolved := strings.TrimSpace(string(out))
	if resolved == "" {
		return "", fmt.Errorf("yt-dlp 無法取得影片下載連結（影片可能有地區限制或需要登入）")
	}
	if idx := strings.Index(resolved, "\n"); idx > 0 {
		resolved = resolved[:idx]
	}
	return resolved, nil
}

// friendlyYTDLPError 把 yt-dlp 的技術性錯誤訊息轉成使用者能理解的提示。
func friendlyYTDLPError(stderr string) string {
	s := strings.ToLower(stderr)
	switch {
	case strings.Contains(s, "sign in") || strings.Contains(s, "age"):
		return "此影片需要登入 YouTube 帳號才能觀看（例如年齡限制），無法直接使用"
	case strings.Contains(s, "private"):
		return "此影片為私人影片，無法存取"
	case strings.Contains(s, "unavailable") || strings.Contains(s, "not available"):
		return "此影片無法取得（可能已被移除或在你的地區不可用）"
	case strings.Contains(s, "copyright"):
		return "此影片因版權限制無法下載"
	case strings.Contains(s, "live"):
		return "此影片為直播串流，目前不支援直播推論"
	case strings.Contains(s, "premiere"):
		return "此影片為首播（Premiere），尚未開始或格式不支援"
	case strings.Contains(s, "drm") || strings.Contains(s, "protected"):
		return "此影片有 DRM 保護，無法下載"
	case strings.Contains(s, "rate limit") || strings.Contains(s, "429"):
		return "YouTube 暫時限制了請求頻率，請稍後再試"
	case strings.Contains(s, "no video formats"):
		return "找不到可用的影片格式"
	default:
		return "無法解析此影片連結，請確認 URL 是否正確且影片為公開狀態"
	}
}

func newVideoSource(input string, fps float64, isURL bool, seekSeconds float64) (*VideoSource, error) {
	if fps <= 0 {
		fps = 15
	}

	args := []string{}
	if seekSeconds > 0 {
		args = append(args, "-ss", fmt.Sprintf("%.3f", seekSeconds))
	}
	args = append(args,
		"-i", input,
		"-vf", fmt.Sprintf("fps=%g", fps),
		"-f", "image2pipe",
		"-vcodec", "mjpeg",
		"-q:v", "5",
		"-an",
		"-",
	)

	cmd := exec.Command("ffmpeg", args...)
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return nil, fmt.Errorf("failed to get stdout pipe: %w", err)
	}
	cmd.Stderr = nil

	if err := cmd.Start(); err != nil {
		return nil, fmt.Errorf("failed to start ffmpeg: %w", err)
	}

	filePath := ""
	if !isURL {
		filePath = input
	}

	vs := &VideoSource{
		cmd:      cmd,
		stdout:   stdout,
		frameCh:  make(chan []byte, 30), // buffer up to 30 frames
		done:     make(chan struct{}),
		filePath: filePath,
		isURL:    isURL,
	}

	go vs.readLoop()
	return vs, nil
}

// readLoop scans ffmpeg stdout for JPEG SOI/EOI markers to extract frames.
func (v *VideoSource) readLoop() {
	defer close(v.done)
	defer close(v.frameCh)

	reader := bufio.NewReaderSize(v.stdout, 1024*1024)
	buf := make([]byte, 0, 512*1024)
	inFrame := false

	for {
		b, err := reader.ReadByte()
		if err != nil {
			v.mu.Lock()
			v.finished = true
			if err != io.EOF {
				v.err = fmt.Errorf("ffmpeg stream ended: %w", err)
			}
			v.mu.Unlock()
			return
		}

		if !inFrame {
			if b == 0xFF {
				next, err := reader.ReadByte()
				if err != nil {
					v.mu.Lock()
					v.finished = true
					v.mu.Unlock()
					return
				}
				if next == 0xD8 {
					buf = buf[:0]
					buf = append(buf, 0xFF, 0xD8)
					inFrame = true
				}
			}
			continue
		}

		buf = append(buf, b)

		if b == 0xD9 && len(buf) >= 2 && buf[len(buf)-2] == 0xFF {
			frame := make([]byte, len(buf))
			copy(frame, buf)

			v.frameCh <- frame // blocks if buffer full, applies backpressure
			atomic.AddInt64(&v.frameCount, 1)
			inFrame = false
		}
	}
}

// ReadFrame returns the next decoded frame, blocking until one is available.
// Returns an error when all frames have been consumed and ffmpeg has finished.
func (v *VideoSource) ReadFrame() ([]byte, error) {
	frame, ok := <-v.frameCh
	if !ok {
		return nil, fmt.Errorf("video playback complete")
	}
	return frame, nil
}

// SetTotalFrames sets the expected total frame count (from ffprobe).
func (v *VideoSource) SetTotalFrames(n int) {
	atomic.StoreInt64(&v.totalFrames, int64(n))
}

// TotalFrames returns the expected total frame count, or 0 if unknown.
func (v *VideoSource) TotalFrames() int {
	return int(atomic.LoadInt64(&v.totalFrames))
}

// FrameCount returns the number of frames decoded so far.
func (v *VideoSource) FrameCount() int {
	return int(atomic.LoadInt64(&v.frameCount))
}

// IsFinished returns true when the video file has been fully decoded
// AND all buffered frames have been consumed.
func (v *VideoSource) IsFinished() bool {
	v.mu.Lock()
	finished := v.finished
	v.mu.Unlock()
	return finished && len(v.frameCh) == 0
}

// CloseWithoutRemove stops the ffmpeg process but does NOT delete the temp file.
// Used when seeking: we need to restart ffmpeg from a different position but keep the file.
func (v *VideoSource) CloseWithoutRemove() error {
	if v.cmd != nil && v.cmd.Process != nil {
		_ = v.cmd.Process.Kill()
		_ = v.cmd.Wait()
	}
	for range v.frameCh {
	}
	<-v.done
	return nil
}

func (v *VideoSource) Close() error {
	if v.cmd != nil && v.cmd.Process != nil {
		_ = v.cmd.Process.Kill()
		_ = v.cmd.Wait()
	}
	// Drain any remaining frames so readLoop can exit
	for range v.frameCh {
	}
	<-v.done
	// Only remove temp files, not URL sources
	if !v.isURL && v.filePath != "" {
		_ = os.Remove(v.filePath)
	}
	return nil
}