package camera

import (
	"context"
	"fmt"
	"time"

	"visiona-agent/server/internal/driver"
)

// maxConsecutiveReadErrors 是 camera 模式下連續讀 frame 失敗的容忍上限。
//
// 原本讀失敗只 sleep 100ms 後無限重試、完全靜默——攝影機中途斷線 / 從未出 frame 時
// 前端只會看到永遠空白、後端也沒任何跡象。改成連續失敗超過上限就 log + 結束 pipeline，
// 讓失敗看得見。100ms * 50 ≈ 5s，足夠容忍偶發抖動，又不會無限卡住。
const maxConsecutiveReadErrors = 50

// SourceType identifies the kind of frame source used in the pipeline.
type SourceType string

const (
	SourceCamera     SourceType = "camera"
	SourceImage      SourceType = "image"
	SourceVideo      SourceType = "video"
	SourceBatchImage SourceType = "batch_image"
)

type InferencePipeline struct {
	source      FrameSource
	sourceType  SourceType
	device      driver.DeviceDriver
	frameCh     chan<- []byte
	resultCh    chan<- *driver.InferenceResult
	cancel      context.CancelFunc
	doneCh      chan struct{}
	frameOffset int // starting frame index (non-zero after seek)
}

func NewInferencePipeline(
	source FrameSource,
	sourceType SourceType,
	device driver.DeviceDriver,
	frameCh chan<- []byte,
	resultCh chan<- *driver.InferenceResult,
) *InferencePipeline {
	return &InferencePipeline{
		source:     source,
		sourceType: sourceType,
		device:     device,
		frameCh:    frameCh,
		resultCh:   resultCh,
		doneCh:     make(chan struct{}),
	}
}

// NewInferencePipelineWithOffset creates a pipeline with a frame offset (used after seek).
func NewInferencePipelineWithOffset(
	source FrameSource,
	sourceType SourceType,
	device driver.DeviceDriver,
	frameCh chan<- []byte,
	resultCh chan<- *driver.InferenceResult,
	frameOffset int,
) *InferencePipeline {
	return &InferencePipeline{
		source:      source,
		sourceType:  sourceType,
		device:      device,
		frameCh:     frameCh,
		resultCh:    resultCh,
		doneCh:      make(chan struct{}),
		frameOffset: frameOffset,
	}
}

func (p *InferencePipeline) Start() {
	ctx, cancel := context.WithCancel(context.Background())
	p.cancel = cancel
	go p.run(ctx)
}

func (p *InferencePipeline) Stop() {
	if p.cancel != nil {
		p.cancel()
	}
}

// Done returns a channel that closes when the pipeline finishes.
// For camera mode this only closes on Stop(); for image/video it
// closes when the source is exhausted.
func (p *InferencePipeline) Done() <-chan struct{} {
	return p.doneCh
}

func (p *InferencePipeline) run(ctx context.Context) {
	defer close(p.doneCh)

	targetInterval := time.Second / 15 // 15 FPS
	inferenceRan := false              // for image mode: only run inference once
	frameIndex := 0                    // video frame counter
	consecutiveReadErrors := 0         // camera 模式：連續讀 frame 失敗計數

	for {
		select {
		case <-ctx.Done():
			return
		default:
		}

		start := time.Now()

		var jpegFrame []byte
		var readErr error

		// Video mode: ReadFrame blocks on channel, need to respect ctx cancel
		if p.sourceType == SourceVideo {
			vs := p.source.(*VideoSource)
			select {
			case <-ctx.Done():
				return
			case frame, ok := <-vs.frameCh:
				if !ok {
					return // all frames consumed
				}
				jpegFrame = frame
			}
		} else {
			jpegFrame, readErr = p.source.ReadFrame()
			if readErr != nil {
				// camera 模式：不再無限靜默重試。連續失敗超過上限就 log + 結束，
				// 避免攝影機從未出 frame / 中途斷線時前端永遠空白、後端毫無跡象。
				// 非 camera 來源（理論上不會走到這，image/batch 有各自路徑）維持原重試行為。
				if p.sourceType == SourceCamera {
					consecutiveReadErrors++
					if consecutiveReadErrors >= maxConsecutiveReadErrors {
						fmt.Printf("[ERROR] camera pipeline aborted after %d consecutive read errors: %v\n",
							consecutiveReadErrors, readErr)
						return
					}
				}
				time.Sleep(100 * time.Millisecond)
				continue
			}
			// 成功讀到 frame，重置連續失敗計數。
			consecutiveReadErrors = 0
		}

		// Send to MJPEG stream
		select {
		case p.frameCh <- jpegFrame:
		default:
		}

		// Batch image mode: process each image sequentially, then advance.
		if p.sourceType == SourceBatchImage {
			mis := p.source.(*MultiImageSource)
			for {
				select {
				case <-ctx.Done():
					return
				default:
				}

				frame, err := mis.ReadFrame()
				if err != nil {
					return
				}

				// Send current frame to MJPEG
				select {
				case p.frameCh <- frame:
				default:
				}

				// Run inference on this image
				result, inferErr := p.device.RunInference(frame)
				if inferErr == nil {
					entry := mis.CurrentEntry()
					result.ImageIndex = mis.CurrentIndex()
					result.TotalImages = mis.TotalImages()
					result.Filename = entry.Filename
					select {
					case p.resultCh <- result:
					default:
					}
				}

				// Move to next image
				if !mis.Advance() {
					// Keep sending last frame for late-connecting MJPEG clients (~2s)
					for i := 0; i < 30; i++ {
						select {
						case <-ctx.Done():
							return
						default:
						}
						select {
						case p.frameCh <- frame:
						default:
						}
						time.Sleep(time.Second / 15)
					}
					return
				}
			}
		}

		// Image mode: only run inference once, then keep sending
		// the same frame to MJPEG so late-connecting clients can see it.
		if p.sourceType == SourceImage {
			if !inferenceRan {
				inferenceRan = true
				result, err := p.device.RunInference(jpegFrame)
				if err == nil {
					select {
					case p.resultCh <- result:
					default:
					}
				}
			}
			elapsed := time.Since(start)
			if elapsed < targetInterval {
				time.Sleep(targetInterval - elapsed)
			}
			continue
		}

		// Camera / Video mode: run inference every frame
		result, err := p.device.RunInference(jpegFrame)
		if err != nil {
			continue
		}

		// Video mode: attach frame progress
		if p.sourceType == SourceVideo {
			result.FrameIndex = p.frameOffset + frameIndex
			frameIndex++
			vs := p.source.(*VideoSource)
			result.TotalFrames = vs.TotalFrames()
		}

		select {
		case p.resultCh <- result:
		default:
		}

		elapsed := time.Since(start)
		if elapsed < targetInterval {
			time.Sleep(targetInterval - elapsed)
		}
	}
}