package application

import (
	"context"
	"encoding/base64"
	"fmt"
	"net/http"
	"time"

	"github.com/mmmy/snapgo/internal/domain"
	"github.com/mmmy/snapgo/internal/infrastructure/clipboard"
)

// VisionSummarizer describes a multimodal model capable of reading an image
// reference (either a public https URL or an inline base64 data URL) and
// returning a textual summary.
type VisionSummarizer interface {
	SummarizeImage(ctx context.Context, prompt string, imageURL string) (string, error)
}

// ObjectDeleter is an optional capability an OSSProvider may implement so the
// summary pipeline can delete the temporary screenshot it uploaded purely so a
// remote model could fetch it. It is kept separate from domain.OSSProvider to
// avoid forcing every provider (or test fake) to implement deletion.
type ObjectDeleter interface {
	Delete(ctx context.Context, key string) error
}

// CaptureSummaryService wires screenshot bytes -> multimodal LLM summary ->
// clipboard. It prefers sending the image inline as a base64 data URL and only
// falls back to an S3 upload (public URL) when the payload exceeds the
// provider's inline size limit. It intentionally does not notify UI state
// itself: the caller emits fine-grained "uploading / recognizing / done"
// progress.
type CaptureSummaryService struct {
	Provider   domain.OSSProvider
	Summarizer VisionSummarizer
	Clipboard  clipboard.Writer
	Prompt     string
	PathPrefix string
	// MaxInlineBytes caps the PNG size eligible for inline base64. Payloads
	// larger than this must go through S3. A value <= 0 disables the inline
	// path entirely (always upload).
	MaxInlineBytes int
	// HTTPClient is used for the public-URL reachability probe. Defaults to a
	// short-timeout client when nil.
	HTTPClient *http.Client
}

// CanInline reports whether the screenshot is small enough to be embedded
// directly in the request as a base64 data URL.
func (s *CaptureSummaryService) CanInline(pngBytes []byte) bool {
	return s.MaxInlineBytes > 0 && len(pngBytes) <= s.MaxInlineBytes
}

// InlineDataURL encodes the PNG as an RFC 2397 data URL suitable for the
// image_url field of an OpenAI-compatible request.
func (s *CaptureSummaryService) InlineDataURL(pngBytes []byte) string {
	return "data:image/png;base64," + base64.StdEncoding.EncodeToString(pngBytes)
}

// UploadImage uploads the screenshot and returns the public URL visible to
// the multimodal provider. Used only when the image is too large to inline.
func (s *CaptureSummaryService) UploadImage(ctx context.Context, pngBytes []byte) (*domain.UploadResult, error) {
	if s.Provider == nil {
		return nil, fmt.Errorf("s3 is not configured")
	}
	if len(pngBytes) == 0 {
		return nil, fmt.Errorf("empty screenshot")
	}
	key := buildObjectKey(s.PathPrefix)
	start := time.Now()
	url, err := s.Provider.Upload(ctx, key, pngBytes, "image/png")
	if err != nil {
		return nil, fmt.Errorf("s3 put object: %w", err)
	}
	return &domain.UploadResult{
		URL:      url,
		Key:      key,
		Provider: s.Provider.Name(),
		Elapsed:  time.Since(start),
	}, nil
}

// EnsureReachable verifies the public URL can actually be fetched, so we can
// surface a clear "link not reachable" message instead of an opaque provider
// error when the bucket is private or fronted by an inaccessible CDN.
func (s *CaptureSummaryService) EnsureReachable(ctx context.Context, imageURL string) error {
	client := s.HTTPClient
	if client == nil {
		client = &http.Client{Timeout: 10 * time.Second}
	}
	probe := func(method string) (int, error) {
		req, err := http.NewRequestWithContext(ctx, method, imageURL, nil)
		if err != nil {
			return 0, err
		}
		resp, err := client.Do(req)
		if err != nil {
			return 0, err
		}
		resp.Body.Close()
		return resp.StatusCode, nil
	}
	status, err := probe(http.MethodHead)
	// Some S3-compatible endpoints reject HEAD; retry with GET before failing.
	if err != nil || status == http.StatusMethodNotAllowed || status == http.StatusForbidden {
		if s, gerr := probe(http.MethodGet); gerr == nil {
			status, err = s, nil
		} else if err == nil {
			err = gerr
		}
	}
	if err != nil {
		return fmt.Errorf("图片链接不可达（模型无法读取上传的截图）：%w", err)
	}
	if status < 200 || status >= 300 {
		return fmt.Errorf("图片链接不可达：HTTP %d，请确认对象存储 bucket 公网可读或已正确配置 PublicURLBase", status)
	}
	return nil
}

// DeleteUploaded removes the temporary object from S3 if the provider supports
// deletion. It is best-effort: a nil return means either success or that the
// provider cannot delete.
func (s *CaptureSummaryService) DeleteUploaded(ctx context.Context, key string) error {
	if key == "" {
		return nil
	}
	deleter, ok := s.Provider.(ObjectDeleter)
	if !ok {
		return nil
	}
	return deleter.Delete(ctx, key)
}

// Summarize asks the configured model to summarize the image reference, which
// may be a public URL or an inline base64 data URL.
func (s *CaptureSummaryService) Summarize(ctx context.Context, imageURL string) (string, error) {
	if s.Summarizer == nil {
		return "", fmt.Errorf("llm is not configured")
	}
	return s.Summarizer.SummarizeImage(ctx, s.Prompt, imageURL)
}

// CopySummary writes the final summary text to the clipboard.
func (s *CaptureSummaryService) CopySummary(_ context.Context, summary string) error {
	if summary == "" {
		return fmt.Errorf("empty summary")
	}
	if s.Clipboard == nil {
		return fmt.Errorf("clipboard is not configured")
	}
	if err := s.Clipboard.WriteText(summary); err != nil {
		return fmt.Errorf("clipboard write failed: %w", err)
	}
	return nil
}