package service

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"path"
	"strings"
	"time"

	"github.com/google/uuid"

	"go-places-api/internal/analysis"
	"go-places-api/internal/blobstore"
	"go-places-api/internal/domain"
	"go-places-api/internal/events"
)

// ImageUpload is one picture submitted by a client.
type ImageUpload struct {
	// Filename is the client-supplied name, used only to pick a storage
	// extension. It never becomes part of the storage path.
	Filename string
	// ContentType is the declared MIME type.
	ContentType string
	// Caption is the description the user attached to this picture.
	Caption string
	// Body streams the encoded picture.
	Body io.Reader
	// Coordinate overrides the location. When nil the EXIF GPS tag is used,
	// and failing that the place's own coordinate applies.
	Coordinate *domain.Coordinate
}

// UploadResult reports what happened to one picture when a batch is submitted.
// Pictures are processed independently so one bad file does not discard the
// good ones.
type UploadResult struct {
	Image domain.Image
	// AnalysisNote explains a degraded analysis, if any.
	AnalysisNote string
	// Err is the reason this picture was rejected.
	Err error
}

// AddImage stores one picture against a place, analyses it to produce badges,
// and links it to other pictures taken at the same place.
//
// The picture is analysed before its bytes are committed: if the payload is not
// a decodable image there is no reason to keep it. Analysis failures are
// recorded on the record rather than discarding an otherwise valid upload,
// because the picture is the valuable part and the badges can be recomputed
// with Reanalyze.
func (s *Service) AddImage(ctx context.Context, author domain.User, placeID string, up ImageUpload) (domain.Image, error) {
	img, _, err := s.addImage(ctx, author, placeID, up)
	return img, err
}

// UploadPictures attaches several pictures to a place in one call. Each picture
// is independent, so failures are reported per picture instead of failing the
// whole batch.
func (s *Service) UploadPictures(ctx context.Context, author domain.User, placeID string, uploads []ImageUpload) ([]UploadResult, error) {
	if strings.TrimSpace(placeID) == "" {
		return nil, fmt.Errorf("%w: place id is required", ErrInvalidInput)
	}
	if len(uploads) == 0 {
		return nil, fmt.Errorf("%w: no pictures were supplied", ErrInvalidInput)
	}
	if author.ID == "" {
		return nil, fmt.Errorf("%w: an authenticated author is required", ErrInvalidInput)
	}

	results := make([]UploadResult, 0, len(uploads))
	for _, up := range uploads {
		img, note, err := s.addImage(ctx, author, placeID, up)
		results = append(results, UploadResult{Image: img, AnalysisNote: note, Err: err})
		if err != nil {
			s.logger.Warn("rejected upload", "placeId", placeID, "filename", up.Filename, "error", err)
		}
	}
	return results, nil
}

// addImage is the shared implementation behind AddImage and UploadPictures.
func (s *Service) addImage(ctx context.Context, author domain.User, placeID string, up ImageUpload) (domain.Image, string, error) {
	if strings.TrimSpace(placeID) == "" {
		return domain.Image{}, "", fmt.Errorf("%w: place id is required", ErrInvalidInput)
	}
	if author.ID == "" {
		return domain.Image{}, "", fmt.Errorf("%w: an authenticated author is required", ErrInvalidInput)
	}
	if up.Body == nil {
		return domain.Image{}, "", fmt.Errorf("%w: the picture is empty", ErrInvalidInput)
	}
	if !s.cfg.AllowsContentType(up.ContentType) {
		return domain.Image{}, "", fmt.Errorf("%w: %q is not an accepted image type",
			ErrUnsupportedType, up.ContentType)
	}

	// Buffer one byte past the limit so an oversized payload is detectable
	// without trusting the client's Content-Length.
	var buf bytes.Buffer
	read, err := io.Copy(&buf, io.LimitReader(up.Body, s.cfg.MaxUploadBytes+1))
	if err != nil {
		return domain.Image{}, "", fmt.Errorf("%w: the picture could not be read: %v", ErrInvalidInput, err)
	}
	if read == 0 {
		return domain.Image{}, "", fmt.Errorf("%w: the picture is empty", ErrInvalidInput)
	}
	if read > s.cfg.MaxUploadBytes {
		return domain.Image{}, "", fmt.Errorf("%w: the picture exceeds the %d byte limit",
			ErrTooLarge, s.cfg.MaxUploadBytes)
	}
	data := buf.Bytes()

	// Analysing first means an undecodable payload never reaches the store.
	result, err := s.analyze.Analyze(ctx, analysis.Input{
		ContentType: up.ContentType,
		Bytes:       data,
	})
	if err != nil {
		return domain.Image{}, "", fmt.Errorf("%w: %v", ErrInvalidInput, err)
	}

	place, err := s.store.GetPlace(ctx, placeID)
	if err != nil {
		return domain.Image{}, "", mapStoreError(err, "place")
	}
	if err := s.store.UpsertUser(ctx, author); err != nil {
		return domain.Image{}, "", mapStoreError(err, "user")
	}

	ext := extensionFor(up.Filename, up.ContentType)
	key := path.Join(author.ID, time.Now().UTC().Format("2006/01"), uuid.NewString()+ext)

	written, err := s.blobs.Put(ctx, key, bytes.NewReader(data), s.cfg.MaxUploadBytes)
	if err != nil {
		if isTooLarge(err) {
			return domain.Image{}, "", fmt.Errorf("%w: %v", ErrTooLarge, err)
		}
		return domain.Image{}, "", fmt.Errorf("service: store picture: %w", err)
	}

	// Precedence for a picture's location: an explicit override, then the EXIF
	// GPS tag, then the place's own coordinate.
	coordinate := effectiveCoordinate(domain.Image{Coordinate: up.Coordinate}, place.Coordinate)
	if up.Coordinate == nil && result.Metadata.Coordinate != nil {
		coordinate = result.Metadata.Coordinate
	}

	img := domain.Image{
		PlaceID:        place.ID,
		StorageKey:     key,
		Caption:        strings.TrimSpace(up.Caption),
		ContentType:    up.ContentType,
		ByteSize:       written,
		Width:          result.Width,
		Height:         result.Height,
		Coordinate:     coordinate,
		TakenAt:        result.Metadata.TakenAt,
		CameraMake:     result.Metadata.Make,
		CameraModel:    result.Metadata.Model,
		Badges:         result.Badges,
		AnalysisStatus: domain.AnalysisCompleted,
		AnalysisError:  result.Note,
	}

	saved, err := s.store.CreateImage(ctx, img)
	if err != nil {
		// Never leave an orphaned blob behind a failed insert.
		if delErr := s.blobs.Delete(ctx, key); delErr != nil {
			s.logger.Warn("failed to roll back image blob", "key", key, "error", delErr)
		}
		return domain.Image{}, "", mapStoreError(err, "image")
	}
	saved.URL = s.ImageURL(saved.StorageKey)

	s.publish(ctx, author, events.TopicImageAnalyzed, map[string]any{
		"imageId":  saved.ID,
		"placeId":  place.ID,
		"badges":   badgeLabels(saved.Badges),
		"degraded": result.Note != "",
	})

	// Linking is separate from accepting the upload, so a failure here is logged
	// rather than reported as an upload error.
	if err := s.linkAfterUpload(ctx, saved); err != nil {
		s.logger.Warn("failed to link new picture", "imageId", saved.ID, "error", err)
	}
	return saved, result.Note, nil
}

// Reanalyze runs the analysis pipeline again over a stored picture. This is how
// badges are recovered after a failure or refreshed after the analyzer changes.
func (s *Service) Reanalyze(ctx context.Context, imageID string) (domain.Image, error) {
	img, err := s.store.GetImage(ctx, imageID)
	if err != nil {
		return domain.Image{}, mapStoreError(err, "image")
	}
	if img.StorageKey == "" {
		return domain.Image{}, fmt.Errorf("%w: the picture has no stored bytes", ErrInvalidInput)
	}

	rc, err := s.blobs.Get(ctx, img.StorageKey)
	if err != nil {
		return domain.Image{}, fmt.Errorf("service: read stored picture: %w", err)
	}
	defer rc.Close()

	// Bound the read by the configured limit even though the blob was written
	// under it, so a corrupted store cannot exhaust memory.
	var buf bytes.Buffer
	if _, err := io.Copy(&buf, io.LimitReader(rc, s.cfg.MaxUploadBytes)); err != nil {
		return domain.Image{}, fmt.Errorf("service: buffer stored picture: %w", err)
	}

	result, err := s.analyze.Analyze(ctx, analysis.Input{
		ContentType: img.ContentType,
		Bytes:       buf.Bytes(),
	})
	if err != nil {
		if setErr := s.store.SetAnalysisState(ctx, img.ID, domain.AnalysisFailed, err.Error()); setErr != nil {
			s.logger.Warn("failed to record analysis failure", "imageId", img.ID, "error", setErr)
		}
		return domain.Image{}, fmt.Errorf("%w: %v", ErrInvalidInput, err)
	}

	if err := s.store.ReplaceBadges(ctx, img.ID, result.Badges); err != nil {
		return domain.Image{}, mapStoreError(err, "badge")
	}
	status := domain.AnalysisCompleted
	if result.Note != "" {
		// Understood, but only partially, which is worth recording so the UI
		// can say the badge set may be incomplete.
		status = domain.AnalysisFailed
	}
	if err := s.store.SetAnalysisState(ctx, img.ID, status, result.Note); err != nil {
		return domain.Image{}, mapStoreError(err, "image")
	}

	updated, err := s.store.GetImage(ctx, img.ID)
	if err != nil {
		return domain.Image{}, mapStoreError(err, "image")
	}
	updated.URL = s.ImageURL(updated.StorageKey)
	return updated, nil
}

// OpenImage returns a reader over a picture's stored bytes for the media route.
func (s *Service) OpenImage(ctx context.Context, imageID string) (domain.Image, io.ReadCloser, error) {
	img, err := s.store.GetImage(ctx, imageID)
	if err != nil {
		return domain.Image{}, nil, mapStoreError(err, "image")
	}
	rc, err := s.blobs.Get(ctx, img.StorageKey)
	if err != nil {
		return domain.Image{}, nil, fmt.Errorf("service: open picture: %w", err)
	}
	return img, rc, nil
}

// ImageByID loads one picture, with its public URL filled in.
func (s *Service) ImageByID(ctx context.Context, id string) (domain.Image, error) {
	img, err := s.store.GetImage(ctx, id)
	if err != nil {
		return domain.Image{}, mapStoreError(err, "image")
	}
	img.URL = s.ImageURL(img.StorageKey)
	return img, nil
}

// ImageByStorageKey looks a picture up by its storage key, which is what the
// media route uses to recover the declared content type and size.
func (s *Service) ImageByStorageKey(ctx context.Context, key string) (domain.Image, error) {
	img, err := s.store.GetImageByStorageKey(ctx, key)
	if err != nil {
		return domain.Image{}, mapStoreError(err, "image")
	}
	img.URL = s.ImageURL(img.StorageKey)
	return img, nil
}

// ContentTypeByStorageKey returns the content type a picture was stored as, or
// an empty string when the key is unknown.
func (s *Service) ContentTypeByStorageKey(ctx context.Context, key string) (string, error) {
	img, err := s.store.GetImageByStorageKey(ctx, key)
	if err != nil {
		return "", mapStoreError(err, "image")
	}
	return img.ContentType, nil
}

// ImageSize returns the stored byte size for a storage key, or zero when the
// key is unknown.
func (s *Service) ImageSize(ctx context.Context, key string) (int64, error) {
	img, err := s.store.GetImageByStorageKey(ctx, key)
	if err != nil {
		return 0, mapStoreError(err, "image")
	}
	return img.ByteSize, nil
}

// extensionFor picks a storage extension from the filename, falling back to one
// implied by the content type.
func extensionFor(filename, contentType string) string {
	if ext := strings.ToLower(path.Ext(filename)); validExtension(ext) {
		return ext
	}
	switch strings.ToLower(strings.TrimSpace(strings.Split(contentType, ";")[0])) {
	case "image/jpeg":
		return ".jpg"
	case "image/png":
		return ".png"
	case "image/webp":
		return ".webp"
	case "image/gif":
		return ".gif"
	default:
		return ".img"
	}
}

// validExtension keeps a client-supplied extension from becoming a path
// fragment or an unexpected suffix.
func validExtension(ext string) bool {
	switch ext {
	case ".jpg", ".jpeg", ".png", ".webp", ".gif":
		return true
	default:
		return false
	}
}

// badgeLabels reduces a badge set to a distinct list of labels for the event
// payload. The local and remote analyzers can each contribute a label for the
// same subject, so duplicates are collapsed rather than published twice.
func badgeLabels(badges []domain.Badge) []string {
	out := make([]string, 0, len(badges))
	seen := make(map[string]struct{}, len(badges))
	for _, b := range badges {
		label := strings.TrimSpace(b.Label)
		if label == "" {
			continue
		}
		if _, dup := seen[label]; dup {
			continue
		}
		seen[label] = struct{}{}
		out = append(out, label)
	}
	return out
}

func isTooLarge(err error) bool {
	return err != nil && strings.Contains(err.Error(), blobstore.ErrTooLarge.Error())
}