Harden preview enrichment and recommendation metadata

backend/services/ranker.go

@@ -10,6 +10,8 @@ import (
 )
 
 const GeminiFallbackReason = "Gemini Vision 응답이 부족해 키워드 기준으로 보강된 결과입니다."
+const FallbackPreviewReason = "Fallback due to missing provider preview."
+const PendingVisualReason = "Ranked candidate pending stronger visual evidence."
 
 type GeminiBatchStats struct {
 	CandidateCap      int      `json:"candidateCap"`
@@ -19,6 +21,7 @@ type GeminiBatchStats struct {
 	Failed            int      `json:"failed"`
 	SequentialRetried int      `json:"sequentialRetried"`
 	RecommendedCount  int      `json:"recommendedCount"`
+	VisualRejectCount int      `json:"visualRejectCount"`
 	Errors            []string `json:"errors,omitempty"`
 }
 
@@ -58,19 +61,25 @@ func RankSearchResults(query string, results []SearchResult) []SearchResult {
 				score -= 4
 			}
 		}
-		if result.ThumbnailURL != "" {
-			score += 2
-		}
 		if result.PreviewVideoURL != "" {
-			score += 3
+			score += 10
+		}
+		if hasUsableThumbnail(result.ThumbnailURL) {
+			score += 5
+		}
+		if isLowValueThumbnail(result.ThumbnailURL) {
+			score -= 8
+		}
+		if strings.TrimSpace(result.PreviewVideoURL) == "" && !hasUsableThumbnail(result.ThumbnailURL) {
+			score -= 10
 		}
 		switch result.Source {
 		case "Google Video":
-			score -= 1
+			score -= 2
 		case "Envato":
-			score += 7
+			score += 5
 		case "Artgrid":
-			score += 7
+			score += 4
 		}
 		scored = append(scored, scoredResult{item: result, score: score})
 	}
@@ -106,6 +115,11 @@ func EvaluateAllCandidatesWithGeminiWithDeadline(service *GeminiService, query s
 		CandidateCap: limit,
 		Requested:    min(limit, len(ranked)),
 	}
+	for _, item := range ranked[:min(limit, len(ranked))] {
+		if strings.TrimSpace(item.PreviewVideoURL) == "" && !hasUsableThumbnail(item.ThumbnailURL) {
+			stats.VisualRejectCount++
+		}
+	}
 	type batchResult struct {
 		index           int
 		recommendations []AIRecommendation
@@ -231,7 +245,7 @@ func BuildFallbackRecommendations(ranked []SearchResult, limit int, reason strin
 
 	fallback := make([]AIRecommendation, 0, min(limit, len(ranked)))
 	for _, item := range ranked[:min(limit, len(ranked))] {
-		fallback = append(fallback, AIRecommendation{
+		fallback = append(fallback, DecorateRecommendationMedia(AIRecommendation{
 			Title:           item.Title,
 			Link:            item.Link,
 			Snippet:         item.Snippet,
@@ -240,7 +254,7 @@ func BuildFallbackRecommendations(ranked []SearchResult, limit int, reason strin
 			Source:          item.Source,
 			Reason:          reason,
 			Recommended:     false,
-		})
+		}))
 	}
 	return fallback
 }
@@ -385,6 +399,8 @@ func looksNegativeReason(reason string) bool {
 func MergeRecommendations(recommended []AIRecommendation, ranked []SearchResult, limit int) []AIRecommendation {
 	merged := make([]AIRecommendation, 0, min(limit, len(ranked)))
 	seen := map[string]bool{}
+	fillerCount := 0
+	maxFiller := min(4, limit)
 
 	for _, item := range recommended {
 		if !item.Recommended {
@@ -394,7 +410,7 @@ func MergeRecommendations(recommended []AIRecommendation, ranked []SearchResult,
 			continue
 		}
 		seen[item.Link] = true
-		merged = append(merged, item)
+		merged = append(merged, DecorateRecommendationMedia(item))
 	}
 
 	for _, item := range recommended {
@@ -404,8 +420,11 @@ func MergeRecommendations(recommended []AIRecommendation, ranked []SearchResult,
 		if looksNegativeReason(item.Reason) || strings.Contains(item.Reason, GeminiFallbackReason) {
 			continue
 		}
+		if strings.TrimSpace(item.PreviewVideoURL) == "" && !hasUsableThumbnail(item.ThumbnailURL) {
+			continue
+		}
 		seen[item.Link] = true
-		merged = append(merged, item)
+		merged = append(merged, DecorateRecommendationMedia(item))
 	}
 
 	if len(merged) < min(12, limit) {
@@ -413,20 +432,24 @@ func MergeRecommendations(recommended []AIRecommendation, ranked []SearchResult,
 			if len(merged) >= min(12, limit) || item.Link == "" || seen[item.Link] {
 				continue
 			}
-			if strings.TrimSpace(item.ThumbnailURL) == "" && strings.TrimSpace(item.PreviewVideoURL) == "" {
+			if fillerCount >= maxFiller {
+				break
+			}
+			if strings.TrimSpace(item.PreviewVideoURL) == "" && !hasUsableThumbnail(item.ThumbnailURL) {
 				continue
 			}
 			seen[item.Link] = true
-			merged = append(merged, AIRecommendation{
+			merged = append(merged, DecorateRecommendationMedia(AIRecommendation{
 				Title:           item.Title,
 				Link:            item.Link,
 				Snippet:         item.Snippet,
 				ThumbnailURL:    item.ThumbnailURL,
 				PreviewVideoURL: item.PreviewVideoURL,
 				Source:          item.Source,
-				Reason:          "Gemini 검토가 부족해 편집용 후보로 추가된 결과입니다.",
+				Reason:          PendingVisualReason,
 				Recommended:     false,
-			})
+			}))
+			fillerCount++
 		}
 	}
 	return merged
@@ -435,31 +458,37 @@ func MergeRecommendations(recommended []AIRecommendation, ranked []SearchResult,
 func BackfillRecommendations(existing []AIRecommendation, ranked []SearchResult, limit int, reason string) []AIRecommendation {
 	merged := make([]AIRecommendation, 0, min(limit, len(ranked)))
 	seen := map[string]bool{}
+	fillerCount := 0
+	maxFiller := min(4, limit)
 	for _, item := range existing {
 		if item.Link == "" || seen[item.Link] {
 			continue
 		}
 		seen[item.Link] = true
-		merged = append(merged, item)
+		merged = append(merged, DecorateRecommendationMedia(item))
 	}
 	for _, item := range ranked {
 		if len(merged) >= limit || item.Link == "" || seen[item.Link] {
 			continue
 		}
-		if strings.TrimSpace(item.ThumbnailURL) == "" && strings.TrimSpace(item.PreviewVideoURL) == "" {
+		if fillerCount >= maxFiller {
+			break
+		}
+		if strings.TrimSpace(item.PreviewVideoURL) == "" && !hasUsableThumbnail(item.ThumbnailURL) {
 			continue
 		}
 		seen[item.Link] = true
-		merged = append(merged, AIRecommendation{
+		merged = append(merged, DecorateRecommendationMedia(AIRecommendation{
 			Title:           item.Title,
 			Link:            item.Link,
 			Snippet:         item.Snippet,
 			ThumbnailURL:    item.ThumbnailURL,
 			PreviewVideoURL: item.PreviewVideoURL,
 			Source:          item.Source,
-			Reason:          reason,
+			Reason:          firstNonEmpty(strings.TrimSpace(reason), FallbackPreviewReason),
 			Recommended:     false,
-		})
+		}))
+		fillerCount++
 	}
 	return merged
 }