refactor: extract TruncateRunes function for safe string truncation with suffix

Signed-off-by: Deluan <deluan@navidrome.org>

# Conflicts:
#	core/share.go
#	core/share_test.go

core/share.go

@@ -13,6 +13,7 @@ import (
 	"github.com/navidrome/navidrome/model"
 	. "github.com/navidrome/navidrome/utils/gg"
 	"github.com/navidrome/navidrome/utils/slice"
+	"github.com/navidrome/navidrome/utils/str"
 )
 
 type Share interface {
@@ -120,21 +121,7 @@ func (r *shareRepositoryWrapper) Save(entity interface{}) (string, error) {
 		return "", model.ErrNotFound
 	}
 
-	const maxContentRunes = 30
+	s.Contents = str.TruncateRunes(s.Contents, 30, "...")
-	const truncateToRunes = 26
-
-	var runeCount int
-	var truncateIndex int
-	for i := range s.Contents {
-		runeCount++
-		if runeCount == truncateToRunes+1 {
-			truncateIndex = i
-		}
-	}
-
-	if runeCount > maxContentRunes {
-		s.Contents = s.Contents[:truncateIndex] + "..."
-	}
 
 	id, err = r.Persistable.Save(s)
 	return id, err

core/share_test.go

@@ -52,7 +52,7 @@ var _ = Describe("Share", func() {
 				entity := &model.Share{Description: "test", ResourceIDs: "789"}
 				_, err := repo.Save(entity)
 				Expect(err).ToNot(HaveOccurred())
-				Expect(entity.Contents).To(Equal("Example Media File But The..."))
+				Expect(entity.Contents).To(Equal("Example Media File But The ..."))
 			})
 
 			It("does not truncate CJK labels shorter than 30 runes", func() {
@@ -68,7 +68,7 @@ var _ = Describe("Share", func() {
 				entity := &model.Share{Description: "test", ResourceIDs: "789"}
 				_, err := repo.Save(entity)
 				Expect(err).ToNot(HaveOccurred())
-				Expect(entity.Contents).To(Equal("私の中の幻想的世界観及びその顕現を想起させたある現実..."))
+				Expect(entity.Contents).To(Equal("私の中の幻想的世界観及びその顕現を想起させたある現実で..."))
 			})
 		})
 

utils/str/str.go

@@ -2,6 +2,7 @@ package str
 
 import (
 	"strings"
+	"unicode/utf8"
 )
 
 var utf8ToAscii = func() *strings.Replacer {
@@ -39,3 +40,25 @@ func LongestCommonPrefix(list []string) string {
 	}
 	return list[0]
 }
+
+// TruncateRunes truncates a string to a maximum number of runes, adding a suffix if truncated.
+// The suffix is included in the rune count, so if maxRunes is 30 and suffix is "...", the actual
+// string content will be truncated to fit within the maxRunes limit including the suffix.
+func TruncateRunes(s string, maxRunes int, suffix string) string {
+	if utf8.RuneCountInString(s) <= maxRunes {
+		return s
+	}
+
+	suffixRunes := utf8.RuneCountInString(suffix)
+	truncateAt := maxRunes - suffixRunes
+	if truncateAt < 0 {
+		truncateAt = 0
+	}
+
+	runes := []rune(s)
+	if truncateAt >= len(runes) {
+		return s + suffix
+	}
+
+	return string(runes[:truncateAt]) + suffix
+}

utils/str/str_test.go

@@ -31,6 +31,72 @@ var _ = Describe("String Utils", func() {
 			Expect(str.LongestCommonPrefix(albums)).To(Equal("/artist/album"))
 		})
 	})
+
+	Describe("TruncateRunes", func() {
+		It("returns string unchanged if under max runes", func() {
+			Expect(str.TruncateRunes("hello", 10, "...")).To(Equal("hello"))
+		})
+
+		It("returns string unchanged if exactly at max runes", func() {
+			Expect(str.TruncateRunes("hello", 5, "...")).To(Equal("hello"))
+		})
+
+		It("truncates and adds suffix when over max runes", func() {
+			Expect(str.TruncateRunes("hello world", 8, "...")).To(Equal("hello..."))
+		})
+
+		It("handles unicode characters correctly", func() {
+			// 6 emoji characters, maxRunes=5, suffix="..." (3 runes)
+			// So content gets 5-3=2 runes
+			Expect(str.TruncateRunes("😀😁😂😃😄😅", 5, "...")).To(Equal("😀😁..."))
+		})
+
+		It("handles multi-byte UTF-8 characters", func() {
+			// Characters like é are single runes
+			Expect(str.TruncateRunes("Café au Lait", 5, "...")).To(Equal("Ca..."))
+		})
+
+		It("works with empty suffix", func() {
+			Expect(str.TruncateRunes("hello world", 5, "")).To(Equal("hello"))
+		})
+
+		It("accounts for suffix length in truncation", func() {
+			// maxRunes=10, suffix="..." (3 runes) -> leaves 7 runes for content
+			result := str.TruncateRunes("hello world this is long", 10, "...")
+			Expect(result).To(Equal("hello w..."))
+			// Verify total rune count is <= maxRunes
+			runeCount := len([]rune(result))
+			Expect(runeCount).To(BeNumerically("<=", 10))
+		})
+
+		It("handles very long suffix gracefully", func() {
+			// If suffix is longer than maxRunes, we still add it
+			// but the content will be truncated to 0
+			result := str.TruncateRunes("hello world", 5, "... (truncated)")
+			// Result will be just the suffix (since truncateAt=0)
+			Expect(result).To(Equal("... (truncated)"))
+		})
+
+		It("handles empty string", func() {
+			Expect(str.TruncateRunes("", 10, "...")).To(Equal(""))
+		})
+
+		It("uses custom suffix", func() {
+			// maxRunes=11, suffix=" [...]" (6 runes) -> content gets 5 runes
+			// "hello world" is 11 runes exactly, so we need a longer string
+			Expect(str.TruncateRunes("hello world extra", 11, " [...]")).To(Equal("hello [...]"))
+		})
+
+		DescribeTable("truncates at rune boundaries (not byte boundaries)",
+			func(input string, maxRunes int, suffix string, expected string) {
+				Expect(str.TruncateRunes(input, maxRunes, suffix)).To(Equal(expected))
+			},
+			Entry("ASCII", "abcdefghij", 5, "...", "ab..."),
+			Entry("Mixed ASCII and Unicode", "ab😀cd", 4, ".", "ab😀."),
+			Entry("All emoji", "😀😁😂😃😄", 3, "…", "😀😁…"),
+			Entry("Japanese", "こんにちは世界", 3, "…", "こん…"),
+		)
+	})
 })
 
 var testPaths = []string{