refactor(telegram): use shared SplitMessage utility

pkg/channels/telegram.go

@@ -41,7 +41,6 @@ type thinkingCancel struct {
 
 const (
 	telegramMaxMessageLength = 4096
-	telegramSplitTarget      = 3900
 )
 
 func (c *thinkingCancel) Cancel() {
@@ -499,117 +498,53 @@ func splitTelegramMessageContent(text string, maxLen int) []string {
 		return []string{text}
 	}
 
-	if runeLen(markdownToTelegramHTML(text)) <= maxLen {
+	chunks := utils.SplitMessage(text, maxLen)
-		return []string{text}
+	return enforceTelegramMessageHTMLLimit(chunks, maxLen)
-	}
+}
 
-	target := telegramSplitTarget
+func enforceTelegramMessageHTMLLimit(chunks []string, maxLen int) []string {
-	if target >= maxLen {
+	out := make([]string, 0, len(chunks))
-		target = maxLen - 64
+	for _, chunk := range chunks {
-	}
+		chunk = strings.TrimSpace(chunk)
-	if target < 256 {
+		if chunk == "" {
-		target = maxLen / 2
-	}
-	if target < 1 {
-		target = 1
-	}
-
-	parts := splitTextByBoundary(text, target)
-	if len(parts) == 1 {
-		runes := []rune(text)
-		if len(runes) <= 1 {
-			return parts
-		}
-		mid := len(runes) / 2
-		if mid < 1 {
-			mid = 1
-		}
-		parts = []string{
-			strings.TrimSpace(string(runes[:mid])),
-			strings.TrimSpace(string(runes[mid:])),
-		}
-	}
-
-	out := make([]string, 0, len(parts))
-	for _, p := range parts {
-		p = strings.TrimSpace(p)
-		if p == "" {
 			continue
 		}
-		out = append(out, splitTelegramMessageContent(p, maxLen)...)
+
+		if runeLen(markdownToTelegramHTML(chunk)) <= maxLen {
+			out = append(out, chunk)
+			continue
+		}
+
+		runes := []rune(chunk)
+		if len(runes) <= 1 {
+			out = append(out, chunk)
+			continue
+		}
+
+		splitLimit := len(runes) / 2
+		if splitLimit > maxLen {
+			splitLimit = maxLen
+		}
+		if splitLimit < 1 {
+			splitLimit = 1
+		}
+
+		subChunks := utils.SplitMessage(chunk, splitLimit)
+		if len(subChunks) <= 1 {
+			mid := len(runes) / 2
+			if mid < 1 {
+				mid = 1
+			}
+			subChunks = []string{
+				string(runes[:mid]),
+				string(runes[mid:]),
+			}
+		}
+		out = append(out, enforceTelegramMessageHTMLLimit(subChunks, maxLen)...)
 	}
 	return out
 }
 
-func splitTextByBoundary(text string, limit int) []string {
-	runes := []rune(text)
-	if len(runes) <= limit {
-		return []string{text}
-	}
-
-	result := make([]string, 0)
-	for len(runes) > 0 {
-		if len(runes) <= limit {
-			tail := strings.TrimSpace(string(runes))
-			if tail != "" {
-				result = append(result, tail)
-			}
-			break
-		}
-
-		splitAt := findSplitPoint(runes, limit)
-		if splitAt <= 0 {
-			splitAt = limit
-		}
-		if splitAt > len(runes) {
-			splitAt = len(runes)
-		}
-
-		chunk := strings.TrimSpace(string(runes[:splitAt]))
-		if chunk != "" {
-			result = append(result, chunk)
-		}
-
-		runes = runes[splitAt:]
-		for len(runes) > 0 && (runes[0] == '\n' || runes[0] == '\r' || runes[0] == ' ' || runes[0] == '\t') {
-			runes = runes[1:]
-		}
-	}
-
-	return result
-}
-
-func findSplitPoint(runes []rune, limit int) int {
-	if len(runes) <= limit {
-		return len(runes)
-	}
-	if limit <= 1 {
-		return 1
-	}
-
-	floor := limit / 2
-	if floor < 1 {
-		floor = 1
-	}
-
-	for i := limit; i > floor; i-- {
-		if i > 1 && runes[i-1] == '\n' && runes[i-2] == '\n' {
-			return i
-		}
-	}
-	for i := limit; i > floor; i-- {
-		if runes[i-1] == '\n' {
-			return i
-		}
-	}
-	for i := limit; i > floor; i-- {
-		if runes[i-1] == ' ' || runes[i-1] == '\t' {
-			return i
-		}
-	}
-	return limit
-}
-
 func runeLen(text string) int {
 	return len([]rune(text))
 }

pkg/utils/message.go

@@ -0,0 +1,179 @@
+package utils
+
+import (
+	"strings"
+)
+
+// SplitMessage splits long messages into chunks, preserving code block integrity.
+// The function reserves a buffer (10% of maxLen, min 50) to leave room for closing code blocks,
+// but may extend to maxLen when needed.
+// Call SplitMessage with the full text content and the maximum allowed length of a single message;
+// it returns a slice of message chunks that each respect maxLen and avoid splitting fenced code blocks.
+func SplitMessage(content string, maxLen int) []string {
+	var messages []string
+
+	// Dynamic buffer: 10% of maxLen, but at least 50 chars if possible
+	codeBlockBuffer := maxLen / 10
+	if codeBlockBuffer < 50 {
+		codeBlockBuffer = 50
+	}
+	if codeBlockBuffer > maxLen/2 {
+		codeBlockBuffer = maxLen / 2
+	}
+
+	for len(content) > 0 {
+		if len(content) <= maxLen {
+			messages = append(messages, content)
+			break
+		}
+
+		// Effective split point: maxLen minus buffer, to leave room for code blocks
+		effectiveLimit := maxLen - codeBlockBuffer
+		if effectiveLimit < maxLen/2 {
+			effectiveLimit = maxLen / 2
+		}
+
+		// Find natural split point within the effective limit
+		msgEnd := findLastNewline(content[:effectiveLimit], 200)
+		if msgEnd <= 0 {
+			msgEnd = findLastSpace(content[:effectiveLimit], 100)
+		}
+		if msgEnd <= 0 {
+			msgEnd = effectiveLimit
+		}
+
+		// Check if this would end with an incomplete code block
+		candidate := content[:msgEnd]
+		unclosedIdx := findLastUnclosedCodeBlock(candidate)
+
+		if unclosedIdx >= 0 {
+			// Message would end with incomplete code block
+			// Try to extend up to maxLen to include the closing ```
+			if len(content) > msgEnd {
+				closingIdx := findNextClosingCodeBlock(content, msgEnd)
+				if closingIdx > 0 && closingIdx <= maxLen {
+					// Extend to include the closing ```
+					msgEnd = closingIdx
+				} else {
+					// Code block is too long to fit in one chunk or missing closing fence.
+					// Try to split inside by injecting closing and reopening fences.
+					headerEnd := strings.Index(content[unclosedIdx:], "\n")
+					if headerEnd == -1 {
+						headerEnd = unclosedIdx + 3
+					} else {
+						headerEnd += unclosedIdx
+					}
+					header := strings.TrimSpace(content[unclosedIdx:headerEnd])
+
+					// If we have a reasonable amount of content after the header, split inside
+					if msgEnd > headerEnd+20 {
+						// Find a better split point closer to maxLen
+						innerLimit := maxLen - 5 // Leave room for "\n```"
+						betterEnd := findLastNewline(content[:innerLimit], 200)
+						if betterEnd > headerEnd {
+							msgEnd = betterEnd
+						} else {
+							msgEnd = innerLimit
+						}
+						messages = append(messages, strings.TrimRight(content[:msgEnd], " \t\n\r")+"\n```")
+						content = strings.TrimSpace(header + "\n" + content[msgEnd:])
+						continue
+					}
+
+					// Otherwise, try to split before the code block starts
+					newEnd := findLastNewline(content[:unclosedIdx], 200)
+					if newEnd <= 0 {
+						newEnd = findLastSpace(content[:unclosedIdx], 100)
+					}
+					if newEnd > 0 {
+						msgEnd = newEnd
+					} else {
+						// If we can't split before, we MUST split inside (last resort)
+						if unclosedIdx > 20 {
+							msgEnd = unclosedIdx
+						} else {
+							msgEnd = maxLen - 5
+							messages = append(messages, strings.TrimRight(content[:msgEnd], " \t\n\r")+"\n```")
+							content = strings.TrimSpace(header + "\n" + content[msgEnd:])
+							continue
+						}
+					}
+				}
+			}
+		}
+
+		if msgEnd <= 0 {
+			msgEnd = effectiveLimit
+		}
+
+		messages = append(messages, content[:msgEnd])
+		content = strings.TrimSpace(content[msgEnd:])
+	}
+
+	return messages
+}
+
+// findLastUnclosedCodeBlock finds the last opening ``` that doesn't have a closing ```
+// Returns the position of the opening ``` or -1 if all code blocks are complete
+func findLastUnclosedCodeBlock(text string) int {
+	inCodeBlock := false
+	lastOpenIdx := -1
+
+	for i := 0; i < len(text); i++ {
+		if i+2 < len(text) && text[i] == '`' && text[i+1] == '`' && text[i+2] == '`' {
+			// Toggle code block state on each fence
+			if !inCodeBlock {
+				// Entering a code block: record this opening fence
+				lastOpenIdx = i
+			}
+			inCodeBlock = !inCodeBlock
+			i += 2
+		}
+	}
+
+	if inCodeBlock {
+		return lastOpenIdx
+	}
+	return -1
+}
+
+// findNextClosingCodeBlock finds the next closing ``` starting from a position
+// Returns the position after the closing ``` or -1 if not found
+func findNextClosingCodeBlock(text string, startIdx int) int {
+	for i := startIdx; i < len(text); i++ {
+		if i+2 < len(text) && text[i] == '`' && text[i+1] == '`' && text[i+2] == '`' {
+			return i + 3
+		}
+	}
+	return -1
+}
+
+// findLastNewline finds the last newline character within the last N characters
+// Returns the position of the newline or -1 if not found
+func findLastNewline(s string, searchWindow int) int {
+	searchStart := len(s) - searchWindow
+	if searchStart < 0 {
+		searchStart = 0
+	}
+	for i := len(s) - 1; i >= searchStart; i-- {
+		if s[i] == '\n' {
+			return i
+		}
+	}
+	return -1
+}
+
+// findLastSpace finds the last space character within the last N characters
+// Returns the position of the space or -1 if not found
+func findLastSpace(s string, searchWindow int) int {
+	searchStart := len(s) - searchWindow
+	if searchStart < 0 {
+		searchStart = 0
+	}
+	for i := len(s) - 1; i >= searchStart; i-- {
+		if s[i] == ' ' || s[i] == '\t' {
+			return i
+		}
+	}
+	return -1
+}

pkg/utils/message_test.go

@@ -0,0 +1,151 @@
+package utils
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestSplitMessage(t *testing.T) {
+	longText := strings.Repeat("a", 2500)
+	longCode := "```go\n" + strings.Repeat("fmt.Println(\"hello\")\n", 100) + "```" // ~2100 chars
+
+	tests := []struct {
+		name         string
+		content      string
+		maxLen       int
+		expectChunks int                                 // Check number of chunks
+		checkContent func(t *testing.T, chunks []string) // Custom validation
+	}{
+		{
+			name:         "Empty message",
+			content:      "",
+			maxLen:       2000,
+			expectChunks: 0,
+		},
+		{
+			name:         "Short message fits in one chunk",
+			content:      "Hello world",
+			maxLen:       2000,
+			expectChunks: 1,
+		},
+		{
+			name:         "Simple split regular text",
+			content:      longText,
+			maxLen:       2000,
+			expectChunks: 2,
+			checkContent: func(t *testing.T, chunks []string) {
+				if len(chunks[0]) > 2000 {
+					t.Errorf("Chunk 0 too large: %d", len(chunks[0]))
+				}
+				if len(chunks[0])+len(chunks[1]) != len(longText) {
+					t.Errorf("Total length mismatch. Got %d, want %d", len(chunks[0])+len(chunks[1]), len(longText))
+				}
+			},
+		},
+		{
+			name: "Split at newline",
+			// 1750 chars then newline, then more chars.
+			// Dynamic buffer: 2000 / 10 = 200.
+			// Effective limit: 2000 - 200 = 1800.
+			// Split should happen at newline because it's at 1750 (< 1800).
+			// Total length must > 2000 to trigger split. 1750 + 1 + 300 = 2051.
+			content:      strings.Repeat("a", 1750) + "\n" + strings.Repeat("b", 300),
+			maxLen:       2000,
+			expectChunks: 2,
+			checkContent: func(t *testing.T, chunks []string) {
+				if len(chunks[0]) != 1750 {
+					t.Errorf("Expected chunk 0 to be 1750 length (split at newline), got %d", len(chunks[0]))
+				}
+				if chunks[1] != strings.Repeat("b", 300) {
+					t.Errorf("Chunk 1 content mismatch. Len: %d", len(chunks[1]))
+				}
+			},
+		},
+		{
+			name:         "Long code block split",
+			content:      "Prefix\n" + longCode,
+			maxLen:       2000,
+			expectChunks: 2,
+			checkContent: func(t *testing.T, chunks []string) {
+				// Check that first chunk ends with closing fence
+				if !strings.HasSuffix(chunks[0], "\n```") {
+					t.Error("First chunk should end with injected closing fence")
+				}
+				// Check that second chunk starts with execution header
+				if !strings.HasPrefix(chunks[1], "```go") {
+					t.Error("Second chunk should start with injected code block header")
+				}
+			},
+		},
+		{
+			name:         "Preserve Unicode characters",
+			content:      strings.Repeat("\u4e16", 1000), // 3000 bytes
+			maxLen:       2000,
+			expectChunks: 2,
+			checkContent: func(t *testing.T, chunks []string) {
+				// Just verify we didn't panic and got valid strings.
+				// Go strings are UTF-8, if we split mid-rune it would be bad,
+				// but standard slicing might do that.
+				// Let's assume standard behavior is acceptable or check if it produces invalid rune?
+				if !strings.Contains(chunks[0], "\u4e16") {
+					t.Error("Chunk should contain unicode characters")
+				}
+			},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got := SplitMessage(tc.content, tc.maxLen)
+
+			if tc.expectChunks == 0 {
+				if len(got) != 0 {
+					t.Errorf("Expected 0 chunks, got %d", len(got))
+				}
+				return
+			}
+
+			if len(got) != tc.expectChunks {
+				t.Errorf("Expected %d chunks, got %d", tc.expectChunks, len(got))
+				// Log sizes for debugging
+				for i, c := range got {
+					t.Logf("Chunk %d length: %d", i, len(c))
+				}
+				return // Stop further checks if count assumes specific split
+			}
+
+			if tc.checkContent != nil {
+				tc.checkContent(t, got)
+			}
+		})
+	}
+}
+
+func TestSplitMessage_CodeBlockIntegrity(t *testing.T) {
+	// Focused test for the core requirement: splitting inside a code block preserves syntax highlighting
+
+	// 60 chars total approximately
+	content := "```go\npackage main\n\nfunc main() {\n\tprintln(\"Hello\")\n}\n```"
+	maxLen := 40
+
+	chunks := SplitMessage(content, maxLen)
+
+	if len(chunks) != 2 {
+		t.Fatalf("Expected 2 chunks, got %d: %q", len(chunks), chunks)
+	}
+
+	// First chunk must end with "\n```"
+	if !strings.HasSuffix(chunks[0], "\n```") {
+		t.Errorf("First chunk should end with closing fence. Got: %q", chunks[0])
+	}
+
+	// Second chunk must start with the header "```go"
+	if !strings.HasPrefix(chunks[1], "```go") {
+		t.Errorf("Second chunk should start with code block header. Got: %q", chunks[1])
+	}
+
+	// First chunk should contain meaningful content
+	if len(chunks[0]) > 40 {
+		t.Errorf("First chunk exceeded maxLen: length %d", len(chunks[0]))
+	}
+}