handle expandable block quotation starts, add test for all md2 formats

pkg/channels/telegram/telegram.go

@@ -635,7 +635,14 @@ func markdownToTelegramMarkdownV2(text string) string {
 			continue
 		}
 
-		// 5. Handle standard Markdown Entities Boundaries
+		// 5. Handle expandable block quotation starts
+		if runes[i] == '>' && runes[i-1] == '*' && runes[i-2] == '*' && (i == 0 || runes[i-3] == '\n') {
+			result.WriteRune(runes[i])
+			i++
+			continue
+		}
+
+		// 6. Handle standard Markdown Entities Boundaries
 		// If they are part of valid markdown boundaries, we write them as-is.
 		// We trust the syntax rules: * _ ~ || [ ]
 		// (Assuming the text is a valid markdown, we don't escape these if formatting is intended)
@@ -668,7 +675,7 @@ func markdownToTelegramMarkdownV2(text string) string {
 			continue
 		}
 
-		// 6. Handle plain text characters
+		// 7. Handle plain text characters
 		// Escape remaining special characters if they aren't forming intended valid markup
 		if needsNormalEscape(runes[i]) {
 			// Check if it's already escaped; if an escape character exists, consume it legitimately

pkg/channels/telegram/telegram_test.go

@@ -4,9 +4,14 @@ import (
 	"fmt"
 	"testing"
 
+	_ "embed"
+
 	"github.com/stretchr/testify/require"
 )
 
+//go:embed testdata/md2_all_formats.txt
+var md2AllFormats string
+
 func Test_markdownToTelegramMarkdownV2(t *testing.T) {
 	cases := []struct {
 		input    string
@@ -24,6 +29,10 @@ func Test_markdownToTelegramMarkdownV2(t *testing.T) {
 			input:    "[inline URL](http://www.example.com/)",
 			expected: "[inline URL](http://www.example.com/)",
 		},
+		{
+			input:    md2AllFormats,
+			expected: md2AllFormats,
+		},
 	}
 
 	for _, tc := range cases {

pkg/channels/telegram/testdata/md2_all_formats.txt

@@ -0,0 +1,31 @@
+*bold \*text*
+_italic \*text_
+__underline__
+~strikethrough~
+||spoiler||
+*bold _italic bold ~italic bold strikethrough ||italic bold strikethrough spoiler||~ __underline italic bold___ bold*
+[inline URL](http://www.example.com/)
+[inline mention of a user](tg://user?id=123456789)
+![👍](tg://emoji?id=5368324170671202286)
+![22:45 tomorrow](tg://time?unix=1647531900&format=wDT)
+![22:45 tomorrow](tg://time?unix=1647531900&format=t)
+![22:45 tomorrow](tg://time?unix=1647531900&format=r)
+![22:45 tomorrow](tg://time?unix=1647531900)
+`inline fixed-width code`
+```
+pre-formatted fixed-width code block
+```
+```python
+pre-formatted fixed-width code block written in the Python programming language
+```
+>Block quotation started
+>Block quotation continued
+>Block quotation continued
+>Block quotation continued
+>The last line of the block quotation
+**>The expandable block quotation started right after the previous block quotation
+>It is separated from the previous block quotation by an empty bold entity
+>Expandable block quotation continued
+>Hidden by default part of the expandable block quotation started
+>Expandable block quotation continued
+>The last line of the expandable block quotation with the expandability mark||