+
+// splitRich cuts the Markdown of a reply into parts of at most limit bytes. It
+// cuts after a blank line outside a code block, so a table, a code block, or a
+// paragraph stays whole. When no such cut fits in a part, it cuts after the
+// last line break outside a code block, then after the last line break in a
+// code block, which it closes at the end of the part and opens again in the
+// next part with the same fence line. A line longer than limit is cut at the
+// limit. It never cuts a character.
+func splitRich(markdown string, limit int) []string {
+ var parts []string
+ for len(markdown) > limit {
+ cut, fence, opening := richCut(markdown, limit)
+ if fence == "" {
+ parts = append(parts, markdown[:cut])
+ markdown = markdown[cut:]
+
+ continue
+ }
+
+ parts = append(parts, markdown[:cut]+fence+"\n")
+ markdown = opening + "\n" + markdown[cut:]
+ }
+
+ return append(parts, markdown)
+}
+
+// richCut returns where splitRich cuts markdown, which is longer than limit.
+// For a cut in a code block, it also returns the fence that closes the block
+// and the line that opens it. Each part before a cut holds text other than
+// space, and a cut in a code block leaves room for the fence, so each cut makes
+// the rest shorter.
+func richCut(markdown string, limit int) (int, string, string) {
+ blank, line, code := 0, 0, 0
+ var fence, opening, inFence, inOpening string
+ for start := 0; start < limit; {
+ end := strings.IndexByte(markdown[start:], '\n')
+ if end < 0 || start+end+1 > limit {
+ break
+ }
+
+ end += start + 1
+ text := strings.TrimRight(markdown[start:end], "\r\n")
+ _, opens := codeFence(text)
+ switch {
+ case fence != "":
+ if closesFence(text, fence) {
+ fence = ""
+ } else if end > len(opening)+1 && end+len(fence)+1 <= limit {
+ code, inFence, inOpening = end, fence, opening
+ }
+ case opens != "":
+ fence, opening = opens, text
+ case strings.TrimSpace(markdown[:end]) == "":
+ case strings.TrimSpace(text) == "":
+ blank = end
+ }
+
+ if fence == "" && strings.TrimSpace(markdown[:end]) != "" {
+ line = end
+ }
+
+ start = end
+ }
+
+ switch {
+ case blank > 0:
+ return blank, "", ""
+ case line > 0:
+ return line, "", ""
+ case code > 0:
+ return code, inFence, inOpening
+ }
+
+ cut := limit
+ for !utf8.RuneStart(markdown[cut]) {
+ cut--
+ }
+
+ return cut, "", ""
+}
+
+// replyParts returns the messages of the Markdown of a reply with message
+// entities. A reply that has no text left after the conversion, such as an
+// empty code block, goes as its Markdown.
+func replyParts(markdown string) []botPart {
+ text, entities := markdownEntities(markdown)
+ if strings.TrimSpace(text) == "" {
+ text, entities = markdown, nil
+ }
+
+ return splitEntities(text, entities, messageUnits)
+}
+
+// splitEntities cuts text into parts with splitMessage, and gives each part the
+// entities in it, with offsets from the start of the part. An entity that
+// crosses a cut becomes one entity in each part.
+func splitEntities(text string, entities []botEntity, limit int) []botPart {
+ var parts []botPart
+ start := 0
+ for _, part := range splitMessage(text, limit) {
+ end := start + utf16Units(part)
+ var kept []botEntity
+ for _, entity := range entities {
+ from := max(entity.Offset, start)
+ to := min(entity.Offset+entity.Length, end)
+ if to <= from {
+ continue
+ }
+
+ entity.Offset = from - start
+ entity.Length = to - from
+ kept = append(kept, entity)
+ }
+
+ parts = append(parts, botPart{
+ text: part,
+ entities: kept,
+ })
+
+ start = end
+ }
+
+ return parts
+}
projects / onechat / blobdiff