telegramfmt: text formatting TG -> Matrix

Signed-off-by: Sumner Evans <sumner.evans@automattic.com>

pkg/connector/telegramfmt/tree.go

@@ -0,0 +1,113 @@
+// mautrix-telegram - A Matrix-Telegram puppeting bridge.
+// Copyright (C) 2024 Sumner Evans
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package telegramfmt
+
+import (
+	"fmt"
+	"sort"
+)
+
+type BodyRange struct {
+	Start  int
+	Length int
+	Value  BodyRangeValue
+}
+
+type BodyRangeList []BodyRange
+
+var _ sort.Interface = BodyRangeList(nil)
+
+func (b BodyRangeList) Len() int {
+	return len(b)
+}
+
+func (b BodyRangeList) Less(i, j int) bool {
+	return b[i].Start < b[j].Start || b[i].Length > b[j].Length
+}
+
+func (b BodyRangeList) Swap(i, j int) {
+	b[i], b[j] = b[j], b[i]
+}
+
+func (b BodyRange) String() string {
+	return fmt.Sprintf("%d:%d:%v", b.Start, b.Length, b.Value)
+}
+
+// End returns the end index of the range.
+func (b BodyRange) End() int {
+	return b.Start + b.Length
+}
+
+// Offset changes the start of the range without affecting the length.
+func (b BodyRange) Offset(offset int) *BodyRange {
+	b.Start += offset
+	return &b
+}
+
+// TruncateStart changes the length of the range, so it starts at the given
+// index and ends at the same index as before.
+func (b BodyRange) TruncateStart(startAt int) *BodyRange {
+	if b.Start < startAt {
+		b.Length -= startAt - b.Start
+		b.Start = startAt
+	}
+	return &b
+}
+
+// TruncateEnd changes the length of the range, so it ends at or before the
+// given index and starts at the same index as before.
+func (b BodyRange) TruncateEnd(maxEnd int) *BodyRange {
+	if b.End() > maxEnd {
+		b.Length = maxEnd - b.Start
+	}
+	return &b
+}
+
+// LinkedRangeTree is a linked tree of formatting entities.
+//
+// It's meant to parse a list of Telegram entity ranges into nodes that either
+// overlap completely or not at all, which enables more natural conversion to
+// HTML.
+type LinkedRangeTree struct {
+	Node    *BodyRange
+	Sibling *LinkedRangeTree
+	Child   *LinkedRangeTree
+}
+
+func ptrAdd(to **LinkedRangeTree, r *BodyRange) {
+	if *to == nil {
+		*to = &LinkedRangeTree{}
+	}
+	(*to).Add(r)
+}
+
+// Add adds the given formatting entity to this tree.
+func (lrt *LinkedRangeTree) Add(r *BodyRange) {
+	if lrt.Node == nil {
+		lrt.Node = r
+		return
+	}
+	lrtEnd := lrt.Node.End()
+	if r.Start >= lrtEnd {
+		ptrAdd(&lrt.Sibling, r.Offset(-lrtEnd))
+		return
+	}
+	if r.End() > lrtEnd {
+		ptrAdd(&lrt.Sibling, r.TruncateStart(lrtEnd).Offset(-lrtEnd))
+	}
+	ptrAdd(&lrt.Child, r.TruncateEnd(lrtEnd).Offset(-lrt.Node.Start))
+}