feat(richtext): add markdown-domain change detection

Changed reports whether inbound markdown differs from stored HTML by comparing
in the markdown domain, so callers can skip rewriting unchanged fields.

pkg/richtext/changedetect.go

@@ -0,0 +1,64 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-present Vikunja and contributors. All rights reserved.
+//
+// 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 richtext
+
+import "strings"
+
+// Changed reports whether inbound markdown differs semantically from stored
+// rich-text HTML, so callers can skip rewriting unchanged fields (avoids CalDAV
+// read-modify-write churning the HTML and bumping Updated). Both sides are
+// canonicalized to markdown before comparing: HTML→markdown isn't an identity, so
+// an HTML-domain compare would always report "changed". Errs to true.
+func Changed(storedHTML, incomingMarkdown string) bool {
+	stored, err := HTMLToMarkdown(storedHTML)
+	if err != nil {
+		return true
+	}
+
+	incoming, err := canonicalMarkdown(incomingMarkdown)
+	if err != nil {
+		return true
+	}
+
+	return normalizeMarkdown(stored) != normalizeMarkdown(incoming)
+}
+
+// HTMLIsEmpty treats "", "<p></p>" and whitespace-only markup as empty.
+func HTMLIsEmpty(htmlInput string) bool {
+	md, err := HTMLToMarkdown(htmlInput)
+	if err != nil {
+		return false
+	}
+	return md == ""
+}
+
+// canonicalMarkdown round-trips markdown through HTML so it matches the shape
+// HTMLToMarkdown yields from stored HTML. No session needed: a <mention-user> tag
+// and an inbound "@username" both reduce to "@username".
+func canonicalMarkdown(md string) (string, error) {
+	h, err := MarkdownToHTML(md)
+	if err != nil {
+		return "", err
+	}
+	return HTMLToMarkdown(h)
+}
+
+func normalizeMarkdown(md string) string {
+	md = strings.ReplaceAll(md, "\r\n", "\n")
+	md = strings.ReplaceAll(md, "\r", "\n")
+	return strings.TrimSpace(md)
+}

pkg/richtext/changedetect_test.go

@@ -0,0 +1,101 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-present Vikunja and contributors. All rights reserved.
+//
+// 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 richtext
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestChanged(t *testing.T) {
+	tests := []struct {
+		name     string
+		stored   string
+		incoming string
+		want     bool
+	}{
+		{
+			name:     "markdown projection equals incoming",
+			stored:   "<p>Hello <strong>world</strong></p>",
+			incoming: "Hello **world**",
+			want:     false,
+		},
+		{
+			name:     "genuinely edited",
+			stored:   "<p>Hello <strong>world</strong></p>",
+			incoming: "Hello **mars**",
+			want:     true,
+		},
+		{
+			name:     "line ending only difference",
+			stored:   "<p>line one</p><p>line two</p>",
+			incoming: "line one\r\n\r\nline two",
+			want:     false,
+		},
+		{
+			name:     "trailing whitespace only difference",
+			stored:   "<p>same</p>",
+			incoming: "same\n\n   ",
+			want:     false,
+		},
+		{
+			name:     "equivalent markdown flavors compare equal",
+			stored:   "<p><em>x</em></p>",
+			incoming: "_x_",
+			want:     false,
+		},
+		{
+			name:     "empty stored vs empty incoming",
+			stored:   "<p></p>",
+			incoming: "",
+			want:     false,
+		},
+		{
+			name:     "empty stored vs new content",
+			stored:   "",
+			incoming: "now has text",
+			want:     true,
+		},
+		{
+			name:     "task list round trip unchanged",
+			stored:   `<ul data-type="taskList"><li data-checked="true" data-type="taskItem"><label><input type="checkbox" checked="checked"><span></span></label><div><p>done</p></div></li></ul>`,
+			incoming: "- [x] done",
+			want:     false,
+		},
+		{
+			name:     "mention round trip unchanged",
+			stored:   `<p>cc <mention-user data-id="user1" data-label="User One">@User One</mention-user></p>`,
+			incoming: "cc @user1",
+			want:     false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.want, Changed(tt.stored, tt.incoming))
+		})
+	}
+}
+
+func TestHTMLIsEmpty(t *testing.T) {
+	assert.True(t, HTMLIsEmpty(""))
+	assert.True(t, HTMLIsEmpty("<p></p>"))
+	assert.True(t, HTMLIsEmpty("   "))
+	assert.True(t, HTMLIsEmpty("<p>   </p>"))
+	assert.False(t, HTMLIsEmpty("<p>content</p>"))
+}