more social card tweaks, and include in RSS as well (#2599)

* move link expander to new file, add test, refactor a bit

* text formatting: include indication if a quote post exists

* rss: include expanded links

bskyweb/cmd/bskyweb/formating.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"fmt"
+	"slices"
+	"strings"
+
+	appbsky "github.com/bluesky-social/indigo/api/bsky"
+)
+
+// Function to expand shortened links in rich text back to full urls, replacing shortened urls in social card meta tags and the noscript output.
+//
+// This essentially reverses the effect of the typescript function `shortenLinks()` in `src/lib/strings/rich-text-manip.ts`
+func ExpandPostText(post *appbsky.FeedPost) string {
+	postText := post.Text
+	var charsAdded int = 0
+	// iterate over facets, check if they're link facets, and if found, grab the uri
+	for _, facet := range post.Facets {
+		linkUri := ""
+		if slices.ContainsFunc(facet.Features, func(feat *appbsky.RichtextFacet_Features_Elem) bool {
+			if feat.RichtextFacet_Link == nil || feat.RichtextFacet_Link.LexiconTypeID != "app.bsky.richtext.facet#link" {
+				return false
+			}
+
+			// bail out if bounds checks fail
+			if int(facet.Index.ByteStart)+charsAdded > len(postText) || int(facet.Index.ByteEnd)+charsAdded > len(postText) {
+				return false
+			}
+			linkText := postText[int(facet.Index.ByteStart)+charsAdded : int(facet.Index.ByteEnd)+charsAdded]
+			linkUri = feat.RichtextFacet_Link.Uri
+
+			// only expand uris that have been shortened (as opposed to those with non-uri anchor text)
+			if strings.HasSuffix(linkText, "...") && strings.Contains(linkUri, linkText[0:len(linkText)-3]) {
+				return true
+			}
+			return false
+		}) {
+			// replace the shortened uri with the full length one from the facet using utf8 byte offsets
+			// NOTE: we already did bounds check above
+			postText = postText[0:int(facet.Index.ByteStart)+charsAdded] + linkUri + postText[int(facet.Index.ByteEnd)+charsAdded:]
+			charsAdded += len(linkUri) - int(facet.Index.ByteEnd-facet.Index.ByteStart)
+		}
+	}
+	// if the post has an embeded link and its url doesn't already appear in postText, append it to
+	// the end to avoid social cards with missing links
+	if post.Embed != nil && post.Embed.EmbedExternal != nil && post.Embed.EmbedExternal.External != nil {
+		externalURI := post.Embed.EmbedExternal.External.Uri
+		if !strings.Contains(postText, externalURI) {
+			postText = fmt.Sprintf("%s\n%s", postText, externalURI)
+		}
+	}
+	// TODO: could embed the actual post text?
+	if post.Embed != nil && (post.Embed.EmbedRecord != nil || post.Embed.EmbedRecordWithMedia != nil) {
+		postText = fmt.Sprintf("%s\n\n[contains quote post or other embeded content]", postText)
+	}
+	return postText
+}