From fa491b1866c639ec0ca56231bcca89648ed02d06 Mon Sep 17 00:00:00 2001
From: Felix Ableitner <me@nutomic.com>
Date: Thu, 26 Sep 2024 15:41:22 +0200
Subject: [PATCH] add helper fn

---
 crates/apub/src/fetcher/post_links.rs | 113 ++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 crates/apub/src/fetcher/post_links.rs

diff --git a/crates/apub/src/fetcher/post_links.rs b/crates/apub/src/fetcher/post_links.rs
new file mode 100644
index 000000000..1b4cb01dc
--- /dev/null
+++ b/crates/apub/src/fetcher/post_links.rs
@@ -0,0 +1,113 @@
+use crate::fetcher::post_or_comment::PostOrComment;
+use activitypub_federation::{config::Data, fetch::object_id::ObjectId};
+use lemmy_api_common::{
+  context::LemmyContext,
+  utils::{generate_local_apub_endpoint, EndpointType},
+};
+use lemmy_utils::{
+  error::LemmyResult,
+  utils::markdown::image_links::{markdown_find_links, markdown_handle_title},
+};
+
+pub async fn markdown_rewrite_remote_post_links_opt(
+  src: Option<String>,
+  context: &Data<LemmyContext>,
+) -> Option<String> {
+  match src {
+    Some(t) => Some(markdown_rewrite_remote_post_links(t, context).await),
+    None => None,
+  }
+}
+
+/// TODO: as it uses ObjectId::dereference, it can currently only be used in apub crate
+pub async fn markdown_rewrite_remote_post_links(
+  mut src: String,
+  context: &Data<LemmyContext>,
+) -> String {
+  let links_offsets = markdown_find_links(&src);
+  let domain = &context.settings().get_protocol_and_hostname();
+
+  // Go through the collected links in reverse order
+  for (start, end) in links_offsets.into_iter().rev() {
+    let (url, extra) = markdown_handle_title(&src, start, end);
+
+    // TODO: call this logic for post.url, comment.text etc
+    // TODO: needs cleanup
+    // TODO: also resolve user and community links
+    if let Ok(parsed) = ObjectId::<PostOrComment>::parse(url) {
+      if parsed.inner().domain() != Some(&context.settings().hostname) {
+        let dereferenced = parsed.dereference(context).await;
+
+        if let Some(mut local_url) = to_local_url(dereferenced, &domain) {
+          // restore title
+          if let Some(extra) = extra {
+            local_url = format!("{local_url} {extra}");
+          }
+          src.replace_range(start..end, local_url.as_str());
+        }
+      }
+    }
+  }
+
+  src
+}
+
+fn to_local_url(dereferenced: LemmyResult<PostOrComment>, domain: &str) -> Option<String> {
+  dereferenced
+    .map(|d| match d {
+      PostOrComment::Post(post) => {
+        generate_local_apub_endpoint(EndpointType::Post, &post.id.to_string(), domain).ok()
+      }
+      PostOrComment::Comment(comment) => {
+        generate_local_apub_endpoint(EndpointType::Comment, &comment.id.to_string(), domain).ok()
+      }
+    })
+    .ok()
+    .flatten()
+    .map(|e| e.to_string())
+}
+
+#[cfg(test)]
+#[expect(clippy::unwrap_used)]
+mod tests {
+
+  use super::*;
+  use pretty_assertions::assert_eq;
+
+  #[tokio::test]
+  async fn test_markdown_rewrite_remote_post_links() {
+    let tests: Vec<_> = vec![
+      (
+        "rewrite remote link",
+        "[link](https://feddit.org/post/3172593)",
+        "[link](https://lemmy-alpha/post/1)",
+      ),
+      (
+        "dont rewrite local link",
+        "[link](https://lemmy-alpha/post/2)",
+        "[link](https://lemmy-alpha/post/2)",
+      ),
+      (
+        "dont rewrite non-fediverse link",
+        "[link](https://example.com/)",
+        "[link](https://example.com/)",
+      ),
+      (
+        "dont rewrite invalid url",
+        "[link](example-com)",
+        "[link](example-com)",
+      ),
+    ];
+
+    let context = LemmyContext::init_test_context().await;
+    for &(msg, input, expected) in &tests {
+      let result = markdown_rewrite_remote_post_links(input.to_string(), &context).await;
+
+      assert_eq!(
+        result, expected,
+        "Testing {}, with original input '{}'",
+        msg, input
+      );
+    }
+  }
+}