radicle-cli/issue: Improve comment templating

Writing a comment, only the most recent comment replied to is shown.
Editing a comment, current contents are not prepared. Manual copy required.

To improve:
 - Chase all replies to the root and quote them. Gracefully handle if
   this proces fails, i.e. a comment in the chain cannot be resolved.
 - If editing, copy the current contents.

crates/radicle-cli/src/commands/issue.rs

@@ -11,6 +11,7 @@ use radicle::cob::common::{Label, Reaction};
 use radicle::cob::issue::{CloseReason, State};
 use radicle::cob::{issue, thread};
 use radicle::crypto;
+use radicle::git::Oid;
 use radicle::issue::cache::Issues as _;
 use radicle::node::device::Device;
 use radicle::node::NodeId;
@@ -521,11 +522,18 @@ pub fn run(options: Options, ctx: impl term::Context) -> anyhow::Result<()> {
             message,
             reply_to,
         } => {
+            let reply_to = reply_to
+                .map(|rev| rev.resolve::<radicle::git::Oid>(repo.raw()))
+                .transpose()?;
+
             let signer = term::signer(&profile)?;
             let issue_id = id.resolve::<cob::ObjectId>(&repo.backend)?;
             let mut issue = issues.get_mut(&issue_id)?;
-            let (body, reply_to) = prompt_comment(message, reply_to, &issue, &repo)?;
-            let comment_id = issue.comment(body, reply_to, vec![], &signer)?;
+
+            let (root_comment_id, _) = issue.root();
+            let body = prompt_comment(message, issue.thread(), reply_to, None)?;
+            let comment_id =
+                issue.comment(body, reply_to.unwrap_or(*root_comment_id), vec![], &signer)?;
 
             if options.quiet {
                 term::print(comment_id);
@@ -543,7 +551,18 @@ pub fn run(options: Options, ctx: impl term::Context) -> anyhow::Result<()> {
             let issue_id = id.resolve::<cob::ObjectId>(&repo.backend)?;
             let comment_id = comment_id.resolve(&repo.backend)?;
             let mut issue = issues.get_mut(&issue_id)?;
-            let (body, _) = prompt_comment(message, None, &issue, &repo)?;
+
+            let comment = issue
+                .thread()
+                .comment(&comment_id)
+                .ok_or(anyhow::anyhow!("comment '{comment_id}' not found"))?;
+
+            let body = prompt_comment(
+                message,
+                issue.thread(),
+                comment.reply_to(),
+                Some(comment.body()),
+            )?;
             issue.edit_comment(comment_id, body, vec![], &signer)?;
 
             if options.quiet {
@@ -892,29 +911,92 @@ where
 }
 
 /// Get a comment from the user, by prompting.
-pub fn prompt_comment<R: WriteRepository + radicle::cob::Store<Namespace = NodeId>>(
+pub fn prompt_comment(
     message: Message,
-    reply_to: Option<Rev>,
-    issue: &issue::Issue,
-    repo: &R,
-) -> anyhow::Result<(String, thread::CommentId)> {
-    let (root, r) = issue.root();
-    let (reply_to, help) = if let Some(rev) = reply_to {
-        let id = rev.resolve::<radicle::git::Oid>(repo.raw())?;
-        let parent = issue
-            .thread()
-            .comment(&id)
-            .ok_or(anyhow::anyhow!("comment '{rev}' not found"))?;
+    thread: &thread::Thread,
+    mut reply_to: Option<Oid>,
+    edit: Option<&str>,
+) -> anyhow::Result<String> {
+    let (chase, missing) = {
+        let mut chase = Vec::with_capacity(thread.len());
+        let mut missing = None;
 
-        (id, parent.body().trim())
-    } else {
-        (*root, r.body().trim())
+        while let Some(id) = reply_to {
+            if let Some(comment) = thread.comment(&id) {
+                chase.push(comment);
+                reply_to = comment.reply_to();
+            } else {
+                missing = reply_to;
+                break;
+            }
+        }
+
+        (chase, missing)
     };
-    let help = format!("\n{}\n", term::format::html::commented(help));
-    let body = message.get(&help)?;
+
+    let quotes = if chase.is_empty() {
+        ""
+    } else {
+        "Quotes (lines starting with '>') will be preserved. Please remove those that you do not intend to keep.\n"
+    };
+
+    let mut buffer = term::format::html::commented(format!("HTML comments, such as this one, are deleted before posting.\n{quotes}Saving an empty file aborts the operation.").as_str());
+    buffer.push('\n');
+
+    for comment in chase.iter().rev() {
+        buffer.reserve(2);
+        buffer.push('\n');
+        comment_quoted(comment, &mut buffer);
+    }
+
+    if let Some(id) = missing {
+        buffer.push('\n');
+        buffer.push_str(
+            term::format::html::commented(
+                format!("The comment with ID {id} that was replied to could not be found.")
+                    .as_str(),
+            )
+            .as_str(),
+        );
+    }
+
+    if let Some(edit) = edit {
+        if !chase.is_empty() {
+            buffer.push_str(
+                "\n<!-- The contents of the comment you are editing follow below this line. -->\n",
+            );
+        }
+        buffer.reserve(2 + edit.len());
+        buffer.push('\n');
+        buffer.push_str(edit);
+    }
+
+    let body = message.get(&buffer)?;
 
     if body.is_empty() {
         anyhow::bail!("aborting operation due to empty comment");
     }
-    Ok((body, reply_to))
+    Ok(body)
+}
+
+fn comment_quoted(comment: &thread::Comment, buffer: &mut String) {
+    let body = comment.body();
+    let lines = body.lines();
+
+    let hint = {
+        let (lower, upper) = lines.size_hint();
+        upper.unwrap_or(lower)
+    };
+
+    buffer.push_str(format!("{} wrote:\n", comment.author()).as_str());
+    buffer.reserve(body.len() + hint * 2);
+
+    for line in lines {
+        buffer.push('>');
+        if !line.is_empty() {
+            buffer.push(' ');
+        }
+        buffer.push_str(line);
+        buffer.push('\n');
+    }
 }