hive-forge: comments --tail N flag (#694 part 3) — last N comments in chronological order

hive-forge/src/verbs/comments.rs

@@ -1,6 +1,17 @@
-//! `comments <number> [--limit N]` — list all comments on an issue
-//! or PR. Closes the curl-fallback gap (#418). Use the global
-//! `--json` flag for JSON output (#421).
+//! `comments <number> [--limit N | --tail N]` — list comments on an
+//! issue or PR. Closes the curl-fallback gap (#418); `--tail`
+//! closes the third of the four #694 gaps (paging-for-long-threads
+//! awkwardness).
+//!
+//! - `--limit N` (default 50, Forgejo's cap) returns the first N
+//!   comments — same shape this verb has always had.
+//! - `--tail N` returns the *last* N comments in chronological
+//!   order. Internally pages through every comment on the issue,
+//!   then slices the tail. Use this for "what was the conclusion
+//!   on this long thread?" without scrolling through the whole
+//!   history.
+//!
+//! Use the global `--json` flag for JSON output (#421).
 
 use anyhow::Result;
 use clap::Args as ClapArgs;
@@ -9,42 +20,52 @@ use serde_json::{Value, json};
 use crate::client::Client;
 use crate::verbs::print_json;
 
+/// Hard cap on `--tail` pagination so a confused caller can't
+/// accidentally paginate forever on a runaway-comment thread.
+/// 20 pages × Forgejo's 50-per-page cap = 1000 comments which
+/// covers every issue in the hyperhive repo today with headroom.
+/// Tune up if a future thread breaches it (the truncated tail
+/// will surface as a smaller-than-expected slice).
+const TAIL_MAX_PAGES: u32 = 20;
+
 #[derive(ClapArgs)]
 pub struct Args {
     /// Issue or PR number.
     number: u64,
-    /// Page size (Forgejo caps at 50 by default).
-    #[arg(long, default_value_t = 50)]
+    /// Page size for the head-of-thread shape (Forgejo caps at 50).
+    /// Mutually exclusive with `--tail`.
+    #[arg(long, default_value_t = 50, conflicts_with = "tail")]
     limit: u64,
+    /// Return the last `N` comments in chronological order. Pages
+    /// through every comment on the issue under the hood, then
+    /// slices the tail. Mutually exclusive with `--limit`.
+    #[arg(long)]
+    tail: Option<usize>,
 }
 
 pub fn run(client: &Client, args: Args) -> Result<()> {
     let repo = client.repo();
-    let v = client.get_json(&format!(
-        "/repos/{repo}/issues/{}/comments?limit={}",
-        args.number, args.limit
-    ))?;
+    let comments = match args.tail {
+        Some(n) => fetch_tail(client, &repo, args.number, n)?,
+        None => fetch_head(client, &repo, args.number, args.limit)?,
+    };
     if client.json_mode() {
-        let trimmed: Vec<Value> = v
-            .as_array()
-            .map(|a| {
-                a.iter()
-                    .map(|c| {
-                        json!({
-                            "id": c.get("id"),
-                            "user": c.get("user").and_then(|u| u.get("login")),
-                            "created_at": c.get("created_at"),
-                            "updated_at": c.get("updated_at"),
-                            "body": c.get("body"),
-                            "url": c.get("html_url"),
-                        })
-                    })
-                    .collect()
+        let trimmed: Vec<Value> = comments
+            .iter()
+            .map(|c| {
+                json!({
+                    "id": c.get("id"),
+                    "user": c.get("user").and_then(|u| u.get("login")),
+                    "created_at": c.get("created_at"),
+                    "updated_at": c.get("updated_at"),
+                    "body": c.get("body"),
+                    "url": c.get("html_url"),
+                })
             })
-            .unwrap_or_default();
+            .collect();
         print_json(&Value::Array(trimmed))
     } else {
-        for c in v.as_array().cloned().unwrap_or_default() {
+        for c in &comments {
             let user = c
                 .get("user")
                 .and_then(|u| u.get("login"))
@@ -58,3 +79,27 @@ pub fn run(client: &Client, args: Args) -> Result<()> {
         Ok(())
     }
 }
+
+/// Fetch the first page's worth of comments (existing behaviour).
+fn fetch_head(client: &Client, repo: &str, number: u64, limit: u64) -> Result<Vec<Value>> {
+    let v = client.get_json(&format!(
+        "/repos/{repo}/issues/{number}/comments?limit={limit}"
+    ))?;
+    Ok(v.as_array().cloned().unwrap_or_default())
+}
+
+/// Fetch every comment via paginated GET, then return the last `n`
+/// items in chronological order. Forgejo orders
+/// `/issues/<n>/comments` oldest-first so the trailing slice maps
+/// directly to "most recent N".
+fn fetch_tail(client: &Client, repo: &str, number: u64, n: usize) -> Result<Vec<Value>> {
+    let all = client.get_json_all(
+        &format!("/repos/{repo}/issues/{number}/comments?limit=50"),
+        TAIL_MAX_PAGES,
+    )?;
+    let total = all.len();
+    if total <= n {
+        return Ok(all);
+    }
+    Ok(all.into_iter().skip(total - n).collect())
+}