From 3a22e40225848b6ddc0f7e31562493dc4db060a2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jakub=20Ber=C3=A1nek?= <berykubik@gmail.com>
Date: Fri, 23 Jan 2026 20:20:55 +0100
Subject: [PATCH] Fix duration subtraction panic in remaining build time
 estimation

---
 src/server/mod.rs        | 26 +++++++++++++++-----------
 src/templates.rs         |  2 +-
 web/templates/queue.html |  6 +++---
 3 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/src/server/mod.rs b/src/server/mod.rs
index c06698c0..f08c1187 100644
--- a/src/server/mod.rs
+++ b/src/server/mod.rs
@@ -357,21 +357,24 @@ pub async fn queue_handler(
         None => None,
     };
 
-    let average_auto_duration = {
+    let average_build_duration = {
         let total_duration = last_ten_builds
             .iter()
             .filter_map(|build| build.duration)
             .map(|d| d.0)
             .sum::<Duration>();
+        let count = last_ten_builds.len() as u32;
         let total_duration = if total_duration.is_zero() {
-            // Default guess of 3 hours
-            Duration::from_secs(3600 * 3)
+            // Default guess of 3 hours per build
+            Duration::from_secs(3600 * 3) * count
         } else {
             total_duration
         };
-        let count = last_ten_builds.len() as u32;
-        let count = if count > 0 { count } else { 1 };
-        total_duration / count
+        if count > 1 {
+            total_duration / count
+        } else {
+            total_duration
+        }
     };
 
     let mut in_queue_count = 0;
@@ -394,18 +397,18 @@ pub async fn queue_handler(
         match &status {
             QueueStatus::Pending(_, _) => {
                 // Try to guess already elapsed time of the pending workflow
-                let subtract_duration = if let Some(workflow) = &pending_workflow {
+                let elapsed = if let Some(workflow) = &pending_workflow {
                     (Utc::now() - workflow.created_at)
                         .to_std()
                         .unwrap_or_default()
                 } else {
                     Duration::ZERO
                 };
-                in_queue.insert(pr.number, average_auto_duration - subtract_duration);
+                in_queue.insert(pr.number, average_build_duration.saturating_sub(elapsed));
             }
             // For an approved PR, assume that it will take the average auto build duration
             QueueStatus::Approved(_) => {
-                in_queue.insert(pr.number, average_auto_duration);
+                in_queue.insert(pr.number, average_build_duration);
             }
             QueueStatus::Failed(_, _)
             | QueueStatus::ReadyForMerge(_, _)
@@ -414,7 +417,7 @@ pub async fn queue_handler(
         }
     }
 
-    let mut expected_remaining_duration = Duration::ZERO;
+    let mut expected_remaining_duration: Option<Duration> = None;
 
     // Rollup members whose rollup is in the queue, and thus its duration will be counted
     let rollup_members: HashSet<PullRequestNumber> = rollups
@@ -429,7 +432,8 @@ pub async fn queue_handler(
         if rollup_members.contains(&pr) {
             continue;
         }
-        expected_remaining_duration += remaining_duration;
+        expected_remaining_duration =
+            Some(expected_remaining_duration.unwrap_or_default() + remaining_duration);
     }
 
     Ok(HtmlTemplate(QueueTemplate {
diff --git a/src/templates.rs b/src/templates.rs
index 82ce4fc8..330a74a8 100644
--- a/src/templates.rs
+++ b/src/templates.rs
@@ -87,7 +87,7 @@ pub struct QueueTemplate {
     // Active workflow for an active pending auto build
     pub pending_workflow: Option<WorkflowModel>,
     // Guesstimated duration to merge all current approved/pending PRs in the queue
-    pub expected_remaining_duration: Duration,
+    pub expected_remaining_duration: Option<Duration>,
 }
 
 impl QueueTemplate {
diff --git a/web/templates/queue.html b/web/templates/queue.html
index 541dc816..28d281b4 100644
--- a/web/templates/queue.html
+++ b/web/templates/queue.html
@@ -192,11 +192,11 @@ <h1>
       {{ stats.total_count }} total, {{ stats.in_queue_count }} in queue,
       {{ stats.failed_count }} failed
     </p>
-    {%- if !expected_remaining_duration.is_zero() -%}
+    {%- if let Some(expected) = expected_remaining_duration -%}
       <div style="margin: 0 5px;">|</div>
       <p style="margin-bottom: 0;"
-         title="Expected duration to merge all current PRs in the queue, assuming that there are no build failures.">
-        Estimated time to merge queue: {{ format_duration(*expected_remaining_duration) }}
+         title="Estimated duration to merge all current PRs in the queue, assuming that there are no build failures.">
+        Estimated time to flush queue: {{ format_duration(**expected) }}
       </p>
     {%- endif -%}
   </div>