From 9d1aa8f7d2837a57b398453c215d035eae767c85 Mon Sep 17 00:00:00 2001
From: spinline <bilal.karatatr.@gmail.com>
Date: Tue, 3 Feb 2026 20:52:09 +0300
Subject: [PATCH] refactor(backend): optimize diff logic and integrate
 DiffResult

---
 backend/src/diff.rs | 49 +++++++++++++++++++++------------------------
 backend/src/main.rs | 25 ++++++-----------------
 2 files changed, 29 insertions(+), 45 deletions(-)

diff --git a/backend/src/diff.rs b/backend/src/diff.rs
index 7051e6e..46360f6 100644
--- a/backend/src/diff.rs
+++ b/backend/src/diff.rs
@@ -1,35 +1,31 @@
 use shared::{AppEvent, Torrent, TorrentUpdate};
 
-pub fn diff_torrents(old: &[Torrent], new: &[Torrent]) -> Vec<AppEvent> {
-    // 1. Structural Change Check
-    // If length differs or any hash at specific index differs (simplistic view), send FullList.
-    // Ideally we should track "Added/Removed", but for simplicity and robustness as per prompt "FullList for big changes",
-    // we fallback to FullList on structural changes.
+#[derive(Debug)]
+pub enum DiffResult {
+    NoChange,
+    FullUpdate,
+    Partial(Vec<AppEvent>),
+}
+
+pub fn diff_torrents(old: &[Torrent], new: &[Torrent]) -> DiffResult {
+    // 1. Structural Check (Length or Order changed)
     if old.len() != new.len() {
-        // Timestamp is needed for FullList? The definition is FullList(Vec, u64).
-        // We'll let the caller handle the timestamp or pass it in?
-        // AppEvent in shared::lib.rs is FullList(Vec<Torrent>, u64).
-        // We'll return just the list decision here, or constructs events.
-        // Let's assume caller adds the u64 (disk space/timestamp).
-        // Actually, let's keep it simple: Return Option<Vec<AppEvent>>.
-        // But simply returning "NeedFullList" signal is easier if we can't accept u64 here.
-        // Let's change signature to return an enum or boolean flag if FullList needed.
-        return vec![]; // Special signal: Empty vec means "No diffs" or "Caller handles FullList"?
-                       // This function is tricky if we don't have the u64.
+        return DiffResult::FullUpdate;
     }
-    
-    // Check for hash mismatch (order changed)
+
     for (i, t) in new.iter().enumerate() {
         if old[i].hash != t.hash {
-            return vec![]; // Signal Full List needed
+            return DiffResult::FullUpdate;
         }
     }
 
+    // 2. Field Updates
     let mut events = Vec::new();
 
     for (i, new_t) in new.iter().enumerate() {
         let old_t = &old[i];
-        
+
+        // Initialize with all None
         let mut update = TorrentUpdate {
             hash: new_t.hash.clone(),
             name: None,
@@ -42,9 +38,10 @@ pub fn diff_torrents(old: &[Torrent], new: &[Torrent]) -> Vec<AppEvent> {
             status: None,
             error_message: None,
         };
-        
+
         let mut has_changes = false;
 
+        // Compare fields
         if old_t.name != new_t.name {
             update.name = Some(new_t.name.clone());
             has_changes = true;
@@ -61,7 +58,6 @@ pub fn diff_torrents(old: &[Torrent], new: &[Torrent]) -> Vec<AppEvent> {
             update.up_rate = Some(new_t.up_rate);
             has_changes = true;
         }
-        // Floating point comparison with epsilon
         if (old_t.percent_complete - new_t.percent_complete).abs() > 0.01 {
             update.percent_complete = Some(new_t.percent_complete);
             has_changes = true;
@@ -87,10 +83,11 @@ pub fn diff_torrents(old: &[Torrent], new: &[Torrent]) -> Vec<AppEvent> {
             events.push(AppEvent::Update(update));
         }
     }
-    
-    if !events.is_empty() {
-        tracing::debug!("Generated {} updates", events.len());
+
+    if events.is_empty() {
+        DiffResult::NoChange
+    } else {
+        tracing::debug!("Generated {} partial updates", events.len());
+        DiffResult::Partial(events)
     }
-    
-    events
 }
diff --git a/backend/src/main.rs b/backend/src/main.rs
index e240d6c..c50661c 100644
--- a/backend/src/main.rs
+++ b/backend/src/main.rs
@@ -91,30 +91,17 @@ async fn main() {
                         .unwrap()
                         .as_secs();
 
-                    let mut structural_change = false;
-                    if previous_torrents.len() != new_torrents.len() {
-                        structural_change = true;
-                    } else {
-                        // Check for order/hash change
-                        for (i, t) in new_torrents.iter().enumerate() {
-                            if previous_torrents[i].hash != t.hash {
-                                structural_change = true;
-                                break;
-                            }
+                    match diff::diff_torrents(&previous_torrents, &new_torrents) {
+                        diff::DiffResult::FullUpdate => {
+                            let _ =
+                                event_bus_tx.send(AppEvent::FullList(new_torrents.clone(), now));
                         }
-                    }
-
-                    if structural_change {
-                        // Structural change -> Send FullList
-                        let _ = event_bus_tx.send(AppEvent::FullList(new_torrents.clone(), now));
-                    } else {
-                        // Same structure -> Calculate partial updates
-                        let updates = diff::diff_torrents(&previous_torrents, &new_torrents);
-                        if !updates.is_empty() {
+                        diff::DiffResult::Partial(updates) => {
                             for update in updates {
                                 let _ = event_bus_tx.send(update);
                             }
                         }
+                        diff::DiffResult::NoChange => {}
                     }
 
                     previous_torrents = new_torrents;