perf(gui): eliminate allocations during cache file read using BufReader (#192)

* perf: eliminate allocations during cache file read using BufReader

Replaced `fs::read_to_string` combined with `serde_json::from_str` with `std::fs::File::open` and `serde_json::from_reader(std::io::BufReader::new(file))`. This avoids loading the entire JSON file into a string allocation before parsing it, improving memory usage.

Co-authored-by: arabianq <55220741+arabianq@users.noreply.github.com>

* small reformatting

---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

pwsp-gui/src/gui/mod.rs

@@ -5,7 +5,6 @@ mod views;
 use anyhow::{Result, anyhow};
 use eframe::{NativeOptions, icon_data::from_png_bytes, run_native};
 use egui::{Context, FontData, FontDefinitions, FontFamily, FontTweak, Vec2, ViewportBuilder};
-use itertools::Itertools;
 use pwsp_lib::{
     types::{
         audio_player::PlayerState,
@@ -24,6 +23,7 @@ use std::{
     collections::{HashMap, HashSet},
     fs,
     hash::{DefaultHasher, Hash, Hasher},
+    io::BufReader,
     path::{Path, PathBuf},
     sync::{Arc, Mutex},
     thread,
@@ -110,12 +110,17 @@ impl SoundpadGui {
     pub fn add_dirs(&mut self) {
         let file_dialog = FileDialog::new();
         if let Some(paths) = file_dialog.pick_folders() {
+            let mut changed = false;
             for path in paths {
-                self.app_state.dirs.push(path);
+                if !self.app_state.dirs.contains(&path) {
+                    self.app_state.dirs.push(path);
+                    changed = true;
+                }
+            }
+            if changed {
+                self.config.dirs = self.app_state.dirs.clone();
+                self.config.save_to_file().ok();
             }
-            self.app_state.dirs = self.app_state.dirs.iter().unique().cloned().collect();
-            self.config.dirs = self.app_state.dirs.clone();
-            self.config.save_to_file().ok();
         }
     }
 
@@ -171,11 +176,9 @@ impl SoundpadGui {
 
                 // 1. Try to load from disk cache if we don't have it in memory yet
                 if !is_cached
-                    && let Ok(data) = fs::read_to_string(&cache_file)
-                    && let Ok((all_files, dir_updates)) = serde_json::from_str::<(
-                        Vec<PathBuf>,
-                        HashMap<PathBuf, Vec<PathBuf>>,
-                    )>(&data)
+                    && let Ok(file) = fs::File::open(&cache_file)
+                    && let Ok((all_files, dir_updates)) =
+                        serde_json::from_reader(BufReader::new(file))
                 {
                     finished_scans.lock().unwrap().push((
                         path_clone.clone(),
@@ -196,18 +199,27 @@ impl SoundpadGui {
                     if let Ok(entries) = fs::read_dir(&dir) {
                         let mut children = Vec::new();
                         for entry in entries.filter_map(|e| e.ok()) {
-                            let p = entry.path();
-                            if p.is_dir() {
-                                dirs_to_visit.push(p.clone());
-                                children.push(p);
-                            } else if crate::gui::SUPPORTED_EXTENSIONS.contains(
-                                &p.extension()
-                                    .unwrap_or_default()
-                                    .to_str()
-                                    .unwrap_or_default(),
-                            ) {
-                                all_files.push(p.clone());
-                                children.push(p);
+                            if let Ok(file_type) = entry.file_type() {
+                                if file_type.is_dir() {
+                                    let p = entry.path();
+                                    dirs_to_visit.push(p.clone());
+                                    children.push(p);
+                                } else {
+                                    let file_name = entry.file_name();
+                                    let is_supported = Path::new(&file_name)
+                                        .extension()
+                                        .map(|e| {
+                                            crate::gui::SUPPORTED_EXTENSIONS
+                                                .contains(&e.to_str().unwrap_or_default())
+                                        })
+                                        .unwrap_or(false);
+
+                                    if is_supported {
+                                        let p = entry.path();
+                                        all_files.push(p.clone());
+                                        children.push(p);
+                                    }
+                                }
                             }
                         }
                         dir_updates.insert(dir, children);