new: FIFO list impl

lib/data/model/server/cpu.dart

@@ -1,9 +1,10 @@
+import 'dart:collection';
+
+import 'package:toolbox/data/model/server/time_seq.dart';
 import 'package:toolbox/data/res/status.dart';
 
-import 'time_seq.dart';
-
-class Cpus extends TimeSeq<OneTimeCpuStatus> {
-  Cpus(super.pre, super.now);
+class Cpus extends TimeSeq<List<OneTimeCpuStatus>> {
+  Cpus(super.init1, super.init2);
 
   @override
   void onUpdate() {
@@ -124,9 +125,11 @@ Cpus parseBsdCpu(String raw) {
       .map((e) => double.parse(e.group(1) ?? '0') * 100)
       .toList();
   if (percents.length != 3) return InitStatus.cpus;
-  return InitStatus.cpus
-    ..now = [
-      OneTimeCpuStatus('cpu', percents[0].toInt(), 0, 0,
-          percents[2].toInt() + percents[1].toInt(), 0, 0, 0)
-    ];
+
+  final init = InitStatus.cpus;
+  init.add([
+    OneTimeCpuStatus('cpu', percents[0].toInt(), 0, 0,
+        percents[2].toInt() + percents[1].toInt(), 0, 0, 0),
+  ]);
+  return init;
 }

lib/data/model/server/disk.dart

@@ -58,8 +58,8 @@ class Disk {
   }
 }
 
-class DiskIO extends TimeSeq<DiskIOPiece> {
-  DiskIO(super.pre, super.now);
+class DiskIO extends TimeSeq<List<DiskIOPiece>> {
+  DiskIO(super.init1, super.init2);
 
   @override
   void onUpdate() {

lib/data/model/server/net_speed.dart

@@ -14,8 +14,8 @@ class NetSpeedPart extends TimeSeqIface<NetSpeedPart> {
   bool same(NetSpeedPart other) => device == other.device;
 }
 
-class NetSpeed extends TimeSeq<NetSpeedPart> {
-  NetSpeed(super.pre, super.now);
+class NetSpeed extends TimeSeq<List<NetSpeedPart>> {
+  NetSpeed(super.init1, super.init2);
 
   @override
   void onUpdate() {
@@ -54,12 +54,8 @@ class NetSpeed extends TimeSeq<NetSpeedPart> {
     String sizeOut,
     String speedIn,
     String speedOut,
-  }) cachedRealVals = (
-    sizeIn: '0kb',
-    sizeOut: '0kb',
-    speedIn: '0kb/s',
-    speedOut: '0kb/s',
-  );
+  }) cachedRealVals =
+      (sizeIn: '0kb', sizeOut: '0kb', speedIn: '0kb/s', speedOut: '0kb/s');
 
   /// Time diff between [pre] and [now]
   BigInt get _timeDiff => BigInt.from(now[0].time - pre[0].time);

lib/data/model/server/time_seq.dart

@@ -1,11 +1,56 @@
-abstract class TimeSeq<T extends TimeSeqIface> {
-  List<T> pre;
-  List<T> now;
+import 'dart:collection';
+
+/// A FIFO queue with fixed capacity.
+abstract class TimeSeq<T extends List<TimeSeqIface>> extends ListBase<T> {
+  final int capacity;
+  late final List<T> _list;
+
+  /// Due to the design, at least two elements are required, otherwise [pre] /
+  /// [now] will throw.
+  TimeSeq(
+    T init1,
+    T init2, {
+    this.capacity = 30,
+  }) : _list = [init1, init2];
+
+  @override
+  void add(element) {
+    if (length == capacity) {
+      _list.removeAt(0);
+    }
+    _list.add(element);
+  }
+
+  @override
+  int get length => _list.length;
+
+  @override
+  set length(int newLength) {
+    throw UnimplementedError();
+  }
+
+  @override
+  T operator [](int index) {
+    return _list[index];
+  }
+
+  @override
+  void operator []=(int index, value) {
+    _list[index] = value;
+  }
+
+  T get pre {
+    return _list[length - 2];
+  }
+
+  T get now {
+    return _list[length - 1];
+  }
+
   void onUpdate();
 
-  void update(List<T> new_) {
-    pre = now;
-    now = new_;
+  void update(T new_) {
+    add(new_);
 
     if (pre.length != now.length) {
       pre.removeWhere((e) => now.any((el) => e.same(el)));
@@ -14,8 +59,6 @@ abstract class TimeSeq<T extends TimeSeqIface> {
 
     onUpdate();
   }
-
-  TimeSeq(this.pre, this.now);
 }
 
 abstract class TimeSeqIface<T> {