Snapshot of main at 9f39a6e1e (2026-11-02)

app/Services/Stats/SlidingWindow.php

@@ -0,0 +1,77 @@
+<?php
+
+namespace App\Services\Stats;
+
+/**
+ * Which keys occur inside a date window that only ever moves forward.
+ *
+ * Built for the network time-lapse: its layers are windows over a day-ordered
+ * list of [day, key] events - "traded in the month ending on this step",
+ * "traded before this date" - and each step moves them on by a week or a
+ * month. Two pointers walk the events once in total, so all steps together
+ * cost one pass, and each step reports only the keys that entered or left.
+ *
+ * Days are 'Y-m-d' strings, which compare correctly as strings.
+ */
+class SlidingWindow
+{
+    /** @var array<string,int> Occurrences of each key inside the window. */
+    private array $count = [];
+
+    private int $enter = 0;
+
+    private int $leave = 0;
+
+    private int $size;
+
+    /** @param array<array{0:string, 1:string}> $events [day, key], ordered by day */
+    public function __construct(private array $events)
+    {
+        $this->size = count($events);
+    }
+
+    /**
+     * Move the window to [$start, $end] (inclusive; null start = no lower
+     * bound) and return what entered and left since the previous call.
+     *
+     * Both bounds may only move forward.
+     *
+     * @return array{added: array<string>, removed: array<string>}
+     */
+    public function slideTo(?string $start, string $end): array
+    {
+        $before = [];
+
+        while ($this->enter < $this->size && $this->events[$this->enter][0] <= $end) {
+            $key = $this->events[$this->enter++][1];
+            $before[$key] ??= ($this->count[$key] ?? 0) > 0;
+            $this->count[$key] = ($this->count[$key] ?? 0) + 1;
+        }
+
+        if ($start !== null) {
+            while ($this->leave < $this->enter && $this->events[$this->leave][0] < $start) {
+                $key = $this->events[$this->leave++][1];
+                $before[$key] ??= ($this->count[$key] ?? 0) > 0;
+
+                if (--$this->count[$key] === 0) {
+                    unset($this->count[$key]);
+                }
+            }
+        }
+
+        $added = [];
+        $removed = [];
+
+        foreach ($before as $key => $was) {
+            $now = isset($this->count[$key]);
+
+            if ($now && !$was) {
+                $added[] = $key;
+            } elseif (!$now && $was) {
+                $removed[] = $key;
+            }
+        }
+
+        return ['added' => $added, 'removed' => $removed];
+    }
+}