From 44c9eab1d16fc632a9e1a2b97db232f1a064a97e Mon Sep 17 00:00:00 2001
From: Moskovkin Ilya <targix8@gmail.com>
Date: Tue, 7 Jul 2026 15:53:09 +0700
Subject: [PATCH] refactor: extract replay URL helpers

---
 src/components/dashboard.tsx | 39 ++++++-------------------
 src/lib/replay-url.ts        | 56 ++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+), 30 deletions(-)
 create mode 100644 src/lib/replay-url.ts

diff --git a/src/components/dashboard.tsx b/src/components/dashboard.tsx
index 124368b..ccfa857 100644
--- a/src/components/dashboard.tsx
+++ b/src/components/dashboard.tsx
@@ -62,6 +62,7 @@ import {
   type Provider,
   type ProviderId,
 } from "@/lib/mock-data";
+import { applyReplayUrlState, parseReplayUrlState } from "@/lib/replay-url";
 import { cn, formatCurrency, formatMs, formatNumber } from "@/lib/utils";
 
 const ranges = ["24h", "7d", "30d"] as const;
@@ -176,8 +177,9 @@ function downloadCsv(filename: string, csv: string) {
   window.setTimeout(() => URL.revokeObjectURL(url), 0);
 }
 
-const REPLAY_PARAM = "replay";
-const STEP_PARAM = "step";
+const replayStepCounts = new Map(
+  replayScenarios.map((scenario) => [scenario.id, scenario.steps.length]),
+);
 
 /** Read an incoming shareable replay link from the URL (client only). */
 function readReplayParams(): { scenarioId: string | null; step: number } {
@@ -185,25 +187,7 @@ function readReplayParams(): { scenarioId: string | null; step: number } {
     return { scenarioId: null, step: 0 };
   }
 
-  const params = new URLSearchParams(window.location.search);
-  const replay = params.get(REPLAY_PARAM);
-
-  if (!replay) {
-    return { scenarioId: null, step: 0 };
-  }
-
-  const scenario = replayScenarios.find((item) => item.id === replay);
-
-  if (!scenario) {
-    return { scenarioId: null, step: 0 };
-  }
-
-  const rawStep = Number(params.get(STEP_PARAM) ?? "0");
-  const step = Number.isFinite(rawStep)
-    ? Math.max(0, Math.min(Math.floor(rawStep), scenario.steps.length - 1))
-    : 0;
-
-  return { scenarioId: replay, step };
+  return parseReplayUrlState(window.location.search, replayStepCounts);
 }
 
 /** Keep the URL in sync with the active replay (no history entries, no scroll). */
@@ -212,15 +196,10 @@ function syncReplayUrl(scenarioId: string | null, step: number) {
     return;
   }
 
-  const url = new URL(window.location.href);
-
-  if (scenarioId) {
-    url.searchParams.set(REPLAY_PARAM, scenarioId);
-    url.searchParams.set(STEP_PARAM, String(step));
-  } else {
-    url.searchParams.delete(REPLAY_PARAM);
-    url.searchParams.delete(STEP_PARAM);
-  }
+  const url = applyReplayUrlState(new URL(window.location.href), {
+    scenarioId,
+    step,
+  });
 
   window.history.replaceState(window.history.state, "", url);
 }
diff --git a/src/lib/replay-url.ts b/src/lib/replay-url.ts
new file mode 100644
index 0000000..1310f41
--- /dev/null
+++ b/src/lib/replay-url.ts
@@ -0,0 +1,56 @@
+export type ReplayUrlState = {
+  scenarioId: string | null;
+  step: number;
+};
+
+export const REPLAY_PARAM = "replay";
+export const STEP_PARAM = "step";
+
+type ReplayStepCounts = ReadonlyMap<string, number> | Record<string, number>;
+
+function getStepCount(stepCounts: ReplayStepCounts, scenarioId: string): number | undefined {
+  if ("get" in stepCounts && typeof stepCounts.get === "function") {
+    return stepCounts.get(scenarioId);
+  }
+
+  return (stepCounts as Record<string, number>)[scenarioId];
+}
+
+export function parseReplayUrlState(
+  search: string | URLSearchParams,
+  stepCounts: ReplayStepCounts,
+): ReplayUrlState {
+  const params = typeof search === "string" ? new URLSearchParams(search) : search;
+  const scenarioId = params.get(REPLAY_PARAM);
+
+  if (!scenarioId) {
+    return { scenarioId: null, step: 0 };
+  }
+
+  const stepCount = getStepCount(stepCounts, scenarioId);
+
+  if (!stepCount || stepCount < 1) {
+    return { scenarioId: null, step: 0 };
+  }
+
+  const rawStep = Number(params.get(STEP_PARAM) ?? "0");
+  const step = Number.isFinite(rawStep)
+    ? Math.max(0, Math.min(Math.floor(rawStep), stepCount - 1))
+    : 0;
+
+  return { scenarioId, step };
+}
+
+export function applyReplayUrlState(url: URL, state: ReplayUrlState): URL {
+  const nextUrl = new URL(url.href);
+
+  if (state.scenarioId) {
+    nextUrl.searchParams.set(REPLAY_PARAM, state.scenarioId);
+    nextUrl.searchParams.set(STEP_PARAM, String(state.step));
+  } else {
+    nextUrl.searchParams.delete(REPLAY_PARAM);
+    nextUrl.searchParams.delete(STEP_PARAM);
+  }
+
+  return nextUrl;
+}