新增 EQ撤销功能，用户调节的参数不满意可以点击回退到上一次，撤销栈最多存放 30 步

client/src/pages/eq/hooks/usePeqUndoHistory.ts

@@ -0,0 +1,123 @@
+import { useCallback, useRef, useState } from "react";
+import { cloneBands } from "../peqMappers";
+
+export const PEQ_UNDO_MAX_STEPS = 30;
+
+export type PeqUndoBand = {
+  freq: number;
+  gain: number;
+  q: number;
+  type: string;
+  enabled: boolean;
+};
+
+export type PeqUndoSnapshot = {
+  abMode: "A" | "B";
+  bandsByMode: { A: PeqUndoBand[]; B: PeqUndoBand[] };
+  preamp: number;
+  autoPre: number;
+};
+
+function cloneSnapshot(snapshot: PeqUndoSnapshot): PeqUndoSnapshot {
+  return {
+    abMode: snapshot.abMode,
+    bandsByMode: {
+      A: cloneBands(snapshot.bandsByMode.A),
+      B: cloneBands(snapshot.bandsByMode.B),
+    },
+    preamp: snapshot.preamp,
+    autoPre: snapshot.autoPre,
+  };
+}
+
+export function peqUndoSnapshotsEqual(
+  a: PeqUndoSnapshot,
+  b: PeqUndoSnapshot,
+): boolean {
+  if (a.abMode !== b.abMode) return false;
+  if (a.preamp !== b.preamp || a.autoPre !== b.autoPre) return false;
+  return (
+    JSON.stringify(a.bandsByMode.A) === JSON.stringify(b.bandsByMode.A) &&
+    JSON.stringify(a.bandsByMode.B) === JSON.stringify(b.bandsByMode.B)
+  );
+}
+
+/**
+ * Undo stack for EQ parameter edits.
+ * - One stack entry = one complete gesture (drag release / confirmed change)
+ * - Max {@link PEQ_UNDO_MAX_STEPS} entries
+ * - No redo
+ */
+export function usePeqUndoHistory(maxSteps = PEQ_UNDO_MAX_STEPS) {
+  const stackRef = useRef<PeqUndoSnapshot[]>([]);
+  const pendingBeforeRef = useRef<PeqUndoSnapshot | null>(null);
+  const [canUndo, setCanUndo] = useState(false);
+
+  const syncCanUndo = useCallback(() => {
+    setCanUndo(stackRef.current.length > 0);
+  }, []);
+
+  const clear = useCallback(() => {
+    stackRef.current = [];
+    pendingBeforeRef.current = null;
+    setCanUndo(false);
+  }, []);
+
+  const push = useCallback(
+    (snapshot: PeqUndoSnapshot) => {
+      stackRef.current.push(cloneSnapshot(snapshot));
+      while (stackRef.current.length > maxSteps) {
+        stackRef.current.shift();
+      }
+      syncCanUndo();
+    },
+    [maxSteps, syncCanUndo],
+  );
+
+  /** Discrete edit: push current state as undo target before mutating. */
+  const captureBefore = useCallback(
+    (snapshot: PeqUndoSnapshot) => {
+      pendingBeforeRef.current = null;
+      push(snapshot);
+    },
+    [push],
+  );
+
+  /** Continuous gesture start (slider / curve drag). */
+  const beginGesture = useCallback((snapshot: PeqUndoSnapshot) => {
+    pendingBeforeRef.current = cloneSnapshot(snapshot);
+  }, []);
+
+  /** Continuous gesture end: commit only if state actually changed. */
+  const commitGesture = useCallback(
+    (current: PeqUndoSnapshot) => {
+      const before = pendingBeforeRef.current;
+      pendingBeforeRef.current = null;
+      if (!before) return;
+      if (peqUndoSnapshotsEqual(before, current)) return;
+      push(before);
+    },
+    [push],
+  );
+
+  const cancelGesture = useCallback(() => {
+    pendingBeforeRef.current = null;
+  }, []);
+
+  const undo = useCallback((): PeqUndoSnapshot | null => {
+    pendingBeforeRef.current = null;
+    const next = stackRef.current.pop() ?? null;
+    syncCanUndo();
+    return next ? cloneSnapshot(next) : null;
+  }, [syncCanUndo]);
+
+  return {
+    canUndo,
+    clear,
+    captureBefore,
+    beginGesture,
+    commitGesture,
+    cancelGesture,
+    undo,
+  };
+}