controller-v2/client/src/pages/eq/hooks/usePeqUndoHistory.ts

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,
  };
}