controller-v2/client/src/pages/eq/peqUndoDiff.ts

import {
  formatBandFreqDisplay,
  formatBandGainDisplay,
  formatBandQDisplay,
  eqInterp,
} from "./utils";
import type { PeqEqUi } from "./constants";
import type { PeqUndoBand, PeqUndoSnapshot } from "./hooks/usePeqUndoHistory";

export type PeqUndoDiffItem = {
  /** Display label already localized where possible */
  text: string;
};

function formatAuto(on: boolean, eqUi: PeqEqUi): string {
  return on ? (eqUi.undoAutoOn ?? "ON") : (eqUi.undoAutoOff ?? "OFF");
}

function bandParamLabel(
  param: "freq" | "gain" | "q" | "type",
  eqUi: PeqEqUi,
): string {
  switch (param) {
    case "freq":
      return eqUi.undoParamFreq ?? "FREQ";
    case "gain":
      return eqUi.undoParamGain ?? "GAIN";
    case "q":
      return eqUi.undoParamQ ?? "Q";
    case "type":
      return eqUi.undoParamType ?? "Filter";
  }
}

function formatBandValue(
  param: "freq" | "gain" | "q" | "type",
  band: PeqUndoBand,
): string {
  switch (param) {
    case "freq":
      return formatBandFreqDisplay(band.freq);
    case "gain":
      return formatBandGainDisplay(band.gain);
    case "q":
      return formatBandQDisplay(band.q);
    case "type":
      return String(band.type);
  }
}

function diffBands(
  fromBands: PeqUndoBand[],
  toBands: PeqUndoBand[],
  mode: "A" | "B",
  eqUi: PeqEqUi,
): PeqUndoDiffItem[] {
  const items: PeqUndoDiffItem[] = [];
  const len = Math.max(fromBands.length, toBands.length);
  for (let i = 0; i < len; i++) {
    const from = fromBands[i];
    const to = toBands[i];
    if (!from || !to) continue;
    const params = ["freq", "gain", "q", "type"] as const;
    for (const param of params) {
      const fromVal = formatBandValue(param, from);
      const toVal = formatBandValue(param, to);
      if (fromVal === toVal) continue;
      const text =
        eqInterp(eqUi.undoBandParam, {
          mode,
          band: i + 1,
          param: bandParamLabel(param, eqUi),
          from: fromVal,
          to: toVal,
        }) ||
        `${mode} Band ${i + 1} ${bandParamLabel(param, eqUi)} ${fromVal} → ${toVal}`;
      items.push({ text });
    }
  }
  return items;
}

/**
 * Diff current state (before clicking Undo) vs restored snapshot (after Undo).
 * `from` is the value user just undid away from; `to` is the restored value.
 */
export function diffPeqUndoSnapshots(
  current: PeqUndoSnapshot,
  restored: PeqUndoSnapshot,
  eqUi: PeqEqUi,
): PeqUndoDiffItem[] {
  const items: PeqUndoDiffItem[] = [];

  if (current.abMode !== restored.abMode) {
    items.push({
      text:
        eqInterp(eqUi.undoSimpleParam, {
          param: eqUi.undoParamAbMode ?? "A/B",
          from: current.abMode,
          to: restored.abMode,
        }) ||
        `A/B ${current.abMode} → ${restored.abMode}`,
    });
  }

  if (current.preamp !== restored.preamp) {
    items.push({
      text:
        eqInterp(eqUi.undoSimpleParam, {
          param: eqUi.undoParamPreamp ?? "Preamp",
          from: formatBandGainDisplay(current.preamp),
          to: formatBandGainDisplay(restored.preamp),
        }) ||
        `Preamp ${formatBandGainDisplay(current.preamp)} → ${formatBandGainDisplay(restored.preamp)}`,
    });
  }

  if (current.autoPre !== restored.autoPre) {
    items.push({
      text:
        eqInterp(eqUi.undoSimpleParam, {
          param: eqUi.undoParamAuto ?? "AUTO",
          from: formatAuto(current.autoPre === 1, eqUi),
          to: formatAuto(restored.autoPre === 1, eqUi),
        }) ||
        `AUTO ${formatAuto(current.autoPre === 1, eqUi)} → ${formatAuto(restored.autoPre === 1, eqUi)}`,
    });
  }

  items.push(
    ...diffBands(current.bandsByMode.A, restored.bandsByMode.A, "A", eqUi),
  );
  items.push(
    ...diffBands(current.bandsByMode.B, restored.bandsByMode.B, "B", eqUi),
  );

  return items;
}

/** Build toast body for an undo action. */
export function formatPeqUndoToast(
  current: PeqUndoSnapshot,
  restored: PeqUndoSnapshot,
  eqUi: PeqEqUi,
): string {
  const diffs = diffPeqUndoSnapshots(current, restored, eqUi);
  if (diffs.length === 0) {
    return eqUi.toastUndoEmpty ?? eqUi.undo ?? "Undo";
  }
  if (diffs.length === 1) {
    return (
      eqInterp(eqUi.toastUndo, { detail: diffs[0]!.text }) ||
      `Undone: ${diffs[0]!.text}`
    );
  }
  const summary = diffs
    .slice(0, 3)
    .map(d => d.text)
    .join(eqUi.undoDetailSep ?? "; ");
  const extra =
    diffs.length > 3
      ? eqInterp(eqUi.undoMoreSuffix, { count: diffs.length - 3 }) ||
        ` (+${diffs.length - 3})`
      : "";
  const detail =
    eqInterp(eqUi.undoMultiple, {
      count: diffs.length,
      summary: `${summary}${extra}`,
    }) || `${diffs.length} changes: ${summary}${extra}`;
  return eqInterp(eqUi.toastUndo, { detail }) || `Undone: ${detail}`;
}