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* `useSignaturePad` — the signature engine on a canvas **you** render
* (confetti `useConfetti` pattern).
*/
import { useCallback, useRef, useState, type RefCallback } from "react";
import { useLatest } from "@usefy/use-latest";
import {
createSignatureEngine,
type SignatureEngine,
type SignatureEngineOptions,
} from "./engine/createEngine";
import type { PNGExportOptions, SignatureData, SVGExportOptions } from "./types";
import { emptySignatureData, emptyToPNG, emptyToSVG } from "./reactFallbacks";
/**
* Options for {@link useSignaturePad}.
*
* @example
* ```tsx
* const pad = useSignaturePad({
* penColor: "#0f172a",
* minDistance: 3,
* onEnd: () => console.log("stroke committed"),
* });
* ```
*/
export interface UseSignaturePadOptions extends SignatureEngineOptions {
/** Fires when a stroke begins (latest callback always used). */
onBegin?: () => void;
/** Fires when a stroke ends (before the state edge). */
onEnd?: () => void;
}
/** Reactive pad state — updated only on engine edges, never per point. */
interface PadState {
isEmpty: boolean;
strokeCount: number;
canUndo: boolean;
canRedo: boolean;
}
const DETACHED_STATE: PadState = {
isEmpty: true,
strokeCount: 0,
canUndo: false,
canRedo: false,
};
/**
* Value returned by {@link useSignaturePad}.
*
* All functions are referentially stable for the component's lifetime
* (they act on whichever engine is attached when called — no stale
* closures). Before a canvas attaches, they are safe no-ops: reads
* return minimal empty artifacts, mutations do nothing.
*
* @example
* ```tsx
* const pad = useSignaturePad();
* return (
* <>
* <canvas ref={pad.canvasRef} style={{ width: "100%", height: 200 }} />
* <button onClick={pad.undo} disabled={!pad.canUndo}>Undo</button>
* <button onClick={pad.clear} disabled={pad.isEmpty}>Clear</button>
* </>
* );
* ```
*/
export interface UseSignaturePadReturn {
/**
* Attach this to the `<canvas>` you own. The engine is created lazily
* on first attach and destroyed on detach/unmount; attaching a
* different canvas destroys the old engine and creates a fresh one.
*/
canvasRef: RefCallback<HTMLCanvasElement>;
/** `true` while no committed strokes exist. Edge-updated. */
isEmpty: boolean;
/** Number of committed strokes. Edge-updated. */
strokeCount: number;
/** Whether {@link undo} would do anything. Edge-updated. */
canUndo: boolean;
/** Whether {@link redo} would do anything. Edge-updated. */
canRedo: boolean;
/** Wipe all ink (single undoable action). */
clear: () => void;
/** Undo the last stroke or clear. */
undo: () => void;
/** Redo the last undone action. */
redo: () => void;
/** Export the committed strokes as PNG (`{ dataURL, blob }`). */
toPNG: (opts?: PNGExportOptions) => Promise<{ dataURL: string; blob: Blob }>;
/** Export the committed strokes as a standalone SVG string. */
toSVG: (opts?: SVGExportOptions) => string;
/** Snapshot the committed strokes as a versioned document. */
toJSON: () => SignatureData;
/** Replace the signature with a stored document. */
fromJSON: (data: SignatureData) => void;
}
/**
* React hook for a signature pad on a canvas **you** render. The engine
* is created lazily when the canvas attaches and destroyed when it
* detaches or the component unmounts. State (`isEmpty`/`strokeCount`/
* `canUndo`/`canRedo`) is driven solely by the engine's edge-only
* `onChange` subscription — **zero React renders while a stroke is being
* drawn**.
*
* `options` are read once, at engine creation (first canvas attach) —
* attach a new canvas (or remount) to apply different options (confetti
* precedent). `onBegin`/`onEnd` are exempt: the latest callbacks are
* always used.
*
* StrictMode-safe: the dev double-invocation attaches → detaches →
* attaches, leaving exactly one live engine and zero orphaned
* listeners/observers.
*
* @example
* ```tsx
* import { useSignaturePad } from "@usefy/signature-pad";
*
* function SignatureField() {
* const pad = useSignaturePad({ penColor: "#0f172a" });
* const save = async () => {
* const { blob } = await pad.toPNG({ background: "#fff" });
* await upload(blob);
* };
* return (
* <div>
* <canvas ref={pad.canvasRef} style={{ width: "100%", height: 200 }} />
* <button onClick={pad.clear} disabled={pad.isEmpty}>Clear</button>
* <button onClick={save} disabled={pad.isEmpty}>Save</button>
* </div>
* );
* }
* ```
*/
export function useSignaturePad(options: UseSignaturePadOptions = {}): UseSignaturePadReturn {
const engineRef = useRef<SignatureEngine | null>(null);
const cleanupRef = useRef<(() => void) | null>(null);
const optionsRef = useLatest(options);
const [state, setState] = useState<PadState>(DETACHED_STATE);
const canvasRef = useCallback<RefCallback<HTMLCanvasElement>>(
(canvas) => {
// Detach: tear the previous engine down completely.
if (engineRef.current) {
cleanupRef.current?.();
cleanupRef.current = null;
engineRef.current.destroy();
engineRef.current = null;
setState(DETACHED_STATE);
}
if (canvas) {
const { onBegin, onEnd, ...engineOptions } = optionsRef.current;
void onBegin;
void onEnd;
const engine = createSignatureEngine(canvas, engineOptions);
engineRef.current = engine;
// Edge-only subscription — this is the ONLY re-render source.
// Value-bail: no-op updates must not re-render (house rule).
const offChange = engine.onChange((e) =>
setState((prev) =>
prev.isEmpty === e.isEmpty &&
prev.strokeCount === e.strokeCount &&
prev.canUndo === e.canUndo &&
prev.canRedo === e.canRedo
? prev
: {
isEmpty: e.isEmpty,
strokeCount: e.strokeCount,
canUndo: e.canUndo,
canRedo: e.canRedo,
},
),
);
const offBegin = engine.onBegin(() => optionsRef.current.onBegin?.());
const offEnd = engine.onEnd(() => optionsRef.current.onEnd?.());
cleanupRef.current = () => {
offChange();
offBegin();
offEnd();
};
}
},
[optionsRef],
);
const clear = useCallback((): void => {
engineRef.current?.clear();
}, []);
const undo = useCallback((): void => {
engineRef.current?.undo();
}, []);
const redo = useCallback((): void => {
engineRef.current?.redo();
}, []);
const toPNG = useCallback(
(opts?: PNGExportOptions): Promise<{ dataURL: string; blob: Blob }> =>
engineRef.current ? engineRef.current.toPNG(opts) : emptyToPNG(opts),
[],
);
const toSVG = useCallback(
(opts?: SVGExportOptions): string =>
engineRef.current ? engineRef.current.toSVG(opts) : emptyToSVG(opts),
[],
);
const toJSON = useCallback(
(): SignatureData => (engineRef.current ? engineRef.current.toJSON() : emptySignatureData()),
[],
);
const fromJSON = useCallback((data: SignatureData): void => {
engineRef.current?.fromJSON(data);
}, []);
return {
canvasRef,
isEmpty: state.isEmpty,
strokeCount: state.strokeCount,
canUndo: state.canUndo,
canRedo: state.canRedo,
clear,
undo,
redo,
toPNG,
toSVG,
toJSON,
fromJSON,
};
}
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