1 files changed, 88 insertions, 0 deletions
diff --git a/packages/integrations/preact/src/signals.ts b/packages/integrations/preact/src/signals.ts
new file mode 100644
index 000000000..88a50327a
--- /dev/null
+++ b/packages/integrations/preact/src/signals.ts
@@ -0,0 +1,88 @@
+import type { Context } from './context.js';
+import { incrementId } from './context.js';
+import type {
+	ArrayObjectMapping,
+	AstroPreactAttrs,
+	PropNameToSignalMap,
+	SignalLike,
+	SignalToKeyOrIndexMap,
+	Signals,
+} from './types.js';
+
+function isSignal(x: any): x is SignalLike {
+	return x != null && typeof x === 'object' && typeof x.peek === 'function' && 'value' in x;
+}
+
+export function restoreSignalsOnProps(ctx: Context, props: Record<string, any>) {
+	// Restore signal props that were mutated for serialization
+	let propMap: PropNameToSignalMap;
+	if (ctx.propsToSignals.has(props)) {
+		propMap = ctx.propsToSignals.get(props)!;
+	} else {
+		propMap = new Map();
+		ctx.propsToSignals.set(props, propMap);
+	}
+	for (const [key, signal] of propMap) {
+		props[key] = signal;
+	}
+	return propMap;
+}
+
+export function serializeSignals(
+	ctx: Context,
+	props: Record<string, any>,
+	attrs: AstroPreactAttrs,
+	map: PropNameToSignalMap,
+) {
+	// Check for signals
+	const signals: Signals = {};
+	for (const [key, value] of Object.entries(props)) {
+		const isPropArray = Array.isArray(value);
+		// `typeof null` is 'object' in JS, so we need to check for `null` specifically
+		const isPropObject =
+			!isSignal(value) && typeof props[key] === 'object' && props[key] !== null && !isPropArray;
+
+		if (isPropObject || isPropArray) {
+			const values = isPropObject ? Object.keys(props[key]) : value;
+			values.forEach((valueKey: number | string, valueIndex: number) => {
+				const signal = isPropObject ? props[key][valueKey] : valueKey;
+				if (isSignal(signal)) {
+					const keyOrIndex = isPropObject ? valueKey.toString() : valueIndex;
+
+					props[key] = isPropObject
+						? Object.assign({}, props[key], { [keyOrIndex]: signal.peek() })
+						: props[key].map((v: SignalLike, i: number) =>
+								i === valueIndex ? [signal.peek(), i] : v,
+							);
+
+					const currentMap = (map.get(key) || []) as SignalToKeyOrIndexMap;
+					map.set(key, [...currentMap, [signal, keyOrIndex]]);
+
+					const currentSignals = (signals[key] || []) as ArrayObjectMapping;
+					signals[key] = [...currentSignals, [getSignalId(ctx, signal), keyOrIndex]];
+				}
+			});
+		} else if (isSignal(value)) {
+			// Set the value to the current signal value
+			// This mutates the props on purpose, so that it will be serialized correct.
+			props[key] = value.peek();
+			map.set(key, value);
+
+			signals[key] = getSignalId(ctx, value);
+		}
+	}
+
+	if (Object.keys(signals).length) {
+		attrs['data-preact-signals'] = JSON.stringify(signals);
+	}
+}
+
+function getSignalId(ctx: Context, item: SignalLike) {
+	let id = ctx.signals.get(item);
+	if (!id) {
+		id = incrementId(ctx);
+		ctx.signals.set(item, id);
+	}
+
+	return id;
+}