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node_modules/preact/compat/src/suspense-list.js

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+import { Component, toChildArray } from 'preact';
+import { suspended } from './suspense.js';
+
+// Indexes to linked list nodes (nodes are stored as arrays to save bytes).
+const SUSPENDED_COUNT = 0;
+const RESOLVED_COUNT = 1;
+const NEXT_NODE = 2;
+
+// Having custom inheritance instead of a class here saves a lot of bytes.
+export function SuspenseList() {
+	this._next = null;
+	this._map = null;
+}
+
+// Mark one of child's earlier suspensions as resolved.
+// Some pending callbacks may become callable due to this
+// (e.g. the last suspended descendant gets resolved when
+// revealOrder === 'together'). Process those callbacks as well.
+const resolve = (list, child, node) => {
+	if (++node[RESOLVED_COUNT] === node[SUSPENDED_COUNT]) {
+		// The number a child (or any of its descendants) has been suspended
+		// matches the number of times it's been resolved. Therefore we
+		// mark the child as completely resolved by deleting it from ._map.
+		// This is used to figure out when *all* children have been completely
+		// resolved when revealOrder is 'together'.
+		list._map.delete(child);
+	}
+
+	// If revealOrder is falsy then we can do an early exit, as the
+	// callbacks won't get queued in the node anyway.
+	// If revealOrder is 'together' then also do an early exit
+	// if all suspended descendants have not yet been resolved.
+	if (
+		!list.props.revealOrder ||
+		(list.props.revealOrder[0] === 't' && list._map.size)
+	) {
+		return;
+	}
+
+	// Walk the currently suspended children in order, calling their
+	// stored callbacks on the way. Stop if we encounter a child that
+	// has not been completely resolved yet.
+	node = list._next;
+	while (node) {
+		while (node.length > 3) {
+			node.pop()();
+		}
+		if (node[RESOLVED_COUNT] < node[SUSPENDED_COUNT]) {
+			break;
+		}
+		list._next = node = node[NEXT_NODE];
+	}
+};
+
+// Things we do here to save some bytes but are not proper JS inheritance:
+// - call `new Component()` as the prototype
+// - do not set `Suspense.prototype.constructor` to `Suspense`
+SuspenseList.prototype = new Component();
+
+SuspenseList.prototype._suspended = function (child) {
+	const list = this;
+	const delegated = suspended(list._vnode);
+
+	let node = list._map.get(child);
+	node[SUSPENDED_COUNT]++;
+
+	return unsuspend => {
+		const wrappedUnsuspend = () => {
+			if (!list.props.revealOrder) {
+				// Special case the undefined (falsy) revealOrder, as there
+				// is no need to coordinate a specific order or unsuspends.
+				unsuspend();
+			} else {
+				node.push(unsuspend);
+				resolve(list, child, node);
+			}
+		};
+		if (delegated) {
+			delegated(wrappedUnsuspend);
+		} else {
+			wrappedUnsuspend();
+		}
+	};
+};
+
+SuspenseList.prototype.render = function (props) {
+	this._next = null;
+	this._map = new Map();
+
+	const children = toChildArray(props.children);
+	if (props.revealOrder && props.revealOrder[0] === 'b') {
+		// If order === 'backwards' (or, well, anything starting with a 'b')
+		// then flip the child list around so that the last child will be
+		// the first in the linked list.
+		children.reverse();
+	}
+	// Build the linked list. Iterate through the children in reverse order
+	// so that `_next` points to the first linked list node to be resolved.
+	for (let i = children.length; i--; ) {
+		// Create a new linked list node as an array of form:
+		// 	[suspended_count, resolved_count, next_node]
+		// where suspended_count and resolved_count are numeric counters for
+		// keeping track how many times a node has been suspended and resolved.
+		//
+		// Note that suspended_count starts from 1 instead of 0, so we can block
+		// processing callbacks until componentDidMount has been called. In a sense
+		// node is suspended at least until componentDidMount gets called!
+		//
+		// Pending callbacks are added to the end of the node:
+		// 	[suspended_count, resolved_count, next_node, callback_0, callback_1, ...]
+		this._map.set(children[i], (this._next = [1, 0, this._next]));
+	}
+	return props.children;
+};
+
+SuspenseList.prototype.componentDidUpdate =
+	SuspenseList.prototype.componentDidMount = function () {
+		// Iterate through all children after mounting for two reasons:
+		// 1. As each node[SUSPENDED_COUNT] starts from 1, this iteration increases
+		//    each node[RELEASED_COUNT] by 1, therefore balancing the counters.
+		//    The nodes can now be completely consumed from the linked list.
+		// 2. Handle nodes that might have gotten resolved between render and
+		//    componentDidMount.
+		this._map.forEach((node, child) => {
+			resolve(this, child, node);
+		});
+	};