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import { BaseNode } from "estree";
type WalkerContext = {
skip: () => void;
remove: () => void;
replace: (node: BaseNode) => void;
};
type WalkerHandler = (
this: WalkerContext,
node: BaseNode,
parent: BaseNode,
key: string,
index: number
) => void
type Walker = {
enter?: WalkerHandler;
leave?: WalkerHandler;
}
export function walk(ast: BaseNode, { enter, leave }: Walker) {
return visit(ast, null, enter, leave);
}
let should_skip = false;
let should_remove = false;
let replacement: BaseNode = null;
const context: WalkerContext = {
skip: () => should_skip = true,
remove: () => should_remove = true,
replace: (node: BaseNode) => replacement = node
};
function replace(parent: any, prop: string, index: number, node: BaseNode) {
if (parent) {
if (index !== null) {
parent[prop][index] = node;
} else {
parent[prop] = node;
}
}
}
function remove(parent: any, prop: string, index: number) {
if (parent) {
if (index !== null) {
parent[prop].splice(index, 1);
} else {
delete parent[prop];
}
}
}
function visit(
node: BaseNode,
parent: BaseNode,
enter: WalkerHandler,
leave: WalkerHandler,
prop?: string,
index?: number
) {
if (node) {
if (enter) {
const _should_skip = should_skip;
const _should_remove = should_remove;
const _replacement = replacement;
should_skip = false;
should_remove = false;
replacement = null;
enter.call(context, node, parent, prop, index);
if (replacement) {
node = replacement;
replace(parent, prop, index, node);
}
if (should_remove) {
remove(parent, prop, index);
}
const skipped = should_skip;
const removed = should_remove;
should_skip = _should_skip;
should_remove = _should_remove;
replacement = _replacement;
if (skipped) return node;
if (removed) return null;
}
for (const key in node) {
const value = (node as any)[key];
if (typeof value !== 'object') {
continue;
}
else if (Array.isArray(value)) {
for (let j = 0, k = 0; j < value.length; j += 1, k += 1) {
if (value[j] !== null && typeof value[j].type === 'string') {
if (!visit(value[j], node, enter, leave, key, k)) {
// removed
j--;
}
}
}
}
else if (value !== null && typeof value.type === 'string') {
visit(value, node, enter, leave, key, null);
}
}
if (leave) {
const _replacement = replacement;
const _should_remove = should_remove;
replacement = null;
should_remove = false;
leave.call(context, node, parent, prop, index);
if (replacement) {
node = replacement;
replace(parent, prop, index, node);
}
if (should_remove) {
remove(parent, prop, index);
}
const removed = should_remove;
replacement = _replacement;
should_remove = _should_remove;
if (removed) return null;
}
}
return node;
}
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