aws-ddk-core
Version:
The AWS DataOps Development Kit is an open source development framework for customers that build data workflows and modern data architecture on AWS.
237 lines (233 loc) • 9.25 kB
JavaScript
;
var identity = require('./nodes/identity.js');
const BREAK = Symbol('break visit');
const SKIP = Symbol('skip children');
const REMOVE = Symbol('remove node');
/**
* Apply a visitor to an AST node or document.
*
* Walks through the tree (depth-first) starting from `node`, calling a
* `visitor` function with three arguments:
* - `key`: For sequence values and map `Pair`, the node's index in the
* collection. Within a `Pair`, `'key'` or `'value'`, correspondingly.
* `null` for the root node.
* - `node`: The current node.
* - `path`: The ancestry of the current node.
*
* The return value of the visitor may be used to control the traversal:
* - `undefined` (default): Do nothing and continue
* - `visit.SKIP`: Do not visit the children of this node, continue with next
* sibling
* - `visit.BREAK`: Terminate traversal completely
* - `visit.REMOVE`: Remove the current node, then continue with the next one
* - `Node`: Replace the current node, then continue by visiting it
* - `number`: While iterating the items of a sequence or map, set the index
* of the next step. This is useful especially if the index of the current
* node has changed.
*
* If `visitor` is a single function, it will be called with all values
* encountered in the tree, including e.g. `null` values. Alternatively,
* separate visitor functions may be defined for each `Map`, `Pair`, `Seq`,
* `Alias` and `Scalar` node. To define the same visitor function for more than
* one node type, use the `Collection` (map and seq), `Value` (map, seq & scalar)
* and `Node` (alias, map, seq & scalar) targets. Of all these, only the most
* specific defined one will be used for each node.
*/
function visit(node, visitor) {
const visitor_ = initVisitor(visitor);
if (identity.isDocument(node)) {
const cd = visit_(null, node.contents, visitor_, Object.freeze([node]));
if (cd === REMOVE)
node.contents = null;
}
else
visit_(null, node, visitor_, Object.freeze([]));
}
// Without the `as symbol` casts, TS declares these in the `visit`
// namespace using `var`, but then complains about that because
// `unique symbol` must be `const`.
/** Terminate visit traversal completely */
visit.BREAK = BREAK;
/** Do not visit the children of the current node */
visit.SKIP = SKIP;
/** Remove the current node */
visit.REMOVE = REMOVE;
function visit_(key, node, visitor, path) {
const ctrl = callVisitor(key, node, visitor, path);
if (identity.isNode(ctrl) || identity.isPair(ctrl)) {
replaceNode(key, path, ctrl);
return visit_(key, ctrl, visitor, path);
}
if (typeof ctrl !== 'symbol') {
if (identity.isCollection(node)) {
path = Object.freeze(path.concat(node));
for (let i = 0; i < node.items.length; ++i) {
const ci = visit_(i, node.items[i], visitor, path);
if (typeof ci === 'number')
i = ci - 1;
else if (ci === BREAK)
return BREAK;
else if (ci === REMOVE) {
node.items.splice(i, 1);
i -= 1;
}
}
}
else if (identity.isPair(node)) {
path = Object.freeze(path.concat(node));
const ck = visit_('key', node.key, visitor, path);
if (ck === BREAK)
return BREAK;
else if (ck === REMOVE)
node.key = null;
const cv = visit_('value', node.value, visitor, path);
if (cv === BREAK)
return BREAK;
else if (cv === REMOVE)
node.value = null;
}
}
return ctrl;
}
/**
* Apply an async visitor to an AST node or document.
*
* Walks through the tree (depth-first) starting from `node`, calling a
* `visitor` function with three arguments:
* - `key`: For sequence values and map `Pair`, the node's index in the
* collection. Within a `Pair`, `'key'` or `'value'`, correspondingly.
* `null` for the root node.
* - `node`: The current node.
* - `path`: The ancestry of the current node.
*
* The return value of the visitor may be used to control the traversal:
* - `Promise`: Must resolve to one of the following values
* - `undefined` (default): Do nothing and continue
* - `visit.SKIP`: Do not visit the children of this node, continue with next
* sibling
* - `visit.BREAK`: Terminate traversal completely
* - `visit.REMOVE`: Remove the current node, then continue with the next one
* - `Node`: Replace the current node, then continue by visiting it
* - `number`: While iterating the items of a sequence or map, set the index
* of the next step. This is useful especially if the index of the current
* node has changed.
*
* If `visitor` is a single function, it will be called with all values
* encountered in the tree, including e.g. `null` values. Alternatively,
* separate visitor functions may be defined for each `Map`, `Pair`, `Seq`,
* `Alias` and `Scalar` node. To define the same visitor function for more than
* one node type, use the `Collection` (map and seq), `Value` (map, seq & scalar)
* and `Node` (alias, map, seq & scalar) targets. Of all these, only the most
* specific defined one will be used for each node.
*/
async function visitAsync(node, visitor) {
const visitor_ = initVisitor(visitor);
if (identity.isDocument(node)) {
const cd = await visitAsync_(null, node.contents, visitor_, Object.freeze([node]));
if (cd === REMOVE)
node.contents = null;
}
else
await visitAsync_(null, node, visitor_, Object.freeze([]));
}
// Without the `as symbol` casts, TS declares these in the `visit`
// namespace using `var`, but then complains about that because
// `unique symbol` must be `const`.
/** Terminate visit traversal completely */
visitAsync.BREAK = BREAK;
/** Do not visit the children of the current node */
visitAsync.SKIP = SKIP;
/** Remove the current node */
visitAsync.REMOVE = REMOVE;
async function visitAsync_(key, node, visitor, path) {
const ctrl = await callVisitor(key, node, visitor, path);
if (identity.isNode(ctrl) || identity.isPair(ctrl)) {
replaceNode(key, path, ctrl);
return visitAsync_(key, ctrl, visitor, path);
}
if (typeof ctrl !== 'symbol') {
if (identity.isCollection(node)) {
path = Object.freeze(path.concat(node));
for (let i = 0; i < node.items.length; ++i) {
const ci = await visitAsync_(i, node.items[i], visitor, path);
if (typeof ci === 'number')
i = ci - 1;
else if (ci === BREAK)
return BREAK;
else if (ci === REMOVE) {
node.items.splice(i, 1);
i -= 1;
}
}
}
else if (identity.isPair(node)) {
path = Object.freeze(path.concat(node));
const ck = await visitAsync_('key', node.key, visitor, path);
if (ck === BREAK)
return BREAK;
else if (ck === REMOVE)
node.key = null;
const cv = await visitAsync_('value', node.value, visitor, path);
if (cv === BREAK)
return BREAK;
else if (cv === REMOVE)
node.value = null;
}
}
return ctrl;
}
function initVisitor(visitor) {
if (typeof visitor === 'object' &&
(visitor.Collection || visitor.Node || visitor.Value)) {
return Object.assign({
Alias: visitor.Node,
Map: visitor.Node,
Scalar: visitor.Node,
Seq: visitor.Node
}, visitor.Value && {
Map: visitor.Value,
Scalar: visitor.Value,
Seq: visitor.Value
}, visitor.Collection && {
Map: visitor.Collection,
Seq: visitor.Collection
}, visitor);
}
return visitor;
}
function callVisitor(key, node, visitor, path) {
if (typeof visitor === 'function')
return visitor(key, node, path);
if (identity.isMap(node))
return visitor.Map?.(key, node, path);
if (identity.isSeq(node))
return visitor.Seq?.(key, node, path);
if (identity.isPair(node))
return visitor.Pair?.(key, node, path);
if (identity.isScalar(node))
return visitor.Scalar?.(key, node, path);
if (identity.isAlias(node))
return visitor.Alias?.(key, node, path);
return undefined;
}
function replaceNode(key, path, node) {
const parent = path[path.length - 1];
if (identity.isCollection(parent)) {
parent.items[key] = node;
}
else if (identity.isPair(parent)) {
if (key === 'key')
parent.key = node;
else
parent.value = node;
}
else if (identity.isDocument(parent)) {
parent.contents = node;
}
else {
const pt = identity.isAlias(parent) ? 'alias' : 'scalar';
throw new Error(`Cannot replace node with ${pt} parent`);
}
}
exports.visit = visit;
exports.visitAsync = visitAsync;