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findGraphRoots.js
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Mon, Feb 10, 12:45

findGraphRoots.js
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/*
MIT License http://www.opensource.org/licenses/mit-license.php
Author Tobias Koppers @sokra
*/
"use strict";
const NO_MARKER = 0;
const IN_PROGRESS_MARKER = 1;
const DONE_MARKER = 2;
const DONE_MAYBE_ROOT_CYCLE_MARKER = 3;
const DONE_AND_ROOT_MARKER = 4;
/**
* @template T
*/
class Node {
/**
* @param {T} item the value of the node
*/
constructor(item) {
this.item = item;
/** @type {Set<Node<T>>} */
this.dependencies = new Set();
this.marker = NO_MARKER;
/** @type {Cycle<T> | undefined} */
this.cycle = undefined;
this.incoming = 0;
}
}
/**
* @template T
*/
class Cycle {
constructor() {
/** @type {Set<Node<T>>} */
this.nodes = new Set();
}
}
/**
* @template T
* @typedef {Object} StackEntry
* @property {Node<T>} node
* @property {Node<T>[]} openEdges
*/
/**
* @template T
* @param {Iterable<T>} items list of items
* @param {function(T): Iterable<T>} getDependencies function to get dependencies of an item (items that are not in list are ignored)
* @returns {Iterable<T>} graph roots of the items
*/
module.exports = (items, getDependencies) => {
/** @type {Map<T, Node<T>>} */
const itemToNode = new Map();
for (const item of items) {
const node = new Node(item);
itemToNode.set(item, node);
}
// early exit when there is only a single item
if (itemToNode.size <= 1) return items;
// grab all the dependencies
for (const node of itemToNode.values()) {
for (const dep of getDependencies(node.item)) {
const depNode = itemToNode.get(dep);
if (depNode !== undefined) {
node.dependencies.add(depNode);
}
}
}
// Set of current root modules
// items will be removed if a new reference to it has been found
/** @type {Set<Node<T>>} */
const roots = new Set();
// Set of current cycles without references to it
// cycles will be removed if a new reference to it has been found
// that is not part of the cycle
/** @type {Set<Cycle<T>>} */
const rootCycles = new Set();
// For all non-marked nodes
for (const selectedNode of itemToNode.values()) {
if (selectedNode.marker === NO_MARKER) {
// deep-walk all referenced modules
// in a non-recursive way
// start by entering the selected node
selectedNode.marker = IN_PROGRESS_MARKER;
// keep a stack to avoid recursive walk
/** @type {StackEntry<T>[]} */
const stack = [
{
node: selectedNode,
openEdges: Array.from(selectedNode.dependencies)
}
];
// process the top item until stack is empty
while (stack.length > 0) {
const topOfStack = stack[stack.length - 1];
// Are there still edges unprocessed in the current node?
if (topOfStack.openEdges.length > 0) {
// Process one dependency
const dependency = topOfStack.openEdges.pop();
switch (dependency.marker) {
case NO_MARKER:
// dependency has not be visited yet
// mark it as in-progress and recurse
stack.push({
node: dependency,
openEdges: Array.from(dependency.dependencies)
});
dependency.marker = IN_PROGRESS_MARKER;
break;
case IN_PROGRESS_MARKER: {
// It's a in-progress cycle
let cycle = dependency.cycle;
if (!cycle) {
cycle = new Cycle();
cycle.nodes.add(dependency);
dependency.cycle = cycle;
}
// set cycle property for each node in the cycle
// if nodes are already part of a cycle
// we merge the cycles to a shared cycle
for (
let i = stack.length - 1;
stack[i].node !== dependency;
i--
) {
const node = stack[i].node;
if (node.cycle) {
if (node.cycle !== cycle) {
// merge cycles
for (const cycleNode of node.cycle.nodes) {
cycleNode.cycle = cycle;
cycle.nodes.add(cycleNode);
}
}
} else {
node.cycle = cycle;
cycle.nodes.add(node);
}
}
// don't recurse into dependencies
// these are already on the stack
break;
}
case DONE_AND_ROOT_MARKER:
// This node has be visited yet and is currently a root node
// But as this is a new reference to the node
// it's not really a root
// so we have to convert it to a normal node
dependency.marker = DONE_MARKER;
roots.delete(dependency);
break;
case DONE_MAYBE_ROOT_CYCLE_MARKER:
// This node has be visited yet and
// is maybe currently part of a completed root cycle
// we found a new reference to the cycle
// so it's not really a root cycle
// remove the cycle from the root cycles
// and convert it to a normal node
rootCycles.delete(dependency.cycle);
dependency.marker = DONE_MARKER;
break;
// DONE_MARKER: nothing to do, don't recurse into dependencies
}
} else {
// All dependencies of the current node has been visited
// we leave the node
stack.pop();
topOfStack.node.marker = DONE_MARKER;
}
}
const cycle = selectedNode.cycle;
if (cycle) {
for (const node of cycle.nodes) {
node.marker = DONE_MAYBE_ROOT_CYCLE_MARKER;
}
rootCycles.add(cycle);
} else {
selectedNode.marker = DONE_AND_ROOT_MARKER;
roots.add(selectedNode);
}
}
}
// Extract roots from root cycles
// We take the nodes with most incoming edges
// inside of the cycle
for (const cycle of rootCycles) {
let max = 0;
/** @type {Set<Node<T>>} */
const cycleRoots = new Set();
const nodes = cycle.nodes;
for (const node of nodes) {
for (const dep of node.dependencies) {
if (nodes.has(dep)) {
dep.incoming++;
if (dep.incoming < max) continue;
if (dep.incoming > max) {
cycleRoots.clear();
max = dep.incoming;
}
cycleRoots.add(dep);
}
}
}
for (const cycleRoot of cycleRoots) {
roots.add(cycleRoot);
}
}
// When roots were found, return them
if (roots.size > 0) {
return Array.from(roots, r => r.item);
} else {
throw new Error("Implementation of findGraphRoots is broken");
}
};

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