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Filename : reducePlan.js
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/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/
"use strict";

const path = require("path");

/**
 * @template T
 * @typedef {Object} TreeNode
 * @property {string} filePath
 * @property {TreeNode} parent
 * @property {TreeNode[]} children
 * @property {number} entries
 * @property {boolean} active
 * @property {T[] | T | undefined} value
 */

/**
 * @template T
 * @param {Map<string, T[] | T} plan
 * @param {number} limit
 * @returns {Map<string, Map<T, string>>} the new plan
 */
module.exports = (plan, limit) => {
	const treeMap = new Map();
	// Convert to tree
	for (const [filePath, value] of plan) {
		treeMap.set(filePath, {
			filePath,
			parent: undefined,
			children: undefined,
			entries: 1,
			active: true,
			value
		});
	}
	let currentCount = treeMap.size;
	// Create parents and calculate sum of entries
	for (const node of treeMap.values()) {
		const parentPath = path.dirname(node.filePath);
		if (parentPath !== node.filePath) {
			let parent = treeMap.get(parentPath);
			if (parent === undefined) {
				parent = {
					filePath: parentPath,
					parent: undefined,
					children: [node],
					entries: node.entries,
					active: false,
					value: undefined
				};
				treeMap.set(parentPath, parent);
				node.parent = parent;
			} else {
				node.parent = parent;
				if (parent.children === undefined) {
					parent.children = [node];
				} else {
					parent.children.push(node);
				}
				do {
					parent.entries += node.entries;
					parent = parent.parent;
				} while (parent);
			}
		}
	}
	// Reduce until limit reached
	while (currentCount > limit) {
		// Select node that helps reaching the limit most effectively without overmerging
		const overLimit = currentCount - limit;
		let bestNode = undefined;
		let bestCost = Infinity;
		for (const node of treeMap.values()) {
			if (node.entries <= 1 || !node.children || !node.parent) continue;
			if (node.children.length === 0) continue;
			if (node.children.length === 1 && !node.value) continue;
			// Try to select the node with has just a bit more entries than we need to reduce
			// When just a bit more is over 30% over the limit,
			// also consider just a bit less entries then we need to reduce
			const cost =
				node.entries - 1 >= overLimit
					? node.entries - 1 - overLimit
					: overLimit - node.entries + 1 + limit * 0.3;
			if (cost < bestCost) {
				bestNode = node;
				bestCost = cost;
			}
		}
		if (!bestNode) break;
		// Merge all children
		const reduction = bestNode.entries - 1;
		bestNode.active = true;
		bestNode.entries = 1;
		currentCount -= reduction;
		let parent = bestNode.parent;
		while (parent) {
			parent.entries -= reduction;
			parent = parent.parent;
		}
		const queue = new Set(bestNode.children);
		for (const node of queue) {
			node.active = false;
			node.entries = 0;
			if (node.children) {
				for (const child of node.children) queue.add(child);
			}
		}
	}
	// Write down new plan
	const newPlan = new Map();
	for (const rootNode of treeMap.values()) {
		if (!rootNode.active) continue;
		const map = new Map();
		const queue = new Set([rootNode]);
		for (const node of queue) {
			if (node.active && node !== rootNode) continue;
			if (node.value) {
				if (Array.isArray(node.value)) {
					for (const item of node.value) {
						map.set(item, node.filePath);
					}
				} else {
					map.set(node.value, node.filePath);
				}
			}
			if (node.children) {
				for (const child of node.children) {
					queue.add(child);
				}
			}
		}
		newPlan.set(rootNode.filePath, map);
	}
	return newPlan;
};