node-nix-parser/src/reorder-operator-expressions/index.js

'use strict';

const util = require("util");

const generateOperatorMap = require("./generate-operator-map");
const findOperatorSequences = require("./find-operator-sequences");
const addPrecedences = require("./add-precedences");

module.exports = function reorderOperatorExpressions(tree, operators) {
	let operatorsWithPrecedence = addPrecedences(operators);
	let operatorMap = generateOperatorMap(operatorsWithPrecedence);

	let sequenceResults = findOperatorSequences(tree, operatorMap);
	let modifiedOperands = sequenceResults.operands.slice();
	let relocatedOperands = new Array(modifiedOperands.length);

	function lookupOperandIndex(i) {
		if (relocatedOperands[i] != null) {
			// FIXME: This shouldn't be recursive; instead, relocation pointers should be updated after a cascading relocation.
			return lookupOperandIndex(relocatedOperands[i]);
		} else {
			return i;
		}
	}

	function getOperand(i) {
		let index = lookupOperandIndex(i);
		let operand = modifiedOperands[lookupOperandIndex(i)];

		return modifiedOperands[lookupOperandIndex(i)];
	}

	operatorsWithPrecedence.forEach((operator) => {
		let currentPrecedence = operator.precedence;
		let sequences = sequenceResults.operatorSequenceMap[currentPrecedence];

		if (sequences != null) {
			sequences.forEach((sequence, sequenceIndex) => {
				let untilIndex = sequence.firstIndex + sequence.length;
				let associativity = sequence.associativity;

				let root, current;

				function addOperator(index) {
					let newNode = {
						type: "operatorExpression",
						operator: sequenceResults.operators[index],
						right: (associativity !== "right") ? getOperand(index + 1) : undefined,
						left: (associativity !== "left" && !operator.unary) ? getOperand(index) : undefined
					}

					if (root == null) {
						root = newNode;
					} else {
						if (associativity === "left") {
							current.left = newNode;
						} else if (associativity === "right") {
							current.right = newNode;
						}
					}

					current = newNode;
				}

				if (associativity === "none") {
					/* Cannot occur more than once... */
					if (sequence.length > 1) {
						// FIXME: This does not yet detect multiple occurrences in different sequences...
						throw new Error(`Operators in series '${operators[sequence.precedence].join(", ")}' may only occur once in a series of operator expressions, but occurred ${sequence.length} times`);
					} else {
						addOperator(sequence.firstIndex);
					}
				} else {
					if (associativity === "left") {
						for (let i = untilIndex - 1; i >= sequence.firstIndex; i--) {
							addOperator(i);
						}

						current.left = getOperand(sequence.firstIndex);
					} else if (associativity === "right") {
						for (let i = sequence.firstIndex; i < untilIndex; i++) {
							addOperator(i);
						}

						current.right = getOperand(untilIndex);
					}
				}

				let newLocation = lookupOperandIndex(sequence.firstIndex);
				modifiedOperands[newLocation] = root;

				for (let i = sequence.firstIndex; i < untilIndex; i++) {
					modifiedOperands[i + 1] = null;
					relocatedOperands[i + 1] = newLocation;
				}

				// console.log(`MODIFIED OPERANDS AFTER PRECEDENCE LEVEL ${currentPrecedence} (pos ${sequence.firstIndex} - ${sequence.firstIndex + sequence.length}):`, modifiedOperands.map((modOp) => {
				// 	return (modOp == null) ? "null" : `<${modOp.type} ${modOp.identifier || modOp.value || modOp.operator}>`;
				// }).join(", "))
			});
		}
	});

	return modifiedOperands[0];
};