node-nix-parser/src/reorder-operator-expressions/find-operator-sequences.js

'use strict';

const util = require("util");

module.exports = function findOperatorSequences(tree, operatorMap) {
	let current = tree;
	let currentIndex = 0;
	let currentSequence;

	let operators = [];
	let operands = [];
	let operatorSequences = [];
	let operatorSequenceMap = {};

	function storeCurrentOperatorSequence() {
		operatorSequences.push(currentSequence);

		if (operatorSequenceMap[currentSequence.precedence] == null) {
			operatorSequenceMap[currentSequence.precedence] = [];
		}

		operatorSequenceMap[currentSequence.precedence].push(currentSequence);
	}

	while (current != null) {
		operators.push(current.operator);

		if (current.left != null) {
			operands.push(current.left);
		} else {
			/* Unary prefix operator */
			operands.push(null);
		}

		if (operatorMap[current.operator] == null) {
			throw new Error(`Encountered unknown '${current.operator}' operator`);
		}

		let associativity = operatorMap[current.operator].associativity;
		let precedence = operatorMap[current.operator].precedence;

		if (currentSequence != null && precedence === currentSequence.precedence) {
			/* Next operator in the same sequence. */
			currentSequence.length += 1;
		} else {
			if (currentSequence != null) {
				/* We were previously working on a different operator. */
				storeCurrentOperatorSequence();
			}

			currentSequence = {
				precedence: precedence,
				associativity: associativity,
				length: 1,
				firstIndex: currentIndex
			}
		}

		if (current.right == null) {
			throw new Error("An error occurred; encountered a `null` right operand, but this should never happen");
		} else {
			if (current.right.type === "operatorExpression") {
				current = current.right;
				currentIndex += 1;
			} else {
				/* Store the very last operand. */
				operands.push(current.right);
				break;
			}
		}
	}

	/* Store the very last sequence we were still working on. */
	storeCurrentOperatorSequence();

	return {
		operators,
		operands,
		operatorSequences,
		operatorSequenceMap
	}
};