better-peg-tracer/lib/index.js

A better tracer for PEG.js

'use strict';

var pad = require("pad");
var chalk = Object.assign(require("chalk"), { enabled: true });
var defaultValue = require("default-value");

module.exports = function createBetterPegTracer(parsedString) {
	var currentLevel = 0;
	var lastWasFail = false;
	var parsedStringLines = parsedString.split("\n");
	var lastSeenRule = [];

	return {
		trace: function trace(event) {
			if (event.type === "rule.fail" || event.type === "rule.match") {
				currentLevel -= 1;
			}

			var ruleIndent = pad("", currentLevel * 4);
			var eventName = event.type.replace(/^rule\./, "");
			var isMultiline = parsedStringLines.length > 1;

			var startLine = event.location.start.line;
			var endLine = event.location.end.line;
			var startColumn = event.location.start.column;
			var endColumn = event.location.end.column;

			var firstLine = parsedStringLines[startLine - 1];
			var lastLine = parsedStringLines[endLine - 1];

			var affectedString = void 0,
			    color = void 0,
			    startPosition = void 0,
			    endPosition = void 0,
			    position = void 0;

			if (isMultiline) {
				startPosition = pad(4, startLine) + ":" + pad(2, startColumn);

				if (startLine !== endLine || startColumn !== endColumn) {
					endPosition = pad(4, endLine) + ":" + pad(2, endColumn);
				}
			} else {
				startPosition = startColumn;

				if (startColumn !== endColumn) {
					endPosition = endColumn;
				}
			}

			position = pad(8, startPosition) + "  " + chalk.white("│") + " " + pad(8, defaultValue(endPosition, ""));

			if (startLine === endLine) {
				if (startColumn === endColumn) {
					/* Not reading a range, but rather attempting to find a match from the current point. */
					if (event.location.start.offset < parsedString.length) {
						affectedString = chalk.gray(firstLine.slice(startColumn - 1) + "  ...");
					} else {
						affectedString = "";
					}
				} else {
					affectedString = firstLine.slice(startColumn - 1, endColumn - 1);
				}
			} else {
				affectedString = firstLine.slice(startColumn - 1) + "   ...   " + lastLine.slice(0, endColumn - 1);
			}

			if (event.type === "rule.enter") {
				lastSeenRule[currentLevel] = event.rule;
			}

			if (event.type === "rule.match") {
				color = chalk.green;
			} else if (event.type === "rule.fail") {
				color = chalk.red;
			} else {
				color = chalk.white;
			}

			var crumbs = lastSeenRule.slice(0, currentLevel).concat([color(event.rule)]);
			var limitedCrumbs = void 0;

			if (crumbs.length > 6) {
				limitedCrumbs = crumbs.slice(0, 2).concat(["... " + (crumbs.length - 5) + " hidden ..."]).concat(crumbs.slice(-3));
			} else {
				limitedCrumbs = crumbs;
			}

			var line = [position, pad(eventName, 5), chalk.gray(pad(limitedCrumbs.join(" -> "), "90")), affectedString].join(" " + chalk.white("│") + " ");

			process.stdout.write(color(line + "\n"));

			if (event.type === "rule.enter") {
				currentLevel += 1;
			}
		}
	};
};