Mini Shell

'use strict';
const stringWidth = require('string-width');
const stripAnsi = require('strip-ansi');
const ansiStyles = require('ansi-styles');

const ESCAPES = new Set([
	'\u001B',
	'\u009B'
]);

const END_CODE = 39;

const wrapAnsi = code => `${ESCAPES.values().next().value}[${code}m`;

// Calculate the length of words split on ' ', ignoring
// the extra characters added by ansi escape codes
const wordLengths = string => string.split(' ').map(character => stringWidth(character));

// Wrap a long word across multiple rows
// Ansi escape codes do not count towards length
const wrapWord = (rows, word, columns) => {
	const characters = [...word];

	let insideEscape = false;
	let visible = stringWidth(stripAnsi(rows[rows.length - 1]));

	for (const [index, character] of characters.entries()) {
		const characterLength = stringWidth(character);

		if (visible + characterLength <= columns) {
			rows[rows.length - 1] += character;
		} else {
			rows.push(character);
			visible = 0;
		}

		if (ESCAPES.has(character)) {
			insideEscape = true;
		} else if (insideEscape && character === 'm') {
			insideEscape = false;
			continue;
		}

		if (insideEscape) {
			continue;
		}

		visible += characterLength;

		if (visible === columns && index < characters.length - 1) {
			rows.push('');
			visible = 0;
		}
	}

	// It's possible that the last row we copy over is only
	// ansi escape characters, handle this edge-case
	if (!visible && rows[rows.length - 1].length > 0 && rows.length > 1) {
		rows[rows.length - 2] += rows.pop();
	}
};

// Trims spaces from a string ignoring invisible sequences
const stringVisibleTrimSpacesRight = str => {
	const words = str.split(' ');
	let last = words.length;

	while (last > 0) {
		if (stringWidth(words[last - 1]) > 0) {
			break;
		}

		last--;
	}

	if (last === words.length) {
		return str;
	}

	return words.slice(0, last).join(' ') + words.slice(last).join('');
};

// The wrap-ansi module can be invoked
// in either 'hard' or 'soft' wrap mode
//
// 'hard' will never allow a string to take up more
// than columns characters
//
// 'soft' allows long words to expand past the column length
const exec = (string, columns, options = {}) => {
	if (options.trim !== false && string.trim() === '') {
		return '';
	}

	let pre = '';
	let ret = '';
	let escapeCode;

	const lengths = wordLengths(string);
	let rows = [''];

	for (const [index, word] of string.split(' ').entries()) {
		if (options.trim !== false) {
			rows[rows.length - 1] = rows[rows.length - 1].trimLeft();
		}

		let rowLength = stringWidth(rows[rows.length - 1]);

		if (index !== 0) {
			if (rowLength >= columns && (options.wordWrap === false || options.trim === false)) {
				// If we start with a new word but the current row length equals the length of the columns, add a new row
				rows.push('');
				rowLength = 0;
			}

			if (rowLength > 0 || options.trim === false) {
				rows[rows.length - 1] += ' ';
				rowLength++;
			}
		}

		// In 'hard' wrap mode, the length of a line is
		// never allowed to extend past 'columns'
		if (options.hard && lengths[index] > columns) {
			const remainingColumns = (columns - rowLength);
			const breaksStartingThisLine = 1 + Math.floor((lengths[index] - remainingColumns - 1) / columns);
			const breaksStartingNextLine = Math.floor((lengths[index] - 1) / columns);
			if (breaksStartingNextLine < breaksStartingThisLine) {
				rows.push('');
			}

			wrapWord(rows, word, columns);
			continue;
		}

		if (rowLength + lengths[index] > columns && rowLength > 0 && lengths[index] > 0) {
			if (options.wordWrap === false && rowLength < columns) {
				wrapWord(rows, word, columns);
				continue;
			}

			rows.push('');
		}

		if (rowLength + lengths[index] > columns && options.wordWrap === false) {
			wrapWord(rows, word, columns);
			continue;
		}

		rows[rows.length - 1] += word;
	}

	if (options.trim !== false) {
		rows = rows.map(stringVisibleTrimSpacesRight);
	}

	pre = rows.join('\n');

	for (const [index, character] of [...pre].entries()) {
		ret += character;

		if (ESCAPES.has(character)) {
			const code = parseFloat(/\d[^m]*/.exec(pre.slice(index, index + 4)));
			escapeCode = code === END_CODE ? null : code;
		}

		const code = ansiStyles.codes.get(Number(escapeCode));

		if (escapeCode && code) {
			if (pre[index + 1] === '\n') {
				ret += wrapAnsi(code);
			} else if (character === '\n') {
				ret += wrapAnsi(escapeCode);
			}
		}
	}

	return ret;
};

// For each newline, invoke the method separately
module.exports = (string, columns, options) => {
	return String(string)
		.normalize()
		.split('\n')
		.map(line => exec(line, columns, options))
		.join('\n');
};