webpack/lib/util/LocConverter.js

Packs ECMAScript/CommonJs/AMD modules for the browser. Allows you to split your codebase into multiple bundles, which can be loaded on demand. Supports loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Alexander Akait @alexander-akait
*/

"use strict";

class LocConverter {
	/**
	 * Creates an instance of LocConverter.
	 * @param {string} input input
	 */
	constructor(input) {
		/** @type {string} */
		this._input = input;
		/** @type {number} */
		this.line = 1;
		/** @type {number} */
		this.column = 0;
		/** @type {number} */
		this.pos = 0;
		// Next `\n` at/after `pos` (`input.length` if none, -1 = unknown);
		// when >= pos there is no `\n` in [pos, _nextNewline).
		/** @type {number} */
		this._nextNewline = -1;
	}

	/**
	 * Returns location converter.
	 * @param {number} pos position
	 * @returns {LocConverter} location converter
	 */
	get(pos) {
		if (this.pos !== pos) {
			const input = this._input;
			if (this.pos < pos) {
				// Advance: O(1) on the same line via the cached next-newline offset,
				// otherwise hop newline-to-newline with native indexOf — each re-scan
				// is bounded by one line, amortized O(1)/byte for monotone callers.
				let next = this._nextNewline;
				if (next < this.pos) {
					next = input.indexOf("\n", this.pos);
					if (next === -1) next = input.length;
				}
				if (pos <= next) {
					this.column += pos - this.pos;
				} else {
					let line = this.line;
					let last = next;
					for (;;) {
						line++;
						next = input.indexOf("\n", last + 1);
						if (next === -1) next = input.length;
						// `next >= input.length` guards termination for out-of-range `pos`.
						if (pos <= next || next >= input.length) break;
						last = next;
					}
					this.line = line;
					this.column = pos - last - 1;
				}
				this._nextNewline = next;
			} else if (this.line === 1) {
				// Retreat on line 1: no `\n` precedes `pos`, the cache stays valid.
				this.column = pos;
			} else {
				// Retreat: count newlines crossed in (pos, this.pos), i.e.
				// exclude the newline at `this.pos` itself. By convention a
				// `\n` is the last column of its line, so when `this.pos`
				// sits on one we're already on the line containing it; only
				// newlines strictly **before** `this.pos` and at-or-after
				// `pos` represent crossed line boundaries. The smallest
				// crossed one is the next newline after the new position.
				let i = input.lastIndexOf("\n", this.pos - 1);
				while (i >= pos) {
					this._nextNewline = i;
					this.line--;
					i = i > 0 ? input.lastIndexOf("\n", i - 1) : -1;
				}
				this.column = i === -1 ? pos : pos - i - 1;
			}
			this.pos = pos;
		}
		return this;
	}
}

module.exports = LocConverter;