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 {
				// WHY: A `\n` counts as the last column of its own line here, so a
				// `this.pos` sitting on one is already on that line. Retreating
				// therefore crosses only the newlines at or after `pos` and strictly
				// before `this.pos` — the newline at `this.pos` is not one of them.
				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;