131 lines
2.9 KiB
JavaScript
131 lines
2.9 KiB
JavaScript
'use strict';
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/**
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* A streaming, character code-based string reader
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*/
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class StreamReader {
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constructor(string, start, end) {
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if (end == null && typeof string === 'string') {
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end = string.length;
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}
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this.string = string;
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this.pos = this.start = start || 0;
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this.end = end;
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}
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/**
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* Returns true only if the stream is at the end of the file.
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* @returns {Boolean}
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*/
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eof() {
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return this.pos >= this.end;
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}
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/**
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* Creates a new stream instance which is limited to given `start` and `end`
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* range. E.g. its `eof()` method will look at `end` property, not actual
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* stream end
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* @param {Point} start
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* @param {Point} end
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* @return {StreamReader}
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*/
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limit(start, end) {
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return new this.constructor(this.string, start, end);
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}
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/**
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* Returns the next character code in the stream without advancing it.
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* Will return NaN at the end of the file.
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* @returns {Number}
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*/
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peek() {
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return this.string.charCodeAt(this.pos);
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}
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/**
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* Returns the next character in the stream and advances it.
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* Also returns <code>undefined</code> when no more characters are available.
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* @returns {Number}
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*/
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next() {
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if (this.pos < this.string.length) {
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return this.string.charCodeAt(this.pos++);
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}
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}
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/**
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* `match` can be a character code or a function that takes a character code
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* and returns a boolean. If the next character in the stream 'matches'
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* the given argument, it is consumed and returned.
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* Otherwise, `false` is returned.
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* @param {Number|Function} match
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* @returns {Boolean}
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*/
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eat(match) {
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const ch = this.peek();
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const ok = typeof match === 'function' ? match(ch) : ch === match;
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if (ok) {
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this.next();
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}
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return ok;
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}
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/**
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* Repeatedly calls <code>eat</code> with the given argument, until it
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* fails. Returns <code>true</code> if any characters were eaten.
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* @param {Object} match
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* @returns {Boolean}
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*/
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eatWhile(match) {
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const start = this.pos;
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while (!this.eof() && this.eat(match)) {}
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return this.pos !== start;
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}
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/**
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* Backs up the stream n characters. Backing it up further than the
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* start of the current token will cause things to break, so be careful.
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* @param {Number} n
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*/
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backUp(n) {
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this.pos -= (n || 1);
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}
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/**
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* Get the string between the start of the current token and the
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* current stream position.
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* @returns {String}
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*/
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current() {
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return this.substring(this.start, this.pos);
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}
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/**
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* Returns substring for given range
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* @param {Number} start
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* @param {Number} [end]
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* @return {String}
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*/
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substring(start, end) {
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return this.string.slice(start, end);
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}
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/**
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* Creates error object with current stream state
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* @param {String} message
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* @return {Error}
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*/
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error(message) {
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const err = new Error(`${message} at char ${this.pos + 1}`);
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err.originalMessage = message;
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err.pos = this.pos;
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err.string = this.string;
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return err;
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}
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}
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module.exports = StreamReader;
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