Implement video filters

utils/parser.js

@@ -0,0 +1,175 @@
+/**
+ * @typedef GetOptions
+ * @property {string} [split] Characters to split on
+ * @property {string} [mode] "until" or "between"; choose where to get the content from
+ * @property {function} [transform] Transformation to apply to result before returning
+ */
+
+const tf = {
+	lc: s => s.toLowerCase()
+}
+
+class Parser {
+	constructor(string) {
+		this.string = string;
+		this.substore = [];
+		this.cursor = 0;
+		this.cursorStore = [];
+		this.mode = "until";
+		this.transform = s => s;
+		this.split = " ";
+	}
+
+	/**
+	 * Return all the remaining text from the buffer, without updating the cursor
+	 * @return {string}
+	 */
+	remaining() {
+		return this.string.slice(this.cursor);
+	}
+
+	/**
+	 * Have we reached the end of the string yet?
+	 * @return {boolean}
+	 */
+	hasRemaining() {
+		return this.cursor < this.string.length
+	}
+
+	/**
+	 * Get the next element from the buffer, either up to a token or between two tokens, and update the cursor.
+	 * @param {GetOptions} [options]
+	 * @returns {string}
+	 */
+	get(options = {}) {
+		["mode", "split", "transform"].forEach(o => {
+			if (!options[o]) options[o] = this[o];
+		});
+		if (options.mode == "until") {
+			let next = this.string.indexOf(options.split, this.cursor+options.split.length-1);
+			if (next == -1) {
+				let result = this.remaining();
+				this.cursor = this.string.length;
+				return result;
+			} else {
+				let result = this.string.slice(this.cursor, next);
+				this.cursor = next + options.split.length;
+				return options.transform(result);
+			}
+		} else if (options.mode == "between") {
+			let start = this.string.indexOf(options.split, this.cursor);
+			let end = this.string.indexOf(options.split, start+options.split.length);
+			let result = this.string.slice(start+options.split.length, end);
+			this.cursor = end + options.split.length;
+			return options.transform(result);
+		}
+	}
+
+	/**
+	 * Get a number of chars from the buffer.
+	 * @param {number} length Number of chars to get
+	 * @param {boolean} [move] Whether to update the cursor
+	 */
+	slice(length, move = false) {
+		let result = this.string.slice(this.cursor, this.cursor+length);
+		if (move) this.cursor += length;
+		return result;
+	}
+
+	/**
+	 * Repeatedly swallow a character.
+	 * @param {string} char
+	 */
+	swallow(char) {
+		let before = this.cursor;
+		while (this.string[this.cursor] == char) this.cursor++;
+		return this.cursor - before;
+	}
+
+	/**
+	 * Push the current cursor position to the store
+	 */
+	store() {
+		this.cursorStore.push(this.cursor);
+	}
+
+	/**
+	 * Pop the previous cursor position from the store
+	 */
+	restore() {
+		this.cursor = this.cursorStore.pop();
+	}
+
+	/**
+	 * Run a get operation, test against an input, return success or failure, and restore the cursor.
+	 * @param {string} value The value to test against
+	 * @param {object} options Options for get
+	 */
+	test(value, options) {
+		this.store();
+		let next = this.get(options);
+		let result = next == value;
+		this.restore();
+		return result;
+	}
+
+	/**
+	 * Run a get operation, test against an input, return success or failure, and restore the cursor on failure.
+	 * @param {string} value The value to test against
+	 * @param {object} options Options for get
+	 */
+	has(value, options) {
+		this.store();
+		let next = this.get(options);
+		let result = next == value;
+		if (!result) this.restore();
+		return result;
+	}
+
+	/**
+	 * Run a get operation, test against an input, and throw an error if it doesn't match.
+	 * @param {string} value
+	 * @param {GetOptions} [options]
+	 */
+	expect(value, options = {}) {
+		let next = this.get(options);
+		if (next != value) throw new Error("Expected "+value+", got "+next);
+	}
+
+	/**
+	 * Seek to or past the next occurance of the string.
+	 * @param {string} toFind
+	 * @param {{moveToMatch?: boolean, useEnd?: boolean}} options both default to false
+	 */
+	seek(toFind, options = {}) {
+		if (options.moveToMatch === undefined) options.moveToMatch = false
+		if (options.useEnd === undefined) options.useEnd = false
+		let index = this.string.indexOf(toFind, this.cursor)
+		if (index !== -1) {
+			index -= this.cursor
+			if (options.useEnd) index += toFind.length
+			if (options.moveToMatch) this.cursor += index
+		}
+		return index
+	}
+
+	/**
+	 * Replace the current string, adding the old one to the substore.
+	 * @param {string} string
+	 */
+	pushSubstore(string) {
+		this.substore.push({string: this.string, cursor: this.cursor, cursorStore: this.cursorStore})
+		this.string = string
+		this.cursor = 0
+		this.cursorStore = []
+	}
+
+	/**
+	 * Replace the current string with the first entry from the substore.
+	 */
+	popSubstore() {
+		Object.assign(this, this.substore.pop())
+	}
+}
+
+module.exports.Parser = Parser