| 1 | // Following http://www.w3.org/TR/css3-selectors/#nth-child-pseudo
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| 2 | // Whitespace as per https://www.w3.org/TR/selectors-3/#lex is " \t\r\n\f"
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| 3 | const whitespace = new Set([9, 10, 12, 13, 32]);
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| 4 | const ZERO = "0".charCodeAt(0);
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| 5 | const NINE = "9".charCodeAt(0);
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| 6 | /**
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| 7 | * Parses an expression.
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| 8 | *
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| 9 | * @throws An `Error` if parsing fails.
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| 10 | * @returns An array containing the integer step size and the integer offset of the nth rule.
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| 11 | * @example nthCheck.parse("2n+3"); // returns [2, 3]
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| 12 | */
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| 13 | export function parse(formula) {
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| 14 | formula = formula.trim().toLowerCase();
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| 15 | if (formula === "even") {
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| 16 | return [2, 0];
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| 17 | }
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| 18 | else if (formula === "odd") {
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| 19 | return [2, 1];
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| 20 | }
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| 21 | // Parse [ ['-'|'+']? INTEGER? {N} [ S* ['-'|'+'] S* INTEGER ]?
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| 22 | let idx = 0;
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| 23 | let a = 0;
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| 24 | let sign = readSign();
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| 25 | let number = readNumber();
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| 26 | if (idx < formula.length && formula.charAt(idx) === "n") {
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| 27 | idx++;
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| 28 | a = sign * (number !== null && number !== void 0 ? number : 1);
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| 29 | skipWhitespace();
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| 30 | if (idx < formula.length) {
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| 31 | sign = readSign();
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| 32 | skipWhitespace();
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| 33 | number = readNumber();
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| 34 | }
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| 35 | else {
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| 36 | sign = number = 0;
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| 37 | }
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| 38 | }
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| 39 | // Throw if there is anything else
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| 40 | if (number === null || idx < formula.length) {
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| 41 | throw new Error(`n-th rule couldn't be parsed ('${formula}')`);
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| 42 | }
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| 43 | return [a, sign * number];
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| 44 | function readSign() {
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| 45 | if (formula.charAt(idx) === "-") {
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| 46 | idx++;
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| 47 | return -1;
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| 48 | }
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| 49 | if (formula.charAt(idx) === "+") {
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| 50 | idx++;
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| 51 | }
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| 52 | return 1;
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| 53 | }
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| 54 | function readNumber() {
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| 55 | const start = idx;
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| 56 | let value = 0;
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| 57 | while (idx < formula.length &&
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| 58 | formula.charCodeAt(idx) >= ZERO &&
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| 59 | formula.charCodeAt(idx) <= NINE) {
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| 60 | value = value * 10 + (formula.charCodeAt(idx) - ZERO);
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| 61 | idx++;
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| 62 | }
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| 63 | // Return `null` if we didn't read anything.
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| 64 | return idx === start ? null : value;
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| 65 | }
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| 66 | function skipWhitespace() {
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| 67 | while (idx < formula.length &&
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| 68 | whitespace.has(formula.charCodeAt(idx))) {
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| 69 | idx++;
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| 70 | }
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| 71 | }
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| 72 | }
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| 73 | //# sourceMappingURL=parse.js.map |
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