moment-of-symmetry/dist/src/notation.js

Moment of Symmetry (MOS) musical scale generation and analysis for Javascript

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.generateNotation = exports.nthNominal = exports.DIAMOND_MOS_ALPHABET = void 0;
const xen_dev_utils_1 = require("xen-dev-utils");
const helpers_1 = require("./helpers");
/** Single characters of valid nominals. */
exports.DIAMOND_MOS_ALPHABET = [
    'J',
    'K',
    'L',
    'M',
    'N',
    'O',
    'P',
    'Q',
    'R',
    'S',
    'T',
    'U',
    'V',
    'W',
    'X',
    'Y',
    'Z',
];
/**
 * Obtain the 0-indexed nth generalized Diamond-mos nominal.
 * @param n Index of the nominal.
 * @returns A single character from J through Z or a multi-character string like 'JJ' starting from n = 17.
 */
function nthNominal(n) {
    if (n < 0 || !Number.isInteger(n)) {
        throw new Error('Invalid nominal index');
    }
    if (n >= exports.DIAMOND_MOS_ALPHABET.length) {
        return (nthNominal(Math.floor(n / exports.DIAMOND_MOS_ALPHABET.length) - 1) +
            exports.DIAMOND_MOS_ALPHABET[n % exports.DIAMOND_MOS_ALPHABET.length]);
    }
    return exports.DIAMOND_MOS_ALPHABET[n];
}
exports.nthNominal = nthNominal;
/**
 * Generate configuration for [Diamond mos notation](https://en.xen.wiki/w/Diamond-mos_notation).
 *
 * Always based on J and 0-indexed even if scale is diatonic.
 * @param mode Mode of a MOS scale such as 'LLsLLLs'.
 * @returns Configuration for notation software.
 */
function generateNotation(mode) {
    const scale = new Map();
    let i = 0;
    const monzo = [0, 0];
    let hasLarge = false;
    let hasSmall = false;
    for (const character of mode) {
        scale.set(nthNominal(i++), [...monzo]);
        if (character === 'L') {
            monzo[0]++;
            hasLarge = true;
        }
        else if (character === 's') {
            monzo[1]++;
            hasSmall = true;
        }
        else {
            throw new Error(`Invalid abstract step '${character}'.`);
        }
    }
    if (!hasLarge || !hasSmall) {
        throw new Error("The scale must contain both 'L' and 's' steps.");
    }
    const equave = [...monzo];
    const numPeriods = (0, xen_dev_utils_1.gcd)(equave[0], equave[1]);
    const period = [equave[0] / numPeriods, equave[1] / numPeriods];
    const gen = (0, helpers_1.mosGeneratorMonzo)(period[0], period[1]);
    const numUnique = period[0] + period[1];
    const edoperiod = 2 * period[0] + period[1];
    const basic = [
        [0, [0, 0], true, undefined],
    ];
    // Exception for nL ns
    if (numUnique === 2) {
        basic.push([2, [gen[0] - 0.5, gen[1] + 0.5], false, undefined]);
    }
    else {
        // Dark mid
        basic.push([
            edoperiod - 2 * gen[0] - gen[1],
            [period[0] - gen[0], period[1] - gen[1]],
            true,
            [period[0] - gen[0] + 0.5, period[1] - gen[1] - 0.5],
        ]);
        let edostep = 2 * gen[0] + gen[1];
        // Bright mid
        basic.push([edostep, [...gen], true, [gen[0] - 0.5, gen[1] + 0.5]]);
        monzo[0] = gen[0];
        monzo[1] = gen[1];
        for (let i = 2; i < numUnique - 1; ++i) {
            edostep += 2 * gen[0] + gen[1];
            monzo[0] += gen[0];
            monzo[1] += gen[1];
            while (edostep >= edoperiod) {
                edostep -= edoperiod;
                monzo[0] -= period[0];
                monzo[1] -= period[1];
            }
            // Imperfect central
            basic.push([edostep, [monzo[0] - 0.5, monzo[1] + 0.5], false, undefined]);
        }
    }
    basic.sort((a, b) => a[0] - b[0]);
    const degrees = [];
    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    for (const [_, center, perfect, mid] of basic) {
        degrees.push({ center, perfect, mid });
    }
    return {
        scale,
        degrees,
        equave,
        period,
        brightGenerator: gen,
    };
}
exports.generateNotation = generateNotation;
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