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function notesBetween(a, b) {
const [tonicA, tonicB] = [a[0], b[0]]
const abs = tonicB.charCodeAt() - tonicA.charCodeAt();
if (abs < 0) {
return abs + 7;
} else {
return abs;
}
}
export class Note {
static natural = '♮';
static sharp = '♯';
static flat = '♭';
static range = ['A', 'B', 'C', 'D', 'E', 'F', 'G'];
static get first() {
return this.range.at(0);
}
static get last() {
return this.range.at(-1);
}
static noSharps = ['B', 'E'];
static get noFlats() {
return this.noSharps.map(n => String.fromCharCode(n.charCodeAt()+1))
}
static fromString(string) {
const [root, accidental] = [string[0], string[1]];
switch (accidental) {
case this.sharp:
if (this.noSharps.includes(root)) {
return new this(String.fromCharCode(root.charCodeAt()+1))
} else {
return new this(root, true);
}
case this.flat:
if (this.noFlats.includes(root)) {
return new this(String.fromCharCode(root.charCodeAt()-1));
} else if (root === Note.first) {
// i don't want to make a ring buffer that accepts
// negative indices, ok???
return new this(Note.last, true);
} else {
const code = root.charCodeAt();
return new this(String.fromCharCode(code-1), true);
}
case undefined:
case this.natural:
return new this(root);
default:
throw new Error('wtf is that accidental', accidental);
}
}
constructor(root, isSharp=false) {
if (isSharp && Note.noSharps.includes(root)) {
throw new Error(`bad note: ${root}${Note.sharp}`);
}
this.root = root;
this.isSharp = isSharp;
}
toString() {
return this.root + (this.isSharp ? Note.sharp : '');
}
toAlternateString() {
if (this.isSharp) {
const next = (this.root === Note.last) ? Note.first : String.fromCharCode(this.root.charCodeAt()+1);
if (Note.noSharps.includes(this.root)) {
return next;
} else {
return next + Note.flat;
}
} else if (Note.noFlats.includes(this.root)) {
const prev = (this.root === Note.first) ? Note.last : String.fromCharCode(this.root.charCodeAt()-1);
return prev + Note.sharp;
} else {
return this.toString();
}
}
toRelativeString(other) {
const alternate = this.toAlternateString();
const otherStr = other.toString();
const delta = otherStr.charCodeAt() - alternate.charCodeAt();
if (delta === -1 || delta === 1) {
return alternate;
} else {
return this.toString();
}
}
}
const ringHandler = {
get(target, prop) {
return target[prop % target.length] || Reflect.get(...arguments);
}
};
export const chromaticScale = new Proxy(
['C', 'C♯', 'D', 'D♯', 'E', 'F', 'F♯', 'G', 'G♯', 'A', 'A♯', 'B'],
ringHandler);
// todo: handle tonics with a flat ‘♭’, so we can deal with [BE]♭.
function scaleFromIntervals(tonic, intervals) {
const scaleIndex = chromaticScale.indexOf(tonic);
if (scaleIndex < 0) {
throw new Error(`tonic ${tonic} not found in scale ${chromaticScale.toString()}`);
}
let scale = [tonic];
let steps = 0;
let lastBase = tonic[0];
for (let i = 0; i < intervals.length; i++) {
steps += intervals[i];
const note = chromaticScale[scaleIndex + steps];
// don't display two base notes in a row by changing
// accidentals.
const delta = notesBetween(lastBase, note);
if (delta === 0) {
const nextBase = chromaticScale[scaleIndex + steps + 1][0];
scale.push(`${nextBase}♭`)
} else if (delta === 1) {
scale.push(`${note}`)
} else {
// we can only be two away, so take the sharp of the
// previous note.
const nextBase = chromaticScale[scaleIndex + steps - 1][0];
scale.push(`${nextBase}♯`)
}
lastBase = scale[scale.length-1];
}
return new Proxy(scale, ringHandler);
}
class Scale {
constructor(tonic, intervals) {
this.scale = scaleFromIntervals(tonic, intervals);
return new Proxy(this, {
get(target, prop) {
if (prop in target) {
return target[prop];
} else {
return target.scale[prop] || Reflect.get(...arguments);
}
}
});
}
get tonic() {
return this.scale[0];
}
get third() {
return this.scale[2];
}
get fifth() {
return this.scale[4];
}
get length() {
return this.scale.length;
}
toString() {
return `[${this.scale.join(", ")}]`;
}
}
export function MajorScale(tonic) {
console.debug(`MajorScale(${tonic})`);
const intervals = [2, 2, 1, 2, 2, 2];
return new Scale(tonic, intervals);
}
export function MinorScale(tonic) {
console.debug(`MinorScale(${tonic})`);
const intervals = [2, 1, 2, 2, 1, 2];
return new Scale(tonic, intervals);
}
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