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packages/core/util.mjs

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+// returns true if the given string is a note
+export const isNote = (name) => /^[a-gA-G][#b]*[0-9]$/.test(name);
+export const tokenizeNote = (note) => {
+  if (typeof note !== 'string') {
+    return [];
+  }
+  const [pc, acc = '', oct] = note.match(/^([a-gA-G])([#b]*)([0-9])?$/)?.slice(1) || [];
+  if (!pc) {
+    return [];
+  }
+  return [pc, acc, oct ? Number(oct) : undefined];
+};
+
+// turns the given note into its midi number representation
+export const toMidi = (note) => {
+  const [pc, acc, oct] = tokenizeNote(note);
+  if (!pc) {
+    throw new Error('not a note: "' + note + '"');
+  }
+  const chroma = { c: 0, d: 2, e: 4, f: 5, g: 7, a: 9, b: 11 }[pc.toLowerCase()];
+  const offset = acc?.split('').reduce((o, char) => o + { '#': 1, b: -1 }[char], 0) || 0;
+  return (Number(oct) + 1) * 12 + chroma + offset;
+};
+export const fromMidi = (n) => {
+  return Math.pow(2, (n - 69) / 12) * 440;
+};
+
+// modulo that works with negative numbers e.g. mod(-1, 3) = 2
+// const mod = (n: number, m: number): number => (n < 0 ? mod(n + m, m) : n % m);
+export const mod = (n, m) => (n < 0 ? mod(n + m, m) : n % m);
+
+export const getPlayableNoteValue = (event) => {
+  let { value: note, context } = event;
+  // if value is number => interpret as midi number as long as its not marked as frequency
+  if (typeof note === 'number' && context.type !== 'frequency') {
+    note = fromMidi(event.value);
+  } else if (typeof note === 'string' && !isNote(note)) {
+    throw new Error('not a note: ' + note);
+  }
+  return note;
+};
+
+// rotate array by n steps (to the left)
+export const rotate = (arr, n) => arr.slice(n).concat(arr.slice(0, n));