Recorder-Tabber/src/lib/score.ts

import { formatQuarterLengths, quartersMatch } from "@/lib/duration";

export type TimeSignature = {
  beats: number;
  beatType: number;
};

export type ScoreEvent = {
  id: string;
  kind: "note" | "rest";
  pitch: string | null;
  quarters: number;
  label: string;
  tied: boolean;
};

export type Measure = {
  id: string;
  events: ScoreEvent[];
  /** A forward repeat barline stands at the start of this measure. */
  repeatForward?: boolean;
  /** A backward repeat ends on this measure. The number is how many times to play the passage. */
  repeatTimes?: number;
};

export type ScoreOrigin = "sample" | "upload" | "blank";

export type Score = {
  title: string;
  attribution: string;
  timeSignature: TimeSignature;
  measures: Measure[];
  origin: ScoreOrigin;
};

export const TIME_SIGNATURES: TimeSignature[] = [
  { beats: 2, beatType: 4 },
  { beats: 3, beatType: 4 },
  { beats: 4, beatType: 4 },
  { beats: 6, beatType: 8 },
  { beats: 3, beatType: 8 },
  { beats: 2, beatType: 2 },
];

export function newId(prefix: string): string {
  return `${prefix}-${Math.random().toString(36).slice(2, 10)}`;
}

export function signatureKey(timeSignature: TimeSignature): string {
  return `${timeSignature.beats}/${timeSignature.beatType}`;
}

export function parseSignature(key: string): TimeSignature {
  const [beats, beatType] = key.split("/").map(Number);
  return { beats, beatType };
}

export function expectedQuarters(timeSignature: TimeSignature): number {
  return (timeSignature.beats * 4) / timeSignature.beatType;
}

export function barStatus(
  measure: Measure,
  timeSignature: TimeSignature,
): { ok: boolean; text: string } {
  const sum = measure.events.reduce((total, event) => total + event.quarters, 0);
  const expected = expectedQuarters(timeSignature);
  const signature = signatureKey(timeSignature);
  if (quartersMatch(sum, expected)) {
    return { ok: true, text: `${signature} · ${formatQuarterLengths(sum)}` };
  }
  return {
    ok: false,
    text: `${formatQuarterLengths(sum)} in this bar; ${signature} holds ${formatQuarterLengths(expected)}.`,
  };
}

export function startBeats(events: ScoreEvent[], timeSignature: TimeSignature): number[] {
  const quartersPerBeat = 4 / timeSignature.beatType;
  let cursor = 0;
  return events.map((event) => {
    const beat = cursor / quartersPerBeat + 1;
    cursor += event.quarters;
    return beat;
  });
}

export function formatBeat(beat: number): string {
  const rounded = Math.round(beat * 100) / 100;
  return Number.isInteger(rounded) ? String(rounded) : String(rounded);
}

/** Extra full beats after the note itself. A half note in 4/4 returns 1. A dotted quarter returns 0. */
export function extraBeatArrows(quarters: number, timeSignature: TimeSignature): number {
  const perBeat = 4 / timeSignature.beatType;
  if (!(perBeat > 0) || !(quarters > 0)) return 0;
  const wholeBeats = Math.floor(quarters / perBeat + 1e-6);
  return Math.max(0, wholeBeats - 1);
}

/** Group a lead into horizontal rows. A row holds about `budget` notes, and never splits a bar. */
export function leadRows<T extends { events: { length: number } }>(measures: T[], budget = 14): T[][] {
  const rows: T[][] = [];
  let current: T[] = [];
  let count = 0;
  for (const measure of measures) {
    const notes = Math.max(1, measure.events.length);
    if (current.length > 0 && count + notes > budget) {
      rows.push(current);
      current = [];
      count = 0;
    }
    current.push(measure);
    count += notes;
  }
  if (current.length > 0) rows.push(current);
  return rows;
}

export function blankScore(): Score {
  return {
    title: "Untitled line",
    attribution: "Hand-entered lead line. Add notes, then read the tabs.",
    timeSignature: { beats: 4, beatType: 4 },
    origin: "blank",
    measures: [{ id: newId("m"), events: [] }],
  };
}