Recorder-Tabber/src/lib/fingering.ts

import { parsePitch } from "@/lib/pitch";

export type HoleState = "open" | "closed" | "half";

export type Fingering = {
  thumb: HoleState;
  /** Holes 1, 2, 3, 4, 5, 6a, 6b, 7a, 7b. */
  holes: HoleState[];
  bell: boolean;
};

export type FingeringSystem = "baroque" | "german";

export const RANGE_LABEL = "C5–D7";
export const LOW_MIDI = 72;
export const HIGH_MIDI = 98;

const HOLE_IDS = ["1", "2", "3", "4", "5", "6a", "6b", "7a", "7b"] as const;

type ThumbCode = "0" | "x" | "-";
type Row = [pitch: string, thumb: ThumbCode, holes: string, bell?: boolean];

/**
 * First-choice Baroque (English) fingerings from the Dolmetsch Online chart
 * for recorders in C (Brian Blood). Octave 1 is concert C5.
 * A listed hole is closed. 6a without 6b, or 7a without 7b, is the half-hole.
 * Thumb 0 is closed, x is pinched, - is open.
 * Alternates on that chart (second B, all-closed D, and so on) are not encoded.
 */
const BAROQUE_ROWS: Row[] = [
  ["C5", "0", "123456a6b7a7b"],
  ["C#5", "0", "123456a6b7a"],
  ["D5", "0", "123456a6b"],
  ["Eb5", "0", "123456a"],
  ["E5", "0", "12345"],
  ["F5", "0", "12346a6b7a7b"],
  ["F#5", "0", "12356a6b"],
  ["G5", "0", "123"],
  ["Ab5", "0", "12456a"],
  ["A5", "0", "12"],
  ["Bb5", "0", "134"],
  ["B5", "0", "1"],
  ["C6", "0", "2"],
  ["C#6", "-", "12"],
  ["D6", "-", "2"],
  ["Eb6", "-", "23456a6b"],
  ["E6", "x", "12345"],
  ["F6", "x", "12346a6b"],
  ["F#6", "x", "1235"],
  ["G6", "x", "123"],
  ["Ab6", "x", "124"],
  ["A6", "x", "12"],
  ["Bb6", "x", "1256a6b"],
  ["B6", "x", "1245"],
  ["C7", "x", "145"],
  ["C#7", "x", "1346a6b", true],
  ["D7", "x", "1346a6b"],
];

/**
 * German differs on F, F♯, and B♭.
 * Low F is Dolmetsch’s German fingering: 0 123 4 (holes 5–7 open).
 * F♯ is thumb, 1, 2, 3, 5, 6, and half-hole 7.
 * B♭ is thumb, 1, 3, 4, 6.
 * Those two accidentals are the school German pattern described by
 * Zach VanderGraaff (Dynamic Music Room). The octave above keeps the same
 * front holes and uses the Dolmetsch second-octave thumb.
 */
const GERMAN_ROWS: Row[] = [
  ["F5", "0", "1234"],
  ["F#5", "0", "12356a6b7a"],
  ["Bb5", "0", "1346a6b"],
  ["F6", "x", "1234"],
  ["F#6", "x", "12356a6b7a"],
  ["Bb6", "x", "1346a6b"],
];

export const CHART_NOTES = [
  "C5",
  "C#5",
  "D5",
  "Eb5",
  "E5",
  "F5",
  "F#5",
  "G5",
  "Ab5",
  "A5",
  "Bb5",
  "B5",
  "C6",
  "C#6",
  "D6",
  "Eb6",
  "E6",
  "F6",
  "F#6",
  "G6",
  "Ab6",
  "A6",
  "Bb6",
  "B6",
  "C7",
  "C#7",
  "D7",
] as const;

function closedSet(spec: string): Set<string> {
  const closed = new Set<string>();
  let index = 0;
  while (index < spec.length) {
    const pair = spec.slice(index, index + 2);
    if (pair === "6a" || pair === "6b" || pair === "7a" || pair === "7b") {
      closed.add(pair);
      index += 2;
    } else {
      closed.add(spec[index]);
      index += 1;
    }
  }
  return closed;
}

function make(thumb: ThumbCode, spec: string, bell = false): Fingering {
  const closed = closedSet(spec);
  return {
    thumb: thumb === "0" ? "closed" : thumb === "x" ? "half" : "open",
    holes: HOLE_IDS.map((id) => (closed.has(id) ? "closed" : "open")),
    bell,
  };
}

function table(rows: Row[]): Map<number, Fingering> {
  const map = new Map<number, Fingering>();
  for (const [pitch, thumb, holes, bell] of rows) {
    const parsed = parsePitch(pitch);
    if (!parsed) throw new Error(`Bad chart pitch ${pitch}`);
    map.set(parsed.midi, make(thumb, holes, bell ?? false));
  }
  return map;
}

const BAROQUE = table(BAROQUE_ROWS);
const GERMAN = table(GERMAN_ROWS);

export function fingeringFor(pitch: string, system: FingeringSystem): Fingering | null {
  const parsed = parsePitch(pitch);
  if (!parsed || parsed.midi < LOW_MIDI || parsed.midi > HIGH_MIDI) return null;
  if (system === "german") {
    const german = GERMAN.get(parsed.midi);
    if (german) return german;
  }
  return BAROQUE.get(parsed.midi) ?? null;
}

export function fingeringCode(fingering: Fingering): string {
  const thumb = fingering.thumb === "closed" ? "0" : fingering.thumb === "half" ? "x" : "-";
  const closed = HOLE_IDS.filter((_, index) => fingering.holes[index] === "closed");
  const bell = fingering.bell ? " bell" : "";
  return `${thumb} ${closed.join(" ")}${bell}`;
}

export function fingeringMarks(fingering: Fingering): string[] {
  const marks: string[] = [];
  if (fingering.thumb === "half") marks.push("pinch");
  const [hole1, hole2, hole3, hole4, hole5, hole6a, hole6b, hole7a, hole7b] = fingering.holes;
  if (hole6a !== hole6b) marks.push("half 6");
  if (hole7a !== hole7b) marks.push("half 7");
  const lowerRightClosed = hole6a === "closed" || hole6b === "closed" || hole7a === "closed" || hole7b === "closed";
  if (hole4 === "closed" && hole5 === "open" && lowerRightClosed) marks.push("fork");
  if (hole1 === "closed" && hole2 === "open" && hole3 === "closed") marks.push("fork");
  if (fingering.bell) marks.push("cover bell");
  return marks;
}

export function fingeringProse(fingering: Fingering): string {
  const thumb =
    fingering.thumb === "closed"
      ? "thumb closed"
      : fingering.thumb === "half"
        ? "thumb pinched"
        : "thumb open";
  const names = ["1", "2", "3", "4", "5", "6a", "6b", "7a", "7b"];
  const closed = names.filter((_, index) => fingering.holes[index] === "closed");
  const holes = closed.length > 0 ? `holes ${closed.join(" ")} closed` : "no front holes closed";
  const bell = fingering.bell ? ", cover the bell" : "";
  return `${thumb}, ${holes}${bell}`;
}

export function germanDiffers(pitch: string): boolean {
  const baroque = fingeringFor(pitch, "baroque");
  const german = fingeringFor(pitch, "german");
  if (!baroque || !german) return false;
  return fingeringCode(baroque) !== fingeringCode(german);
}