Recorder-Tabber/src/lib/musicxml.ts

import { XMLParser } from "fast-xml-parser";
import { durationLabel } from "@/lib/duration";
import { parsePitch } from "@/lib/pitch";
import { newId, type Measure, type Score, type ScoreEvent, type TimeSignature } from "@/lib/score";

type XNode = Record<string, unknown>;

export type ParseSuccess = {
  ok: true;
  score: Score;
  warnings: string[];
};

export type ParseFailure = {
  ok: false;
  error: string;
};

const parser = new XMLParser({
  preserveOrder: true,
  ignoreAttributes: false,
  attributeNamePrefix: "@_",
  removeNSPrefix: true,
  trimValues: true,
});

function isNode(value: unknown): value is XNode {
  return typeof value === "object" && value !== null && !Array.isArray(value);
}

function tagOf(node: XNode): string | null {
  return Object.keys(node).find((key) => key !== ":@" ) ?? null;
}

function children(node: XNode): XNode[] {
  const tag = tagOf(node);
  if (!tag) return [];
  const value = node[tag];
  if (!Array.isArray(value)) return [];
  return value.filter(isNode);
}

function textOf(node: XNode): string {
  const tag = tagOf(node);
  if (!tag) return "";
  const value = node[tag];
  if (typeof value === "string" || typeof value === "number") return String(value).trim();
  if (!Array.isArray(value)) return "";
  for (const item of value) {
    if (isNode(item) && "#text" in item && item["#text"] != null) return String(item["#text"]).trim();
  }
  return "";
}

function attrs(node: XNode): Record<string, string> {
  const raw = node[":@"];
  if (!isNode(raw)) return {};
  const result: Record<string, string> = {};
  for (const [key, value] of Object.entries(raw)) result[key.replace(/^@_/, "")] = String(value);
  return result;
}

function findChild(nodes: XNode[], name: string): XNode | undefined {
  return nodes.find((node) => tagOf(node) === name);
}

function childText(nodes: XNode[], name: string): string | null {
  const child = findChild(nodes, name);
  if (!child) return null;
  const text = textOf(child);
  return text === "" ? null : text;
}

function hasTag(nodes: XNode[], name: string): boolean {
  return nodes.some((node) => tagOf(node) === name);
}

function findDeep(nodes: XNode[], name: string): XNode | undefined {
  for (const node of nodes) {
    if (tagOf(node) === name) return node;
    const nested = findDeep(children(node), name);
    if (nested) return nested;
  }
  return undefined;
}

function tieStarts(nodes: XNode[]): boolean {
  for (const node of nodes) {
    const tag = tagOf(node);
    if (tag === "tie" && attrs(node).type === "start") return true;
    if (tag === "notations") {
      for (const inner of children(node)) {
        if (tagOf(inner) === "tied" && attrs(inner).type === "start") return true;
      }
    }
  }
  return false;
}

function pitchFrom(noteKids: XNode[]): { name: string; midi: number } | null {
  const pitch = findChild(noteKids, "pitch");
  if (!pitch) return null;
  const kids = children(pitch);
  const step = childText(kids, "step");
  const octave = childText(kids, "octave");
  if (!step || !octave) return null;
  const alter = Number(childText(kids, "alter") ?? "0");
  const accidental =
    alter === 1 ? "#" : alter === -1 ? "b" : alter === 2 ? "##" : alter === -2 ? "bb" : "";
  if (![0, 1, -1, 2, -2].includes(alter)) return null;
  const parsed = parsePitch(`${step}${accidental}${octave}`);
  return parsed ? { name: parsed.name, midi: parsed.midi } : null;
}

type Candidate = {
  onset: number;
  kind: "note" | "rest";
  midi: number;
  pitch: string | null;
  quarters: number;
  label: string;
  tied: boolean;
};

function onsetKey(value: number): number {
  return Math.round(value * 1000) / 1000;
}

export function parseMusicXml(xml: string): ParseSuccess | ParseFailure {
  const cleaned = xml.replace(/<!DOCTYPE[\s\S]*?>/gi, "");
  let root: unknown;
  try {
    root = parser.parse(cleaned);
  } catch {
    return { ok: false, error: "The recognizer returned text that is not MusicXML." };
  }
  if (!Array.isArray(root)) return { ok: false, error: "The recognizer returned text that is not MusicXML." };

  const scoreNode = findDeep(root.filter(isNode), "score-partwise");
  if (!scoreNode) {
    return {
      ok: false,
      error: "The recognizer did not return a partwise score. No notes were invented.",
    };
  }

  const top = children(scoreNode);
  const work = findChild(top, "work");
  const title =
    (work && childText(children(work), "work-title")) ||
    childText(top, "movement-title") ||
    "Uploaded page";

  const parts = top.filter((node) => tagOf(node) === "part");
  if (parts.length === 0) {
    return { ok: false, error: "The score has no part to read as a lead line." };
  }

  const warnings: string[] = [];
  if (parts.length > 1) warnings.push("Only the first part was read. Other parts were left out.");

  let divisions = 1;
  let timeSignature: TimeSignature = { beats: 4, beatType: 4 };
  let sawTime = false;
  let timeChanged = false;
  let sawLowerStaff = false;
  let reduced = false;
  let sawGrace = false;
  let sawTie = false;

  const measures: Measure[] = [];

  for (const [measureIndex, measureNode] of children(parts[0]).filter((node) => tagOf(node) === "measure").entries()) {
    let cursor = 0;
    let lastDuration = 0;
    const grouped = new Map<number, Candidate[]>();

    for (const element of children(measureNode)) {
      const tag = tagOf(element);
      if (tag === "attributes") {
        const kids = children(element);
        const nextDivisions = childText(kids, "divisions");
        if (nextDivisions && Number(nextDivisions) > 0) divisions = Number(nextDivisions);
        const time = findChild(kids, "time");
        if (time) {
          const timeKids = children(time);
          const beats = Number(childText(timeKids, "beats"));
          const beatType = Number(childText(timeKids, "beat-type"));
          if (beats > 0 && beatType > 0) {
            if (!sawTime) {
              timeSignature = { beats, beatType };
              sawTime = true;
            } else if (timeSignature.beats !== beats || timeSignature.beatType !== beatType) {
              timeChanged = true;
            }
          }
        }
        continue;
      }
      if (tag === "backup" || tag === "forward") {
        const delta = Number(childText(children(element), "duration") ?? "0");
        cursor += tag === "backup" ? -delta : delta;
        continue;
      }
      if (tag !== "note") continue;

      const kids = children(element);
      if (hasTag(kids, "grace")) {
        sawGrace = true;
        continue;
      }
      const isChord = hasTag(kids, "chord");
      const duration = Number(childText(kids, "duration") ?? "0");
      const staff = childText(kids, "staff");
      if (staff && staff !== "1") {
        sawLowerStaff = true;
        if (!isChord) {
          cursor += duration;
          lastDuration = duration;
        }
        continue;
      }

      const onset = onsetKey(isChord ? cursor - lastDuration : cursor);
      if (!isChord) {
        cursor += duration;
        lastDuration = duration;
      }

      const type = childText(kids, "type");
      const dots = kids.filter((node) => tagOf(node) === "dot").length;
      const modification = findChild(kids, "time-modification");
      let tuplet = false;
      if (modification) {
        const actual = Number(childText(children(modification), "actual-notes"));
        const normal = Number(childText(children(modification), "normal-notes"));
        tuplet = actual === 3 && normal === 2;
      }
      const quarters = divisions > 0 ? duration / divisions : 0;
      const tied = tieStarts(kids);
      if (tied) sawTie = true;

      if (hasTag(kids, "rest")) {
        const list = grouped.get(onset) ?? [];
        list.push({
          onset,
          kind: "rest",
          midi: -1,
          pitch: null,
          quarters,
          label: durationLabel(quarters, type, dots, tuplet),
          tied: false,
        });
        grouped.set(onset, list);
        continue;
      }

      const pitch = pitchFrom(kids);
      if (!pitch) continue;
      const list = grouped.get(onset) ?? [];
      list.push({
        onset,
        kind: "note",
        midi: pitch.midi,
        pitch: pitch.name,
        quarters,
        label: durationLabel(quarters, type, dots, tuplet),
        tied,
      });
      grouped.set(onset, list);
    }

    const events: ScoreEvent[] = [];
    for (const onset of [...grouped.keys()].sort((a, b) => a - b)) {
      const candidates = grouped.get(onset) ?? [];
      const notes = candidates.filter((candidate) => candidate.kind === "note");
      if (notes.length > 1) reduced = true;
      const chosen = notes.length > 0 ? notes.reduce((best, note) => (note.midi > best.midi ? note : best)) : candidates[0];
      if (!chosen || chosen.quarters <= 0) continue;
      events.push({
        id: newId("e"),
        kind: chosen.kind,
        pitch: chosen.pitch,
        quarters: chosen.quarters,
        label: chosen.label,
        tied: chosen.tied,
      });
    }

    measures.push({ id: newId("m"), events });
    void measureIndex;
  }

  if (sawLowerStaff) warnings.push("Notes on lower staves were left out. The tab follows the top staff.");
  if (reduced) warnings.push("Chords and overlapping voices were reduced to the highest note.");
  if (sawGrace) warnings.push("Grace notes were left out so the beat stays aligned.");
  if (timeChanged) warnings.push("A later time signature was ignored. The tab uses the first one.");
  if (sawTie) warnings.push("Tied notes stay separate so the bar lines do not move.");

  const eventCount = measures.reduce((total, measure) => total + measure.events.length, 0);
  if (eventCount === 0) {
    return {
      ok: false,
      error: "The recognizer finished, but it did not find a lead note or a rest. No notes were invented.",
    };
  }

  return {
    ok: true,
    warnings,
    score: {
      title,
      attribution: "Read from your image. Correct anything that looks wrong before you play.",
      timeSignature,
      measures: measures.length > 0 ? measures : [{ id: newId("m"), events: [] }],
      origin: "upload",
    },
  };
}