/**
 * Minimal ChordPro parser + SVG leadsheet formatter (issue #155).
 *
 * Deliberately hand-rolled instead of pulling in a chord-sheet library: the
 * subset a leadsheet needs is small (directives, `[chord]` markers, comments,
 * chorus fences), and the SVG layout would be custom code either way — this
 * keeps the plugin dependency-free (supply-chain lesson from #136).
 *
 * Supported ChordPro:
 * - `{title: …}` / `{t: …}`, `{subtitle: …}`/`{st: …}`/`{artist: …}`,
 *   `{key: …}`, `{capo: …}`, `{tempo: …}`
 * - `{comment: …}` / `{c: …}` — shown as an italic line
 * - `{start_of_chorus}`/`{soc}` … `{end_of_chorus}`/`{eoc}` — indented block
 * - lyric lines with inline `[C]`/`[Am7]`/… chord markers
 * - `#` comment lines (ignored), blank lines (verse separation)
 */

export interface SheetMeta {
  title: string;
  subtitle: string;
  key: string;
  capo: string;
  tempo: string;
}

export interface SheetLine {
  kind: 'pair' | 'comment' | 'blank';
  /** Lyric text with the chord markers removed. */
  lyrics: string;
  /** Chords with the lyric column (character index) they sit above. */
  chords: { at: number; chord: string }[];
  chorus: boolean;
}

export interface Sheet {
  meta: SheetMeta;
  lines: SheetLine[];
}

const DIRECTIVE = /^\{\s*([a-z_]+)\s*(?::\s*(.*?))?\s*\}\s*$/i;
const CHORD = /\[([^\][\n]+)\]/g;

export function parseChordPro(source: string): Sheet {
  const meta: SheetMeta = { title: '', subtitle: '', key: '', capo: '', tempo: '' };
  const lines: SheetLine[] = [];
  let chorus = false;

  for (const raw of source.split('\n')) {
    const line = raw.replace(/\s+$/, '');
    if (line.trimStart().startsWith('#')) continue;

    const directive = DIRECTIVE.exec(line.trim());
    if (directive) {
      const name = directive[1]!.toLowerCase();
      const value = (directive[2] ?? '').trim();
      if (name === 'title' || name === 't') meta.title = value;
      else if (name === 'subtitle' || name === 'st' || name === 'artist') meta.subtitle = value;
      else if (name === 'key') meta.key = value;
      else if (name === 'capo') meta.capo = value;
      else if (name === 'tempo') meta.tempo = value;
      else if (name === 'start_of_chorus' || name === 'soc') chorus = true;
      else if (name === 'end_of_chorus' || name === 'eoc') chorus = false;
      else if (name === 'comment' || name === 'c') {
        lines.push({ kind: 'comment', lyrics: value, chords: [], chorus });
      }
      // Unknown directives are ignored on purpose (forward compatibility).
      continue;
    }

    if (line.trim() === '') {
      lines.push({ kind: 'blank', lyrics: '', chords: [], chorus });
      continue;
    }

    let lyrics = '';
    const chords: { at: number; chord: string }[] = [];
    let last = 0;
    for (const match of line.matchAll(CHORD)) {
      lyrics += line.slice(last, match.index);
      chords.push({ at: lyrics.length, chord: match[1]! });
      last = match.index! + match[0].length;
    }
    lyrics += line.slice(last);
    lines.push({ kind: 'pair', lyrics, chords, chorus });
  }

  // Trim leading/trailing blank lines.
  while (lines[0]?.kind === 'blank') lines.shift();
  while (lines[lines.length - 1]?.kind === 'blank') lines.pop();
  return { meta, lines };
}

/** Monospace metrics — fixed so the static SVG lays out identically wherever
 * it renders (editor sandbox, public view, PDF export). */
const CHAR_W = 8.4;
const LINE_H = 18;
const PAD = 12;
const CHORUS_INDENT = 2;

function escapeXml(value: string): string {
  return value
    .replaceAll('&', '&')
    .replaceAll('<', '&lt;')
    .replaceAll('>', '&gt;')
    .replaceAll('"', '&quot;');
}

/** The sheet as a self-contained SVG: chords above lyrics, monospace grid. */
export function sheetToSvg(sheet: Sheet): string {
  const parts: string[] = [];
  let y = PAD + 4;
  let maxCols = 0;

  const push = (text: string, x: number, options: string): void => {
    parts.push(`<text x="${x}" y="${y}" ${options}>${escapeXml(text)}</text>`);
  };

  if (sheet.meta.title) {
    y += 20;
    push(sheet.meta.title, PAD, 'font-size="18" font-weight="bold" font-family="sans-serif"');
    maxCols = Math.max(maxCols, (sheet.meta.title.length * 11) / CHAR_W);
  }
  const subtitleBits = [
    sheet.meta.subtitle,
    sheet.meta.key && `Key: ${sheet.meta.key}`,
    sheet.meta.capo && `Capo: ${sheet.meta.capo}`,
    sheet.meta.tempo && `♩ ${sheet.meta.tempo}`,
  ].filter(Boolean) as string[];
  if (subtitleBits.length > 0) {
    y += LINE_H;
    push(subtitleBits.join(' — '), PAD, 'font-size="13" fill="#555" font-family="sans-serif"');
    maxCols = Math.max(maxCols, subtitleBits.join(' — ').length);
  }
  if (sheet.meta.title || subtitleBits.length > 0) y += 8;

  for (const line of sheet.lines) {
    const indent = line.chorus ? CHORUS_INDENT : 0;
    const x = PAD + indent * CHAR_W;
    if (line.kind === 'blank') {
      y += LINE_H * 0.7;
      continue;
    }
    if (line.kind === 'comment') {
      y += LINE_H;
      push(
        line.lyrics,
        x,
        'font-size="13" font-style="italic" fill="#555" font-family="sans-serif"',
      );
      maxCols = Math.max(maxCols, indent + line.lyrics.length);
      continue;
    }
    if (line.chords.length > 0) {
      y += LINE_H;
      for (const { at, chord } of line.chords) {
        parts.push(
          `<text x="${PAD + (indent + at) * CHAR_W}" y="${y}" font-size="13" font-weight="bold"` +
            ` fill="#1d4ed8" font-family="ui-monospace, SFMono-Regular, Menlo, monospace">` +
            `${escapeXml(chord)}</text>`,
        );
        maxCols = Math.max(maxCols, indent + at + chord.length);
      }
    }
    y += LINE_H;
    push(
      line.lyrics,
      x,
      'font-size="14" font-family="ui-monospace, SFMono-Regular, Menlo, monospace" xml:space="preserve"',
    );
    maxCols = Math.max(maxCols, indent + line.lyrics.length);
  }

  const width = Math.max(240, Math.ceil(PAD * 2 + maxCols * CHAR_W));
  const height = y + PAD;
  return (
    `<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 ${width} ${height}"` +
    ` width="${width}" height="${height}" role="img">` +
    parts.join('') +
    `</svg>`
  );
}

/** Parse + render in one step; throws on an empty sheet so callers can show
 * their empty-state hint instead of a blank box. */
export function chordProToSvg(source: string): string {
  const sheet = parseChordPro(source);
  if (sheet.lines.length === 0 && !sheet.meta.title) {
    throw new Error('empty sheet');
  }
  return sheetToSvg(sheet);
}