noteman-slicer/noteman_slicer/lilypond.py

"""Re-engrave a slice with LilyPond, when the scan is past saving.

Optional. LilyPond is a system package rather than a wheel, so its absence
hides the feature and nothing else changes.

The tool renders a tight-cropped PNG and hands it to the ordinary render
pipeline at the trim stage, so a replaced slice flows through staff-height
normalisation, song scale, pad and encode untouched — which is what makes it
sit at the same note size as the scanned systems around it without any manual
scaling.
"""

from __future__ import annotations

import shutil
import subprocess
import tempfile
from pathlib import Path

import cv2
import numpy as np

RENDER_DPI = 600
TIMEOUT_S = 120

# Read off the page by counting accidentals, which is how you actually read a
# key signature. Both names are shown because either identifies the same
# signature; the major spelling is what LilyPond gets, and it prints the same
# accidentals as the relative minor would.
KEY_SIGNATURES: tuple[tuple[str, str], ...] = (
    ("7♭ — C♭ major / A♭ minor", "ces"),
    ("6♭ — G♭ major / E♭ minor", "ges"),
    ("5♭ — D♭ major / B♭ minor", "des"),
    ("4♭ — A♭ major / F minor", "aes"),
    ("3♭ — E♭ major / C minor", "ees"),
    ("2♭ — B♭ major / G minor", "bes"),
    ("1♭ — F major / D minor", "f"),
    ("— C major / A minor", "c"),
    ("1♯ — G major / E minor", "g"),
    ("2♯ — D major / B minor", "d"),
    ("3♯ — A major / F♯ minor", "a"),
    ("4♯ — E major / C♯ minor", "e"),
    ("5♯ — B major / G♯ minor", "b"),
    ("6♯ — F♯ major / D♯ minor", "fis"),
    ("7♯ — C♯ major / A♯ minor", "cis"),
)

# Kaipaava's five-staff system uses all but the alto.
CLEFS: tuple[tuple[str, str], ...] = (
    ("Treble", "treble"),
    ("Treble 8 (tenor)", "treble_8"),
    ("Bass", "bass"),
    ("Alto", "alto"),
)

# Notes are entered in \relative mode, so only intervals larger than a fourth
# need an octave mark. The reference pitch is the middle of each clef's staff,
# so the first note of a part usually needs no mark either.
RELATIVE_REFERENCE = {
    "treble": "c''",
    "treble_8": "c'",
    "alto": "c'",
    "bass": "c",
}

_PREAMBLE = """\\version "2.24.0"
\\paper {
  indent = 0\\mm
  ragged-right = ##f
  oddHeaderMarkup = ##f evenHeaderMarkup = ##f
  oddFooterMarkup = ##f evenFooterMarkup = ##f
  print-page-number = ##f
}
"""


def generate(replacement, key: str, time: str) -> str:
    """Build LilyPond source from a slice's structured replacement.

    The time signature is used for spacing and bar checks but not printed
    unless asked for: the printed score repeats the key at every system and the
    time signature only at the first, so a re-engraved middle slice showing one
    would stand out immediately in the scroll.
    """
    key = replacement.key or key
    time = replacement.time or time

    staves = []
    for voice in replacement.voices:
        hide = "" if replacement.print_time else "      \\omit Staff.TimeSignature\n"
        body = voice.notes.strip() or "s1"
        reference = RELATIVE_REFERENCE.get(voice.clef, "c'")
        staff = (
            "    \\new Staff {\n"
            f"{hide}"
            f"      \\clef {voice.clef}\n"
            f"      \\key {key} \\major\n"
            f"      \\time {time}\n"
            f"      \\relative {reference} {{ {body} }}\n"
            "    }\n"
        )
        if voice.lyrics.strip():
            staff += f"    \\addlyrics {{ {voice.lyrics.strip()} }}\n"
        staves.append(staff)

    if not staves:
        staves.append("    \\new Staff { s1 }\n")

    return (
        _PREAMBLE
        + "\\score {\n  \\new ChoirStaff <<\n"
        + "".join(staves)
        + "  >>\n  \\layout { }\n}\n"
    )


class LilypondError(RuntimeError):
    """LilyPond refused the source. Carries its diagnostics verbatim."""


def available() -> bool:
    return shutil.which("lilypond") is not None


def version() -> str | None:
    if not available():
        return None
    try:
        out = subprocess.run(
            ["lilypond", "--version"], capture_output=True, text=True, timeout=20
        )
    except (OSError, subprocess.SubprocessError):
        return None
    return out.stdout.splitlines()[0] if out.stdout else None


def render(source: str, dpi: int = RENDER_DPI) -> np.ndarray:
    """Engrave `source` and return it as a grayscale array, cropped to the ink.

    Raises LilypondError with LilyPond's own message on failure — a syntax
    error has to be readable without leaving the editor.
    """
    if not available():
        raise LilypondError("LilyPond is not installed")

    with tempfile.TemporaryDirectory(prefix="noteman-slicer-ly-") as workdir:
        work = Path(workdir)
        (work / "slice.ly").write_text(source, encoding="utf-8")
        try:
            result = subprocess.run(
                [
                    "lilypond",
                    "-dcrop=#t",
                    "-dbackend=cairo",
                    "--png",
                    f"-dresolution={dpi}",
                    "-o",
                    "out",
                    "slice.ly",
                ],
                cwd=work,
                capture_output=True,
                text=True,
                timeout=TIMEOUT_S,
            )
        except subprocess.TimeoutExpired as error:
            raise LilypondError(f"LilyPond timed out after {TIMEOUT_S}s") from error

        # LilyPond still writes a page when it rejects the source, so the exit
        # code has to be checked first — otherwise a broken snippet silently
        # becomes a garbage slice.
        if result.returncode != 0:
            raise LilypondError(result.stderr.strip() or f"exit status {result.returncode}")

        # -dcrop writes out.cropped.png; the uncropped page is the fallback if
        # a LilyPond build ever stops honouring it.
        for name in ("out.cropped.png", "out.png"):
            image = work / name
            if image.exists():
                gray = cv2.imread(str(image), cv2.IMREAD_GRAYSCALE)
                if gray is not None:
                    return gray

        raise LilypondError(result.stderr.strip() or result.stdout.strip() or "no output")