"""FpcalcFingerprinter — Chromaprint fingerprint via the ``fpcalc`` binary.

``fpcalc -json <file>`` emits ``{"duration": float, "fingerprint": str}``. The
binary ships in the Docker image (``libchromaprint-tools``). Any failure (binary
missing, bad file, timeout) degrades to ``None`` — the pipeline then falls back
to tag-only metadata (plan §6.2: one external dependency must never crash it).
"""

import asyncio
import json
import shutil
from pathlib import Path

from app.core.logging import get_logger
from app.domain.entities.metadata import Fingerprint

log = get_logger(__name__)

_TIMEOUT_SECONDS = 30


class FpcalcFingerprinter:
    """Implements :class:`app.domain.ports.AudioFingerprinter`."""

    def __init__(self, binary: str = "fpcalc") -> None:
        self._binary = binary

    def is_available(self) -> bool:
        return shutil.which(self._binary) is not None

    async def calculate(self, path: Path) -> Fingerprint | None:
        if not self.is_available():
            return None
        try:
            proc = await asyncio.create_subprocess_exec(
                self._binary,
                "-json",
                str(path),
                stdout=asyncio.subprocess.PIPE,
                stderr=asyncio.subprocess.PIPE,
            )
            async with asyncio.timeout(_TIMEOUT_SECONDS):
                stdout, _stderr = await proc.communicate()
        except (TimeoutError, OSError):
            log.warning("fpcalc_failed", path=str(path))
            return None

        if proc.returncode != 0:
            log.warning("fpcalc_nonzero", path=str(path), returncode=proc.returncode)
            return None

        try:
            data = json.loads(stdout)
            fingerprint = str(data["fingerprint"])
            duration = round(float(data["duration"]))
        except (json.JSONDecodeError, KeyError, ValueError):
            log.warning("fpcalc_bad_output", path=str(path))
            return None

        if not fingerprint or duration <= 0:
            return None
        return Fingerprint(fingerprint=fingerprint, duration_seconds=duration)