from __future__ import annotations

import json
import subprocess
from pathlib import Path

MAX_SECONDS = 120
MAX_BIT_ERROR = 2
MAX_ALIGN_OFFSET = 120


def chromaprint(path: Path) -> str | None:
    try:
        p = subprocess.run(
            ["fpcalc", "-length", str(MAX_SECONDS), "-json", str(path)],
            capture_output=True, text=True, timeout=180, check=True,
        )
        value = json.loads(p.stdout).get("fingerprint")
        return value if isinstance(value, str) and value else None
    except (OSError, subprocess.SubprocessError, ValueError, json.JSONDecodeError):
        return None


def _popcount(value: int) -> int:
    return value.bit_count()


def similarity(a: str, b: str) -> float:
    """Compare Chromaprint fingerprints using the AcoustID alignment method.

    This is deliberately bounded to the local fingerprint comparison and does
    not contact the AcoustID service.
    """
    if not a or not b:
        return 0.0
    try:
        import chromaprint as cp
        aa = [int(x) for x in cp.decode_fingerprint(a.encode())[0]]
        bb = [int(x) for x in cp.decode_fingerprint(b.encode())[0]]
    except (ImportError, AttributeError, TypeError, ValueError):
        return 0.0
    if not aa or not bb:
        return 0.0

    counts = [0] * (len(aa) + len(bb) + 1)
    for i, av in enumerate(aa):
        for j in range(max(0, i - MAX_ALIGN_OFFSET), min(len(bb), i + MAX_ALIGN_OFFSET)):
            if _popcount(av ^ bb[j]) <= MAX_BIT_ERROR:
                counts[i - j + len(bb)] += 1
    return max(counts) / min(len(aa), len(bb))