"""File-type sniffing for ``simurg inspect`` (spec CLI-020)."""

from __future__ import annotations

import gzip
from pathlib import Path

KINDS = ("idat", "bpm", "egt", "gtc", "csv_manifest", "samplesheet", "vcf", "unknown")


def _head(path: Path, n: int = 4096) -> bytes:
    with path.open("rb") as fh:
        b = fh.read(n)
    if b[:2] == b"\x1f\x8b":
        try:
            with gzip.open(path, "rb") as gz:
                return gz.read(n)
        except OSError:
            return b
    return b


def detect_kind(path: str | Path) -> str:
    p = Path(path)
    head = _head(p)
    name = p.name.lower()
    if head[:4] == b"IDAT":
        return "idat"
    if head[:3] == b"BPM":
        return "bpm"
    if head[:3] == b"gtc":
        return "gtc"
    if head.startswith(b"##fileformat=VCF"):
        return "vcf"
    if name.endswith(".egt") or (len(head) >= 5 and head[:4] == b"\x03\x00\x00\x00"):
        return "egt"
    text = head.decode("utf-8", errors="replace").lower()
    if "[assay]" in text or ("[heading]" in text and "descriptor file name" in text):
        return "csv_manifest"
    if "sentrixbarcode_a" in text or "beadchipname" in text or "[data]" in text:
        return "samplesheet"
    return "unknown"