from __future__ import annotations
import hashlib, json, os, time, datetime as _dt, subprocess
from pathlib import Path
from typing import Any

ROOT = Path(__file__).resolve().parents[2]

def utc_now() -> str:
    return _dt.datetime.now(_dt.timezone.utc).strftime("%Y-%m-%dT%H:%M:%S.%fZ")

def sha256_bytes(b: bytes) -> str:
    return hashlib.sha256(b).hexdigest()

def sha256_text(s: str) -> str:
    return sha256_bytes(s.encode("utf-8"))

def sha256_file(p: str | Path, chunk: int = 1 << 20) -> str:
    h = hashlib.sha256()
    with open(p, "rb") as f:
        while True:
            b = f.read(chunk)
            if not b:
                break
            h.update(b)
    return h.hexdigest()

def sha256_json(obj: Any) -> str:
    return sha256_text(json.dumps(obj, sort_keys=True, separators=(",", ":"), default=str))

def git_commit(root: Path = ROOT) -> str | None:
    try:
        return subprocess.check_output(["git", "-C", str(root), "rev-parse", "HEAD"], text=True, stderr=subprocess.DEVNULL).strip()
    except Exception:
        return None

def append_jsonl(path: str | Path, rec: dict) -> None:
    path = Path(path)
    path.parent.mkdir(parents=True, exist_ok=True)
    line = json.dumps(rec, ensure_ascii=False, default=str) + "\n"
    with open(path, "a", encoding="utf-8") as f:
        f.write(line)
        f.flush()
        os.fsync(f.fileno())

def read_jsonl(path: str | Path) -> list[dict]:
    out = []
    p = Path(path)
    if not p.exists():
        return out
    with open(p, encoding="utf-8") as f:
        for line in f:
            line = line.strip()
            if line:
                out.append(json.loads(line))
    return out

def write_json(path: str | Path, obj: Any) -> None:
    path = Path(path)
    path.parent.mkdir(parents=True, exist_ok=True)
    with open(path, "w", encoding="utf-8") as f:
        json.dump(obj, f, indent=2, ensure_ascii=False, default=str)

def read_json(path: str | Path) -> Any:
    with open(path, encoding="utf-8") as f:
        return json.load(f)

class Timer:
    """Wall-clock span timer (perf_counter). Call sync() hooks around spans for accelerators."""
    def __init__(self):
        self.spans: dict[str, float] = {}
        self._t0: dict[str, float] = {}
    def start(self, name: str):
        self._t0[name] = time.perf_counter()
    def stop(self, name: str) -> float:
        dt = (time.perf_counter() - self._t0.pop(name)) * 1000.0
        self.spans[name] = self.spans.get(name, 0.0) + dt
        return dt
    def ms(self) -> dict[str, float]:
        return dict(self.spans)