"""Validation helpers: ext size/depth, UUID, inp_hash/out_hash format."""

from __future__ import annotations

import base64
import json
import re
from typing import Any

EXT_MAX_SIZE = 4096
EXT_MAX_DEPTH = 5
DEFAULT_MAX_PAR_LENGTH = 100

_UUID_RE = re.compile(
    r"^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$"
)
_ALLOWED_HASH_ALGS = frozenset(("sha-256", "sha-384", "sha-512"))


def _json_depth(obj: Any, depth: int = 0) -> int:
    if depth > EXT_MAX_DEPTH:
        return depth
    if isinstance(obj, dict):
        return max((_json_depth(v, depth + 1) for v in obj.values()), default=depth + 1)
    if isinstance(obj, list):
        return max((_json_depth(x, depth + 1) for x in obj), default=depth + 1)
    return depth


def validate_ext(ext: dict[str, Any] | None) -> None:
    """Raise ValueError if ext exceeds EXT_MAX_SIZE or nesting depth EXT_MAX_DEPTH."""
    if not ext:
        return
    raw = json.dumps(ext)
    if len(raw.encode("utf-8")) > EXT_MAX_SIZE:
        raise ValueError("ect: ext exceeds max size (4096 bytes)")
    if _json_depth(ext) > EXT_MAX_DEPTH:
        raise ValueError("ect: ext exceeds max nesting depth (5)")


def valid_uuid(s: str) -> bool:
    """Return True if s is a UUID string (RFC 9562)."""
    return bool(_UUID_RE.match(s))


def validate_hash_format(s: str) -> None:
    """Raise ValueError if s is non-empty and not algorithm:base64url (sha-256, sha-384, sha-512)."""
    if not s:
        return
    idx = s.find(":")
    if idx <= 0:
        raise ValueError("ect: inp_hash/out_hash must be algorithm:base64url (e.g. sha-256:...)")
    alg = s[:idx].lower()
    if alg not in _ALLOWED_HASH_ALGS:
        raise ValueError("ect: inp_hash/out_hash must be algorithm:base64url (e.g. sha-256:...)")
    encoded = s[idx + 1:]
    if not encoded:
        raise ValueError("ect: inp_hash/out_hash must be algorithm:base64url (e.g. sha-256:...)")
    pad = 4 - len(encoded) % 4
    if pad != 4:
        encoded += "=" * pad
    try:
        base64.urlsafe_b64decode(encoded)
    except Exception:
        raise ValueError("ect: inp_hash/out_hash must be algorithm:base64url (e.g. sha-256:...)") from None