"""Server-side signing examples for Merchant Payin v2, using built-in modules.

The issued secret is used literally; never base64-decode it or put it in browser
code. Request targets and body bytes must be the ones actually sent over HTTP.
"""

import hashlib
import hmac
import re


def _bytes(value):
    if isinstance(value, str):
        return value.encode("utf-8")
    if isinstance(value, (bytes, bytearray)):
        return bytes(value)
    raise TypeError("The raw body must be a UTF-8 string or bytes.")


def _secret_bytes(secret):
    if not isinstance(secret, str) or not secret:
        raise TypeError("A literal Shop secret is required.")
    return secret.encode("utf-8")


def sign_request(timestamp, nonce, method, target, raw_body, secret):
    """Return lowercase-hex HMAC-SHA512 of the exact five-component request."""
    if not isinstance(timestamp, str) or not re.fullmatch(r"(0|[1-9][0-9]*)", timestamp):
        raise TypeError("Timestamp must be canonical Unix seconds as a string.")
    if not isinstance(nonce, str) or not re.fullmatch(
        r"[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}", nonce, re.I
    ):
        raise TypeError("Nonce must be UUID v4.")
    if not isinstance(method, str) or not re.fullmatch(r"[A-Za-z]+", method):
        raise TypeError("Invalid HTTP method.")
    if not isinstance(target, str) or not re.fullmatch(r"/(?!/)[^\r\n#]*", target):
        raise TypeError("Use the exact path and encoded query.")
    prefix = "\n".join((timestamp, nonce, method.upper(), target, "")).encode("utf-8")
    return hmac.new(_secret_bytes(secret), prefix + _bytes(raw_body), hashlib.sha512).hexdigest()


def verify_webhook(raw_body, timestamp, signature, secret):
    """Verify timestamp + '.' + raw body with a constant-time comparison.

    Also check freshness in the HTTP receiver (recommended ±300 seconds) and
    commit id/status_id with the business effect atomically. A delayed overdue
    notification must not downgrade a previously accepted success.
    """
    if not isinstance(timestamp, str) or not re.fullmatch(r"(0|[1-9][0-9]*)", timestamp):
        return False
    if not isinstance(signature, str) or not re.fullmatch(r"[0-9a-f]{128}", signature):
        return False
    canonical = timestamp.encode("utf-8") + b"." + _bytes(raw_body)
    expected = hmac.new(_secret_bytes(secret), canonical, hashlib.sha512).hexdigest()
    return hmac.compare_digest(expected, signature)