# Copyright (c) 2026 Tiago Pinto <tiago@donttrustverify.pt>
# SPDX-License-Identifier: MIT
#
# Independent producer-side implementation of
# draft-fassbender-scitt-time-anchor-03, written from the published
# Internet-Draft alone. See README.md and CONSTRUCTION.md.
"""calendar_client.py: OpenTimestamps Calendar Server protocol.

The profile does not specify this protocol; it imports it from [OTS]
(Appendix D, preamble). Implemented from the pinned release:

  - submission: POST of the raw digest to {url}/digest, with header
    Accept: application/vnd.opentimestamps.v1; the response is a
    serialised Timestamp relative to the submitted value
    ([OTS] calendar.py:47-76)
  - upgrade: GET {url}/timestamp/{hex(commitment)}; 200 gives a
    serialised Timestamp relative to the commitment, any other status
    means not yet available ([OTS] calendar.py:78-100)

Not security-critical: compromise of a calendar is addressed in profile
Section 6.3, and verification never contacts a calendar (Section 3.2).

Inline comments below are in Portuguese, the implementer's working
language.
"""

import urllib.request

import ots_wire

HEADERS = {'Accept': 'application/vnd.opentimestamps.v1',
           'User-Agent': 'interop-fassbender-03'}
MAX_RESPONSE = 10000   # calendar.py:71-73


def _parse_timestamp(resp_bytes: bytes) -> ots_wire.Node:
    """A resposta do calendário é um Timestamp sem cabeçalho de
    ficheiro: só a estrutura recursiva (timestamp.py:130-183)."""
    r = ots_wire.Reader(resp_bytes)
    node = ots_wire.Node.deserialize(r)
    if not r.at_eof():
        raise ots_wire.WireError("lixo após a resposta do calendário")
    return node


def submit(url: str, digest: bytes, timeout=30) -> ots_wire.Node:
    """HTTP-POST(url, digest) do D.1 passo 4 / D.3 passo 4."""
    req = urllib.request.Request(url.rstrip('/') + '/digest',
                                 data=digest, headers=HEADERS)
    with urllib.request.urlopen(req, timeout=timeout) as resp:
        if resp.status != 200:
            raise IOError(f"calendário devolveu {resp.status}")
        body = resp.read(MAX_RESPONSE + 1)
        if len(body) > MAX_RESPONSE:
            raise IOError("resposta do calendário excede o limite")
    return _parse_timestamp(body)


def get_timestamp(url: str, commitment: bytes, timeout=30):
    """Pedido de upgrade: devolve Node ou None se ainda não houver
    caminho Bitcoin (OTS-UPGRADE devolve NULL nesse caso, §1.4)."""
    req = urllib.request.Request(
        url.rstrip('/') + '/timestamp/' + commitment.hex(),
        headers=HEADERS)
    try:
        with urllib.request.urlopen(req, timeout=timeout) as resp:
            if resp.status != 200:
                return None
            body = resp.read(MAX_RESPONSE + 1)
            if len(body) > MAX_RESPONSE:
                return None
        return _parse_timestamp(body)
    except Exception:
        return None