"""Validated parser for the official Siscomex NCM JSON download."""

from dataclasses import dataclass
from datetime import datetime
import hashlib
import json


@dataclass(frozen=True)
class NcmEntry:
    code: str
    description: str
    valid_from: str
    valid_to: str


@dataclass(frozen=True)
class NcmPayload:
    version: str
    act: str
    sha256: str
    entries: tuple[NcmEntry, ...]


def parse_ncm_payload(payload: bytes) -> NcmPayload:
    try:
        document = json.loads(payload)
    except (TypeError, json.JSONDecodeError) as error:
        raise ValueError("payload is not valid JSON") from error
    if not isinstance(document, dict):
        raise ValueError("payload root must be an object")
    nomenclaturas = document.get("Nomenclaturas")
    version = document.get("Data_Ultima_Atualizacao_NCM")
    act = document.get("Ato")
    if not isinstance(nomenclaturas, list) or not nomenclaturas:
        raise ValueError("Nomenclaturas must be a nonempty list")
    if not isinstance(version, str) or not isinstance(act, str):
        raise ValueError("dataset metadata is invalid")
    entries = []
    for item in nomenclaturas:
        if not isinstance(item, dict):
            raise ValueError("Nomenclaturas item must be an object")
        values = tuple(item.get(name) for name in ("Codigo", "Descricao", "Data_Inicio", "Data_Fim"))
        if not all(isinstance(value, str) for value in values):
            raise ValueError("Nomenclaturas item schema is invalid")
        code, description, valid_from, valid_to = values
        entries.append(NcmEntry("".join(char for char in code if char.isdigit()), description, valid_from, valid_to))
    return NcmPayload(version, act, hashlib.sha256(payload).hexdigest(), tuple(entries))