"""Pure contract for informed-decision forwarding and notifications.

Dev and request validation only. This module does not read a token, open a
socket, register a submitter, or decide a hub decision. ``drafted_by`` is
asserted provenance; it is never an authenticated identity.
"""
from __future__ import annotations

import hashlib
import json
import re
from dataclasses import dataclass
from typing import Any, Mapping

KIND = "informed-decision.memo-intake"
VERSION = 1
OVERVIEW_LINE = "The signed-in overview is the authoritative review entry point."
PROVENANCE_NOTE = (
    "drafted_by is asserted provenance, not authenticated identity. "
    "A forwarded token proves only the hub submitter."
)
RESOLVING_VERBS = frozenset({"accept", "decline"})
NOTIFICATION_FIELDS = ("memo_id", "question", "memo_class", "submitter")
MAX_QUESTION = 400
MAX_DRAFTED_BY = 200
MAX_PACKET_BYTES = 256 * 1024
MAX_ENVELOPE_BYTES = 1024 * 1024
MAX_PACKET_ITEMS = 32
MAX_NOTIFICATION_BYTES = 8192

_KEY_RE = re.compile(r"^[A-Za-z0-9._:-]{8,128}$")
_MEMO_ID_RE = re.compile(r"^[a-z0-9][a-z0-9-]{2,62}$")
_SLUG_RE = re.compile(r"^[a-z0-9][a-z0-9-]{1,62}$")
_UUID_RE = re.compile(r"^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$")
_SHA_RE = re.compile(r"^sha256:[0-9a-f]{64}$")
_ERROR_RE = re.compile(r"^[a-z0-9_]{1,64}$")

ENVELOPE_KEYS = {
    "kind", "version", "idempotency_key", "memo_class", "review_group",
    "drafted_by", "serves", "approval_intent", "memo", "packet",
}
ENVELOPE_REQUIRED = ENVELOPE_KEYS - {"drafted_by", "serves"}
INTENT_KEYS = {"action", "principal", "purpose", "target"}
TARGET_KEYS = {"id", "type", "system"}
PACKET_KEYS = {"item_id", "media_type", "content"}
MEDIA_TYPES = {"text/markdown", "text/plain", "application/json"}

# Shapes only. A hit is refused by code; the matched text is never echoed.
_SECRET_MARKERS = (
    re.compile(r"-----BEGIN [A-Z ]*PRIVATE KEY-----"),
    re.compile(r"\bBearer\s+[A-Za-z0-9._~+/=-]{16,}"),
    re.compile(r"\beyJ[A-Za-z0-9_-]{8,}\.eyJ[A-Za-z0-9_-]{8,}\.[A-Za-z0-9_-]{8,}"),
    re.compile(r"\b(hvs|hvb|hvr)\.[A-Za-z0-9_-]{20,}"),
    re.compile(
        r"\b(sk-(or-)?[A-Za-z0-9_-]{20,}|ghp_[A-Za-z0-9]{30,}|"
        r"github_pat_[A-Za-z0-9_]{30,}|glpat-[A-Za-z0-9_-]{20,}|"
        r"AKIA[0-9A-Z]{16}|xox[abpr]-[A-Za-z0-9-]{10,})"
    ),
    re.compile(
        r"(?i)\b(password|passwd|client_secret|secret|api[_-]?key|access[_-]?token|token)"
        r"\s*[:=]\s*['\"]?(?=[A-Za-z0-9_+.=-]*\d)[A-Za-z0-9_+.=-]{12,}(?=['\"\s,;)]|$)"
    ),
    re.compile(r"://[^/@\s:]+:[^/@\s]+@"),
)


class ContractError(ValueError):
    def __init__(self, code: str, status: int = 400) -> None:
        super().__init__(code)
        self.code = code
        self.status = status


def canonical(value: Any) -> str:
    return json.dumps(value, sort_keys=True, separators=(",", ":"), ensure_ascii=False)


def digest(value: Any) -> str:
    return hashlib.sha256(canonical(value).encode("utf-8")).hexdigest()


def scan_secrets(value: Any) -> None:
    for text in _strings(value):
        for pattern in _SECRET_MARKERS:
            if pattern.search(text):
                raise ContractError("secret_marker")


def stable_idempotency_key(decision_id: str, memo_id: str) -> str:
    _uuid(decision_id, "hub_decision_id")
    _memo_id(memo_id)
    return f"state-hub.{decision_id}.{memo_id}"


def resolution_applies(verb: str, serves: Mapping | None) -> bool:
    """Terminal human accept/decline with resolves=on-answer only."""
    if verb not in RESOLVING_VERBS:
        return False
    if not isinstance(serves, Mapping):
        return False
    return serves.get("resolves") == "on-answer"


def correlate_resolution(
    memo_id: str, *, post_status: int | None, existing: Mapping | None
) -> str:
    """Classify a resolve attempt. A 409 is a conflict only after the existing
    resolution was read; an unreadable 409 stays retryable."""
    _memo_id(memo_id)
    if post_status is None:
        return "failed"
    if 200 <= post_status < 300:
        return "resolved"
    if post_status != 409:
        return "failed"
    if not isinstance(existing, Mapping):
        return "failed"
    rationale = existing.get("rationale")
    if not isinstance(rationale, str):
        return "failed"
    if f"memo {memo_id} " in rationale:
        return "already_resolved"
    return "conflict"


def safe_error_code(value: Any, fallback: str) -> str:
    if isinstance(value, str) and _ERROR_RE.match(value):
        return value
    return fallback


@dataclass(frozen=True)
class Notification:
    memo_id: str
    question: str
    memo_class: str
    submitter: str

    def as_body(self) -> dict[str, str]:
        return {
            "memo_id": self.memo_id,
            "question": self.question,
            "memo_class": self.memo_class,
            "submitter": self.submitter,
        }

    @property
    def body_digest(self) -> str:
        return digest(self.as_body())

    def message_subject(self) -> str:
        return f"Decision memo {self.memo_id}"

    def message_text(self) -> str:
        return OVERVIEW_LINE + "\n" + canonical(self.as_body())


def parse_delivery_id(value: str | None) -> str:
    if value is None or value == "":
        raise ContractError("delivery_id_required")
    if not isinstance(value, str) or not _KEY_RE.match(value):
        raise ContractError("delivery_id_invalid")
    return value


def parse_notification(payload: Any) -> Notification:
    if not isinstance(payload, dict):
        raise ContractError("invalid_notification")
    if set(payload) - set(NOTIFICATION_FIELDS):
        raise ContractError("unknown_field")
    if set(NOTIFICATION_FIELDS) - set(payload):
        raise ContractError("missing_field")
    scan_secrets(payload)
    if any("://" in text for text in _strings(payload)):
        raise ContractError("notification_has_link")
    return Notification(
        memo_id=_memo_id(payload["memo_id"]),
        question=_one_question(payload["question"]),
        memo_class=_slug(payload["memo_class"], "memo_class"),
        submitter=_slug(payload["submitter"], "submitter"),
    )


def build_envelope(
    *,
    decision_id: str,
    memo: Mapping,
    packet: list,
    memo_class: str,
    review_group: str,
    approval_intent: Mapping,
    drafted_by: str | None = None,
    resolves: str = "on-answer",
) -> dict:
    if not isinstance(memo, Mapping) or not isinstance(memo.get("id"), str):
        raise ContractError("invalid_memo")
    envelope: dict[str, Any] = {
        "kind": KIND,
        "version": VERSION,
        "idempotency_key": stable_idempotency_key(decision_id, memo["id"]),
        "memo_class": memo_class,
        "review_group": review_group,
        "serves": {"hub_decision_id": decision_id, "resolves": resolves},
        "approval_intent": dict(approval_intent),
        "memo": dict(memo),
        "packet": list(packet),
    }
    if drafted_by is not None:
        envelope["drafted_by"] = drafted_by
    return validate_envelope(envelope)


def validate_envelope(envelope: Any) -> dict:
    if not isinstance(envelope, dict):
        raise ContractError("invalid_envelope")
    extra = set(envelope) - ENVELOPE_KEYS
    if extra:
        raise ContractError("unknown_field")
    missing = ENVELOPE_REQUIRED - set(envelope)
    if missing:
        raise ContractError("missing_field")
    if envelope["kind"] != KIND or type(envelope["version"]) is not int or envelope["version"] != VERSION:
        raise ContractError("unsupported_kind")
    scan_secrets(envelope)
    _packet(envelope["packet"])
    _bounded_tree(envelope)
    encoded = canonical(envelope).encode("utf-8")
    if len(encoded) > MAX_ENVELOPE_BYTES:
        raise ContractError("envelope_too_large")

    memo = envelope["memo"]
    if not isinstance(memo, dict):
        raise ContractError("invalid_memo")
    memo_id = _memo_id(memo.get("id"))
    if "question" in memo:
        _one_question(memo["question"])
    key = _text(envelope["idempotency_key"], pattern=_KEY_RE, code="idempotency_key_invalid")
    if "serves" in envelope:
        decision_id = _serves(envelope["serves"])
        if key != stable_idempotency_key(decision_id, memo_id):
            raise ContractError("idempotency_key_not_stable")
    elif not (memo_id.startswith("review-") and _UUID_RE.fullmatch(memo_id[7:]) and key == memo_id):
        # Lifecycle service supplies its retained snapshot id/key. Never invent
        # a Hub decision relationship or rewrite that immutable envelope.
        raise ContractError("lifecycle_handoff_key_invalid")
    _slug(envelope["memo_class"], "memo_class")
    _slug(envelope["review_group"], "review_group")
    drafted_by = envelope.get("drafted_by")
    if drafted_by is not None:
        _text(drafted_by, max_len=MAX_DRAFTED_BY, code="drafted_by_invalid")
    _intent(envelope["approval_intent"])
    if "submitter" in envelope or "actor" in envelope.get("approval_intent", {}):
        raise ContractError("unknown_field")
    return json.loads(canonical(envelope))


def submission_digest(envelope: Mapping) -> str:
    body = {key: value for key, value in envelope.items() if key != "idempotency_key"}
    return digest(body)


def bounded_receipt(body: Any, expected_memo_id: str) -> dict[str, str]:
    if not isinstance(body, dict):
        raise ContractError("receipt_incomplete")
    memo_id = body.get("memo_id")
    approval_id = body.get("approval_id")
    binding = body.get("approval_binding_digest")
    if memo_id != expected_memo_id or not isinstance(approval_id, str) or not _UUID_RE.match(approval_id):
        raise ContractError("receipt_mismatch")
    if not isinstance(binding, str) or not _SHA_RE.match(binding):
        raise ContractError("receipt_incomplete")
    return {
        "memo_id": memo_id,
        "approval_id": approval_id,
        "approval_binding_digest": binding,
    }


def _serves(serves: Any) -> str:
    if not isinstance(serves, dict) or set(serves) != {"hub_decision_id", "resolves"}:
        raise ContractError("invalid_serves")
    if serves["resolves"] not in ("on-answer", "never"):
        raise ContractError("unknown_enum")
    return _uuid(serves["hub_decision_id"], "hub_decision_id")


def _intent(intent: Any) -> None:
    if not isinstance(intent, dict) or set(intent) != INTENT_KEYS:
        raise ContractError("invalid_intent")
    for field in ("action", "principal", "purpose"):
        _text(intent[field], max_len=400, code="invalid_intent")
    target = intent["target"]
    if not isinstance(target, dict) or set(target) != TARGET_KEYS:
        raise ContractError("invalid_intent")
    for field in TARGET_KEYS:
        _text(target[field], max_len=200, code="invalid_intent")


def _packet(packet: Any) -> None:
    if not isinstance(packet, list) or not packet or len(packet) > MAX_PACKET_ITEMS:
        raise ContractError("packet_required" if not packet else "packet_unbounded")
    seen: set[str] = set()
    for item in packet:
        if not isinstance(item, dict) or set(item) != PACKET_KEYS:
            raise ContractError("invalid_packet")
        if item["media_type"] not in MEDIA_TYPES:
            raise ContractError("unsupported_media_type")
        content = item["content"]
        if not isinstance(content, str) or len(content.encode("utf-8")) > MAX_PACKET_BYTES:
            raise ContractError("packet_too_large")
        item_id = _text(item["item_id"], max_len=200, code="invalid_packet")
        if item_id in seen:
            raise ContractError("duplicate_packet_item")
        seen.add(item_id)


def _one_question(value: Any) -> str:
    text = _text(value, max_len=MAX_QUESTION, code="question_invalid")
    if "\n" in text or "\r" in text or "://" in text:
        raise ContractError("question_invalid")
    if text.count("?") != 1 or not text.endswith("?"):
        raise ContractError("question_not_one_question")
    return text


def _memo_id(value: Any) -> str:
    return _text(value, pattern=_MEMO_ID_RE, code="memo_id_invalid")


def _slug(value: Any, code: str) -> str:
    return _text(value, pattern=_SLUG_RE, code=code + "_invalid")


def _uuid(value: Any, code: str) -> str:
    return _text(value, pattern=_UUID_RE, code=code + "_invalid")


def _text(value: Any, *, max_len: int = 128, pattern: re.Pattern[str] | None = None, code: str) -> str:
    if not isinstance(value, str) or not value or len(value) > max_len:
        raise ContractError(code)
    if pattern is not None and not pattern.match(value):
        raise ContractError(code)
    return value


def _bounded_tree(value: Any) -> None:
    total = 0

    def walk(node: Any, key: str | None = None) -> None:
        nonlocal total
        if isinstance(node, str):
            size = len(node.encode("utf-8"))
            if size > MAX_PACKET_BYTES:
                raise ContractError("field_too_large")
            if key == "question":
                _one_question(node)
            total += size
        elif isinstance(node, dict):
            for child_key, child in node.items():
                if not isinstance(child_key, str):
                    raise ContractError("invalid_type")
                walk(child_key, None)
                walk(child, child_key)
        elif isinstance(node, list):
            for child in node:
                walk(child, key)
        elif isinstance(node, bool) or type(node) in (int, float) or node is None:
            # type() excludes bool; bool subclasses int, so it must be named first.
            return
        else:
            raise ContractError("invalid_type")
        if total > MAX_ENVELOPE_BYTES:
            raise ContractError("envelope_too_large")

    walk(value)


def _strings(value: Any):
    if isinstance(value, str):
        yield value
    elif isinstance(value, dict):
        for key, child in value.items():
            if isinstance(key, str):
                yield key
            yield from _strings(child)
    elif isinstance(value, list):
        for child in value:
            yield from _strings(child)