from __future__ import annotations

from collections.abc import Mapping, Sequence
from dataclasses import dataclass
import hashlib
from sqlalchemy.orm import Session

from govoplan_core.core.distribution_lists import (
    DistributionChannelPolicyDecision,
    DistributionChannelPolicyRequest,
)
from govoplan_policy.backend.policy_overrides import resolution_policy_overrides


CHANNELS = frozenset({"email", "postal", "internal_mail", "portal"})


@dataclass(frozen=True, slots=True)
class DistributionChannelPolicyResolution:
    allowed_channels: frozenset[str]
    source_path: tuple[Mapping[str, object], ...] = ()
    diagnostics: tuple[Mapping[str, object], ...] = ()


class DistributionChannelPolicyProvider:
    def resolve_distribution_channel(
        self,
        session: object,
        principal: object,
        *,
        request: DistributionChannelPolicyRequest,
    ) -> DistributionChannelPolicyDecision:
        resolution = _resolve(session, principal, request)
        channel = request.candidate.channel
        allowed = channel in resolution.allowed_channels
        malformed = any(
            item.get("code") == "distribution_channel_policy.invalid"
            for item in resolution.diagnostics
        )
        if malformed and not allowed:
            reason_code = "policy.invalid_fail_closed"
            explanation = (
                "Distribution is blocked because an applicable channel policy is invalid."
            )
        elif allowed:
            reason_code = "policy.channel_allowed"
            explanation = f"The {channel} channel is permitted by the effective Policy."
        else:
            reason_code = "policy.channel_blocked"
            explanation = f"The {channel} channel is blocked by the effective Policy."
        return DistributionChannelPolicyDecision(
            allowed=allowed,
            reason_code=reason_code,
            explanation=explanation,
            source_path=resolution.source_path,
            requirements=(() if allowed else (f"policy.channel.{channel}",)),
            details={
                "allowed_channels": sorted(resolution.allowed_channels),
                "diagnostics": [dict(item) for item in resolution.diagnostics],
            },
        )


def resolve_distribution_channel_policy_rows(
    rows: object,
) -> DistributionChannelPolicyResolution:
    allowed_channels = set(CHANNELS)
    source_path: list[Mapping[str, object]] = []
    diagnostics: list[Mapping[str, object]] = []
    for row in rows if isinstance(rows, (list, tuple)) else ():
        policy, malformed = validate_distribution_channel_policy(row.policy)
        if malformed:
            allowed_channels.clear()
            applied_fields: tuple[str, ...] = ("configuration_status",)
            source_policy: Mapping[str, object] = {
                "configuration_status": "invalid_fail_closed",
                "target_key": row.target_key,
            }
            diagnostics.append(
                {
                    "code": "distribution_channel_policy.invalid",
                    "severity": "error",
                    "scope": row.scope_key,
                    "target_key": row.target_key,
                }
            )
        else:
            configured = policy.get("allowed_channels")
            blocked = policy.get("blocked_channels", ())
            if isinstance(configured, tuple):
                allowed_channels.intersection_update(configured)
            if isinstance(blocked, tuple):
                allowed_channels.difference_update(blocked)
            applied_fields = tuple(sorted(policy))
            source_policy = {
                key: list(value) if isinstance(value, tuple) else value
                for key, value in policy.items()
            }
            source_policy = {**source_policy, "target_key": row.target_key}
        source_path.append(
            {
                "scope_type": row.scope_type,
                "scope_id": row.scope_id,
                "label": f"{row.scope_type.capitalize()} distribution-channel policy",
                "applied_fields": list(applied_fields),
                "policy": dict(source_policy),
            }
        )
    return DistributionChannelPolicyResolution(
        allowed_channels=frozenset(allowed_channels),
        source_path=tuple(source_path),
        diagnostics=tuple(diagnostics),
    )


def validate_distribution_channel_policy(
    value: object,
) -> tuple[dict[str, tuple[str, ...]], bool]:
    if not isinstance(value, Mapping):
        return {}, True
    supported = {"allowed_channels", "blocked_channels"}
    if any(str(key) not in supported for key in value):
        return {}, True
    policy: dict[str, tuple[str, ...]] = {}
    for key, raw in value.items():
        if not isinstance(raw, Sequence) or isinstance(raw, (str, bytes)):
            return {}, True
        channels = tuple(dict.fromkeys(str(item).strip() for item in raw))
        if any(channel not in CHANNELS for channel in channels):
            return {}, True
        policy[str(key)] = channels
    return policy, False


def _resolve(
    session: object,
    principal: object,
    request: DistributionChannelPolicyRequest,
) -> DistributionChannelPolicyResolution:
    if not isinstance(session, Session):
        return DistributionChannelPolicyResolution(allowed_channels=CHANNELS)
    group_ids = tuple(getattr(principal, "group_ids", ()) or ())
    account_id = str(getattr(principal, "account_id", "") or "")
    membership_id = str(getattr(principal, "membership_id", "") or "")
    target_keys = ["*", _target_key("list", request.list_id)]
    if request.purpose:
        target_keys.extend(
            (
                _target_key("purpose", request.purpose),
                _target_key(
                    f"list:{request.list_id}:purpose",
                    request.purpose,
                ),
            )
        )
    rows = resolution_policy_overrides(
        session,
        policy_family="distribution_channels",
        target_keys=target_keys,
        tenant_id=request.tenant_id,
        group_ids=group_ids,
        user_ids=(account_id, membership_id),
    )
    return resolve_distribution_channel_policy_rows(rows)


def _target_key(prefix: str, value: str) -> str:
    candidate = f"{prefix}:{value}"
    if len(candidate) <= 120:
        return candidate
    digest = hashlib.sha256(value.encode("utf-8")).hexdigest()
    return f"{prefix[:78]}:sha256:{digest[:32]}"


__all__ = [
    "CHANNELS",
    "DistributionChannelPolicyProvider",
    "DistributionChannelPolicyResolution",
    "resolve_distribution_channel_policy_rows",
    "validate_distribution_channel_policy",
]