from __future__ import annotations

from collections.abc import Mapping

from govoplan_core.core.policy import (
    FunctionAssignmentGovernanceDecision,
    FunctionAssignmentGovernanceRequest,
    PolicySourceStep,
)
from govoplan_core.security.module_permissions import scopes_grant_compatible


SUPPORTED_PROFILES = {
    "holder_grant",
    "holder_with_authority_clearance",
    "authority_only",
    "unavailable",
}


class FunctionAssignmentGovernancePolicyProvider:
    def resolve_function_assignment_action(
        self,
        session: object | None = None,
        *,
        request: FunctionAssignmentGovernanceRequest,
    ) -> FunctionAssignmentGovernanceDecision:
        del session
        policy = _policy(request.function_settings)
        profile = (
            str(policy.get(f"{request.kind}_profile") or "unavailable")
            .strip()
            .casefold()
        )
        if profile not in SUPPORTED_PROFILES:
            return _decision(
                request,
                policy,
                profile="unavailable",
                allowed=False,
                reason=f"Unsupported function assignment profile: {profile}.",
                requirements=("valid_profile",),
            )
        required_steps = _required_steps(
            request.kind,
            profile,
            recipient_acceptance=_bool(
                policy.get("recipient_acceptance_required"),
                default=request.kind == "grant",
            ),
        )
        authority_function_id = _text(policy.get("authority_function_id"))
        requirements: list[str] = []
        if "authority" in required_steps and authority_function_id is None:
            requirements.append("authority_function")
        evidence_required = _bool(
            policy.get("evidence_required"),
            default=False,
        )
        if evidence_required and not request.context.get("has_evidence"):
            requirements.append("evidence")
        allowed, reason = _action_decision(
            request,
            profile=profile,
            required_steps=required_steps,
        )
        if profile == "unavailable":
            allowed = False
            reason = "Function assignment requests and grants are disabled."
        if requirements and request.action == "submit":
            allowed = False
            reason = _requirements_reason(requirements)
        return _decision(
            request,
            policy,
            profile=profile,
            allowed=allowed,
            reason=reason,
            required_steps=required_steps,
            authority_function_id=authority_function_id,
            evidence_required=evidence_required,
            requirements=tuple(requirements),
        )


def _action_decision(
    request: FunctionAssignmentGovernanceRequest,
    *,
    profile: str,
    required_steps: tuple[str, ...],
) -> tuple[bool, str | None]:
    context = request.context
    action = request.action
    if action == "submit":
        if request.kind == "request":
            if not bool(context.get("candidate_is_actor")):
                return False, "A function request must target the requesting identity."
            if profile == "authority_only":
                allowed = bool(context.get("actor_is_authority"))
                return (
                    allowed,
                    None
                    if allowed
                    else "Only the designated authority may initiate this assignment.",
                )
            return True, None
        if profile == "authority_only":
            allowed = bool(context.get("actor_is_authority"))
            reason = "Only the designated authority may initiate this grant."
        else:
            allowed = bool(context.get("actor_is_holder"))
            reason = "An effective function holder must initiate this grant."
        return allowed, None if allowed else reason
    if action == "approve_holder":
        allowed = "holder" in required_steps and bool(context.get("actor_is_holder"))
        return allowed, None if allowed else "A current holder must approve."
    if action == "approve_authority":
        allowed = "authority" in required_steps and bool(
            context.get("actor_is_authority")
        )
        return allowed, None if allowed else "The designated authority must approve."
    if action == "accept_recipient":
        allowed = "recipient" in required_steps and bool(
            context.get("candidate_is_actor")
        )
        return allowed, None if allowed else "The candidate must accept this grant."
    if action in {"reject", "request_changes"}:
        if request.current_state == "awaiting_holder":
            allowed = bool(context.get("actor_is_holder"))
            reason = "A current holder must act at the holder review step."
        elif request.current_state == "awaiting_authority":
            allowed = bool(context.get("actor_is_authority"))
            reason = "The designated authority must act at the authority step."
        elif request.current_state == "awaiting_recipient":
            allowed = bool(context.get("candidate_is_actor"))
            reason = "Only the candidate may act at recipient acceptance."
        else:
            allowed = False
            reason = "The current state does not accept this review action."
        return allowed, None if allowed else reason
    if action == "respond":
        allowed = request.current_state == "changes_requested" and (
            bool(context.get("actor_is_initiator"))
            or bool(context.get("candidate_is_actor"))
        )
        return (
            allowed,
            None
            if allowed
            else "Only the initiator or candidate may respond to requested changes.",
        )
    if action == "withdraw":
        allowed = bool(context.get("actor_is_initiator"))
        return (
            allowed,
            None if allowed else "Only the initiator may withdraw this change.",
        )
    if action == "recover":
        allowed = _has_scope(request, "idm:function_change:admin")
        return (
            allowed,
            None if allowed else "Administrative recovery permission is required.",
        )
    if action == "apply":
        allowed = bool(context.get("approvals_complete"))
        return allowed, None if allowed else "Required decisions are incomplete."
    return False, f"Unsupported function assignment action: {action}."


def _required_steps(
    kind: str,
    profile: str,
    *,
    recipient_acceptance: bool,
) -> tuple[str, ...]:
    if profile == "holder_grant":
        steps = ["holder"]
    elif profile == "holder_with_authority_clearance":
        steps = ["holder", "authority"]
    elif profile == "authority_only":
        steps = ["authority"]
    else:
        steps = []
    if kind == "grant" and recipient_acceptance:
        steps.append("recipient")
    return tuple(steps)


def _decision(
    request: FunctionAssignmentGovernanceRequest,
    policy: Mapping[str, object],
    *,
    profile: str,
    allowed: bool,
    reason: str | None,
    required_steps: tuple[str, ...] = (),
    authority_function_id: str | None = None,
    evidence_required: bool = False,
    requirements: tuple[str, ...] = (),
) -> FunctionAssignmentGovernanceDecision:
    recipient_required = "recipient" in required_steps
    return FunctionAssignmentGovernanceDecision(
        allowed=allowed,
        reason=reason,
        profile=profile,
        required_steps=required_steps,
        authority_function_id=authority_function_id,
        evidence_required=evidence_required,
        recipient_acceptance_required=recipient_required,
        separation_of_duties=_bool(
            policy.get("separation_of_duties"),
            default=True,
        ),
        quorum=_bounded_int(policy.get("quorum"), default=1, minimum=1, maximum=20),
        maximum_validity_days=_optional_positive_int(
            policy.get("maximum_validity_days"),
            maximum=3650,
        ),
        request_expiry_hours=_bounded_int(
            policy.get("request_expiry_hours"),
            default=336,
            minimum=1,
            maximum=8760,
        ),
        source_path=(
            PolicySourceStep(
                scope_type="tenant",
                scope_id=request.tenant_id,
                label="Organization function assignment policy",
                applied_fields=tuple(sorted(policy)),
                policy=policy,
            ),
        ),
        requirements=requirements,
        details={
            "function_id": request.function_id,
            "kind": request.kind,
            "action": request.action,
        },
    )


def _policy(settings: Mapping[str, object]) -> dict[str, object]:
    raw = settings.get("assignment_governance")
    return dict(raw) if isinstance(raw, Mapping) else {}


def _requirements_reason(requirements: list[str]) -> str:
    labels = {
        "authority_function": "a designated authority function",
        "evidence": "the required evidence",
        "valid_profile": "a supported governance profile",
    }
    return (
        "Submission requires "
        + ", ".join(labels.get(item, item.replace("_", " ")) for item in requirements)
        + "."
    )


def _has_scope(
    request: FunctionAssignmentGovernanceRequest,
    scope: str,
) -> bool:
    return scopes_grant_compatible(request.actor.scopes, scope)


def _text(value: object) -> str | None:
    text = str(value).strip() if value is not None else ""
    return text or None


def _bool(value: object, *, default: bool) -> bool:
    return value if isinstance(value, bool) else default


def _bounded_int(
    value: object,
    *,
    default: int,
    minimum: int,
    maximum: int,
) -> int:
    try:
        number = int(value) if value is not None else default
    except (TypeError, ValueError):
        return default
    return max(minimum, min(number, maximum))


def _optional_positive_int(value: object, *, maximum: int) -> int | None:
    if value is None:
        return None
    try:
        number = int(value)
    except (TypeError, ValueError):
        return None
    return max(1, min(number, maximum))


__all__ = [
    "FunctionAssignmentGovernancePolicyProvider",
    "SUPPORTED_PROFILES",
]