from typing import Any

from django.core.exceptions import ValidationError
from django.db import transaction

from apps.reviews.models import ApproverGroup, ReviewSettings
from apps.users.models import User, UserRole
from config.errors import ConflictError


def review_settings_update(
    *,
    default_min_approvals: int | None = None,
    allow_any_approver: bool | None = None,
) -> ReviewSettings:
    settings = ReviewSettings.load()

    if default_min_approvals is not None:
        if default_min_approvals < 1:
            raise ValidationError(
                {
                    "default_min_approvals": (
                        "Minimum approvals must be at least 1."
                    )
                }
            )
        settings.default_min_approvals = default_min_approvals

    if allow_any_approver is not None:
        settings.allow_any_approver = allow_any_approver

    settings.save()
    return settings


def _validate_experimenter(user: User) -> None:
    if user.role != UserRole.EXPERIMENTER:
        raise ValidationError(
            {
                "experimenter": (
                    f"User '{user.username}' has role '{user.role}'. "
                    f"Only users with the '{UserRole.EXPERIMENTER}' role "
                    f"can be assigned an approver group."
                )
            }
        )
    if not user.is_active:
        raise ValidationError(
            {"experimenter": "The experimenter must be an active user."}
        )


def _validate_approvers(approvers: list[User]) -> None:
    invalid = [u for u in approvers if u.role != UserRole.APPROVER]
    if invalid:
        names = ", ".join(u.username for u in invalid)
        raise ValidationError(
            {
                "approvers": (
                    f"The following users do not have the "
                    f"'{UserRole.APPROVER}' role: {names}"
                )
            }
        )


def _validate_min_approvals(
    min_approvals: int,
    approver_count: int | None = None,
) -> None:
    if min_approvals < 1:
        raise ValidationError(
            {"min_approvals": "Minimum approvals must be at least 1."}
        )
    if approver_count is not None and min_approvals > approver_count:
        raise ValidationError(
            {
                "min_approvals": (
                    f"min_approvals ({min_approvals}) cannot exceed the "
                    f"number of assigned approvers ({approver_count})."
                )
            }
        )


@transaction.atomic
def approver_group_create(
    *,
    experimenter: User,
    approver_ids: list[Any] | None = None,
    min_approvals: int = 1,
) -> ApproverGroup:
    _validate_experimenter(experimenter)
    if ApproverGroup.objects.filter(experimenter=experimenter).exists():
        raise ConflictError(
            ValidationError(
                {
                    "experimenter": (
                        f"An approver group already exists for "
                        f"experimenter '{experimenter.username}'."
                    )
                }
            )
        )
    approvers: list[User] = []
    if approver_ids:
        approvers = list(
            User.objects.filter(pk__in=approver_ids, is_active=True)
        )
        found_ids = {str(u.pk) for u in approvers}
        missing = [
            str(aid) for aid in approver_ids if str(aid) not in found_ids
        ]
        if missing:
            raise ValidationError(
                {
                    "approvers": (
                        f"Users not found or inactive: {', '.join(missing)}"
                    )
                }
            )
        _validate_approvers(approvers)

    _validate_min_approvals(
        min_approvals, len(approvers) if approvers else None
    )

    group = ApproverGroup(
        experimenter=experimenter,
        min_approvals=min_approvals,
    )
    group.save()

    if approvers:
        group.approvers.set(approvers)

    return group


@transaction.atomic
def approver_group_update(
    *,
    group: ApproverGroup,
    approver_ids: list[Any] | None = None,
    min_approvals: int | None = None,
) -> ApproverGroup:
    approvers: list[User] | None = None

    if approver_ids is not None:
        approvers = list(
            User.objects.filter(pk__in=approver_ids, is_active=True)
        )
        found_ids = {str(u.pk) for u in approvers}
        missing = [
            str(aid) for aid in approver_ids if str(aid) not in found_ids
        ]
        if missing:
            raise ValidationError(
                {
                    "approvers": (
                        f"Users not found or inactive: {', '.join(missing)}"
                    )
                }
            )
        _validate_approvers(approvers)

    if min_approvals is not None:
        approver_count = (
            len(approvers)
            if approvers is not None
            else group.approvers.count()
        )
        _validate_min_approvals(min_approvals, approver_count)
        group.min_approvals = min_approvals

    group.save()

    if approvers is not None:
        group.approvers.set(approvers)

    return group


@transaction.atomic
def approver_group_delete(*, group: ApproverGroup) -> None:
    group.delete()


@transaction.atomic
def approver_group_add_approver(
    *,
    group: ApproverGroup,
    approver: User,
) -> ApproverGroup:
    _validate_approvers([approver])

    if group.approvers.filter(pk=approver.pk).exists():
        raise ValidationError(
            {
                "approver": (
                    f"User '{approver.username}' is already in this "
                    f"approver group."
                )
            }
        )

    group.approvers.add(approver)
    return group


@transaction.atomic
def approver_group_remove_approver(
    *,
    group: ApproverGroup,
    approver: User,
) -> ApproverGroup:
    if not group.approvers.filter(pk=approver.pk).exists():
        raise ValidationError(
            {
                "approver": (
                    f"User '{approver.username}' is not in this "
                    f"approver group."
                )
            }
        )

    remaining = group.approvers.count() - 1
    if remaining < group.min_approvals:
        raise ValidationError(
            {
                "approver": (
                    f"Cannot remove approver: would leave {remaining} "
                    f"approver(s), but {group.min_approvals} required."
                )
            }
        )

    group.approvers.remove(approver)
    return group