from __future__ import annotations

from collections.abc import Iterable
from datetime import datetime
from typing import Mapping, Sequence

from sqlalchemy import select, func
from sqlalchemy.exc import IntegrityError
from sqlalchemy.orm import Session, joinedload, selectinload

from models import (
    FinancialInput,
    Project,
    Role,
    Scenario,
    ScenarioStatus,
    SimulationParameter,
    User,
    UserRole,
)
from services.exceptions import EntityConflictError, EntityNotFoundError


class ProjectRepository:
    """Persistence operations for Project entities."""

    def __init__(self, session: Session) -> None:
        self.session = session

    def list(self, *, with_children: bool = False) -> Sequence[Project]:
        stmt = select(Project).order_by(Project.created_at)
        if with_children:
            stmt = stmt.options(selectinload(Project.scenarios))
        return self.session.execute(stmt).scalars().all()

    def count(self) -> int:
        stmt = select(func.count(Project.id))
        return self.session.execute(stmt).scalar_one()

    def recent(self, limit: int = 5) -> Sequence[Project]:
        stmt = (
            select(Project)
            .order_by(Project.updated_at.desc())
            .limit(limit)
        )
        return self.session.execute(stmt).scalars().all()

    def get(self, project_id: int, *, with_children: bool = False) -> Project:
        stmt = select(Project).where(Project.id == project_id)
        if with_children:
            stmt = stmt.options(joinedload(Project.scenarios))
        result = self.session.execute(stmt)
        if with_children:
            result = result.unique()
        project = result.scalar_one_or_none()
        if project is None:
            raise EntityNotFoundError(f"Project {project_id} not found")
        return project

    def exists(self, project_id: int) -> bool:
        stmt = select(Project.id).where(Project.id == project_id).limit(1)
        return self.session.execute(stmt).scalar_one_or_none() is not None

    def create(self, project: Project) -> Project:
        self.session.add(project)
        try:
            self.session.flush()
        except IntegrityError as exc:  # pragma: no cover - reliance on DB constraints
            raise EntityConflictError(
                "Project violates uniqueness constraints") from exc
        return project

    def find_by_names(self, names: Iterable[str]) -> Mapping[str, Project]:
        normalised = {name.strip().lower()
                      for name in names if name and name.strip()}
        if not normalised:
            return {}
        stmt = select(Project).where(func.lower(Project.name).in_(normalised))
        records = self.session.execute(stmt).scalars().all()
        return {project.name.lower(): project for project in records}

    def delete(self, project_id: int) -> None:
        project = self.get(project_id)
        self.session.delete(project)


class ScenarioRepository:
    """Persistence operations for Scenario entities."""

    def __init__(self, session: Session) -> None:
        self.session = session

    def list_for_project(self, project_id: int) -> Sequence[Scenario]:
        stmt = (
            select(Scenario)
            .where(Scenario.project_id == project_id)
            .order_by(Scenario.created_at)
        )
        return self.session.execute(stmt).scalars().all()

    def count(self) -> int:
        stmt = select(func.count(Scenario.id))
        return self.session.execute(stmt).scalar_one()

    def count_by_status(self, status: ScenarioStatus) -> int:
        stmt = select(func.count(Scenario.id)).where(Scenario.status == status)
        return self.session.execute(stmt).scalar_one()

    def recent(self, limit: int = 5, *, with_project: bool = False) -> Sequence[Scenario]:
        stmt = select(Scenario).order_by(
            Scenario.updated_at.desc()).limit(limit)
        if with_project:
            stmt = stmt.options(joinedload(Scenario.project))
        return self.session.execute(stmt).scalars().all()

    def list_by_status(
        self,
        status: ScenarioStatus,
        *,
        limit: int | None = None,
        with_project: bool = False,
    ) -> Sequence[Scenario]:
        stmt = (
            select(Scenario)
            .where(Scenario.status == status)
            .order_by(Scenario.updated_at.desc())
        )
        if with_project:
            stmt = stmt.options(joinedload(Scenario.project))
        if limit is not None:
            stmt = stmt.limit(limit)
        return self.session.execute(stmt).scalars().all()

    def get(self, scenario_id: int, *, with_children: bool = False) -> Scenario:
        stmt = select(Scenario).where(Scenario.id == scenario_id)
        if with_children:
            stmt = stmt.options(
                joinedload(Scenario.financial_inputs),
                joinedload(Scenario.simulation_parameters),
            )
        result = self.session.execute(stmt)
        if with_children:
            result = result.unique()
        scenario = result.scalar_one_or_none()
        if scenario is None:
            raise EntityNotFoundError(f"Scenario {scenario_id} not found")
        return scenario

    def exists(self, scenario_id: int) -> bool:
        stmt = select(Scenario.id).where(Scenario.id == scenario_id).limit(1)
        return self.session.execute(stmt).scalar_one_or_none() is not None

    def create(self, scenario: Scenario) -> Scenario:
        self.session.add(scenario)
        try:
            self.session.flush()
        except IntegrityError as exc:  # pragma: no cover
            raise EntityConflictError("Scenario violates constraints") from exc
        return scenario

    def find_by_project_and_names(
        self,
        project_id: int,
        names: Iterable[str],
    ) -> Mapping[str, Scenario]:
        normalised = {name.strip().lower()
                      for name in names if name and name.strip()}
        if not normalised:
            return {}
        stmt = (
            select(Scenario)
            .where(
                Scenario.project_id == project_id,
                func.lower(Scenario.name).in_(normalised),
            )
        )
        records = self.session.execute(stmt).scalars().all()
        return {scenario.name.lower(): scenario for scenario in records}

    def delete(self, scenario_id: int) -> None:
        scenario = self.get(scenario_id)
        self.session.delete(scenario)


class FinancialInputRepository:
    """Persistence operations for FinancialInput entities."""

    def __init__(self, session: Session) -> None:
        self.session = session

    def list_for_scenario(self, scenario_id: int) -> Sequence[FinancialInput]:
        stmt = (
            select(FinancialInput)
            .where(FinancialInput.scenario_id == scenario_id)
            .order_by(FinancialInput.created_at)
        )
        return self.session.execute(stmt).scalars().all()

    def bulk_upsert(self, inputs: Iterable[FinancialInput]) -> Sequence[FinancialInput]:
        entities = list(inputs)
        self.session.add_all(entities)
        try:
            self.session.flush()
        except IntegrityError as exc:  # pragma: no cover
            raise EntityConflictError(
                "Financial input violates constraints") from exc
        return entities

    def delete(self, input_id: int) -> None:
        stmt = select(FinancialInput).where(FinancialInput.id == input_id)
        entity = self.session.execute(stmt).scalar_one_or_none()
        if entity is None:
            raise EntityNotFoundError(f"Financial input {input_id} not found")
        self.session.delete(entity)

    def latest_created_at(self) -> datetime | None:
        stmt = (
            select(FinancialInput.created_at)
            .order_by(FinancialInput.created_at.desc())
            .limit(1)
        )
        return self.session.execute(stmt).scalar_one_or_none()


class SimulationParameterRepository:
    """Persistence operations for SimulationParameter entities."""

    def __init__(self, session: Session) -> None:
        self.session = session

    def list_for_scenario(self, scenario_id: int) -> Sequence[SimulationParameter]:
        stmt = (
            select(SimulationParameter)
            .where(SimulationParameter.scenario_id == scenario_id)
            .order_by(SimulationParameter.created_at)
        )
        return self.session.execute(stmt).scalars().all()

    def bulk_upsert(
        self, parameters: Iterable[SimulationParameter]
    ) -> Sequence[SimulationParameter]:
        entities = list(parameters)
        self.session.add_all(entities)
        try:
            self.session.flush()
        except IntegrityError as exc:  # pragma: no cover
            raise EntityConflictError(
                "Simulation parameter violates constraints") from exc
        return entities

    def delete(self, parameter_id: int) -> None:
        stmt = select(SimulationParameter).where(
            SimulationParameter.id == parameter_id)
        entity = self.session.execute(stmt).scalar_one_or_none()
        if entity is None:
            raise EntityNotFoundError(
                f"Simulation parameter {parameter_id} not found")
        self.session.delete(entity)


class RoleRepository:
    """Persistence operations for Role entities."""

    def __init__(self, session: Session) -> None:
        self.session = session

    def list(self) -> Sequence[Role]:
        stmt = select(Role).order_by(Role.name)
        return self.session.execute(stmt).scalars().all()

    def get(self, role_id: int) -> Role:
        stmt = select(Role).where(Role.id == role_id)
        role = self.session.execute(stmt).scalar_one_or_none()
        if role is None:
            raise EntityNotFoundError(f"Role {role_id} not found")
        return role

    def get_by_name(self, name: str) -> Role | None:
        stmt = select(Role).where(Role.name == name)
        return self.session.execute(stmt).scalar_one_or_none()

    def create(self, role: Role) -> Role:
        self.session.add(role)
        try:
            self.session.flush()
        except IntegrityError as exc:  # pragma: no cover - DB constraint enforcement
            raise EntityConflictError(
                "Role violates uniqueness constraints") from exc
        return role


class UserRepository:
    """Persistence operations for User entities and their role assignments."""

    def __init__(self, session: Session) -> None:
        self.session = session

    def list(self, *, with_roles: bool = False) -> Sequence[User]:
        stmt = select(User).order_by(User.created_at)
        if with_roles:
            stmt = stmt.options(selectinload(User.roles))
        return self.session.execute(stmt).scalars().all()

    def _apply_role_option(self, stmt, with_roles: bool):
        if with_roles:
            stmt = stmt.options(
                joinedload(User.role_assignments).joinedload(UserRole.role),
                selectinload(User.roles),
            )
        return stmt

    def get(self, user_id: int, *, with_roles: bool = False) -> User:
        stmt = select(User).where(User.id == user_id).execution_options(
            populate_existing=True)
        stmt = self._apply_role_option(stmt, with_roles)
        result = self.session.execute(stmt)
        if with_roles:
            result = result.unique()
        user = result.scalar_one_or_none()
        if user is None:
            raise EntityNotFoundError(f"User {user_id} not found")
        return user

    def get_by_email(self, email: str, *, with_roles: bool = False) -> User | None:
        stmt = select(User).where(User.email == email).execution_options(
            populate_existing=True)
        stmt = self._apply_role_option(stmt, with_roles)
        result = self.session.execute(stmt)
        if with_roles:
            result = result.unique()
        return result.scalar_one_or_none()

    def get_by_username(self, username: str, *, with_roles: bool = False) -> User | None:
        stmt = select(User).where(User.username ==
                                  username).execution_options(populate_existing=True)
        stmt = self._apply_role_option(stmt, with_roles)
        result = self.session.execute(stmt)
        if with_roles:
            result = result.unique()
        return result.scalar_one_or_none()

    def create(self, user: User) -> User:
        self.session.add(user)
        try:
            self.session.flush()
        except IntegrityError as exc:  # pragma: no cover - DB constraint enforcement
            raise EntityConflictError(
                "User violates uniqueness constraints") from exc
        return user

    def assign_role(
        self,
        *,
        user_id: int,
        role_id: int,
        granted_by: int | None = None,
    ) -> UserRole:
        stmt = select(UserRole).where(
            UserRole.user_id == user_id,
            UserRole.role_id == role_id,
        )
        assignment = self.session.execute(stmt).scalar_one_or_none()
        if assignment:
            return assignment

        assignment = UserRole(
            user_id=user_id,
            role_id=role_id,
            granted_by=granted_by,
        )
        self.session.add(assignment)
        try:
            self.session.flush()
        except IntegrityError as exc:  # pragma: no cover - DB constraint enforcement
            raise EntityConflictError(
                "Assignment violates constraints") from exc
        return assignment

    def revoke_role(self, *, user_id: int, role_id: int) -> None:
        stmt = select(UserRole).where(
            UserRole.user_id == user_id,
            UserRole.role_id == role_id,
        )
        assignment = self.session.execute(stmt).scalar_one_or_none()
        if assignment is None:
            raise EntityNotFoundError(
                f"Role {role_id} not assigned to user {user_id}")
        self.session.delete(assignment)
        self.session.flush()


DEFAULT_ROLE_DEFINITIONS: tuple[dict[str, str], ...] = (
    {
        "name": "admin",
        "display_name": "Administrator",
        "description": "Full platform access with user management rights.",
    },
    {
        "name": "project_manager",
        "display_name": "Project Manager",
        "description": "Manage projects, scenarios, and associated data.",
    },
    {
        "name": "analyst",
        "display_name": "Analyst",
        "description": "Review dashboards and scenario outputs.",
    },
    {
        "name": "viewer",
        "display_name": "Viewer",
        "description": "Read-only access to assigned projects and reports.",
    },
)


def ensure_default_roles(role_repo: RoleRepository) -> list[Role]:
    """Ensure standard roles exist, creating missing ones.

    Returns all current role records in creation order.
    """

    roles: list[Role] = []
    for definition in DEFAULT_ROLE_DEFINITIONS:
        existing = role_repo.get_by_name(definition["name"])
        if existing:
            roles.append(existing)
            continue
        role = Role(**definition)
        roles.append(role_repo.create(role))
    return roles


def ensure_admin_user(
    user_repo: UserRepository,
    role_repo: RoleRepository,
    *,
    email: str,
    username: str,
    password: str,
) -> User:
    """Ensure an administrator user exists and holds the admin role."""

    user = user_repo.get_by_email(email, with_roles=True)
    if user is None:
        user = User(
            email=email,
            username=username,
            password_hash=User.hash_password(password),
            is_active=True,
            is_superuser=True,
        )
        user_repo.create(user)
    else:
        if not user.is_active:
            user.is_active = True
        if not user.is_superuser:
            user.is_superuser = True
        user_repo.session.flush()

    admin_role = role_repo.get_by_name("admin")
    if admin_role is None:  # pragma: no cover - safety if ensure_default_roles wasn't called
        admin_role = role_repo.create(
            Role(
                name="admin",
                display_name="Administrator",
                description="Full platform access with user management rights.",
            )
        )

    user_repo.assign_role(
        user_id=user.id,
        role_id=admin_role.id,
        granted_by=user.id,
    )
    return user