from __future__ import annotations

import functools
import secrets

from flask import (
    Blueprint,
    flash,
    g,
    redirect,
    render_template,
    request,
    session,
    url_for,
)
from markupsafe import Markup
from werkzeug.security import check_password_hash, generate_password_hash

from .constants import ROLE_LABELS
from .db import active_admin_count, ensure_default_household, get_db, user_count


auth_bp = Blueprint("auth", __name__, url_prefix="/auth")


def login_required(view):
    @functools.wraps(view)
    def wrapped_view(**kwargs):
        if g.user is None:
            return redirect(url_for("auth.login"))
        return view(**kwargs)

    return wrapped_view


def admin_required(view):
    @functools.wraps(view)
    def wrapped_view(**kwargs):
        if g.user is None:
            return redirect(url_for("auth.login"))
        if g.user["role"] != "admin":
            flash("Dieser Bereich ist für Admins gedacht.", "error")
            return redirect(url_for("main.dashboard"))
        return view(**kwargs)

    return wrapped_view


def ensure_csrf_token() -> str:
    token = session.get("_csrf_token")
    if not token:
        token = session["_csrf_token"] = secrets.token_hex(24)
    return token


def normalize_login_value(raw: str) -> str:
    return raw.strip().lower()


def validate_identity_fields(database, username: str, email: str | None, current_user_id: int | None = None) -> str | None:
    if not username:
        return "Bitte einen Benutzernamen eintragen."

    existing_user = database.execute(
        "SELECT id FROM users WHERE LOWER(username) = LOWER(?)",
        (username,),
    ).fetchone()
    if existing_user and int(existing_user["id"]) != current_user_id:
        return "Dieser Benutzername ist bereits vergeben."

    if email:
        existing_email = database.execute(
            "SELECT id FROM users WHERE LOWER(email) = LOWER(?)",
            (email,),
        ).fetchone()
        if existing_email and int(existing_email["id"]) != current_user_id:
            return "Diese E-Mail-Adresse wird bereits verwendet."

    return None


@auth_bp.app_context_processor
def inject_csrf_input():
    return {
        "csrf_input": lambda: Markup(
            f'<input type="hidden" name="csrf_token" value="{ensure_csrf_token()}">'
        ),
        "csrf_token_value": ensure_csrf_token(),
    }


@auth_bp.before_app_request
def load_logged_in_user():
    user_id = session.get("user_id")
    if user_id is None:
        g.user = None
    else:
        g.user = get_db().execute(
            """
            SELECT users.*,
                   households.name AS household_name
            FROM users
            LEFT JOIN households ON households.id = users.household_id
            WHERE users.id = ?
            """,
            (user_id,),
        ).fetchone()
        if g.user is not None and not g.user["is_active"]:
            session.clear()
            g.user = None

    endpoint = request.endpoint or ""
    if user_count() == 0 and endpoint not in {"auth.setup", "static", "uploaded_file"}:
        return redirect(url_for("auth.setup"))

    if request.method == "POST" and endpoint != "static":
        token = session.get("_csrf_token")
        form_token = request.form.get("csrf_token")
        if not token or token != form_token:
            flash("Die Sitzung muss kurz neu geladen werden. Bitte versuche es noch einmal.", "error")
            return redirect(request.referrer or url_for("main.dashboard"))


@auth_bp.route("/setup", methods=("GET", "POST"))
def setup():
    if user_count() > 0:
        return redirect(url_for("auth.login"))

    if request.method == "POST":
        household_name = request.form.get("household_name", "").strip() or "Unser Haushalt"
        username = normalize_login_value(request.form.get("username", ""))
        email = normalize_login_value(request.form.get("email", "")) or None
        display_name = request.form.get("display_name", "").strip()
        password = request.form.get("password", "")
        password_repeat = request.form.get("password_repeat", "")
        database = get_db()

        error = validate_identity_fields(database, username, email)
        if error is None and not password:
            error = "Bitte ein Passwort vergeben."
        elif error is None and password != password_repeat:
            error = "Die Passwörter stimmen nicht überein."

        if error is None:
            database.execute(
                "INSERT INTO households (name) VALUES (?)",
                (household_name,),
            )
            household_id = ensure_default_household(database)
            database.execute(
                """
                INSERT INTO users (household_id, username, email, display_name, role, password_hash)
                VALUES (?, ?, ?, ?, 'admin', ?)
                """,
                (household_id, username, email, display_name, generate_password_hash(password)),
            )
            database.commit()
            flash("Der erste Haushalt-Zugang ist angelegt. Du kannst dich jetzt anmelden.", "success")
            return redirect(url_for("auth.login"))

        flash(error, "error")

    return render_template("auth/setup.html")


@auth_bp.route("/login", methods=("GET", "POST"))
def login():
    if user_count() == 0:
        return redirect(url_for("auth.setup"))

    if request.method == "POST":
        identity = normalize_login_value(request.form.get("username", ""))
        password = request.form.get("password", "")
        remember_me = request.form.get("remember_me") == "1"
        database = get_db()
        user = database.execute(
            """
            SELECT users.*, households.name AS household_name
            FROM users
            LEFT JOIN households ON households.id = users.household_id
            WHERE LOWER(users.username) = LOWER(?) OR LOWER(COALESCE(users.email, '')) = LOWER(?)
            """,
            (identity, identity),
        ).fetchone()

        error = None
        if user is None or not check_password_hash(user["password_hash"], password):
            error = "Login oder Passwort passen nicht zusammen."
        elif not user["is_active"]:
            error = "Dieser Zugang ist derzeit nicht aktiv."

        if error is None:
            session.clear()
            session.permanent = remember_me
            session["user_id"] = user["id"]
            ensure_csrf_token()
            return redirect(url_for("main.dashboard"))

        flash(error, "error")

    return render_template("auth/login.html")


@auth_bp.route("/profile", methods=("GET", "POST"))
@login_required
def profile():
    database = get_db()

    if request.method == "POST":
        username = normalize_login_value(request.form.get("username", ""))
        email = normalize_login_value(request.form.get("email", "")) or None
        display_name = request.form.get("display_name", "").strip()

        error = validate_identity_fields(database, username, email, current_user_id=g.user["id"])
        if error is None:
            database.execute(
                """
                UPDATE users
                SET username = ?, email = ?, display_name = ?, updated_at = CURRENT_TIMESTAMP
                WHERE id = ?
                """,
                (username, email, display_name, g.user["id"]),
            )
            database.commit()
            flash("Dein Profil wurde aktualisiert.", "success")
            return redirect(url_for("auth.profile"))

        flash(error, "error")

    return render_template("auth/profile.html", role_labels=ROLE_LABELS)


@auth_bp.post("/password")
@login_required
def change_password():
    current_password = request.form.get("current_password", "")
    new_password = request.form.get("new_password", "")
    new_password_repeat = request.form.get("new_password_repeat", "")

    error = None
    if not check_password_hash(g.user["password_hash"], current_password):
        error = "Das aktuelle Passwort stimmt nicht."
    elif not new_password:
        error = "Bitte ein neues Passwort eintragen."
    elif new_password != new_password_repeat:
        error = "Die neuen Passwörter stimmen nicht überein."

    if error is None:
        get_db().execute(
            """
            UPDATE users
            SET password_hash = ?, updated_at = CURRENT_TIMESTAMP
            WHERE id = ?
            """,
            (generate_password_hash(new_password), g.user["id"]),
        )
        get_db().commit()
        flash("Dein Passwort wurde geändert.", "success")
    else:
        flash(error, "error")

    return redirect(url_for("auth.profile"))


@auth_bp.post("/logout")
def logout():
    session.clear()
    flash("Du bist abgemeldet.", "info")
    return redirect(url_for("auth.login"))


def validate_admin_user_form(
    database,
    *,
    username: str,
    email: str | None,
    role: str,
    is_active: bool,
    password: str,
    password_repeat: str,
    current_user_id: int | None = None,
) -> str | None:
    error = validate_identity_fields(database, username, email, current_user_id=current_user_id)
    if error:
        return error
    if role not in ROLE_LABELS:
        return "Bitte eine gültige Rolle auswählen."
    if current_user_id is None and not password:
        return "Bitte ein Passwort vergeben."
    if password and password != password_repeat:
        return "Die Passwörter stimmen nicht überein."
    if current_user_id == g.user["id"] and not is_active:
        return "Du kannst deinen eigenen Zugang hier nicht deaktivieren."
    return None


def can_remove_last_admin(target_user_id: int, new_role: str, is_active: bool) -> bool:
    if g.user is None:
        return False
    if target_user_id != g.user["id"] and g.user["role"] == "admin":
        target = get_db().execute("SELECT * FROM users WHERE id = ?", (target_user_id,)).fetchone()
        if target is None:
            return False
        if target["role"] != "admin" or not target["is_active"]:
            return False
        if new_role == "admin" and is_active:
            return False
        return active_admin_count(g.user["household_id"]) <= 1
    return False