/*
 * Copyright (C) 2024-present Puter Technologies Inc.
 *
 * This file is part of Puter.
 *
 * Puter is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published
 * by the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

/**
 * SMS-to-card fallback: the shared rule for whether a phone-gated user has run
 * out of SMS attempts and may verify a card instead.
 *
 * Two consumers need the same answer, so it lives here rather than inside the
 * controller: `/send-confirm-phone` (which counts attempts and opens the
 * fallback) and `/whoami` (which tells a reloading GUI the fallback is already
 * open — the send route can't, because by then every send is rejected by its
 * own rate limit before any handler runs).
 */
import type { EventClient } from '../clients/event/EventClient';
import type { PreludeClient } from '../clients/prelude/PreludeClient';
import type { IConfig } from '../types';
import { BoundedTtlMap } from './boundedTtlMap';

/**
 * `/send-confirm-phone` route rate limit: how many verification texts one
 * account can ask for per window. This is also the definition of "out of SMS
 * attempts" — the fallback opens on the last send this allows, because requests
 * past it are rejected in middleware and never reach a handler.
 */
export const SEND_PHONE_RATE_LIMIT = 10;
export const SEND_PHONE_RATE_WINDOW_MS = 60 * 60_000;

/**
 * How long the fallback stays open once it opens. Deliberately much longer than
 * the attempt counter's window: the counter exists to detect exhaustion, and
 * once detected the user needs time to finish the card flow (and to come back
 * to it) without racing the counter's expiry.
 */
export const CARD_FALLBACK_OPEN_TTL_SECONDS = 24 * 60 * 60;

/** Attempt counter, TTL-tied to the send rate-limit window. */
export const phoneAttemptsKey = (userId: number): string =>
    `phone-verify-attempts:${userId}`;

/** Eligibility flag, the only thing the card endpoints read. */
export const cardFallbackFlagKey = (userId: number): string =>
    `card-fallback-open:${userId}`;

/** The user fields the rule reads. */
export interface PhoneGatedUser {
    id?: number | null;
    requires_phone_verification?: boolean | number | null;
}

/** Reads one system-KV key; resolves whatever was stored (or null/undefined). */
export type ReadKvFlag = (key: string) => Promise<unknown>;

/**
 * How many SMS send attempts open the fallback. Defaults to the full send
 * allowance — the fallback is meant to appear only once SMS has actually run
 * out for this user, not as a competing option alongside a working SMS flow.
 *
 * A lower `after_attempts` is honoured (it makes the card path reachable
 * without burning ten texts, which is what QA wants), and any value above the
 * send allowance is clamped down to it: requests past the route limit are
 * rejected in middleware and never reach the attempt counter, so a higher
 * threshold could never be crossed.
 */
export function cardFallbackAfterAttempts(
    config: Pick<IConfig, 'phone_verification_card_fallback'>,
): number {
    const cfg = config.phone_verification_card_fallback;
    return Math.min(
        typeof cfg?.after_attempts === 'number' && cfg.after_attempts > 0
            ? cfg.after_attempts
            : SEND_PHONE_RATE_LIMIT,
        SEND_PHONE_RATE_LIMIT,
    );
}

export interface CardFallbackDeps {
    /** Whether an SMS provider is set up. */
    smsConfigured: () => boolean;
    /**
     * Whether the owning extension reports the card gate on; null when none is
     * installed.
     */
    probeCardVerification: () => Promise<boolean | null>;
}

/** The clients that answer {@link CardFallbackDeps}. */
export interface CardFallbackClients {
    prelude?: Pick<PreludeClient, 'isConfigured'> | null;
    event?: Pick<EventClient, 'emitAndWait'> | null;
}

/**
 * Deps over the live clients. `clients` is read at call time, not captured, so
 * a client swapped after construction (tests) is what gets asked.
 */
export function cardFallbackDepsFrom(
    clients: CardFallbackClients,
): CardFallbackDeps {
    return {
        smsConfigured: () => Boolean(clients.prelude?.isConfigured()),
        probeCardVerification: async () => {
            const status: { enabled: boolean | null } = { enabled: null };
            await clients.event?.emitAndWait(
                'puter.card-verification.status',
                status,
                {},
            );
            return status.enabled;
        },
    };
}

/**
 * Memoized answer to the card-gate probe. The probe is side-effect free, but it
 * is asked on a polled endpoint, so cache it briefly rather than fanning out an
 * event per request. Only the _default_ is cached: an explicit `enabled: false`
 * short-circuits below without ever consulting this, so the operator's kill
 * switch still takes effect immediately.
 */
const CARD_STATUS_TTL_MS = 60_000;
const cardStatusCache = new BoundedTtlMap<'status', boolean | null>({
    maxEntries: 1,
    ttlMs: CARD_STATUS_TTL_MS,
});

/** Drops the memoized probe answer. For tests, and for a config reload. */
export function resetCardVerificationStatusCache(): void {
    cardStatusCache.clear();
}

/**
 * Whether an installed extension reports the card gate on; null when nothing
 * answers. Memoized per {@link CARD_STATUS_TTL_MS}.
 */
export async function isCardVerificationEnabled(
    deps: CardFallbackDeps,
): Promise<boolean | null> {
    const cached = cardStatusCache.get('status');
    if (cached !== undefined) return cached;
    let enabled: boolean | null = null;
    try {
        enabled = await deps.probeCardVerification();
    } catch (e) {
        // Treat a broken probe as "no card gate": offering a card path that may
        // not work is worse than not offering one.
        console.warn('[card-verification] status probe failed:', e);
    }
    cardStatusCache.set('status', enabled);
    return enabled;
}

/**
 * Whether the SMS-to-card fallback is switched on.
 *
 * `enabled` is a tri-state. Set explicitly, it wins either way — that is the
 * opt-out. Left unset, the fallback follows the pair it bridges: on wherever
 * both halves actually work, off otherwise. Without that conjunction the offer
 * could show up on a deployment with no card gate behind it, where taking it
 * strands the user on a dialog that can only fail.
 */
export async function isCardFallbackEnabled(
    config: Pick<IConfig, 'phone_verification_card_fallback'>,
    deps: CardFallbackDeps,
): Promise<boolean> {
    const configured = config.phone_verification_card_fallback?.enabled;
    if (typeof configured === 'boolean') return configured;
    if (!deps.smsConfigured()) return false;
    return (await isCardVerificationEnabled(deps)) === true;
}

/**
 * Whether this user may verify a card in place of the phone gate right now.
 *
 * Reads only the eligibility flag, never the raw attempt counter: the counter
 * expires with the send rate-limit window, so deriving eligibility from it
 * would revoke the offer mid-flow. The cheap disqualifiers (not phone-gated,
 * feature off) come first, so an ordinary `/whoami` never reaches the KV read.
 * Every KV failure fails closed.
 */
export async function isCardFallbackEligible(
    config: Pick<IConfig, 'phone_verification_card_fallback'>,
    user: PhoneGatedUser,
    readFlag: ReadKvFlag,
    deps: CardFallbackDeps,
): Promise<boolean> {
    if (!user.requires_phone_verification) return false;
    if (typeof user.id !== 'number') return false;
    if (!(await isCardFallbackEnabled(config, deps))) return false;
    try {
        return (await readFlag(cardFallbackFlagKey(user.id))) === true;
    } catch (e) {
        console.warn('[card-verification] fallback flag read failed:', e);
        return false;
    }
}