import { createHash, randomBytes } from 'node:crypto';

import {
  BadRequestException,
  ForbiddenException,
  HttpException,
  HttpStatus,
  Injectable,
  NotFoundException,
} from '@nestjs/common';
import {
  InvitationListView,
  InvitationPreview,
  InvitationStatus,
  InvitationView,
} from '@dorfteich/shared';
import { Invitation, User } from '@prisma/client';

import { AuditService } from '../audit/audit.service';
import { AppConfig } from '../config/app-config.service';
import { MailService } from '../mail/mail.service';
import { PrismaService } from '../prisma/prisma.service';
import { RateLimitService } from '../rate-limit/rate-limit.service';
import { InstanceSettingsService } from '../settings/instance-settings.service';

export const INVITATION_TTL_SECONDS = 14 * 24 * 60 * 60;

// Anti-spam backstop besides the open-invitations quota: without it a
// revoke-and-recreate loop would allow unlimited mail volume while never
// exceeding the quota.
const CREATE_LIMIT = { limit: 20, windowSeconds: 24 * 60 * 60 };

/**
 * Peer invitations (issue #332). A user invites an e-mail address; the
 * mailed single-use token lets exactly one signup through even while
 * registration is closed (auth.service). Open (pending, unexpired)
 * invitations count against the per-user quota
 * `invitations.maxOpenPerUser` — 0 turns the feature off. Only the
 * SHA-256 hash of the token is stored (auth-tokens pattern); revoked and
 * accepted rows are kept so the settings UI can show history.
 */
@Injectable()
export class InvitationsService {
  constructor(
    private readonly prisma: PrismaService,
    private readonly mail: MailService,
    private readonly rateLimits: RateLimitService,
    private readonly settings: InstanceSettingsService,
    private readonly audit: AuditService,
    private readonly config: AppConfig,
  ) {}

  async create(user: User, email: string): Promise<InvitationView> {
    const maxOpen = (await this.settings.get('invitations.maxOpenPerUser')) as number;
    if (maxOpen === 0) throw new ForbiddenException({ code: 'invitations_disabled' });
    if ((await this.openCount(user.id)) >= maxOpen) {
      throw new BadRequestException({ code: 'invitation_quota_reached' });
    }
    const limit = await this.rateLimits.hit(
      'invitation-create',
      user.id,
      CREATE_LIMIT.limit,
      CREATE_LIMIT.windowSeconds,
    );
    if (!limit.allowed) {
      throw new HttpException({ code: 'rate_limited' }, HttpStatus.TOO_MANY_REQUESTS);
    }

    const raw = randomBytes(32).toString('base64url');
    const row = await this.prisma.invitation.create({
      data: {
        inviterId: user.id,
        email: email.toLowerCase(),
        tokenHash: hashToken(raw),
        expiresAt: new Date(Date.now() + INVITATION_TTL_SECONDS * 1000),
      },
    });
    // The invitee has no account and no locale yet — the instance default
    // decides the mail language. The greeting falls back to the address.
    await this.mail.enqueue(
      row.email,
      'invitation',
      {
        displayName: row.email,
        inviterName: user.displayName,
        link: `${this.config.env.APP_BASE_URL}/signup?invitation=${raw}`,
      },
      (await this.settings.get('instance.defaultLocale')) as 'de' | 'en',
    );
    await this.audit.record({
      action: 'invitation.created',
      actorId: user.id,
      targetType: 'invitation',
      targetId: row.id,
    });
    return this.viewOf(row);
  }

  async list(user: User): Promise<InvitationListView> {
    const rows = await this.prisma.invitation.findMany({
      where: { inviterId: user.id },
      orderBy: { createdAt: 'desc' },
      take: 100,
    });
    return {
      invitations: rows.map((row) => this.viewOf(row)),
      open: await this.openCount(user.id),
      maxOpen: (await this.settings.get('invitations.maxOpenPerUser')) as number,
    };
  }

  async revoke(user: User, id: string): Promise<void> {
    const row = await this.prisma.invitation.findFirst({
      where: { id, inviterId: user.id },
    });
    if (!row) throw new NotFoundException();
    if (row.acceptedAt) throw new BadRequestException({ code: 'invitation_already_accepted' });
    if (row.revokedAt) return; // idempotent
    await this.prisma.invitation.update({ where: { id }, data: { revokedAt: new Date() } });
    await this.audit.record({
      action: 'invitation.revoked',
      actorId: user.id,
      targetType: 'invitation',
      targetId: id,
    });
  }

  /** What the signup screen may show for a link before it is used. */
  async preview(raw: string): Promise<InvitationPreview> {
    const row = await this.prisma.invitation.findUnique({
      where: { tokenHash: hashToken(raw) },
      include: { inviter: true },
    });
    if (!row || row.revokedAt || row.acceptedAt || row.expiresAt <= new Date()) {
      throw new BadRequestException({ code: 'token_invalid' });
    }
    return { email: row.email, inviterName: row.inviter.displayName };
  }

  /**
   * Atomically claims the token (only one signup can flip acceptedAt from
   * null). Returns the row, or null for unknown/revoked/expired/used
   * tokens. The caller un-redeems if the signup fails afterwards.
   */
  async redeem(raw: string): Promise<Invitation | null> {
    const result = await this.prisma.invitation.updateMany({
      where: {
        tokenHash: hashToken(raw),
        revokedAt: null,
        acceptedAt: null,
        expiresAt: { gt: new Date() },
      },
      data: { acceptedAt: new Date() },
    });
    if (result.count === 0) return null;
    return this.prisma.invitation.findUnique({ where: { tokenHash: hashToken(raw) } });
  }

  /** Ties the redeemed invitation to the account it created. */
  async markAccepted(id: string, userId: string): Promise<void> {
    await this.prisma.invitation.update({ where: { id }, data: { acceptedUserId: userId } });
  }

  /** Rolls a redeem back when the signup it gated failed (e.g. duplicate
   * username) — the invitee must be able to try again with the same link. */
  async unredeem(id: string): Promise<void> {
    await this.prisma.invitation.updateMany({
      where: { id, acceptedUserId: null },
      data: { acceptedAt: null },
    });
  }

  private openCount(inviterId: string): Promise<number> {
    return this.prisma.invitation.count({
      where: { inviterId, revokedAt: null, acceptedAt: null, expiresAt: { gt: new Date() } },
    });
  }

  private viewOf(row: Invitation): InvitationView {
    return {
      id: row.id,
      email: row.email,
      status: statusOf(row),
      createdAt: row.createdAt.toISOString(),
      expiresAt: row.expiresAt.toISOString(),
    };
  }
}

function statusOf(row: Invitation): InvitationStatus {
  if (row.revokedAt) return 'revoked';
  if (row.acceptedAt) return 'accepted';
  if (row.expiresAt <= new Date()) return 'expired';
  return 'pending';
}

function hashToken(raw: string): string {
  return createHash('sha256').update(raw).digest('hex');
}