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

import { Injectable } from '@nestjs/common';
import { Session, User } from '@prisma/client';

import { PrismaService } from '../prisma/prisma.service';

const SESSION_TTL_MS = 30 * 24 * 60 * 60 * 1000; // sliding 30 days
const REFRESH_AT_MOST_EVERY_MS = 60 * 60 * 1000; // avoid write storms

export interface ValidatedSession {
  session: Session;
  user: User;
}

/**
 * Opaque server-side sessions (ADR 0007). The cookie value is 32 random
 * bytes; the database stores only its SHA-256 hash as the row id, so a
 * database leak cannot be replayed as cookies.
 */
@Injectable()
export class SessionsService {
  constructor(private readonly prisma: PrismaService) {}

  async create(userId: string, userAgent: string | undefined): Promise<string> {
    const raw = randomBytes(32).toString('base64url');
    await this.prisma.session.create({
      data: {
        id: hashSessionToken(raw),
        userId,
        expiresAt: new Date(Date.now() + SESSION_TTL_MS),
        userAgent: summarizeUserAgent(userAgent),
      },
    });
    return raw;
  }

  async validate(raw: string): Promise<ValidatedSession | null> {
    const session = await this.prisma.session.findUnique({
      where: { id: hashSessionToken(raw) },
      include: { user: true },
    });
    if (!session || session.expiresAt <= new Date()) return null;
    if (session.user.status === 'DISABLED') return null;

    // Sliding expiration, refreshed at most once per hour.
    if (Date.now() - session.lastSeenAt.getTime() > REFRESH_AT_MOST_EVERY_MS) {
      await this.prisma.session.update({
        where: { id: session.id },
        data: { lastSeenAt: new Date(), expiresAt: new Date(Date.now() + SESSION_TTL_MS) },
      });
    }
    const { user, ...bare } = session;
    return { session: bare as Session, user };
  }

  async destroyByRawToken(raw: string): Promise<void> {
    await this.prisma.session.deleteMany({ where: { id: hashSessionToken(raw) } });
  }

  async destroyById(sessionId: string, userId: string): Promise<boolean> {
    const result = await this.prisma.session.deleteMany({
      where: { id: sessionId, userId },
    });
    return result.count > 0;
  }

  /** Logs the user out everywhere, optionally keeping one session alive. */
  async destroyAllForUser(userId: string, exceptSessionId?: string): Promise<void> {
    await this.prisma.session.deleteMany({
      where: { userId, ...(exceptSessionId ? { id: { not: exceptSessionId } } : {}) },
    });
  }

  listForUser(userId: string): Promise<Session[]> {
    return this.prisma.session.findMany({
      where: { userId, expiresAt: { gt: new Date() } },
      orderBy: { lastSeenAt: 'desc' },
    });
  }
}

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

/** Browser + OS, never the raw string (fingerprinting hygiene). */
function summarizeUserAgent(ua: string | undefined): string | null {
  if (!ua) return null;
  const browser =
    ua.match(/(Firefox|Edg|OPR|Chrome|Safari)\/[\d.]+/)?.[1]?.replace('Edg', 'Edge') ?? 'Browser';
  const os = ua.match(/\((Windows|Macintosh|X11; Linux|Android|iPhone|iPad)[^)]*\)/)?.[1] ?? '';
  const osName = os
    .replace('Macintosh', 'macOS')
    .replace('X11; Linux', 'Linux')
    .replace(/iPhone|iPad/, 'iOS');
  return osName ? `${browser} · ${osName}` : browser;
}